Re-description of ‘Steneosaurus’ obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England

Re-description of ‘Steneosaurus’ obtusidens Andrews, 1909, an unusual macrophagous... Abstract Teleosaurids were a clade of crocodylomorphs that attained near-global distribution during the Jurassic Period. Within Teleosauridae, one particular sub-clade of durophagous/macrophagous taxa achieved large body sizes and were apex predators in shallow marine environments during the Late Jurassic and Early Cretaceous in Europe and around the coast of the Tethys Seaway. Unfortunately, the origins of this clade are still poorly understood. ‘Steneosaurus’ obtusidens is a little-studied macrophagous species from the Oxford Clay Formation (Callovian, Middle Jurassic) of the UK and near Migné-les-Lourdines (Middle Callovian) in France. Despite being considered a sister taxon of the Late Jurassic taxon Machimosaurus, the taxonomy of ‘S.’ obtusidens remains unclear. Although three different synonymies have been proposed (variously a subjective synonym of other taxa), these taxonomic hypotheses have not been based on detailed anatomical comparisons and thus have not been tested. Here, we re-describe the holotype of ‘S.’ obtusidens, demonstrate that it is indeed a valid taxon, restrict the referred specimens to a fragmentary skeleton, nearly complete skull, and partial rostrum, and establish a new monotypic genus, Lemmysuchus. Our re-description reveals five autapomorphies for Lemmysuchus obtusidens and nine apomorphic characters that support the tribe Machimosaurini (Lemmysuchus + Machimosaurus). INTRODUCTION Teleosaurid crocodylomorphs were a near-globally distributed clade that inhabited shallow marine and brackish ecosystems throughout the Jurassic (Buffetaut et al., 1981; Buffetaut, 1982a, b; Vignaud, 1993; Hua & Buffetaut, 1997; Hua, 1999; Johnson et al., 2015) and survived into the Early Cretaceous (Fanti et al., 2016; Jouve et al., 2016). These animals are often viewed as marine analogues of extant gavials because of their elongate and tubular snout, dorsally directed orbits and high tooth count, all of which suggest a primarily piscivorous diet (Andrews, 1909, 1913; Buffetaut, 1982a, b). However, within Teleosauridae, some taxa have been considered to be durophagous and/or macrophagous, because they had shorter snouts, proportionally enlarged supratemporal fenestrae (i.e. increased jaw adductor musculature), blunt tooth crown apices, serrated carinae and extensive enamel ornamentation (Eudes-Deslongchamps, 1864, 1867, 1869; Andrews, 1909, 1913; Buffetaut, 1982a; Hua et al., 1994; Hua & Buffetaut, 1997; Hua, 1999; Martin & Vincent, 2013; Young & Steel, 2014; Young et al., 2014a, b, 2015a, b; Fanti et al., 2016; Jouve et al. (2016). The Late Jurassic–Early Cretaceous (Oxfordian to Hauterivian) taxon Machimosaurus is the best-studied macrophagous teleosaurid, known from both cranial and postcranial remains and isolated teeth from numerous countries (Sauvage & Liénard, 1879; Krebs, 1968; see Young et al., 2014a for an overview). Here, we use the taxonomy of Young et al. (2014a), rather than that of Martin, Vincent & Falconnet (2015) following the rationale of Foffa, Young & Brusatte (2015) and because a new phylogenetic analysis of Machimosaurus supports the multi-taxic hypothesis (see Fanti et al., 2016). The sister taxon to Machimosaurus, ‘Steneosaurus’ obtusidens Andrews, 1909, is a controversial taxon from the Middle Jurassic of Europe. Over the past three decades, its validity has been questioned, and three different subjective species (both Machimosaurus and Steneosaurus) synonymies have been proposed (see Adams-Tresman, 1987; Hua et al., 1994; Pierce, Angielczyk & Rayfield, 2009). Recent studies, however, have considered ‘S.’ obtusidens to be a distinct taxon (Martin & Vincent, 2013; Young et al. 2014a, 2015a). This taxonomic confusion hinders our understanding of the origins of the macrophagous teleosaurid sub-clade Machimosaurini. Thus, the aim of this paper is to shed light on the early evolution of durophagous/macrophagous teleosaurids by re-investigating the validity of ‘S.’ obtusidens. We re-describe the holotype of ‘S.’ obtusidens (which consists of a complete cranium and mandible, and the majority of the postcranial skeleton), demonstrate that it is a valid taxon and establish a new monotypic genus, Lemmysuchus obtusidens. We restrict the referred specimens of this species to a fragmentary skeleton, a nearly complete skull and a partial rostrum, and show that most of the cranial and postcranial material previously referred to ‘S.’ obtusidens belongs to other taxa. In addition, we assign three isolated teeth [two from the Oxford Clay Formation (OCF) and one from the Cornbrash Formation] to Machimosaurini indet. Finally, based on the holotype and referred specimens, we conclude that ‘S.’ obtusidens was present in the Callovian OCF of England and the Erymnoceras coronatum ammonite Zone (thus being contemporaneous with the Peterborough Member of the OCF) of Migné-les-Lourdines of France. ‘STENEOSAURUS’ OBTUSIDENS: HISTORICAL BACKGROUND Historical setting The holotype of ‘S.’ obtusidens (Natural History Museum, London, NHMUK PV R 3168) is part of the Leeds Fossil Collection (Peterborough Member, OCF; Middle Callovian) held at the NHMUK. Charles Andrews established the name Steneosaurus obtusidens for NHMUK PV R 3168 (Andrews, 1909) when he described the Leeds Collection teleosaurids. Later, Andrews (1913) tentatively referred two more Leeds Collection specimens to ‘S.’ obtusidens (NHMUK PV R 3169 and NHMUK PV R 3898). Andrews (1913) listed no specific criteria for the referral of these two specimens to ‘S.’ obtusidens and his decision may simply have been based on the large size and robustness that both specimens share with the holotype. Andrews (1913) later noted similarities between ‘S.’ obtusidens and Steneosaurus durobrivensis Andrews, 1909, stating that (Andrews, 1913: 131): ‘if it were not for the peculiarity of the teeth, [the former] might almost have been referred to that species [S. durobrivensis]’. The possibility that the ‘S.’ obtusidens morphotype is a late ontogenetic variant of S. durobrivensis has also been raised (Andrews, 1913; Steel, 1973) (note that S. durobrivensis is now considered to be a subjective junior synonym of Steneosaurus edwardsi Eudes-Deslongchamps, 1868; see Johnson et al., 2015). The first worker to formally synonymize ‘S.’ obtusidens with S. durobrivensis (=S. edwardsi) was Adams-Tresman (1987). As noted by Young et al. (2015a), the anatomical comparisons made between ‘S.’ obtusidens and S. edwardsi (as S. durobrivensis) were not based on the ‘S.’ obtusidens holotype (NHMUK PV R 3168), but on referred specimens (i.e. NHMUK PV R 3169, Peterborough Museum and Art Gallery, Peterborough, PETMG R39 and PETMG R178). We agree with Adams-Tresman (1987) that PETMG R39 matches the ‘S.’ obtusidens holotype (see Discussion). However, the other two specimens lack the apomorphies of the ‘S.’ obtusidens holotype (see description below), and thus cannot be referred to this taxon (we argue that they instead should be referred to S. edwardsi, see Discussion). This means that Adams-Tresman’s (1987) discussion regarding tooth morphology and dorsal osteoderm ornamentation were correct and NHMUK PV R 3169 and PETMG R178 do indeed belong to S. edwardsi. However, we show below that these characteristics are distinct from those in the ‘S.’ obtusidens holotype, NHMUK PV R 3168. Young et al. (2015a) also noted that Adams-Tresman (1987) did not discuss the presence of three sacral vertebrae in the ‘S.’ obtusidens holotype, while Andrews (1913: 132) considered it likely to be an ‘individual peculiarity’ of the holotype. The neotype of Machimosaurus mosae Sauvage & Liénard, 1879 also has three sacral vertebrae (Hua, 1999; Young et al., 2014a). Another set of characteristics not mentioned by Adams-Tresman (1987) are the pronounced socket-like reception pits along the maxilla and dentaries for the opposing tooth row. Again, this may have been due to Andrews (1913: 131) being unsure if they were a natural characteristic or a result of postmortem deformation. However, this is another characteristic that the ‘S.’ obtusidens holotype (NHMUK PV R 3168) shares with Machimosaurus (Buffetaut, 1982b; Lepage et al., 2008; Young et al., 2014a; note that Young et al., 2014a considered vertically orientated, interlocking dentition, with pronounced reception pits at the premaxillary, maxillary and dentary interalveolar spaces to be a Machimosaurus apomorphy). It is unclear whether Adams-Tresman (1987) was being selective in what characteristics the ‘S.’ obtusidens referred specimens and the S. durobrivensis holotype and referred specimens shared, or simply being cautious in regards to morphologies unique to the ‘S.’ obtusidens holotype. ‘Steneosaurus’ obtusidens was also considered to be a subjective junior synonym of the Kimmeridgian species Machimosaurus hugii von Meyer, 1837 (Hua et al., 1994; Hua, 1996, 1999). However, these authors noted that the taxonomy of blunt-toothed teleosaurids still required further study. More recently, Pierce et al. (2009) suggested that ‘S.’ obtusidens, Steneosaurus hulkei Andrews, 1913 and S. durobrivensis (all Callovian taxa; the species S. edwardsi was not mentioned) were subjective junior synonyms of M. hugii. This synonymy and corresponding species diagnoses have been criticized and rejected (see Martin & Vincent, 2013; Young et al., 2014a; Johnson et al., 2015) and, indeed, all phylogenetic analyses that include the relevant taxa do not support any of the two proposed synonymies (S. durobrivensis = S. edwardsi and M. hugii). In these analyses, ‘S.’ obtusidens is consistently found to be the sister taxon of Machimosaurus, while S. durobrivensis (=S. edwardsi) is the sister taxon to this sub-clade (Young et al., 2012; Martin & Vincent, 2013; Young, 2014; Fanti et al., 2016; Young et al., 2016a). Recent papers have agreed that ‘S.’ obtusidens is a distinct taxon (Martin & Vincent, 2013; Young et al. 2014a, 2015a). Finally, Jouve et al. (2016) established the tribe Machimosaurini for ‘S.’ obtusidens, Machimosaurus and indeterminate Bathonian specimens (based on shared craniodental morphologies; see Introduction). Geological setting The OCF is a Jurassic (Callovian – lower Oxfordian) lithostratigraphic unit that is well known from extensive exposures that extend from the western Dorset coast to northern Yorkshire of England (Selden, Baker & Phipps, 2008). The entire OCF is composed of two main facies: the lowermost Peterborough Member and an upper facies that comprises the Stewartby Member and Weymouth Member (Cox, Hudson & Martill, 1992; Martill et al., 1994; Selden et al., 2008). The Peterborough Member, referred to in older literature as the Lower Oxford Clay, consists of compact olive-coloured shaly clays and black and organic-rich fissile shales (Hudson & Martill, 1994; Martill et al., 1994). This member contains a diverse vertebrate fauna, including: bony fish and chondrichthyans, marine reptiles (ichthyosaurs, plesiosaurs, pliosaurs and thalattosuchians) and rare dinosaur and pterosaur remains (Martill et al., 1994). Oxygen isotope values (Kenig et al., 1994) indicate that the OCF was deposited in a shallow marine, open-shelf environment. The Cornbrash Formation is a Bathonian–Callovian (Middle Jurassic) lithostratigraphic unit that underlies the OCF (Wright, 1977). This stratigraphic section consists of medium- to fine-grained limestone that is bioturbated, yields many reptilian fossils and stretches from the Weymouth area to the Scarborough area in the UK (Cox & Sumbler, 2002), similar to the OCF. The Cornbrash Formation is comprised of two main units, the Cornbrash Limestone and the Cornbrash Shales, which form a transgressional marine cycle (Wright, 1977). The Cornbrash Formation represents a section of the Great Oolite Group (Sellwood et al., 1985). Migné-les-Lourdines (the locality of specimen LPP.M.21) is a small town just north of Poitiers, France. The Coronatum Zone (ammonite zone named after E. coronatum) in France is Middle Callovian (Brunet, 1969; Vignaud P, unpublished data) and corresponds to the Peterborough Member of the OCF in the UK. At Migné-les-Lourdines, this ammonite zone is represented by a white calcareous limestone (Brunet, 1969). ABBREVIATIONS Institutional CAMSM, Sedgewick Museum of Earth Sciences, University of Cambridge, Cambridge, UK; DORCM, Dorset County Museum, Dorchester, UK; GLAHM, The Hunterian Museum, Glasgow, UK; GPIT, Paläontologische Sammlung der Eberhard Karls Universität Tübingen, Tübingen, Germany; LPP, Institut de paléoprimatologie, paléontologie, humaine; évolution et paléoenvironnements Université de Poitiers, Poitiers, France; MNHN, Muséum national d’histoire naturelle, Paris, France; NHMUK, Natural History Museum, London, UK; NMS, Naturmuseum Solothurn, Solothurn, Switzerland; NOTNH, Nottingham Natural History Museum, Nottingham, UK; OUMNH, Oxford University Museum of Natural History, Oxford, UK;. PETMG, Peterborough Museum and Art Gallery, Peterborough, UK; SMNS, Staatliches Museum für Naturkunde Stuttgart, Baden-Württemberg, Germany. Anatomical XII, cranial nerve 12; ac dep, acetabular depression; ac in, acetabular incision (acetabular notch); an, angular; ant f, anterior flange of second sacral vertebra; ant pr, anterior process of ilium; ar, articular; art f, articular facet; atl, atlas; ax, axis; bas, basisphenoid; cen, vertebral centrum; clp, lateral process of calcaneum; cmp, medial process of calcaneum; cor, coronoid; cor gr, coronoid groove; den, dentary; fm, foramen magnum; fo, foramina; fr, frontal; ft, ‘fourth trochanter’ rugose area; fem h, femoral head; fib, fibula; gf, glenoid fossa; hc, humeral concavity; hs, humeral shaft; if, incisive foramina; isch bl, ischial blade; jug, jugal; k, keel of osteoderms; lac?, uncertain lacrimal area; le, lateral epicondyle (of humerus); m con, medial condyle of femur; me, medial epicondyle (of humerus); mx, maxilla; mx gr, maxillary groove; na, nasal; ns, neural spine; oc, occipital condyle; od, odontoid; or, orbit; pal, palatine; par, parietal; pat, pathology; pit, ornamentation pit on dorsal surface of osteoderms; pmx, premaxilla; pmx1-2, first and second premaxillary tooth; pn, pubic neck; po, postorbital; poz, postzygapophyses; pp, pubic plate; prf, prefrontal; prz, prezygapophyses; pt, pterygoid; pub, pubis; q, quadrate; rib h, rib head; s1, first sacral vertebra; s2, second sacral vertebra; s3, third sacral (refers to first caudal) vertebra; spl, splenial; sq, squamosal; st h, sternal head; sub r, sub-horizontal anterior ridge of ilium; sup cr, supraacetabular crest of ilium; sup occ, supraoccipital; supr fen; supratemporal fenestra; san, surangular; tub, tuberculum; tp, transverse process; t tub, tibial tuberosity; vac?, vacuity. SYSTEMATIC PALAEONTOLOGY Crocodylomorpha Hay, 1930 (sensu Nesbitt, 2011) Thalattosuchia Fraas, 1901 (sensu Young & Andrade, 2009) Teleosauridae Geoffroy Saint-Hilaire, 1831 Machimosaurini Jouve et al., 2016 Machimosaurini indeterminate v 1905 Machimosaurus rigauxi Sauvage – Blake, p. 26, Plate 1, fig. 5a–c v 2014a Machimosaurus rigauxi Sauvage – Young et al., p. 3 We have identified isolated teeth that have a characteristic Machimosaurini dental pattern (see Lemmysuchus description): GPIT/RE/301, CAMSM J64508 and OUMNH J.14464. The first tooth crown GPIT/RE/301 (Fig. 12E–I) is from the OCF of Peterborough and was excavated before 1906. It was sold to the Eberhard Karls Universität in Tübingen, Germany, during the first decade of the 20th century. A note in the collections by E. Buffetaut in 1981 suggested that it could be ‘S.’ obtusidens, while another specimen note by B. Stürtz (a commercial fossil collector from Bonn) suggested that it might belong to Machimosaurus but was similar to the genus Steneosaurus. The tooth is conical, robust with a blunt apex and posteriorly curved. The majority of the root is missing. The tooth is single-cusped and has no accessory cusps or cingula. The enamel ridges are well defined and pronounced and are close in parallel vertical rows. The enamel ornamentation is similar to the L. obtusidens holotype (NHMUK PV R 3168), with randomly arranged ridges near the apex that are straight, parallel and closely packed together towards the root of the tooth. Another isolated tooth, CAMSM J64508 (Fig. 12J–P), was collected in Fletton (Cambridgeshire) and is also possibly from the Leeds Collection. It has originally been regarded (by whom is unknown) as a pliosaurid of the genus Simolestes, most likely for its size. However, the curvature, blunt apex, presence of pronounced carinae and ornamentation patterns distinguish it from any late Middle Jurassic pliosaurids. The tooth is conical and has a circular cross-section which is maintained through the whole apicobasal length. As typical in Machimosaurus and L. obtusidens, the tip of the crown is blunt (Young et al., 2014a, b). The considerable size of the crown (~5 cm apicobasal length) and the height-to-length ratio suggests CAMSM J64508 may be one of the large dentary or premaxillary pseudocaniniform teeth. The crown is clearly ornamented by long continuous and evenly spaced apicobasal ridges that occur with the same density on the labial, mesial and lingual sides. As in Machimosaurus and L. obtusidens, the ornamental ridges on the apex become shorter until they form the characteristic anastomosed pattern (Young et al., 2014a, 2015a, b). Interestingly, this ornamentation pattern is convergent with the Late Jurassic metriorhynchid Torvoneustes carpenteri (Wilkinson,Young & Benton, 2008). In CAMSM J64508, the carinae are present although almost indistinguishable for most of the crown length (Fig. 12J–P). However, they can be observed in the apical ‘anastomosed region’. The carinal keel is considerably clearer on one side than the other. The ornamentation pattern of the apex contacts the carinae forming false serrations (Young et al., 2015a). Tooth OUMNH J.14464 (Fig. 12Q–T) is from the Cornbrash Formation and was figured by Blake as Machimosaurus rigauxi Sauvage, 1879 (Blake, 1905: 26: Plate 1, fig. 5a–c). The crown of this tooth is intact and the root is missing. The apex is slightly pointed and the entire tooth is conical and mediolaterally thickened. The mesial and distal carinae are faint, not as pronounced as in GPIT/RE/301, and when viewed with the naked eye terminate in the middle of the tooth. The numerous enamel ridges run ventrally parallel and close together. At the apex, the ridges are disoriented and extend in random patterns, much as how Andrews (1913) described the teeth of the L. obtusidens holotype (NHMUK PV R 3168). The two tooth crowns from the OCF (GPIT/RE/301 and CAMSM J64508) may be referable to L. obtusidens. However, as they are isolated crowns, we refrain from making that assignment. The M. rigauxi tooth (OUMNH J.14464) is interesting as it is from the Cornbrash Formation, a lithostratigraphic unit that L. obtusidens is currently not known from. Lemmysuchus gen. nov. (Figs 1–21) urn:lsid:zoobank.org:act:83D7C69A-4009-478E- 8D6E-A05F39E190D1 Type species Steneosaurus obtusidens Andrews, 1909 [following recommendation 67B of the International Commission on Zoological Nomenclature (ICZN) code]. Now referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Diagnosis Same as the only known species (monotypic genus). Etymology ‘Lemmy’s crocodile’. Lemmy referring to Ian Fraser Kilmister, better known as ‘Lemmy’, the deceased founder, bassist and lead singer of Motörhead, and suchus is the Latinized form of the Greek soukhos (σοῦχος), meaning crocodile. Lemmysuchus obtusidens (Andrews, 1909) comb. nov. urn:lsid:zoobank.org:act:83D7C69A-4009-478E- 8D6E-A05F39E190D1 v* 1909 Steneosaurus obtusidens Andrews, p. 306, Plate 9 figure 2 v 1913 Steneosaurus obtusidens Andrews – Andrews, p. 130, Text-fig. 50, Plate 7 all figures (partim) v 1969 Steneosaurus cf heberti Morel de Glasville – Brunet, Plate 1 figure b-b (LPP.M.21) v 1973 Steneosaurus obtusidens Andrews – Steel, p. 33, figure 13.13 v 1987 Steneosaurus durobrivensis Andrews – Adams-Tresman, p. 205 (partim) 1993 Steneosaurus cf heberti Morel de Glasville – Vignaud v 1994 Machimosaurus hugii von Meyer – Hua et al., p. 15 (partim) v 1996 Machimosaurus hugii von Meyer – Hua, p. 1562 (partim) v 2009 Machimosaurus hugii von Meyer – Pierce et al., p. 1085 (partim) v 2013 Steneosaurus obtusidens Andrews – Martin & Vincent, p. 192 v 2014a ‘Steneosaurus’ obtusidens Andrews – Young et al., p. 3 v 2014b ‘Steneosaurus’ obtusidens Andrews – Young et al., p. 2 v 2016 ‘Steneosaurus’ obtusidens Andrews – Jouve et al., p. 4 Holotype NHMUK PV R 3168, complete cranium and mandible in articulation, atlas–axis complex, 6 postaxial cervical vertebrae, 14 dorsal vertebrae, 3 sacral vertebrae, 21 caudal vertebrae, 1 complete cervical rib and 20 cervical rib fragments, 49 dorsal rib fragments (fewer than 5 complete ribs), 2 gastralia fragments, 1 right scapula, 1 distal fragment of a humerus, 1 ulna, 1 right ilium, both ischia, 1 pubis, both femora, 1 tibia, possible pieces of fibulae or carpals/tarsal elements, 5 ankle bones (including a calcaneum, distal tarsal and astragalus), 4 phalanges, numerous dermal osteoderms (~56), 33 isolated teeth and numerous bone fragments (Figs 1–3, 12A–D, 13–21). Figure 1. View largeDownload slide Photograph (A) and line drawing (B) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in dorsal view with additional details of the premaxillary dentition. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 1. View largeDownload slide Photograph (A) and line drawing (B) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in dorsal view with additional details of the premaxillary dentition. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 2. View largeDownload slide Photograph (A, C) and line drawing (B, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 2. View largeDownload slide Photograph (A, C) and line drawing (B, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 3. View largeDownload slide Photograph (A, B) and line drawings (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in anterior (A, C) and occipital (B, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 3. View largeDownload slide Photograph (A, B) and line drawings (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in anterior (A, C) and occipital (B, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Etymology ‘Lemmy’s blunt-toothed crocodile’. From the Latin for blunt (obtusus) and tooth (dens). Named for the blunt apices of the teeth. Type locality Peterborough, England, UK. The exact age and area of collection of this specimen is not known, original Leeds Collection Number 6. Type horizon Peterborough Member, OCF, Ancholme Group. Middle Callovian, Middle Jurassic. Referred specimens PETMG R39, largely incomplete rostrum, fragment of right mandibular ramus, partial dorsal osteoderm and five dorsal vertebral centra. PETMG R31, five vertebral centra (two dorsals and three sacrals), are associated with PETMG R39 and very likely belong to the same individual (see Discussion) (Peterborough Member, OCF, Ancholme Group; Middle Callovian). LPP.M.21, nearly complete skull (left lateral portion not preserved from the orbit to the squamosal) and mandible (anterior region is preserved) (E. coronatum ammonite Zone, Middle Callovian). NOTNH FS3361, partial rostrum, including the premaxillae and part of the maxillae (horizon and locality unknown, thought to be OCF because of the state of preservation). Emended diagnosis Teleosaurid crocodylomorph with the following unique combination of characters [proposed autapomorphic characters are indicated by an asterisk (*)]: the rostrum external surface is strongly convex, in particular the nasals*; partial or complete fusion of the internasal suture*; axis lacks diapophyses (shared with Steneosaurus bollensis Jaeger, 1828; see Westphal, 1962); the ilium anterior process is small and anteroposteriorly shortened*; on the ilium the acetabulum is shallow and poorly developed*; shallow supraacetabular crest on the ilium*; the dorsal osteoderm ornamentation is composed of small-to-large, irregularly shaped pits that radiate from the centre of the keel and are arranged in a starburst pattern (to a certain extent similar to M. mosae; Hua, 1999; Young et al., 2014a)*. Characteristics shared with Machimosaurus Lemmysuchus obtusidens shares the following nine synapomorphies with Machimosaurus (sensuYoung et al., 2014a): (1) conical teeth with blunt/rounded apices; (2) tooth enamel ornamentation varies along the crown, that is, in the basal region enamel ornamentation is composed of numerous apicobasally aligned ridges of high relief, which transition into an anastomosed pattern in the apical region; (3) teeth have true and false denticles on the carinae; (4) ratio of crown apicobasal height to basal transverse width can be as low as 1.8 in the posterior teeth; (5) pronounced socket-like reception pits along the maxilla and dentaries for the opposing tooth row; (6) the supratemporal fossae are parallelogram-shaped in dorsal view; (7) three sacral vertebrae; (8) ischial blade posterior margin is blunt and sub-square in shape and (9) proximal tibia strongly deflects anteriorly. However, L. obtusidens lacks the following eight Machimosaurus autapomorphies (sensuYoung et al., 2014a; note that the two axis neural spine autapomorphies cannot be determined in L. obtusidens due to preservation): Three alveoli per premaxilla (L. obtusidens has four alveoli per premaxilla). The first premaxillary alveoli are orientated strongly anteroventrally (L. obtusidens lacks this condition). 18–22 alveoli per maxilla (L. obtusidens has at least 29 alveoli per maxilla). 19–25 alveoli per dentary (L. obtusidens has ~29 alveoli per dentary). Presence of carinae is variable in Machimosaurus spp. (in L. obtusidens all teeth have carinae). The rostrum is broad and mesorostrine, constituting fewer than 60% of the basicranial length (in L. obtusidens, the rostrum is 61.2% of basicranial length and is less broad, thus falling slightly outside the condition seen in Machimosaurus). Ratio of maximum supratemporal fossa length to basicranial length is greater than 27% (in L. obtusidens, this ratio is 25.8%). Medial quadrate hemicondyle is considerably smaller than the lateral hemicondyle (in L. obtusidens both condyles are large and similar in size). Lemmysuchus obtusidens (NHMUK PV R3168), Machimosaurus, Steneosaurus heberti Morel de Glasville, 1876 (MNHN.F 1890-13) and S. edwardsi (NHMUK PV R3701) share three characteristics: (1) anterior processes of the jugals are very elongate and slender, so that they largely restrict a lacrimal-maxilla contact on the external surface, except for the anterolateral margins of the lacrimals which do contact the maxillae (Fig. 6); (2) the Meckelian canal (=groove) is not deeply excavated on the dorsal surface of the splenials (Fig. 9) in contrast to other thalattosuchians such as Steneosaurus leedsi Andrews, 1909 (NHMUK PV R3320) and (3) the closure of the antorbital fenestrae (Fig. 22D–G) (see description below on how we conclude that L. obtusidens lacks these fenestrae). Note that Young et al. (2014a) listed the absence of antorbital fenestrae was shared by Machimosaurus (SMNS 91415) and S. heberti. Lemmysuchus obtusidens also shares one characteristic with S. heberti (MNHN.F 1890-13); sharp dorsoposterior curvature of the posterior mandibular rami (as opposed to gradual curvature in S. edwardsi) (PETMG 178) (Fig. 22A–C). Character note Lemmysuchus obtusidens has two characteristics that are well developed in the holotype but not clear in other OCF teleosaurid specimens (because of the typically poor preservation of skulls, through dorsoventral crushing and/or shearing). These are: (1) a large nuchal crest on the supraoccipital and (2) large and pronounced paired occipital tuberosities (somewhat similar to those seen in dyrosaurid crocodyliforms, which are developed to a much greater extent; e.g. MNHN.F ALG 1). These characteristics, albeit in a reduced form, are also seen in Teleosaurus cadomensis Lamouroux, 1820 (MNHN cast of an adult skull, MNHN.F AC 8746; Jouve, 2009), S. heberti (MNHN.F 1890-13) and Machimosaurus buffetauti Young et al., 2015 (SMNS 91415; Martin & Vincent, 2013; Young et al., 2014a). Description The holotype of L. obtusidens, NHMUK PV R 3168, comprises a nearly complete skeleton (Figs 1–3, 12A–D, 13–21) (Andrews, 1909, 1913). The cranium and mandible adhere together so tightly that the cranium palatal view and mandible dorsal view is inaccessible; LPP.M.21, however, preserves the palatal view, which is easily accessible (Fig. 8C, D), and NOTNH FS3361 preserves part of the rostrum, including the premaxillae (Figs 10, 11). The cranium has experienced dorsoventral compression and has numerous fractures making it difficult to discern sutures from breaks. However, PETMG R39 is well preserved (Figs 4–6), and the preorbital area, cranium palatal surface and part of the mandibular dorsal surface can be described from this specimen. Figure 4. View largeDownload slide Photograph (A, C) and line drawing (B, D) of PETMG R39, referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 4. View largeDownload slide Photograph (A, C) and line drawing (B, D) of PETMG R39, referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 5. View largeDownload slide Photograph (B, D) and line drawing (B, D) of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 5. View largeDownload slide Photograph (B, D) and line drawing (B, D) of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 6. View largeDownload slide Close-up of right lateral view of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov, showing in detail the maxilla, jugal, nasal and lacrimal bones. Outlines the jugal-maxilla and lacrimal-jugal contacts. Note the absence of antorbital fenestrae. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 6. View largeDownload slide Close-up of right lateral view of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov, showing in detail the maxilla, jugal, nasal and lacrimal bones. Outlines the jugal-maxilla and lacrimal-jugal contacts. Note the absence of antorbital fenestrae. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 7. View largeDownload slide Partial mandible section of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov., in (A) dorsal, (B) lateral, (C) ventrolateral, (D) ventral and (E) anterior views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 7. View largeDownload slide Partial mandible section of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov., in (A) dorsal, (B) lateral, (C) ventrolateral, (D) ventral and (E) anterior views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 8. View largeDownload slide Photographs (A, C) and line drawings (B, D) of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 8. View largeDownload slide Photographs (A, C) and line drawings (B, D) of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 9. View largeDownload slide Photograph (A) and line drawing (B) in dorsal view of the mandibular interior of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 9. View largeDownload slide Photograph (A) and line drawing (B) in dorsal view of the mandibular interior of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 10. View largeDownload slide Dorsal (A, B), left lateral (C, D), ventral (E, F) and right lateral (G, H) photographs and line drawings of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Note the small incisive foramina and the number of alveoli in the premaxillae and maxilla. Scale bar: 10 cm. Figure 10. View largeDownload slide Dorsal (A, B), left lateral (C, D), ventral (E, F) and right lateral (G, H) photographs and line drawings of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Note the small incisive foramina and the number of alveoli in the premaxillae and maxilla. Scale bar: 10 cm. Figure 11. View largeDownload slide Ventral close-up of (A) photo and (B) line drawing of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 11. View largeDownload slide Ventral close-up of (A) photo and (B) line drawing of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Cranium: The cranium of L. obtusidens (NHMUK PV R 3168) (Figs 1–3) is ~1.4 m long (Andrews, 1909, 1913). It is similar to Machimosaurus in terms of overall anatomy and robusticity. The rostrum is more robust but comparatively shorter than those of other Middle Jurassic teleosaurids (e.g. S. leedsi, S. heberti, Mycterosuchus nasutus) (Andrews, 1913) and comprises 61.2% of the total skull length [the 51% ratio given in Andrews (1913) was a typographical error]. The anterior premaxilla and dentaries are laterally expanded as in other teleosaurids (e.g. Andrews, 1909, 1913; Hua, 1999; Martin & Vincent, 2013; Young et al., 2014a). In NHMUK PV R 3168 (Fig. 1), the preorbital region is deformed, possibly due to an infection of the bone caused by a bite (there is a large tooth deeply embedded in this region of the cranium). Conversely, PETMG R39 (Figs 4, 5) and LPP.M.21 (Fig. 8A, B) are well preserved in this area. Based on NHMUK PV R 3168 (Figs 1–3), LPP.M.21 (Fig. 8) and PETMG R39 (Figs 4, 5), the orbits would have been large, oval in shape and oriented more anteroposteriorly than in most other teleosaurids (such as S. leedsi NHMUK PV R 3806). In dorsal view, the supratemporal fenestrae (Fig. 1) are considerably longer than wide and are considerably longer than the orbits. The cranial description refers to the holotype (NMHUK PV R 3168) unless otherwise specified. Due to the fragility and heaviness of the NHMUK PV R 3168 cranium, the authors were unable to flip it over to observe the palates. Therefore, all information pertaining to the palatal surface comes from LPP.M.21. Premaxillae: The premaxillae (Figs 1, 2, 3A, C) are large and robust, surround the external narial opening and face anterodorsally. The external nares are laterally expanded and their posterior margins do not reach beyond the third premaxillary alveolar pair. The anterior two-thirds of the premaxilla is laterally expanded and the anterior margin is ventrally deflected, giving the snout a scoop-like appearance. In LPP.M.21 (Fig. 8A, B) and NOTNH FS3361 (Figs 10, 11), the incisive foramen (=naso-oral fenestra) is very small and is situated in the middle of the suture of the premaxillae. In dorsal view, the premaxilla–maxilla suture is well developed and W-shaped. The left premaxilla–maxilla suture is directed proximodistally parallel towards the middle of the rostrum with two small, pointed, posterior-oriented processes edges in dorsal view. The premaxilla contains four teeth, with the fourth (posterior-most) being the largest. The first two premaxillary alveoli are nearly confluent, with a thin interalveolar lamina separating them. The interalveolar lamina is missing in NOTNH FS3361 and LPP.M.21, making it appear as though there were only three premaxillary teeth present (this feature is noted in Vignaud, 1997). There is a diastema between the last premaxillary tooth and the first maxillary tooth. In life, large dentary caniniform teeth would have been present (as in Machimosaurus and other large teleosaurids; Andrews, 1909, 1913; Martin & Vincent, 2013). Maxillae: The maxillae (Figs 1, 2, 3A, C) form a substantial part of the rostrum. Their lateral margins are sub-parallel in dorsal view. The maxilla separates the nasals from the premaxillae. The precise maxillary tooth count is difficult to determine but there are ~29 alveolar pairs (Andrews, 1913). The specimen LPP.M.21 has 29 alveolar pairs (Fig. 8C, D) and NOTNH FS3361 preserves ~26 alveolar pairs (the posterior portion of the maxilla is missing) (Fig. 10E, F). The lateral surface of the maxilla is ornamented by well-spaced, deep foramina that are visible in both dorsal, lateral and anterior views (Figs 1, 2, 3A, B). The maxillary tooth row ends anterior to the anterior-most border of the sub-orbital fenestra. Numerous, deep reception pits for dentary teeth are along the middle and anterior regions of the ventral-lateral margin of the maxillae (Fig. 2). The posterolateral regions of both maxillae in PETMG R39 have a groove which follows approximately parallel with the long anterior process of the jugal (Figs 4–6). This feature is shared with Machimosaurus, S. heberti (MNHN.F 1890-13) and S. edwardsi (Martin & Vincent, 2013; Young et al., 2014a). There is a small pathology on the ventral right maxilla in NOTNH FS3361 (Fig. 10). Jugals: The jugals are triradiate and form the lateral border of the orbit (Figs 1, 2, 4–6, 8A, B) as in other teleosaurids (Andrews, 1909, 1913). The jugal is dorsally compressed by the postorbital-squamosal and is ventrally compressed by the dentary due to poor preservation. The anterior margin of the jugal runs between the lacrimal and posterior regions of the maxilla (Figs 2, 3A, C). This feature is shared among S. edwardsi (PETMG R175), S. heberti (MNHN.F 1890-13), L. obtusidens (PETMG R39) (Figs 4–6), M. hugii (NMS 7012) and possibly also M. buffetauti (the holotype SMNS 91415 is poorly preserved in this region). However, it is only in Lemmysuchus and Machimosaurus that the jugal is extremely elongate, it anteriorly extends and reaches the anterior end of the lacrimal. The postorbital-jugal or quadratojugal-jugal contacts cannot be seen clearly in NHMUK PV R 3168, as the specimen is crushed in those areas. In LPP.M.21, the postorbital-jugal contact is anteroposteriorly straight (Fig. 8A, B). The quadratojugal-jugal contact is not clear in either NHMUK PV R 3168 or LPP.M.21. Nasals: The nasals (Figs 1, 2, 3A, C) are large triangular bones exposed on the dorsal surface of the posterior rostrum and orbital area. Both nasals (in NHMUK PV R 3168) are missing their anterior and posterior regions. The nasal anterior processes extend past the third maxillary tooth. Deformation, due to an embedded tooth previously mentioned from another animal (which is circular and has left a striated impression behind), obscures the view of the anterior region of the nasal anterior processes. The nasals have a little ornamentation, consisting of faint ridges. There is a faint internasal midline suture on the anterior rostrum; further posteriorly there is no internasal suture, suggesting the nasals are partially or completely fused. This is seen in NHMUK PV R 3168 as well as LPP.M.21 (Fig. 8A, B), NOTNH FS3361 (Fig. 10A, B) and PETMG 39 (Fig. 4A, B). Both nasals form the beginning of a dorsally directed ‘dome’ towards the medial contact with the frontal. PETMG 39 (Figs 4, 5) and NOTNH FS3361 (Fig. 10) show the beginning of the ‘dome’ in the anterior nasals (as the posterior nasals are not preserved in NOTNH FS3361). In LPP.M.21 (Fig. 8A, B), it is not clear if the nasals are convex (due to dorsoventral crushing, although this could be an ontogenetic feature), and the nasal anterior processes are approximately one-third of the posterior rostrum and have well-developed near-parallel suture contacts with the maxillae. Prefrontals: The prefrontals (Figs 1, 2) are slightly sub-circular in dorsal view and form the anteromedial border of the orbits. The prefrontal contacts the nasal medially and the lacrimal laterally. The frontal-prefrontal contact cannot be clearly seen even in the better preserved PETMG R39 due to breaks in this area (Figs 4–6). In LPP.M.21 (and to some extent on the right side in NOTNH FS3361), the prefrontal contacts the frontal posteromedially at a straight angle (Figs. 8A, B). The prefrontals are well developed and tear-shaped (Figs. 8A, B, 10). Lacrimals: The lacrimals are better preserved in PETMG R39 (Figs 4–6) and LPP.M.21 (Fig. 8A, B) than in NHMUK PV R 3168 (Figs 1, 2) even though the medial and posterior margins are not preserved well. The lacrimals are large and triangular as in other teleosaurid taxa (Andrews, 1909, 1913) and constitute most of the anterior-lateral border of the orbits. Andrews (1913) reported paired openings ~5–7 cm anterior to the lacrimal in NHMUK PV R 3168 that he considered to be antorbital fenestrae, describing them as no more than 5 cm in length and longer than wide (Andrews, 1913). PETMG R39 (Figs 4–6), NOTNH FS3361 (Fig. 10) and LPP.M.21 (Fig. 8A, B) show that L. obtusidens did not have antorbital fenestrae. As such, we interpret these ‘openings’ in NHMUK PV R 3168 to be cracks caused by compression. Frontal: The frontal (Figs 1, 2, 3A, C) is a large and deep (dorsoventrally thickened) bone with no evidence of a midline suture. The anterior region slightly slopes anteriorly in conjunction with the posterior nasal and descends posteriorly, giving it a ‘domed’ appearance (Figs 2, 3A, C). The anterior process is not preserved; however, it is well preserved in LPP.M.21 (Fig. 8A, B), showing that it is as short as in most other teleosaurids (e.g. S. leedsi; see Andrews, 1913). The frontal contributes to the posteromedial border of the orbits (Figs 1, 2) and is well seen in LPP.M.21 (Fig. 8A, B). The frontal forms a straight vertical contact with the postorbital in dorsal view and forms the anterior medial borders of the supratemporal fenestrae. The ornamentation on the frontal does not differ from other OCF teleosaurids and consists of pronounced irregular ridges radiating from the centre of the bone. Postorbitals: The large, robust postorbitals (Figs 1, 3A, C) form the lateral and part of the posteroventral border of the orbits. In lateral view, the dorsoventral suture of the postorbital contacts the squamosal and the left postorbital strongly contacts the frontal and forms the posterior margin of the orbit. Because both postorbitals are broken, the postorbital bars are not preserved in NHMUK PV R 3168. In LPP.M.21, the postorbital bar is similar to other OCF teleosaurids (Fig. 8A, B). It forms the posterior margin of the orbit, is slightly anteroposteriorly thickened and of standard mediolateral length. Parietal: The unornamented parietal (Figs 1, 2, 3A, C) is a single bone with no trace of a midline suture that contributes to the medial and posterior borders of the supratemporal fenestrae. Dorsally the parietal does not overhang the occipital condyle. The parietal bar is relatively thin and anteroposteriorly elongated. The posterior region of the parietal is anteriorly concave. In LPP.M.21, there is little to no ornamentation on the parietal (Fig. 8A, B). Squamosals: The squamosals (Figs 2, 3B, D) are large, anteroposteriorly elongate, L-shaped bones and are well preserved in LPP.M.21 (Fig. 8A, B). The squamosal forms the posterolateral border of the supratemporal fenestrae and its posterolateral surface is concave. It contacts the quadrate posteroventrally in lateral view. The squamosal bar is robust and anteriorly contacts the postorbital bar (together forming the supratemporal arch). In NHMUK PV R 3168, the left squamosal is distorted and flattened due to poor preservation. Quadrates: The quadrates (Figs 1, 3B, D) are large, robust and are strongly sutured to the squamosals and quadratojugals. The anterodorsal region of the quadrate contacts the squamosal and quadratojugal while the posteroventral margin articulates with the angular (=jaw joint) and medially contacts the exoccipital. The posteroventral lateral and medial hemicondyles are approximately the same size and length. They are both elongated mediolaterally, are oval in shape and have rounded posterior edges. In occipital view, the hemicondyles posteriorly extend further than the exoccipitals. The right quadrate is well preserved while the left quadrate is not. In LPP.M.21, the quadrates are large and mediolaterally expanded in ventral view (Fig. 8C, D). Quadratojugals: The quadratojugals are dorsally and ventrally compressed and are not visible in dorsal view. The posterior region of the quadratojugal is expanded mediolaterally to accommodate the quadrate and extends slightly further than the outermost tip of the quadrate. Ectopterygoids: Only the right ectopterygoid is preserved in NHMUK PV R 3168. Anteriorly it contacts with the maxilla. The contact with the pterygoids and palatines cannot clearly be seen. The dorsal surface of the ectopterygoid is slightly concave. The right ectopterygoid is preserved in LPP.M.21 and curves ventromedially (Fig. 8A, B). Supraoccipital: The supraoccipital is positioned ventral to the parietal and is only visible in occipital view (Fig. 3B, D). The ventral edge is not triangular but curved so it appears as two ‘lobes’ (Fig. 3). A large nuchal crest (Fig. 3B, D) is situated directly in the middle of the supraoccipital. Exoccipital: The exoccipitals make up the majority of the occipital surface of the cranium. The right side has been medially compressed and the dorsal rim curves medially, while the left side tilts dorsally and flares mediolaterally. The exoccipitals are dorsally expanded above the foramen magnum, as in M. buffetauti and M. mosae (Hua, 1999; Martin & Vincent, 2013). Laterally, the exoccipitals descend rapidly, so in occipital view, they appear almost box-like. The exoccipitals contribute to the occipital condyle. The paraoccipital processes are small and the lateral wings are elongate and robust. The foramen for cranial nerve XII is small and parallel to the foramen magnum (Fig. 3B, D). Basioccipital: The basioccipital contributes to the ventral region of the foramen magnum and is slightly wider than tall. The occipital condyle is larger and more circular than the foramen magnum. In ventral view (LPP.M.21), two well-developed and slightly anteroposteriorly elongated basioccipital tuberosities are visible, with the left one being larger due to variable preservation (Fig. 8C, D). Pterygoid: The right pterygoid wing is present in the holotype (NHMUK PV R 3168), but it is poorly preserved; it is unclear how complete the pterygoid wing is in this specimen without access to the palatal view. The left pterygoid is similarly broken but the lateral pterygoid wing is accessible laterodorsally. It is large and elongated craniocaudally and lateromedially. The dorsal surface of the wing is concave and the posterior region curves anteromedially, possibly due to breakage. In ventral view (LPP.M.21), the pterygoid is thin and elongated and contributes to the medial and posterior borders of the sub-orbital fenestrae, which are tear-shaped (thin anteriorly, wide and slightly rounded posteriorly) (Fig. 8). In LPP.M.21, the anterior process of the pterygoid articulates with the palatines (Fig. 8C, D). Palatines: All information from the palatines comes from LPP.M.21 and PETMG R39. The palatines (Fig. 8C, D) are dorsoventrally thin, elongate bones and are similar in form to other teleosaurids, such as S. leedsi (NHMUK PV R 3806) (Andrews, 1913). In LPP.M.21, the anterior regions of both palatines are not preserved and both posterior regions are slightly deformed; however, PETMG R39 preserves the anterior palatines that are slightly rounded, have small anterior processes and articulate with the posterior processes of the maxillae (Fig. 4C, D). The palatines contact one another along the skull midline until posteriorly they are separated by the anterior process of the pterygoid. The anterior extensions of the palatine are nearly parallel to the maxillary tooth row, similar to M. buffetauti (Martin & Vincent, 2013). Basisphenoid: The anterior surface of the basisphenoid (LPP.M.21) is deformed (Fig. 8C, D). This structure has two elongated posterolaterally directed processes and comes into posterior contact with the quadrate. Other elements: The proötic and laterosphenoid are not visible in dorsal or ventral views, and as a result we could not properly describe these bones. Mandible: The mandible of NHMUK PV R 3168 is diagenetically deformed and attached to the cranium so that the dorsal surface is not visible. The mandibular symphysis measures ~58 cm, contributing ~42.3% of the entire length (Young et al., 2015a). Among other specimens, only a short segment of the right mandibular ramus in PETMG R39 is preserved and it clearly shows the contact among the dentary, angular and splenials to be posterior to the mandibular symphysis on the ventral side. The majority of the mandible is also preserved in LPP.M.21, as the posterior-most areas are missing. Our mandibular description refers to the holotype (NHMUK PV R 3168) unless otherwise specified. Dentary: The dentary (Figs 1, 2, 3A, C) is a long major element of the lateral surface of the lower jaw, as in the majority of crocodylomorphs. The anterior end of the dentary is spatulate and laterally enlarged as in Machimosaurus (Young et al., 2014a). There are ~29 (possibly one or two more alveoli) alveoli per dentary (at least 25 alveoli per dentary in LPP.M.21) of which ~22–24 are adjacent to the mandibular symphysis (Andrews, 1913; Young et al., 2015a). Many of the teeth are missing but those still in situ are well preserved and complete. The four anterior-most teeth are elevated dorsally when compared to the rest of the tooth row, as normally seen in teleosaurids such as S. leedsi (Andrews, 1913). The dentition is strongly heterodont compared to other teleosaurids; the teeth in the anterior region are large and have a higher crown base to length ratio, whereas the posterior crowns are characterised by a lower ratio. The interalveolar distance is generally smaller than half the alveolar length but always longer than a quarter of the alveolar length. Surangular and angular: The surangular (Fig. 2) is thin and posteriorly elongated in lateral view. The surangular, in conjunction with the angular and articular bones, is anteroposteriorly elongated and forms a distinctive ‘V’ shape. The anterior region of each surangular gradually terminates near the last alveolus of the dentary. The posterior margin of the surangular is rounded and it bounds a small mandibular fenestra. The angular (Fig. 2) is elongate and occupies a more extensive area than the surangular in lateral view. The angular is more robust than the surangular with a strong dorsal curvature (Fig. 2) which articulates with the retroarticular process of the articular. The dorsal and the ventral surfaces of the angular are not viewable in NHMUK PV R 3168. The prearticulars, which are supposed to be present (Andrews, 1913), are not seen. Articular: The anterior region of the articular of NHMUK PV R 3168 is hidden by the quadrate and surrounding bones. The retroarticular process is, however, extremely elongate and triangular-shaped in dorsal view and it bears a strongly pronounced anteroposterior keel, which separates the medial and lateral grooves. Both grooves are concave, in particular the lateral ones. The posterior end of the retroarticular process is slightly rounded, concave and curves dorsolaterally. The glenoid fossa is large and faces mediodorsally. Splenial: All of the information on the splenial comes from LPP.M.21. Only the anterior regions of these bones are preserved. The splenial (Fig. 9) is situated medially and is mediolaterally thinner in width than the dentaries. Both splenials begin at approximately the 15th mandibular alveoli in the dentaries. While the coronoids are not preserved, the sulci where they are hosted are. They participate with the mandibular symphysis, and the anterior extension begins at approximately the 21st alveoli of the dentaries and continue parallel, and eventually past, the tooth row. Dentition: As discussed above, the dentition of NHMUK PV R 3168 is both heterodont and serrated (with both true and false denticles; Young et al., 2015a). The holotype has 33 isolated teeth, as well as in situ teeth: ~29 in each dentary, 4 per premaxilla and ~29 (possibly more) per maxilla (verified by LPP.M.21). The teeth (Fig. 12A–D) are conical, robust, single-cusped and bicarinate, as in Machimosaurus (Martin & Vincent, 2013; Young et al., 2015a, b; Foffa et al., 2015;,Fanti et al., 2016). They have a blunt apex in comparison to other Steneosaurus species (Andrews, 1913). The enamel is thinner towards the base of the crown and becomes progressively thicker towards the apex (Fig. 12A–D), much like in Machimosaurus (Young & Steel, 2014). Figure 12. View largeDownload slide Isolated tooth crowns of Lemmysuchus obtusidens (Andrews, 1909) comb. nov. NHMUK PV R 3168 (holotype) in (A) mesial view and (B) lingual close-up view and PETMG R39 (C, D) close-up detailed view of erupting tooth. Isolated tooth crowns referred to Machimosaurini indet.: GPIT/RE/301 [in E (posterior), F (labial), G (anterior), H (lingual) and I (dorsal) views)]; CAMSM J64508 [in J (posterior), K (labial), L (anterior), M (lingual), N (dorsal) views, O (ventral) and P (apex close-up) views]; OUMNH J.14464 [in Q (posterior), R (labial), S (anterior) and T (lingual) views]. Scale bar: (A) 2 cm; (B–T) 1 cm. Figure 12. View largeDownload slide Isolated tooth crowns of Lemmysuchus obtusidens (Andrews, 1909) comb. nov. NHMUK PV R 3168 (holotype) in (A) mesial view and (B) lingual close-up view and PETMG R39 (C, D) close-up detailed view of erupting tooth. Isolated tooth crowns referred to Machimosaurini indet.: GPIT/RE/301 [in E (posterior), F (labial), G (anterior), H (lingual) and I (dorsal) views)]; CAMSM J64508 [in J (posterior), K (labial), L (anterior), M (lingual), N (dorsal) views, O (ventral) and P (apex close-up) views]; OUMNH J.14464 [in Q (posterior), R (labial), S (anterior) and T (lingual) views]. Scale bar: (A) 2 cm; (B–T) 1 cm. There are many protruding apicobasal enamel ridges on these teeth, giving them a ‘wrinkled’ texture. These apicobasal ridges are close to one another and run parallel from the base of the crown to approximately three quarters of the entire tooth. At the apex, the ridges are considerably shorter and are organized in the typical anastomosed pattern that has been described for other members of Machimosaurini (Young et al., 2014a, 2015a; Jouve et al., 2016). Teeth with blunter apices are situated in the middle and posterior regions of the tooth row and those with sharper apices are near the anterior. The teeth have true denticles and false denticles (Young et al., 2015a), although the latter cannot be seen clearly with the naked eye. True denticles are situated on the carina and false denticles are formed via interactions between the carina and enamel ridges (Young et al., 2015a). Postcranial skeleton: vertebral column and ribs: Most of the vertebral column of NHMUK PV R 3168 is preserved, so our description of vertebrae is based on this specimen unless otherwise specified. The first (atlas) and second (axis) vertebrae are fused together, forming the well-developed ‘complex’ (Fig. 13A) that is common in teleosaurids (Andrews, 1913; Martin & Vincent, 2013). The axis neural arch is not present and the odontoid and intercentrum are not distinct from one another due to the degree of atlas–axis fusion. The lateral surfaces of the axis are concave and have large protruding regions for the parapophyses. There are no diapophyses present behind the odontoid process on the axis, which is slightly larger than the atlas. Figure 13. View largeDownload slide Atlas–axis complex (A), cervical rib (B) and proximal thoracic rib (C) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Note there are no axial diapophyses and that the odontoid and intercentrum cannot clearly be distinguished. Atlas–axis complex is in lateral view, cervical rib is in ventral view, thoracic rib is in medial view. Refer to main text for the abbreviations list. Scale bar: 5 cm. Figure 13. View largeDownload slide Atlas–axis complex (A), cervical rib (B) and proximal thoracic rib (C) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Note there are no axial diapophyses and that the odontoid and intercentrum cannot clearly be distinguished. Atlas–axis complex is in lateral view, cervical rib is in ventral view, thoracic rib is in medial view. Refer to main text for the abbreviations list. Scale bar: 5 cm. The centra of the remaining six cervical vertebrae are amphicoelous, slightly longer in width than height, and have sub-circular anterior and posterior articular surfaces. There is a small notch in the middle of the dorsal margin of the centrum that is visible in anterior view. In lateral view, the centra are slightly spool-shaped with concave ventral margins similar to Machimosaurus (Martin & Vincent, 2013). The prezygapophyses are slightly anterior to the centrum edge, with the anterior articular facets facing ventrally and curving inwards. The postzygapophyses extend laterally just above the base of the neural spine. The posterior articular facets face dorsally and the transverse processes are laterally wide. The neural spine is rectangular and nearly as tall as the centrum. Only one complete cervical rib is preserved. It is T-shaped in dorsal view and has a distinct dorsomedial curvature (Fig. 13B). Both the tubercular and capitular processes of this rib are rounded, and its tubercular is larger than the capitular. The distal area behind the processes is short and does not extend posteriorly while the area in front is considerably more elongated. Fourteen robust thoracic vertebrae are preserved in NHMUK PV R 3168 although only one is complete. The centra (Fig. 14) are massive and appear spool-shaped in ventral view. The articular surfaces are amphicoelous and oval (slightly taller in length than wide). The neural spine is short and broad, and not as tall as the centrum. The transverse processes are long and wide and are positioned approximately at the centre of the neural arch. They are broadened anteroposteriorly, with rounded proximal ends (Fig. 14). There is a second projection on the transverse process, separated from the vertebral body by a small concavity. This projection is small, circular and laterally faced. Figure 14. View largeDownload slide Dorsal vertebra of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in (A) anterior, (B) left lateral, (C) posterior, (D) right lateral, (E) dorsal and (F) ventral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 14. View largeDownload slide Dorsal vertebra of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in (A) anterior, (B) left lateral, (C) posterior, (D) right lateral, (E) dorsal and (F) ventral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. The dorsal ribs (Fig. 13C) are dichocephalous and have robust heads and bodies. The capitulum of these ribs is proximodistally lengthened and dorsally rounded (Fig. 13C) and each neck is elongated, separating the capitulum from the tuberculum. The articular facets are flat and separated from the top of the tuberculum. The tuberculum is a small nodule located in the middle of the rib body. The articular facet and tuberculum are both laterally shifted so that they are nearly situated on the lateral edge of the body. The costal groove is deep and runs from the ventral tuberculum to near the end of the rib body, disrupting an otherwise sub-circular cross-section. The sternal end of the rib is anteroposteriorly flat, straight and thin in width. There are three sacral vertebrae (Fig. 15) (Andrews, 1913). The first two are true sacral vertebrae and the first caudal vertebra acts as a pseudo-sacral, as it looks and functions as a third sacral. This ‘third’ sacral has large, mediolaterally expanding transverse processes and an expanded lateral iliac attachment area, much like the two true sacrals. The neural spines are short and robust and the sacral ribs curve and contact one another (Andrews, 1913). The anterior margin of the posterior area of the second sacral vertebra (Fig. 15B, D) has a large, expanded projecting flange. The presence of a ‘third’ sacral vertebra is an autapomorphy shared by L. obtusidens and Machimosaurus spp. within Thalattosuchia (Young et al., 2014a). Figure 15. View largeDownload slide Sacral vertebrae of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in correct anatomical order. (A) Anterior, (B) dorsal, (C) posterior, (D) left lateral and (E) right lateral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 15. View largeDownload slide Sacral vertebrae of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in correct anatomical order. (A) Anterior, (B) dorsal, (C) posterior, (D) left lateral and (E) right lateral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Only 21 caudal vertebrae are preserved. However, it is likely that the total caudal vertebral count is similar to that of S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701), of around 36–38 (Andrews, 1913) or even higher (as in S. edwardsi PETMG R275). The caudal vertebrae become increasingly thinner and smaller from anterior to posterior. The typical posterior caudal vertebral centrum is thin, taller than wide and strongly hourglass-shaped. The neural spines are thin, tall and higher than the centrum. Shoulder girdle and fore-limb: No coracoids are preserved. The scapula (Fig. 16A, B) is of the typical thalattosuchian type similar to S. leedsi (NHMUK PV R 3806) (Andrews, 1909, 1913), being an elongate bone with a slender body. The proximal and distal regions extend mediolaterally, with the distal end being slightly larger. The scapular glenoid fossa (Fig. 16B) is half-moon shaped. The proximal region of the humerus (Fig. 16C, D) is poorly preserved, so the deltopectoral crest and proximal head cannot be properly described. However, the proximal edge of the humeral head appears to be slightly curved, as seen in other OCF teleosaurids such as S. leedsi (NHMUK PV R 3806). The shaft of the humerus is straight and the distal end is rounded. There is a concave, oval (Andrews, 1913) depression in the middle of the distal end of the humerus in lateral view (Fig. 16D). The ulna is similar in shape to other Callovian teleosaurids such as S. leedsi (Andrews, 1913). The proximal region is slightly deformed and fractured. The radius is a squat, straight bone and is unornamented. Figure 16. View largeDownload slide Scapula (A, B) and humerus (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Scapula in (A) lateral and (B) medial views; humerus in medial (C) and lateral (D) views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 16. View largeDownload slide Scapula (A, B) and humerus (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Scapula in (A) lateral and (B) medial views; humerus in medial (C) and lateral (D) views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Pelvic girdle and hind-limb: The ischium (Fig. 17A, B) is squat and robust and only preserved in NHMUK PV R 3168. The two proximal articulation processes are divided by a small yet deep oval notch. The smaller process has a circular proximal head while the larger process is posterolaterally curved. A large protruding ridge runs proximodistally in line with the second proximal process. Two small, sub-circular ‘bumps’, presumably for muscle attachment, are present ~10 cm from the posterior edge. These are not as prominent in other teleosaurids, such as S. leedsi. The ischial blade (Fig. 17A, B) is large, expanded and thick, with the posteroventral, sub-square border. The anterior flange is thin and broken. Figure 17. View largeDownload slide Pelvis of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Ischium in (A) medial and (B) lateral views, ilium in (C) medial and (D) lateral views and pubis in (E) medial and (F) lateral views. Note that the acetabulum (D) is weakly concave and that the supraacetabular crest (D) is greatly reduced, and the pubic boot (E, F) is missing. Also, the medial and lateral sides of the ilium are not completely prepared. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 17. View largeDownload slide Pelvis of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Ischium in (A) medial and (B) lateral views, ilium in (C) medial and (D) lateral views and pubis in (E) medial and (F) lateral views. Note that the acetabulum (D) is weakly concave and that the supraacetabular crest (D) is greatly reduced, and the pubic boot (E, F) is missing. Also, the medial and lateral sides of the ilium are not completely prepared. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Both NHMUK PV R 3168 and PETMG R39 preserve an ilium. However, in the latter specimen, it is still articulated with the sacrum and femoral head, is missing the anterior side and is still partially covered in matrix. Conversely, the NHMUK PV R 3168 ilia (Fig. 17C, D) are well preserved, square-shaped and compact. The anterior-facing vertical outer rim has a slight sub-horizontal curvature (Fig. 17C, D). The medial attachment points of the sacral ribs are faint (Fig. 17C) so that it is difficult to tell the anterior iliac facet and posterior iliac facet apart from one another (Fig. 17C). The acetabular depression (or acetabular notch) is a smooth U-shaped arch in lateral view (Fig. 17C) and is halfway through the ventral articulating points with the pubis and ischium. The anterior articulation facet in front of the incision is larger than that of the posterior articulation facet and extends ventrally. The supraacetabular crest (Fig. 17D) is poorly developed, as is the shallow acetabulum (Fig. 17D). The preacetabular (=anterior process) (Fig. 17D) is shortened (with respect to other thalattosuchians) and well rounded and curves laterally. The majority of one pubis is preserved in NHMUK PV R 3168 (Fig. 17E, F) but the pubic boot is missing. Conversely, the ventral part of the pubis is possibly preserved in matrix in PETMG 39 (PETMG R31) (Fig. 24D). The body and distal region of the neck of the NHMUK PV R 3168 pubis are deformed into curving medially. The anterodistal pubic plate is expanded and rounded along the ventral rim (Fig. 17E, F). All the information on the hind-limb comes from NHMK PV R 3168. The femur (Fig. 18) is slender and long, with a weak sigmoidal curvature throughout the shaft, which is typical of many teleosaurids (Andrews, 1909, 1913). The proximal head (Fig. 18) extends medially into the acetabulum while the anterior region of the femoral head is ventrally curved. There is a large concavity on the posterolateral surface of the head. The posterior margin of the head is rugose, and this rugosity continues down through the neck of the femur. In dorsal view, the head is circular to sub-circular, with an expanded posteromedial tuber. The ‘fourth trochanter’ (i.e. no true process, just the rugose area mentioned before) is small compared to other Callovian teleosaurids and is situated on the medial neck of the femur (Fig. 18). The two posterodistal condyles – medial (greater) and lateral (lesser) – are clearly visible with the medial condyle being slightly larger (Fig. 18). Figure 18. View largeDownload slide Femur of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) medial and (B) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 18. View largeDownload slide Femur of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) medial and (B) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. The tibia (Fig. 19) is a robust bone with the proximal end being larger than the distal end. In dorsal view, the proximal end is heart-shaped. The tibial tuberosity (Fig. 19A, C) is large and projects posterodistally. In lateral view, it is directed ventrally at a sharply obtuse angle (Fig. 19C). The medial side of the tibial neck is slightly concave, while the lateral side is flat (Andrews, 1913). The distal end is rounded, although it is obstructed by the distal area of the fibula. The fibula (Fig. 19) is an elongate, slender and straight bone, with only the distal half preserved. It is slightly smaller in width (Fig. 19A) than the tibia. Figure 19. View largeDownload slide Tibia of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) posterior, (B) anterior and (C) lateral views. Note the anterior deflection of the proximal region. Refer to the main text for the abbreviations list. Note the distal area of the fibula attached to the tibia. Scale bar: 5 cm. Figure 19. View largeDownload slide Tibia of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) posterior, (B) anterior and (C) lateral views. Note the anterior deflection of the proximal region. Refer to the main text for the abbreviations list. Note the distal area of the fibula attached to the tibia. Scale bar: 5 cm. There are three ankles bones (Fig. 20): the calcaneum (Fig. 20A–D), astragalus (Fig. 20E–G) and cuboid (Fig. 20H, I). They are all robust and large, with well-developed articulation surfaces. Excluding the clear difference in the large size, the three ankle bones resemble those of other teleosaurids (Andrews, 1913). All metacarpal and metatarsal fragments are slender, as are four complete phalanges (all relatively the same length). Figure 20. View largeDownload slide Ankle of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, including the calcaneum (A–D), astragalus (E–G) and cuboid (H, I). Calcaneum in (A) right dorsolateral, (B) anterior, (C) left dorsolateral and (D) posterior views; astragalus in (E) dorsal, (F) ventral and (G) posterior views; cuboid in (H) dorsal and (I) ventral views. Scale bar: 5 cm. Figure 20. View largeDownload slide Ankle of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, including the calcaneum (A–D), astragalus (E–G) and cuboid (H, I). Calcaneum in (A) right dorsolateral, (B) anterior, (C) left dorsolateral and (D) posterior views; astragalus in (E) dorsal, (F) ventral and (G) posterior views; cuboid in (H) dorsal and (I) ventral views. Scale bar: 5 cm. Osteoderms: Fifty-six dorsal, mostly unarticulated osteoderms are present in NHMUK PV R 3168. Smaller osteoderms are box-shaped (Fig. 21C), whereas larger ones are elongate and oval (Fig. 21A, B). A prominent anteroposteriorly directed keel is present (Fig. 21A), being more pronounced in larger osteoderms. The pits on the dorsal surface of larger osteoderms (Fig. 21A) are oval, elongate, deep and spaced apart. They radiate outwards from the centre of the keel in a ‘starburst’ pattern. The pits generally become larger further from the centre of the osteoderms. Some pits merge with one another along the outermost lateral margins of the osteoderms. The ventral surfaces of all osteoderms are smooth and unaltered. Figure 21. View largeDownload slide A–C, dorsal osteoderms of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. All are in dorsal view. Note the characteristic ornamentation pattern, with elongated pits radiating from the centre of the keel. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 21. View largeDownload slide A–C, dorsal osteoderms of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. All are in dorsal view. Note the characteristic ornamentation pattern, with elongated pits radiating from the centre of the keel. Refer to the main text for the abbreviations list. Scale bar: 5 cm. DISCUSSION Specimens previously referred to ‘Steneosaurus’ obtusidens Andrews (1913) referred two large, but very incomplete, specimens to ‘S.’ obtusidens: NHMUK PV R 3169 and NHMUK PV R 3898. The former comprises one scapula, right coracoid, left ulna, one radius, right ilium, femora, pubes, tibiae, a fibula, five carpal/tarsal bones, one hyoid, three tracheal rings, five osteoderms and numerous teeth and fragmentary elements. Nine characteristics differentiate NHMUK PV R 3169 from L. obtusidens: The tibial tuberosity is not angled as in L. obtusidens (NHMUK PV R 3168). Instead it is directed almost 180° horizontally, similar to S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701 and PETMG R178) (Fig. 23A–C). While the femur of NHMUK PV R 3169 is long and gracile, somewhat similar to L. obtusidens (NHMUK PV R 3168), it is slightly smaller in length and width (possibly from a smaller individual; Fig. 24A–C). In dorsal view, the femoral head is larger and more triangular than that of L. obtusidens (NHMUK PV R 3168), due to an enlarged posteromedial tuber (Fig. 24A–C). This is somewhat similar to the condition seen in the metriorhynchid Tyrannoneustes lythrodectikos (GLAHM V1145; Young et al., 2013). The greater femoral condyle of the NHMUK PV R 3169 is much larger than the lesser condyle (Fig. 25A–C), as opposed to L. obtusidens (NHMUK PV R 3168) in which the greater condyle is only slightly larger than the lesser condyle. The ilium has a slender, elongate anterior process, as opposed to the short, stubby anterior process of L. obtusidens (NHMUK PV R 3168) (Fig. 24D–F). The ilium has only two sacral rib articulation surfaces, and these are large and well developed. In L. obtusidens (NHMUK PV R 3168), the ilia have three poorly developed sacral rib articulation surfaces (Fig. 24D–F). The acetabulum is deep, and the anterior-most ridge of the ilium is vertical, whereas in L. obtusidens (NHMUK PV R 3168), the acetabulum is poorly concave (see Fig. 17D). The anterodistal rim if the pubic plate is straighter and sub-square, whereas in L. obtusidens (NHMUK PV R 3168), the pubic plate rim is rounded and circular. The osteoderms of NHMUK PV R 3169 are an enigma. Out of the five osteoderms preserved, two have a dorsal pitting pattern similar to that of L. obtusidens (NHMUK PV R 3168). These pits are elongated and radiate out from the centre of the keel. The other three are similar with those seen in S. edwardsi (NHMUK PV R 3701 and PETMG R178). The pits are not elongated and occur in a random arrangement (Fig. 23D–F). Thus, we can conclude that NHMUK PV R 3169 is not L. obtusidens and is morphologically more similar to S. edwardsi (NHMUK PV R 3701) or S. leedsi (NHMUK PV R 3806). Figure 22. View largeDownload slide Comparative photographs of (A) Steneosaurus heberti (MNHN.F 1890-13), (B) Steneosaurus edwardsi (PETMG 178) and (C) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., showing the dorsoposterior curvature of the retroarticular process. Comparative photographs of (D) S. heberti (MNHN.F 1890-13) holotype, (E) S. edwardsi (NHMUK PV R 2865), (F) L. obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype and (G) Machimosaurus buffetauti (SMNS 91415), showing the absence of antorbital fenestrae. Figure 22. View largeDownload slide Comparative photographs of (A) Steneosaurus heberti (MNHN.F 1890-13), (B) Steneosaurus edwardsi (PETMG 178) and (C) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., showing the dorsoposterior curvature of the retroarticular process. Comparative photographs of (D) S. heberti (MNHN.F 1890-13) holotype, (E) S. edwardsi (NHMUK PV R 2865), (F) L. obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype and (G) Machimosaurus buffetauti (SMNS 91415), showing the absence of antorbital fenestrae. Figure 23. View largeDownload slide Comparative line drawings of the tibiae in posterior (left) and lateral (right) views of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) NHMUK PV R 3169 and (C) Steneosaurus edwardsi (PETMG R178); comparative line drawings of the dorsal osteoderms in dorsal view of (D) L. obtusidens holotype (NHMUK PV R 3168), (E) NHMUK PV R 3169 and (F) S. edwardsi (PETMG R178). Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 23. View largeDownload slide Comparative line drawings of the tibiae in posterior (left) and lateral (right) views of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) NHMUK PV R 3169 and (C) Steneosaurus edwardsi (PETMG R178); comparative line drawings of the dorsal osteoderms in dorsal view of (D) L. obtusidens holotype (NHMUK PV R 3168), (E) NHMUK PV R 3169 and (F) S. edwardsi (PETMG R178). Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 24. View largeDownload slide Comparative line drawings of the femora in medial view of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and Steneosaurus edwardsi [(B) NHMUK PV R 3898; (C) PETMG R178]; comparative line drawings of the ilia in medial view of (D) L. obtusidens holotype (NHMUK PV R 3168) and S. edwardsi [(E) NHMUK PV R 3898; (F) PETMG R178]. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 24. View largeDownload slide Comparative line drawings of the femora in medial view of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and Steneosaurus edwardsi [(B) NHMUK PV R 3898; (C) PETMG R178]; comparative line drawings of the ilia in medial view of (D) L. obtusidens holotype (NHMUK PV R 3168) and S. edwardsi [(E) NHMUK PV R 3898; (F) PETMG R178]. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 25. View largeDownload slide Four articulated vertebrae of PETMG R39, referred to Lemmysuchus obtusidens (Andrews (1909)comb. nov., in (A) left and (B) right lateral views. Five articulated vertebrae (two dorsal, three sacral), incomplete ilium, femur and pubis (ischium?) of PETMG R31, which is thought to correspond to PETMG R39, in (C) left and (D) right lateral views. Scale bar: 10 cm. Figure 25. View largeDownload slide Four articulated vertebrae of PETMG R39, referred to Lemmysuchus obtusidens (Andrews (1909)comb. nov., in (A) left and (B) right lateral views. Five articulated vertebrae (two dorsal, three sacral), incomplete ilium, femur and pubis (ischium?) of PETMG R31, which is thought to correspond to PETMG R39, in (C) left and (D) right lateral views. Scale bar: 10 cm. Andrews’ (1913) second L. obtusidens referred specimen, NHMUK PV R 3898, consists of an ilium, ischium and femur. All three bones are very large and robust. However, the features in these bones differ vastly from those seen in the L. obtusidens holotype (NHMUK PV R 3168). The ilium of NHMUK PV R 3898 has: (1) an elongate and slender anterior process, (2) a pronounced supraacetabular crest and (3) a strongly concave acetabulum (Fig. 23E; see Johnson et al., 2015). This differs from the L. obtusidens (NHMUK PV R 3168) ilium, which has a short anterior process, a greatly reduced supraacetabular crest, and a shallow acetabulum (Fig. 25D). The ischium of NHMUK PV R 3898 has a sub-triangular posteroventral margin of the ischial blade (Johnson et al., 2015), as opposed to the broad, sub-square posteroventral margin in L. obtusidens (NHMUK PV R 3168). As Johnson et al. (2015) showed, these morphologies exclude NHMUK PV R 3898 from L. obtusidens and demonstrate that it in fact pertains to S. edwardsi. Two additional specimens from the Peterborough Member of the OCF are here referred to as L. obtusidens: PETMG R39 and PETMG R178. The first specimen, PETMG R39, is a partial skull (Figs 4–6) and partial mandible (only preserving the anterior end of the mandibular symphyseal region) (Fig. 7), four articulated dorsal vertebrae (Fig. 25A, B), an osteoderm fragment, sacrum and some isolated bone fragments (Fig. 25C, D). Parts of this specimen have been referred to PETMG R31, another specimen that it has been constantly mixed and stored with. However, a specimen registration entry mentions that PETMG R31 ‘fits with R39’. Nevertheless, the preservation and texture of the bones and the matrix are identical in both specimens, which importantly also share autapomorphies of L. obtusidens. Based on these lines of evidence, we consider PETMG R39 and PETMG R31 belonging to the same individual and both pertain to L. obtusidens. The skull of PETMG R39 (Figs 4–6) includes the nasals, posterior maxillae, jugal and anterior orbit. Several alveoli are visible on both lateral sides of the maxillae. The alveoli are separated by variable interalveolar spaces (always fewer than one alveolus length but longer than half) and most teeth are still in situ. Two erupting teeth show the typical Machimosaurini crown ornamentation. This specimen is referable to L. obtusidens due to the following features: (1) closure of the antorbital fenestrae; (2) there is a slight beginning of a ‘dome’ near the posterior section of the nasals; (3) the teeth have blunt apices, denticles and the characteristic Machimosaurini enamel ornamentation pattern and (4) an extreme anteroposterior elongation of the jugal. PETMG R31 consists of five articulated vertebrae (two complete dorsal, two complete and one incomplete sacral), incomplete ilium, femur and pubis (or ischium?) (Fig. 25C, D). The sacral vertebrae largely resemble the L. obtusidens holotype (NHMUK PV R 3168). Although the posterior-most vertebra is incomplete, one of its ribs is partially preserved, and there is little doubt that it is a sacral rib due to its shape and dimension, with an expanded flange. The fragmentary status of the specimen and abundant matrix around the bones does not allow direct comparison of other elements. Thus, PETMG R31 pertains to Lemmysuchus based on the presence of three sacral vertebrae, and the fact that it likely belongs with PETMG R39. The second specimen, PETMG R178, represents a nearly complete skeleton. However, it lacks characteristics seen in the L. obtusidens holotype (NHMUK PV R 3168). The dorsal rim of larger cervical ribs does not curve dorsomedially. The shape and position of the tuberculum in the dorsal ribs is similar to S. edwardsi (NHMUK PV R 3701), whereas L. obtusidens (NHMUK PV R 3168) displays a more medial position of the tuberculum. The ilium has a deep well-developed acetabulum and an elongate, slender anterior process, which differs from the shallow acetabulum and the proportionally shorter anterior process seen in L. obtusidens (NHMUK PV R 3168) (Fig. 24D, E). The ischium is gracile and the posteroventral margin of the ischial blade is sub-triangular in shape, which differs from the robust ischium with a square-shaped posteroventral ischial blade of L. obtusidens (NHMUK PV R 3168). The proximal tibia is not strongly deflected anteriorly as in L. obtusidens (NHMUK PV R 3168) and Machimosaurus (Hua, 1999). The skull of PETMG R178 lacks the strongly convex (‘domed’) nasals seen in L. obtusidens (NHMUK PV R 3168 and PETMG R39), although this may be due to preservation. The dorsal osteoderm ornamentation differs from that seen in L. obtusidens (NHMUK PV R 3168). The pitting pattern is random, as seen in S. edwardsi (NHMUK PV R 3701). Thus, PETMG R178 is not referable to L. obtusidens and is more morphologically similar to S. edwardsi. Hua et al. (1994) described a fragmentary skeleton from the upper Callovian of Villers-sur-Mer, Calvados, France, and referred it to ‘S.’ obtusidens. It was the first non-English specimen referred to L. obtusidens. However, comparing the figures from Hua et al. (1994) with the L. obtusidens holotype (NHMUK PV R 3168) shows that the ischium, ilium and dorsal osteoderms do not match. In the French specimen, the ilium anterior process is much more elongated and slender than that seen in the Lemmysuchus holotype (NHMUK PV R 3168). The supraacetabular crest is pronounced, the acetabular depression is strongly concave and the posterior margin of the ischial blade is sub-triangular. The osteoderm (Hua et al., 1994; fig. 1a) lacks the ‘starburst’ pattern of pits. As with PETMG R178, this specimen more closely resembles S. edwardsi than L. obtusidens. Foffa et al. (2015) described an incomplete mandible (DORCM G3939), which preserves the symphyseal region up to approximately the 19th alveoli (alveoli one and two are missing). Due to the incompleteness of its preservation, the lower jaw could not be confidently assigned to a taxon but was referred to ‘S.’ cf. obtusidens. It is difficult to determine for certainty whether DORCM G3939 is L. obtusidens, as so little of it is preserved; however, the high symphyseal tooth count, the Meckelian groove not being exposed on the dorsal surface of the splenials, the blunt tooth apices, the anastomosed apical enamel ornamentation, presence of denticles and deep reception pits place it within Machimosaurini. If this specimen does belong to L. obtusidens, it expands the stratigraphic range of this taxon into the early Oxfordian. Comparison with other OCF teleosaurids Lemmysuchus obtusidens (NHMUK PV R 3168, PETMG R39) has numerous teleosaurid apomorphies including: a laterally expanded premaxilla and anterior dentary, and a relatively small frontal (Andrews, 1913). However, L. obtusidens has a number of autapomorphies, particularly in the postcranial skeleton (Tables 1 and 2). Table 1. Comparison of cranial characters between Lemmysuchus obtusidens and selected specimens of other teleosaurids Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  SMNS 91415, Martin & Vincent (2013), Young et al. (2014a)   MNHN.F 1890-13  MNHN.F RJN 118, NHMUK PV R 3701, PETMG R178  NHMUK PV R 3806  PETMG R39 (+ PETMG R31)  LPP.M.21  Antorbital fenestrae  Absent  Absent  Absent  Absent  Present  Nasal dorsal surface  Strongly convex  Slightly convex  Slightly convex  Slightly convex  Slightly convex  Frontal ornamentation  Yes: large circular pits  Yes: well-developed pits/ridges  Yes: ridges  Yes: circular pits  Yes: ridges  Supratemporal fenestra shape  Rectangular (anteroposteriorly elongated)  Rectangular (anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Occipital tuberosities  Yes: pronounced  Yes: pronounced  Yes: pronounced  No  No  Nuchal crest  Pronounced  Reduced  Reduced  Small  Small  Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  SMNS 91415, Martin & Vincent (2013), Young et al. (2014a)   MNHN.F 1890-13  MNHN.F RJN 118, NHMUK PV R 3701, PETMG R178  NHMUK PV R 3806  PETMG R39 (+ PETMG R31)  LPP.M.21  Antorbital fenestrae  Absent  Absent  Absent  Absent  Present  Nasal dorsal surface  Strongly convex  Slightly convex  Slightly convex  Slightly convex  Slightly convex  Frontal ornamentation  Yes: large circular pits  Yes: well-developed pits/ridges  Yes: ridges  Yes: circular pits  Yes: ridges  Supratemporal fenestra shape  Rectangular (anteroposteriorly elongated)  Rectangular (anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Occipital tuberosities  Yes: pronounced  Yes: pronounced  Yes: pronounced  No  No  Nuchal crest  Pronounced  Reduced  Reduced  Small  Small  View Large Table 2. Comparison of postcranial characters between Lemmysuchus obtusidens and selected specimens of other teleosaurids Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti and M. mosae, Young et al. (2014a)  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  MNHN.F 1890-13  NHMUK PV R 3701  NHMUK PV R 3806  PETMG R39 (PETMG R31)  PETMG R178  Ilium  Short anterior process; shallow acetabulum; faint supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long slender process, deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Ischium  Broad ischial blade; sub-square posteroventral margin  Somewhat broad ischial blade; sub- square posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Number of sacral vertebrae  3 (2 true, 1 pseudo)  3  2  2  2  Femur  Sub-triangular head (dorsal view); medial condyle slightly larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; slightly sigmoidal  Triangular to ‘kidney-bean’ shaped head (dorsal view); medial condyle much larger than lateral condyle; slightly sigmoidal  Triangular head (dorsal view); medial condyle much larger than lateral condyle; sigmoidal  Tibial tuberosity  Sharply angled  Sharply angled  Horizontal  Horizontal  Horizontal  Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti and M. mosae, Young et al. (2014a)  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  MNHN.F 1890-13  NHMUK PV R 3701  NHMUK PV R 3806  PETMG R39 (PETMG R31)  PETMG R178  Ilium  Short anterior process; shallow acetabulum; faint supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long slender process, deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Ischium  Broad ischial blade; sub-square posteroventral margin  Somewhat broad ischial blade; sub- square posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Number of sacral vertebrae  3 (2 true, 1 pseudo)  3  2  2  2  Femur  Sub-triangular head (dorsal view); medial condyle slightly larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; slightly sigmoidal  Triangular to ‘kidney-bean’ shaped head (dorsal view); medial condyle much larger than lateral condyle; slightly sigmoidal  Triangular head (dorsal view); medial condyle much larger than lateral condyle; sigmoidal  Tibial tuberosity  Sharply angled  Sharply angled  Horizontal  Horizontal  Horizontal  View Large Andrews (1913) recognized some of these autapomorphies: (1) three sacral vertebrae; (2) blunt, heavily ornamented teeth and (3) a unique osteoderm pattern (however, points 1 and 2 are now recognized as characters shared with Machimosaurus, see Diagnosis and Discussion; Young et al., 2014a, 2015a; Jouve et al., 2016). While Andrews (1913) gave a generally good description of the skull, we disagree with some of his observations regarding the antorbital fenestrae, lacrimal and sacral vertebrae. These autapomorphies readily distinguish it from two common OCF teleosaurids, S. leedsi and S. edwardsi. The skull of L. obtusidens (NHMUK PV R 3168) is marked similar to Machimosaurus (Table 1; see Krebs, 1967; Buffetaut, 1982a; Martin & Vincent, 2013; Young et al., 2014a; Fanti et al., 2016) in being large and robust. This is opposite of S. leedsi (NHMUK PV R 3806), which has a slender skull. Steneosaurus edwardsi (NHMUK PV R 3701, PETMG R178) has a large skull similar to L. obtusidens (NHMUK PV R 3168), with some specimens of S. edwardsi being even larger than the L. obtusidens holotype. Both S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) lack the dorsoventrally deep ‘domed’ nasals-frontal as seen in L. obtusidens (NHMUK PV R 3168). The supratemporal fossae in L. obtusidens (NHMUK PV R 3168) extend further anteriorly along the frontal than those of S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701). The articular, surangular and angular bones of L. obtusidens (NHMUK PV R 3168) are more elongated anteroposteriorly than lateromedially, giving them a combined ‘V’ shape. This differs in comparison to S. edwardsi (NHMUK PV R3 701), in which the three bones are not elongated anteroposteriorly. Steneosaurus leedsi (NHMUK PV R 3806) displays the same shape and anteroposterior elongation as L. obtusidens (NHMUK PV R 3168), although it is smaller and slenderer. The Meckelian groove is not excavated on the dorsal surface of the symphyseal splenial in L. obtusidens (NHMUK PV R 3168) (Fig. 26E), which it shares with M. mosae neotype (Fig. 26F), S. edwardsi (NHMUK PV R 3701) (Fig. 26C) and S. hulkei (NHMUK PV R 2074) (Fig. 26D). Other thalattosuchians, such as S. leedsi (NHM UK PV R 3806, NHMUK PV R 3320) (Fig. 26A, B), have the Meckelian groove deeply excavated on the dorsal surface of the splenial. As mentioned before, L. obtusidens (PETMG R39) lacks any evidence of antorbital fenestrae (contraAndrews, 1913), the condition shared with S. edwardsi (PETMG R178), Machimosaurus, and S. heberti (MNHN.F 1890-13). Small, slit-like fenestrae are present in S. leedsi (NHMUKPV R 3806). The teeth of S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) are more elongate and slender than those of L. obtusidens (NHMUK PV R 3168) and have pointed apices continuously throughout the maxillae and dentaries, as well as lacking an anastomosed apical pattern. Figure 26. View largeDownload slide Comparative photographs of Steneosaurus leedsi (A) NHMUK PV R 3806; (B) NHMUK PV R 3220, (C) Steneosaurus edwardsi (NHMUK PV R 3701), (D) Steneosaurus hulkei (NHMUK PV R 2074), (E) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168) and (F) Machimosaurus mosae (taken from Young et al. 2014a, fig. 19), showing the shallow vs. deep excavation of the Meckelian groove. Note that (A–B) are much more deeply excavated and exposed than (C–F). Scale bar: 10 cm. Figure 26. View largeDownload slide Comparative photographs of Steneosaurus leedsi (A) NHMUK PV R 3806; (B) NHMUK PV R 3220, (C) Steneosaurus edwardsi (NHMUK PV R 3701), (D) Steneosaurus hulkei (NHMUK PV R 2074), (E) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168) and (F) Machimosaurus mosae (taken from Young et al. 2014a, fig. 19), showing the shallow vs. deep excavation of the Meckelian groove. Note that (A–B) are much more deeply excavated and exposed than (C–F). Scale bar: 10 cm. Aside from the osteoderms and sacral vertebrae, Andrews (1913) largely neglected to describe the postcranial skeleton. Herein, we have shown the postcrania of L. obtusidens to be distinctive (Table 2). One striking difference found in L. obtusidens (NHMUK PV R 3168) is the absence of axial diapophyses. These processes are present in S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701). Steneosaurus bollensis, however, also lacks the axial diapophyses (see Westphal, 1962). The two primordial sacrals in L. obtusidens (NHMUK PV R 3168) are similar in form to S. leedsi (NMHUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The anterior projecting flange on the second sacral vertebra is seen in S. leedsi (NHMUK PV R 3806), although it is much smaller and does not extend anteriorly (Fig. 27B) as in L. obtusidens (NHMUK PV R 3168) (Fig. 27A). The cervical rib of L. obtusidens (NHMUK PV R 3168) (Fig. 28A) has a distinct medial curvature in the dorsal rim. The cervical ribs of S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) both have straight, T-shaped dorsal rims (Fig. 28B–D). The area posterior to the tubercular and capitular processes of the cervical rib is also shorter than the anterior area in L. obtusidens (NHMUK PV R 3168), whereas in S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806), they are more elongated (Fig. 28) and are approximately the same length. Figure 27. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and (B) Steneosaurus leedsi (NHMUK PV R 3806) articulated sacral vertebrae. Note that the anterior projecting flange on the second sacral vertebra in S. leedsi (B) does not extend anteriorly and is small. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 27. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and (B) Steneosaurus leedsi (NHMUK PV R 3806) articulated sacral vertebrae. Note that the anterior projecting flange on the second sacral vertebra in S. leedsi (B) does not extend anteriorly and is small. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 28. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701); (D) PETMG R178, cervical ribs. Scale bar: 5 cm. Figure 28. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701); (D) PETMG R178, cervical ribs. Scale bar: 5 cm. There are three features seen in the dorsal ribs of L. obtusidens (NHMUK PV R 3168) in conjunction with S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) (Fig. 29): Both the tuberculum and articular facet are shifted onto the medial edge of the rib in L. obtusidens (NHMUK PV R 3168), as described before. The position of these articular surfaces in L. obtusidens (NHMUK PV R 3168) could be due to either the massive size of the ribs causing the tuberculum to shift medially or are solely due to deformation. In S. leedsi (NHMUK PV R 3806), the tuberculum and articular surface are situated directly in the middle of the rib and are small. In S. edwardsi (NHMUK PV R 3701), the tuberculum is also situated medially, but closer to the lateromedial edge of the rib. The proximal head of the ribs in L. obtusidens (NHMUK PV R 3168) and S. edwardsi (NHMUK PV R 3701) are elongated proximodistally and are rectangular in dorsal view. In medial view, the dorsal edges of the two specimens appear curved. In S. leedsi (NHMUK PV R 3806), the rib head is as long as it is wide. It is flat and circular in dorsal view and straight in medial view. The sternal rib end is flat in L. obtusidens (NHMUK PV R 3168) and S. edwardsi (NHMUK PV R 3701), while in S. leedsi (NHMUK PV R 3806), it is more rounded, similar to metriorhynchids (Wilkinson et al., 2008). Figure 29. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701) dorsal ribs. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 29. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701) dorsal ribs. Refer to the main text for the abbreviations list. Scale bar: 5 cm. There is also a combination of six pelvic and hind-limb characteristics that readily distinguishes L. obtusidens from S. leedsi and S. edwardsi (Table 2). These characteristics were not noted by Andrews (1909, 1913) and are here listed for the first time: The iliac anterior process in L. obtusidens is short and squat, as opposed to the elongate, slightly thinner processes S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The poorly developed sacral rib attachment areas and acetabulum of L. obtusidens (NHMUK PV R 3168) differs from S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) in that in L. obtusidens, they are both poorly developed (possibly due to preservation). The posteroventral margin of the ischial plate in L. obtusidens (NHMUK PV R 3168) is sub-square in shape, and is not as blunt or widened as seen in metriorhynchids (e.g. Wilkinson et al., 2008), but is broader than the sub-triangular posterior margin seen in S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The anterodistal rim of the pubic plate is curved in a circular fashion, much like that seen in S. leedsi (NHMUK PV R 3806). This differs from S. edwardsi (NHMUK PV R 3701), in that the anterodistal pubic plate rim is straight and square-like with a sharp anterodistal edge. The sigmoidal curvature of the L. obtusidens (NHMUK PV R 3168) femur is most similar to S. leedsi (NHMUK PV R 3806) in being weak. In S. edwardsi (NHMUK PV R 3701, NHMUK PV R 3898), the curvature throughout the femur is strongly pronounced (Johnson et al., 2015). In L. obtusidens (NHMUK PV R 3168), there is a distinctive sharply angled tibial tuberosity that is shared with Machimosaurus (Hua, 1999). In S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701), the tibial tuberosity is horizontal and shows no angle. The dorsal surface ‘starburst’ osteoderm ornamentation of L. obtusidens (NHMUK PV R 3168) differs from the ornamentations seen in S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) (Fig. 23D– F). In S. edwardsi (NHMUK PV R 3701 and PETMG R178), the majority of pits are circular in shape and are not as deep as L. obtusidens (NHMUK PV R 3168). The pits are closely packed together and are distributed in a random pattern, as opposed to the ‘starburst’ pattern in L. obtusidens (NHMUK PV R 3168). In S. leedsi (NHMUK PV R 3806), the majority of the pits are circular, with some being oval in shape. The pits radiate outwards in a sub-circular fashion and are closely packed together, which differs from L. obtusidens (NMHUK PV R 3168). Andrews (1909, 1913) described the postcranial material (not including the dorsal osteoderms) of L. obtusidens as so similar ‘to that of S. durobrivensis [that] special description is unnecessary.’ However, here we have shown that not only is the postcrania of L. obtusidens distinct, but there were at least two different postcranial morphotypes among OCF teleosaurids. A robust, stockier morphotype was represented by Lemmysuchus (i.e. stout ilia and tibiae, broad ischial blade, large centra and three sacral vertebrae), and a slenderer morphotype was represented by S. leedsi and S. edwardsi (with a gracile ilia, tibiae, and ischial blade, smaller centra, and two sacral vertebrae). These differences may reflect habitat partitioning among sympatric teleosaurids, with L. obtusidens suggested as being more terrestrial, and/or living in higher energy environments. Body length The basicranial length of the L. obtusidens holotype (NHMUK PV R 3168) is ~1.16 m. The vertebral column is not completely preserved. There is one dorsal and one cervical vertebra missing, and the majority of the caudal region is missing. Using the Young et al. (2016b), basicranial length vs. body length equations yields a total body length estimate of between 556.995 and 558.173 cm. Using the femoral length vs. body length equations yields a total body length estimate of between 575.742 ad 582.3 cm. Young et al. (2016b) found femoral-based estimates to be the more reliable than cranial-based estimates, thus a body length of ~5.8 m seems likely for L. obtusidens. Lemmysuchus obtusidens has long been considered to be the largest teleosaurid in the OCF (see Andrews, 1913; Young et al., 2015a). However, as noted above, the largest specimen previously referred to L. obtusidens (NHMUK PV R 3898) has recently been re-assigned to S. edwardsi (Johnson et al., 2015). Young et al. (2016b) found NHMUK PV R 3898 to be between 659.51 and 666.66 cm using the femoral-based equations. Thus, S. edwardsi is the largest known crocodylomorph of the Middle Jurassic. CONCLUSIONS Here, we re-describe the holotype of ‘S.’ obtusidens (NHMUK PV R 3168), demonstrate that it is indeed a valid species and establish a new monotypic genus, Lemmysuchus, for the taxon. It has five autapomorphies and shares nine synapomorphies with Machimosaurus, thus supporting Machimosaurini (Lemmysuchus + Machimosaurus) (Young et al., 2015b; Jouve et al., 2016). This suite of characteristics falsifies the hypothesis that L. obtusidens is a subjective junior synonym of S. edwardsi. Additionally, L. obtusidens lacks eight of the Machimosaurus autapomorphies (including three premaxillary alveoli, a considerably smaller medial hemicondyle and variable presence of carinae) listed by Young et al. (2014a), thus falsifying the hypothesis that L. obtusidens is a subjective junior synonym of M. hugii. Moreover, most specimens previously referred to L. obtusidens are herein considered to pertain to other taxa. We conclude that only three specimens can reliably be referred to L. obtusidens: a nearly complete skull (LPP.M.21) from the E. coronatum ammonite Zone of Migné-les-Lourdines, France; an incomplete skull with associated postcranial elements from the OCF of England (PETMG R39) and a partial rostrum thought to be from the OCF (NOTNH FS3361). As such, L. obtusidens was a somewhat rare taxon in the Callovian of Europe, currently known only from England and France. This contrasts with its sister taxon Machimosaurus, which was widespread and common in European and Tethys shallow marine and brackish ecosystems during the Late Jurassic. [Version of Record, published online 07 August 2017; http://zoobank.org/ urn:lsid:zoobank.org:pub:ADB5B0F9-7D9C-48CF-BBB6-1451BA209584] ACKNOWLEDGEMENTS We thank G. Wass (PETMG), P. Tomlinson (DORCM) and M. Riley (CAMSM) for access to collections and their much appreciated assistance and advice; G. Garcia for photographs of LPP.M.21; P. Hurst and K. Webb (NHMUK Image Resources) for photography of the Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and R. Holmes and J. Liston for advice and guidance. MTY received support for his visits to France (FR-TAF-4021) and Germany (DE-TAF-5132) from the SYNTHESYS Project, which is financed by the European Community Research Infrastructure Action, under the FP7 ‘Capacities’ Program. He would like to thank R. Allain (MNHN), R. Schoch (SMNS), D. Vasilyan and M. 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Re-description of ‘Steneosaurus’ obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England

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Abstract

Abstract Teleosaurids were a clade of crocodylomorphs that attained near-global distribution during the Jurassic Period. Within Teleosauridae, one particular sub-clade of durophagous/macrophagous taxa achieved large body sizes and were apex predators in shallow marine environments during the Late Jurassic and Early Cretaceous in Europe and around the coast of the Tethys Seaway. Unfortunately, the origins of this clade are still poorly understood. ‘Steneosaurus’ obtusidens is a little-studied macrophagous species from the Oxford Clay Formation (Callovian, Middle Jurassic) of the UK and near Migné-les-Lourdines (Middle Callovian) in France. Despite being considered a sister taxon of the Late Jurassic taxon Machimosaurus, the taxonomy of ‘S.’ obtusidens remains unclear. Although three different synonymies have been proposed (variously a subjective synonym of other taxa), these taxonomic hypotheses have not been based on detailed anatomical comparisons and thus have not been tested. Here, we re-describe the holotype of ‘S.’ obtusidens, demonstrate that it is indeed a valid taxon, restrict the referred specimens to a fragmentary skeleton, nearly complete skull, and partial rostrum, and establish a new monotypic genus, Lemmysuchus. Our re-description reveals five autapomorphies for Lemmysuchus obtusidens and nine apomorphic characters that support the tribe Machimosaurini (Lemmysuchus + Machimosaurus). INTRODUCTION Teleosaurid crocodylomorphs were a near-globally distributed clade that inhabited shallow marine and brackish ecosystems throughout the Jurassic (Buffetaut et al., 1981; Buffetaut, 1982a, b; Vignaud, 1993; Hua & Buffetaut, 1997; Hua, 1999; Johnson et al., 2015) and survived into the Early Cretaceous (Fanti et al., 2016; Jouve et al., 2016). These animals are often viewed as marine analogues of extant gavials because of their elongate and tubular snout, dorsally directed orbits and high tooth count, all of which suggest a primarily piscivorous diet (Andrews, 1909, 1913; Buffetaut, 1982a, b). However, within Teleosauridae, some taxa have been considered to be durophagous and/or macrophagous, because they had shorter snouts, proportionally enlarged supratemporal fenestrae (i.e. increased jaw adductor musculature), blunt tooth crown apices, serrated carinae and extensive enamel ornamentation (Eudes-Deslongchamps, 1864, 1867, 1869; Andrews, 1909, 1913; Buffetaut, 1982a; Hua et al., 1994; Hua & Buffetaut, 1997; Hua, 1999; Martin & Vincent, 2013; Young & Steel, 2014; Young et al., 2014a, b, 2015a, b; Fanti et al., 2016; Jouve et al. (2016). The Late Jurassic–Early Cretaceous (Oxfordian to Hauterivian) taxon Machimosaurus is the best-studied macrophagous teleosaurid, known from both cranial and postcranial remains and isolated teeth from numerous countries (Sauvage & Liénard, 1879; Krebs, 1968; see Young et al., 2014a for an overview). Here, we use the taxonomy of Young et al. (2014a), rather than that of Martin, Vincent & Falconnet (2015) following the rationale of Foffa, Young & Brusatte (2015) and because a new phylogenetic analysis of Machimosaurus supports the multi-taxic hypothesis (see Fanti et al., 2016). The sister taxon to Machimosaurus, ‘Steneosaurus’ obtusidens Andrews, 1909, is a controversial taxon from the Middle Jurassic of Europe. Over the past three decades, its validity has been questioned, and three different subjective species (both Machimosaurus and Steneosaurus) synonymies have been proposed (see Adams-Tresman, 1987; Hua et al., 1994; Pierce, Angielczyk & Rayfield, 2009). Recent studies, however, have considered ‘S.’ obtusidens to be a distinct taxon (Martin & Vincent, 2013; Young et al. 2014a, 2015a). This taxonomic confusion hinders our understanding of the origins of the macrophagous teleosaurid sub-clade Machimosaurini. Thus, the aim of this paper is to shed light on the early evolution of durophagous/macrophagous teleosaurids by re-investigating the validity of ‘S.’ obtusidens. We re-describe the holotype of ‘S.’ obtusidens (which consists of a complete cranium and mandible, and the majority of the postcranial skeleton), demonstrate that it is a valid taxon and establish a new monotypic genus, Lemmysuchus obtusidens. We restrict the referred specimens of this species to a fragmentary skeleton, a nearly complete skull and a partial rostrum, and show that most of the cranial and postcranial material previously referred to ‘S.’ obtusidens belongs to other taxa. In addition, we assign three isolated teeth [two from the Oxford Clay Formation (OCF) and one from the Cornbrash Formation] to Machimosaurini indet. Finally, based on the holotype and referred specimens, we conclude that ‘S.’ obtusidens was present in the Callovian OCF of England and the Erymnoceras coronatum ammonite Zone (thus being contemporaneous with the Peterborough Member of the OCF) of Migné-les-Lourdines of France. ‘STENEOSAURUS’ OBTUSIDENS: HISTORICAL BACKGROUND Historical setting The holotype of ‘S.’ obtusidens (Natural History Museum, London, NHMUK PV R 3168) is part of the Leeds Fossil Collection (Peterborough Member, OCF; Middle Callovian) held at the NHMUK. Charles Andrews established the name Steneosaurus obtusidens for NHMUK PV R 3168 (Andrews, 1909) when he described the Leeds Collection teleosaurids. Later, Andrews (1913) tentatively referred two more Leeds Collection specimens to ‘S.’ obtusidens (NHMUK PV R 3169 and NHMUK PV R 3898). Andrews (1913) listed no specific criteria for the referral of these two specimens to ‘S.’ obtusidens and his decision may simply have been based on the large size and robustness that both specimens share with the holotype. Andrews (1913) later noted similarities between ‘S.’ obtusidens and Steneosaurus durobrivensis Andrews, 1909, stating that (Andrews, 1913: 131): ‘if it were not for the peculiarity of the teeth, [the former] might almost have been referred to that species [S. durobrivensis]’. The possibility that the ‘S.’ obtusidens morphotype is a late ontogenetic variant of S. durobrivensis has also been raised (Andrews, 1913; Steel, 1973) (note that S. durobrivensis is now considered to be a subjective junior synonym of Steneosaurus edwardsi Eudes-Deslongchamps, 1868; see Johnson et al., 2015). The first worker to formally synonymize ‘S.’ obtusidens with S. durobrivensis (=S. edwardsi) was Adams-Tresman (1987). As noted by Young et al. (2015a), the anatomical comparisons made between ‘S.’ obtusidens and S. edwardsi (as S. durobrivensis) were not based on the ‘S.’ obtusidens holotype (NHMUK PV R 3168), but on referred specimens (i.e. NHMUK PV R 3169, Peterborough Museum and Art Gallery, Peterborough, PETMG R39 and PETMG R178). We agree with Adams-Tresman (1987) that PETMG R39 matches the ‘S.’ obtusidens holotype (see Discussion). However, the other two specimens lack the apomorphies of the ‘S.’ obtusidens holotype (see description below), and thus cannot be referred to this taxon (we argue that they instead should be referred to S. edwardsi, see Discussion). This means that Adams-Tresman’s (1987) discussion regarding tooth morphology and dorsal osteoderm ornamentation were correct and NHMUK PV R 3169 and PETMG R178 do indeed belong to S. edwardsi. However, we show below that these characteristics are distinct from those in the ‘S.’ obtusidens holotype, NHMUK PV R 3168. Young et al. (2015a) also noted that Adams-Tresman (1987) did not discuss the presence of three sacral vertebrae in the ‘S.’ obtusidens holotype, while Andrews (1913: 132) considered it likely to be an ‘individual peculiarity’ of the holotype. The neotype of Machimosaurus mosae Sauvage & Liénard, 1879 also has three sacral vertebrae (Hua, 1999; Young et al., 2014a). Another set of characteristics not mentioned by Adams-Tresman (1987) are the pronounced socket-like reception pits along the maxilla and dentaries for the opposing tooth row. Again, this may have been due to Andrews (1913: 131) being unsure if they were a natural characteristic or a result of postmortem deformation. However, this is another characteristic that the ‘S.’ obtusidens holotype (NHMUK PV R 3168) shares with Machimosaurus (Buffetaut, 1982b; Lepage et al., 2008; Young et al., 2014a; note that Young et al., 2014a considered vertically orientated, interlocking dentition, with pronounced reception pits at the premaxillary, maxillary and dentary interalveolar spaces to be a Machimosaurus apomorphy). It is unclear whether Adams-Tresman (1987) was being selective in what characteristics the ‘S.’ obtusidens referred specimens and the S. durobrivensis holotype and referred specimens shared, or simply being cautious in regards to morphologies unique to the ‘S.’ obtusidens holotype. ‘Steneosaurus’ obtusidens was also considered to be a subjective junior synonym of the Kimmeridgian species Machimosaurus hugii von Meyer, 1837 (Hua et al., 1994; Hua, 1996, 1999). However, these authors noted that the taxonomy of blunt-toothed teleosaurids still required further study. More recently, Pierce et al. (2009) suggested that ‘S.’ obtusidens, Steneosaurus hulkei Andrews, 1913 and S. durobrivensis (all Callovian taxa; the species S. edwardsi was not mentioned) were subjective junior synonyms of M. hugii. This synonymy and corresponding species diagnoses have been criticized and rejected (see Martin & Vincent, 2013; Young et al., 2014a; Johnson et al., 2015) and, indeed, all phylogenetic analyses that include the relevant taxa do not support any of the two proposed synonymies (S. durobrivensis = S. edwardsi and M. hugii). In these analyses, ‘S.’ obtusidens is consistently found to be the sister taxon of Machimosaurus, while S. durobrivensis (=S. edwardsi) is the sister taxon to this sub-clade (Young et al., 2012; Martin & Vincent, 2013; Young, 2014; Fanti et al., 2016; Young et al., 2016a). Recent papers have agreed that ‘S.’ obtusidens is a distinct taxon (Martin & Vincent, 2013; Young et al. 2014a, 2015a). Finally, Jouve et al. (2016) established the tribe Machimosaurini for ‘S.’ obtusidens, Machimosaurus and indeterminate Bathonian specimens (based on shared craniodental morphologies; see Introduction). Geological setting The OCF is a Jurassic (Callovian – lower Oxfordian) lithostratigraphic unit that is well known from extensive exposures that extend from the western Dorset coast to northern Yorkshire of England (Selden, Baker & Phipps, 2008). The entire OCF is composed of two main facies: the lowermost Peterborough Member and an upper facies that comprises the Stewartby Member and Weymouth Member (Cox, Hudson & Martill, 1992; Martill et al., 1994; Selden et al., 2008). The Peterborough Member, referred to in older literature as the Lower Oxford Clay, consists of compact olive-coloured shaly clays and black and organic-rich fissile shales (Hudson & Martill, 1994; Martill et al., 1994). This member contains a diverse vertebrate fauna, including: bony fish and chondrichthyans, marine reptiles (ichthyosaurs, plesiosaurs, pliosaurs and thalattosuchians) and rare dinosaur and pterosaur remains (Martill et al., 1994). Oxygen isotope values (Kenig et al., 1994) indicate that the OCF was deposited in a shallow marine, open-shelf environment. The Cornbrash Formation is a Bathonian–Callovian (Middle Jurassic) lithostratigraphic unit that underlies the OCF (Wright, 1977). This stratigraphic section consists of medium- to fine-grained limestone that is bioturbated, yields many reptilian fossils and stretches from the Weymouth area to the Scarborough area in the UK (Cox & Sumbler, 2002), similar to the OCF. The Cornbrash Formation is comprised of two main units, the Cornbrash Limestone and the Cornbrash Shales, which form a transgressional marine cycle (Wright, 1977). The Cornbrash Formation represents a section of the Great Oolite Group (Sellwood et al., 1985). Migné-les-Lourdines (the locality of specimen LPP.M.21) is a small town just north of Poitiers, France. The Coronatum Zone (ammonite zone named after E. coronatum) in France is Middle Callovian (Brunet, 1969; Vignaud P, unpublished data) and corresponds to the Peterborough Member of the OCF in the UK. At Migné-les-Lourdines, this ammonite zone is represented by a white calcareous limestone (Brunet, 1969). ABBREVIATIONS Institutional CAMSM, Sedgewick Museum of Earth Sciences, University of Cambridge, Cambridge, UK; DORCM, Dorset County Museum, Dorchester, UK; GLAHM, The Hunterian Museum, Glasgow, UK; GPIT, Paläontologische Sammlung der Eberhard Karls Universität Tübingen, Tübingen, Germany; LPP, Institut de paléoprimatologie, paléontologie, humaine; évolution et paléoenvironnements Université de Poitiers, Poitiers, France; MNHN, Muséum national d’histoire naturelle, Paris, France; NHMUK, Natural History Museum, London, UK; NMS, Naturmuseum Solothurn, Solothurn, Switzerland; NOTNH, Nottingham Natural History Museum, Nottingham, UK; OUMNH, Oxford University Museum of Natural History, Oxford, UK;. PETMG, Peterborough Museum and Art Gallery, Peterborough, UK; SMNS, Staatliches Museum für Naturkunde Stuttgart, Baden-Württemberg, Germany. Anatomical XII, cranial nerve 12; ac dep, acetabular depression; ac in, acetabular incision (acetabular notch); an, angular; ant f, anterior flange of second sacral vertebra; ant pr, anterior process of ilium; ar, articular; art f, articular facet; atl, atlas; ax, axis; bas, basisphenoid; cen, vertebral centrum; clp, lateral process of calcaneum; cmp, medial process of calcaneum; cor, coronoid; cor gr, coronoid groove; den, dentary; fm, foramen magnum; fo, foramina; fr, frontal; ft, ‘fourth trochanter’ rugose area; fem h, femoral head; fib, fibula; gf, glenoid fossa; hc, humeral concavity; hs, humeral shaft; if, incisive foramina; isch bl, ischial blade; jug, jugal; k, keel of osteoderms; lac?, uncertain lacrimal area; le, lateral epicondyle (of humerus); m con, medial condyle of femur; me, medial epicondyle (of humerus); mx, maxilla; mx gr, maxillary groove; na, nasal; ns, neural spine; oc, occipital condyle; od, odontoid; or, orbit; pal, palatine; par, parietal; pat, pathology; pit, ornamentation pit on dorsal surface of osteoderms; pmx, premaxilla; pmx1-2, first and second premaxillary tooth; pn, pubic neck; po, postorbital; poz, postzygapophyses; pp, pubic plate; prf, prefrontal; prz, prezygapophyses; pt, pterygoid; pub, pubis; q, quadrate; rib h, rib head; s1, first sacral vertebra; s2, second sacral vertebra; s3, third sacral (refers to first caudal) vertebra; spl, splenial; sq, squamosal; st h, sternal head; sub r, sub-horizontal anterior ridge of ilium; sup cr, supraacetabular crest of ilium; sup occ, supraoccipital; supr fen; supratemporal fenestra; san, surangular; tub, tuberculum; tp, transverse process; t tub, tibial tuberosity; vac?, vacuity. SYSTEMATIC PALAEONTOLOGY Crocodylomorpha Hay, 1930 (sensu Nesbitt, 2011) Thalattosuchia Fraas, 1901 (sensu Young & Andrade, 2009) Teleosauridae Geoffroy Saint-Hilaire, 1831 Machimosaurini Jouve et al., 2016 Machimosaurini indeterminate v 1905 Machimosaurus rigauxi Sauvage – Blake, p. 26, Plate 1, fig. 5a–c v 2014a Machimosaurus rigauxi Sauvage – Young et al., p. 3 We have identified isolated teeth that have a characteristic Machimosaurini dental pattern (see Lemmysuchus description): GPIT/RE/301, CAMSM J64508 and OUMNH J.14464. The first tooth crown GPIT/RE/301 (Fig. 12E–I) is from the OCF of Peterborough and was excavated before 1906. It was sold to the Eberhard Karls Universität in Tübingen, Germany, during the first decade of the 20th century. A note in the collections by E. Buffetaut in 1981 suggested that it could be ‘S.’ obtusidens, while another specimen note by B. Stürtz (a commercial fossil collector from Bonn) suggested that it might belong to Machimosaurus but was similar to the genus Steneosaurus. The tooth is conical, robust with a blunt apex and posteriorly curved. The majority of the root is missing. The tooth is single-cusped and has no accessory cusps or cingula. The enamel ridges are well defined and pronounced and are close in parallel vertical rows. The enamel ornamentation is similar to the L. obtusidens holotype (NHMUK PV R 3168), with randomly arranged ridges near the apex that are straight, parallel and closely packed together towards the root of the tooth. Another isolated tooth, CAMSM J64508 (Fig. 12J–P), was collected in Fletton (Cambridgeshire) and is also possibly from the Leeds Collection. It has originally been regarded (by whom is unknown) as a pliosaurid of the genus Simolestes, most likely for its size. However, the curvature, blunt apex, presence of pronounced carinae and ornamentation patterns distinguish it from any late Middle Jurassic pliosaurids. The tooth is conical and has a circular cross-section which is maintained through the whole apicobasal length. As typical in Machimosaurus and L. obtusidens, the tip of the crown is blunt (Young et al., 2014a, b). The considerable size of the crown (~5 cm apicobasal length) and the height-to-length ratio suggests CAMSM J64508 may be one of the large dentary or premaxillary pseudocaniniform teeth. The crown is clearly ornamented by long continuous and evenly spaced apicobasal ridges that occur with the same density on the labial, mesial and lingual sides. As in Machimosaurus and L. obtusidens, the ornamental ridges on the apex become shorter until they form the characteristic anastomosed pattern (Young et al., 2014a, 2015a, b). Interestingly, this ornamentation pattern is convergent with the Late Jurassic metriorhynchid Torvoneustes carpenteri (Wilkinson,Young & Benton, 2008). In CAMSM J64508, the carinae are present although almost indistinguishable for most of the crown length (Fig. 12J–P). However, they can be observed in the apical ‘anastomosed region’. The carinal keel is considerably clearer on one side than the other. The ornamentation pattern of the apex contacts the carinae forming false serrations (Young et al., 2015a). Tooth OUMNH J.14464 (Fig. 12Q–T) is from the Cornbrash Formation and was figured by Blake as Machimosaurus rigauxi Sauvage, 1879 (Blake, 1905: 26: Plate 1, fig. 5a–c). The crown of this tooth is intact and the root is missing. The apex is slightly pointed and the entire tooth is conical and mediolaterally thickened. The mesial and distal carinae are faint, not as pronounced as in GPIT/RE/301, and when viewed with the naked eye terminate in the middle of the tooth. The numerous enamel ridges run ventrally parallel and close together. At the apex, the ridges are disoriented and extend in random patterns, much as how Andrews (1913) described the teeth of the L. obtusidens holotype (NHMUK PV R 3168). The two tooth crowns from the OCF (GPIT/RE/301 and CAMSM J64508) may be referable to L. obtusidens. However, as they are isolated crowns, we refrain from making that assignment. The M. rigauxi tooth (OUMNH J.14464) is interesting as it is from the Cornbrash Formation, a lithostratigraphic unit that L. obtusidens is currently not known from. Lemmysuchus gen. nov. (Figs 1–21) urn:lsid:zoobank.org:act:83D7C69A-4009-478E- 8D6E-A05F39E190D1 Type species Steneosaurus obtusidens Andrews, 1909 [following recommendation 67B of the International Commission on Zoological Nomenclature (ICZN) code]. Now referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Diagnosis Same as the only known species (monotypic genus). Etymology ‘Lemmy’s crocodile’. Lemmy referring to Ian Fraser Kilmister, better known as ‘Lemmy’, the deceased founder, bassist and lead singer of Motörhead, and suchus is the Latinized form of the Greek soukhos (σοῦχος), meaning crocodile. Lemmysuchus obtusidens (Andrews, 1909) comb. nov. urn:lsid:zoobank.org:act:83D7C69A-4009-478E- 8D6E-A05F39E190D1 v* 1909 Steneosaurus obtusidens Andrews, p. 306, Plate 9 figure 2 v 1913 Steneosaurus obtusidens Andrews – Andrews, p. 130, Text-fig. 50, Plate 7 all figures (partim) v 1969 Steneosaurus cf heberti Morel de Glasville – Brunet, Plate 1 figure b-b (LPP.M.21) v 1973 Steneosaurus obtusidens Andrews – Steel, p. 33, figure 13.13 v 1987 Steneosaurus durobrivensis Andrews – Adams-Tresman, p. 205 (partim) 1993 Steneosaurus cf heberti Morel de Glasville – Vignaud v 1994 Machimosaurus hugii von Meyer – Hua et al., p. 15 (partim) v 1996 Machimosaurus hugii von Meyer – Hua, p. 1562 (partim) v 2009 Machimosaurus hugii von Meyer – Pierce et al., p. 1085 (partim) v 2013 Steneosaurus obtusidens Andrews – Martin & Vincent, p. 192 v 2014a ‘Steneosaurus’ obtusidens Andrews – Young et al., p. 3 v 2014b ‘Steneosaurus’ obtusidens Andrews – Young et al., p. 2 v 2016 ‘Steneosaurus’ obtusidens Andrews – Jouve et al., p. 4 Holotype NHMUK PV R 3168, complete cranium and mandible in articulation, atlas–axis complex, 6 postaxial cervical vertebrae, 14 dorsal vertebrae, 3 sacral vertebrae, 21 caudal vertebrae, 1 complete cervical rib and 20 cervical rib fragments, 49 dorsal rib fragments (fewer than 5 complete ribs), 2 gastralia fragments, 1 right scapula, 1 distal fragment of a humerus, 1 ulna, 1 right ilium, both ischia, 1 pubis, both femora, 1 tibia, possible pieces of fibulae or carpals/tarsal elements, 5 ankle bones (including a calcaneum, distal tarsal and astragalus), 4 phalanges, numerous dermal osteoderms (~56), 33 isolated teeth and numerous bone fragments (Figs 1–3, 12A–D, 13–21). Figure 1. View largeDownload slide Photograph (A) and line drawing (B) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in dorsal view with additional details of the premaxillary dentition. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 1. View largeDownload slide Photograph (A) and line drawing (B) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in dorsal view with additional details of the premaxillary dentition. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 2. View largeDownload slide Photograph (A, C) and line drawing (B, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 2. View largeDownload slide Photograph (A, C) and line drawing (B, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 20 cm. Figure 3. View largeDownload slide Photograph (A, B) and line drawings (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in anterior (A, C) and occipital (B, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 3. View largeDownload slide Photograph (A, B) and line drawings (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Skull in anterior (A, C) and occipital (B, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Etymology ‘Lemmy’s blunt-toothed crocodile’. From the Latin for blunt (obtusus) and tooth (dens). Named for the blunt apices of the teeth. Type locality Peterborough, England, UK. The exact age and area of collection of this specimen is not known, original Leeds Collection Number 6. Type horizon Peterborough Member, OCF, Ancholme Group. Middle Callovian, Middle Jurassic. Referred specimens PETMG R39, largely incomplete rostrum, fragment of right mandibular ramus, partial dorsal osteoderm and five dorsal vertebral centra. PETMG R31, five vertebral centra (two dorsals and three sacrals), are associated with PETMG R39 and very likely belong to the same individual (see Discussion) (Peterborough Member, OCF, Ancholme Group; Middle Callovian). LPP.M.21, nearly complete skull (left lateral portion not preserved from the orbit to the squamosal) and mandible (anterior region is preserved) (E. coronatum ammonite Zone, Middle Callovian). NOTNH FS3361, partial rostrum, including the premaxillae and part of the maxillae (horizon and locality unknown, thought to be OCF because of the state of preservation). Emended diagnosis Teleosaurid crocodylomorph with the following unique combination of characters [proposed autapomorphic characters are indicated by an asterisk (*)]: the rostrum external surface is strongly convex, in particular the nasals*; partial or complete fusion of the internasal suture*; axis lacks diapophyses (shared with Steneosaurus bollensis Jaeger, 1828; see Westphal, 1962); the ilium anterior process is small and anteroposteriorly shortened*; on the ilium the acetabulum is shallow and poorly developed*; shallow supraacetabular crest on the ilium*; the dorsal osteoderm ornamentation is composed of small-to-large, irregularly shaped pits that radiate from the centre of the keel and are arranged in a starburst pattern (to a certain extent similar to M. mosae; Hua, 1999; Young et al., 2014a)*. Characteristics shared with Machimosaurus Lemmysuchus obtusidens shares the following nine synapomorphies with Machimosaurus (sensuYoung et al., 2014a): (1) conical teeth with blunt/rounded apices; (2) tooth enamel ornamentation varies along the crown, that is, in the basal region enamel ornamentation is composed of numerous apicobasally aligned ridges of high relief, which transition into an anastomosed pattern in the apical region; (3) teeth have true and false denticles on the carinae; (4) ratio of crown apicobasal height to basal transverse width can be as low as 1.8 in the posterior teeth; (5) pronounced socket-like reception pits along the maxilla and dentaries for the opposing tooth row; (6) the supratemporal fossae are parallelogram-shaped in dorsal view; (7) three sacral vertebrae; (8) ischial blade posterior margin is blunt and sub-square in shape and (9) proximal tibia strongly deflects anteriorly. However, L. obtusidens lacks the following eight Machimosaurus autapomorphies (sensuYoung et al., 2014a; note that the two axis neural spine autapomorphies cannot be determined in L. obtusidens due to preservation): Three alveoli per premaxilla (L. obtusidens has four alveoli per premaxilla). The first premaxillary alveoli are orientated strongly anteroventrally (L. obtusidens lacks this condition). 18–22 alveoli per maxilla (L. obtusidens has at least 29 alveoli per maxilla). 19–25 alveoli per dentary (L. obtusidens has ~29 alveoli per dentary). Presence of carinae is variable in Machimosaurus spp. (in L. obtusidens all teeth have carinae). The rostrum is broad and mesorostrine, constituting fewer than 60% of the basicranial length (in L. obtusidens, the rostrum is 61.2% of basicranial length and is less broad, thus falling slightly outside the condition seen in Machimosaurus). Ratio of maximum supratemporal fossa length to basicranial length is greater than 27% (in L. obtusidens, this ratio is 25.8%). Medial quadrate hemicondyle is considerably smaller than the lateral hemicondyle (in L. obtusidens both condyles are large and similar in size). Lemmysuchus obtusidens (NHMUK PV R3168), Machimosaurus, Steneosaurus heberti Morel de Glasville, 1876 (MNHN.F 1890-13) and S. edwardsi (NHMUK PV R3701) share three characteristics: (1) anterior processes of the jugals are very elongate and slender, so that they largely restrict a lacrimal-maxilla contact on the external surface, except for the anterolateral margins of the lacrimals which do contact the maxillae (Fig. 6); (2) the Meckelian canal (=groove) is not deeply excavated on the dorsal surface of the splenials (Fig. 9) in contrast to other thalattosuchians such as Steneosaurus leedsi Andrews, 1909 (NHMUK PV R3320) and (3) the closure of the antorbital fenestrae (Fig. 22D–G) (see description below on how we conclude that L. obtusidens lacks these fenestrae). Note that Young et al. (2014a) listed the absence of antorbital fenestrae was shared by Machimosaurus (SMNS 91415) and S. heberti. Lemmysuchus obtusidens also shares one characteristic with S. heberti (MNHN.F 1890-13); sharp dorsoposterior curvature of the posterior mandibular rami (as opposed to gradual curvature in S. edwardsi) (PETMG 178) (Fig. 22A–C). Character note Lemmysuchus obtusidens has two characteristics that are well developed in the holotype but not clear in other OCF teleosaurid specimens (because of the typically poor preservation of skulls, through dorsoventral crushing and/or shearing). These are: (1) a large nuchal crest on the supraoccipital and (2) large and pronounced paired occipital tuberosities (somewhat similar to those seen in dyrosaurid crocodyliforms, which are developed to a much greater extent; e.g. MNHN.F ALG 1). These characteristics, albeit in a reduced form, are also seen in Teleosaurus cadomensis Lamouroux, 1820 (MNHN cast of an adult skull, MNHN.F AC 8746; Jouve, 2009), S. heberti (MNHN.F 1890-13) and Machimosaurus buffetauti Young et al., 2015 (SMNS 91415; Martin & Vincent, 2013; Young et al., 2014a). Description The holotype of L. obtusidens, NHMUK PV R 3168, comprises a nearly complete skeleton (Figs 1–3, 12A–D, 13–21) (Andrews, 1909, 1913). The cranium and mandible adhere together so tightly that the cranium palatal view and mandible dorsal view is inaccessible; LPP.M.21, however, preserves the palatal view, which is easily accessible (Fig. 8C, D), and NOTNH FS3361 preserves part of the rostrum, including the premaxillae (Figs 10, 11). The cranium has experienced dorsoventral compression and has numerous fractures making it difficult to discern sutures from breaks. However, PETMG R39 is well preserved (Figs 4–6), and the preorbital area, cranium palatal surface and part of the mandibular dorsal surface can be described from this specimen. Figure 4. View largeDownload slide Photograph (A, C) and line drawing (B, D) of PETMG R39, referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 4. View largeDownload slide Photograph (A, C) and line drawing (B, D) of PETMG R39, referred to as Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 5. View largeDownload slide Photograph (B, D) and line drawing (B, D) of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 5. View largeDownload slide Photograph (B, D) and line drawing (B, D) of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in left (A, B) and right (C, D) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 6. View largeDownload slide Close-up of right lateral view of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov, showing in detail the maxilla, jugal, nasal and lacrimal bones. Outlines the jugal-maxilla and lacrimal-jugal contacts. Note the absence of antorbital fenestrae. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 6. View largeDownload slide Close-up of right lateral view of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov, showing in detail the maxilla, jugal, nasal and lacrimal bones. Outlines the jugal-maxilla and lacrimal-jugal contacts. Note the absence of antorbital fenestrae. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 7. View largeDownload slide Partial mandible section of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov., in (A) dorsal, (B) lateral, (C) ventrolateral, (D) ventral and (E) anterior views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 7. View largeDownload slide Partial mandible section of PETMG R39, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov., in (A) dorsal, (B) lateral, (C) ventrolateral, (D) ventral and (E) anterior views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 8. View largeDownload slide Photographs (A, C) and line drawings (B, D) of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 8. View largeDownload slide Photographs (A, C) and line drawings (B, D) of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Skull in dorsal (A, B) and palatal (C, D) views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 9. View largeDownload slide Photograph (A) and line drawing (B) in dorsal view of the mandibular interior of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 9. View largeDownload slide Photograph (A) and line drawing (B) in dorsal view of the mandibular interior of LPP.M.21, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 10. View largeDownload slide Dorsal (A, B), left lateral (C, D), ventral (E, F) and right lateral (G, H) photographs and line drawings of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Note the small incisive foramina and the number of alveoli in the premaxillae and maxilla. Scale bar: 10 cm. Figure 10. View largeDownload slide Dorsal (A, B), left lateral (C, D), ventral (E, F) and right lateral (G, H) photographs and line drawings of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Note the small incisive foramina and the number of alveoli in the premaxillae and maxilla. Scale bar: 10 cm. Figure 11. View largeDownload slide Ventral close-up of (A) photo and (B) line drawing of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 11. View largeDownload slide Ventral close-up of (A) photo and (B) line drawing of NOTNH FS3361, referred to Lemmysuchus obtusidens (Andrews, 1909) comb. nov. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Cranium: The cranium of L. obtusidens (NHMUK PV R 3168) (Figs 1–3) is ~1.4 m long (Andrews, 1909, 1913). It is similar to Machimosaurus in terms of overall anatomy and robusticity. The rostrum is more robust but comparatively shorter than those of other Middle Jurassic teleosaurids (e.g. S. leedsi, S. heberti, Mycterosuchus nasutus) (Andrews, 1913) and comprises 61.2% of the total skull length [the 51% ratio given in Andrews (1913) was a typographical error]. The anterior premaxilla and dentaries are laterally expanded as in other teleosaurids (e.g. Andrews, 1909, 1913; Hua, 1999; Martin & Vincent, 2013; Young et al., 2014a). In NHMUK PV R 3168 (Fig. 1), the preorbital region is deformed, possibly due to an infection of the bone caused by a bite (there is a large tooth deeply embedded in this region of the cranium). Conversely, PETMG R39 (Figs 4, 5) and LPP.M.21 (Fig. 8A, B) are well preserved in this area. Based on NHMUK PV R 3168 (Figs 1–3), LPP.M.21 (Fig. 8) and PETMG R39 (Figs 4, 5), the orbits would have been large, oval in shape and oriented more anteroposteriorly than in most other teleosaurids (such as S. leedsi NHMUK PV R 3806). In dorsal view, the supratemporal fenestrae (Fig. 1) are considerably longer than wide and are considerably longer than the orbits. The cranial description refers to the holotype (NMHUK PV R 3168) unless otherwise specified. Due to the fragility and heaviness of the NHMUK PV R 3168 cranium, the authors were unable to flip it over to observe the palates. Therefore, all information pertaining to the palatal surface comes from LPP.M.21. Premaxillae: The premaxillae (Figs 1, 2, 3A, C) are large and robust, surround the external narial opening and face anterodorsally. The external nares are laterally expanded and their posterior margins do not reach beyond the third premaxillary alveolar pair. The anterior two-thirds of the premaxilla is laterally expanded and the anterior margin is ventrally deflected, giving the snout a scoop-like appearance. In LPP.M.21 (Fig. 8A, B) and NOTNH FS3361 (Figs 10, 11), the incisive foramen (=naso-oral fenestra) is very small and is situated in the middle of the suture of the premaxillae. In dorsal view, the premaxilla–maxilla suture is well developed and W-shaped. The left premaxilla–maxilla suture is directed proximodistally parallel towards the middle of the rostrum with two small, pointed, posterior-oriented processes edges in dorsal view. The premaxilla contains four teeth, with the fourth (posterior-most) being the largest. The first two premaxillary alveoli are nearly confluent, with a thin interalveolar lamina separating them. The interalveolar lamina is missing in NOTNH FS3361 and LPP.M.21, making it appear as though there were only three premaxillary teeth present (this feature is noted in Vignaud, 1997). There is a diastema between the last premaxillary tooth and the first maxillary tooth. In life, large dentary caniniform teeth would have been present (as in Machimosaurus and other large teleosaurids; Andrews, 1909, 1913; Martin & Vincent, 2013). Maxillae: The maxillae (Figs 1, 2, 3A, C) form a substantial part of the rostrum. Their lateral margins are sub-parallel in dorsal view. The maxilla separates the nasals from the premaxillae. The precise maxillary tooth count is difficult to determine but there are ~29 alveolar pairs (Andrews, 1913). The specimen LPP.M.21 has 29 alveolar pairs (Fig. 8C, D) and NOTNH FS3361 preserves ~26 alveolar pairs (the posterior portion of the maxilla is missing) (Fig. 10E, F). The lateral surface of the maxilla is ornamented by well-spaced, deep foramina that are visible in both dorsal, lateral and anterior views (Figs 1, 2, 3A, B). The maxillary tooth row ends anterior to the anterior-most border of the sub-orbital fenestra. Numerous, deep reception pits for dentary teeth are along the middle and anterior regions of the ventral-lateral margin of the maxillae (Fig. 2). The posterolateral regions of both maxillae in PETMG R39 have a groove which follows approximately parallel with the long anterior process of the jugal (Figs 4–6). This feature is shared with Machimosaurus, S. heberti (MNHN.F 1890-13) and S. edwardsi (Martin & Vincent, 2013; Young et al., 2014a). There is a small pathology on the ventral right maxilla in NOTNH FS3361 (Fig. 10). Jugals: The jugals are triradiate and form the lateral border of the orbit (Figs 1, 2, 4–6, 8A, B) as in other teleosaurids (Andrews, 1909, 1913). The jugal is dorsally compressed by the postorbital-squamosal and is ventrally compressed by the dentary due to poor preservation. The anterior margin of the jugal runs between the lacrimal and posterior regions of the maxilla (Figs 2, 3A, C). This feature is shared among S. edwardsi (PETMG R175), S. heberti (MNHN.F 1890-13), L. obtusidens (PETMG R39) (Figs 4–6), M. hugii (NMS 7012) and possibly also M. buffetauti (the holotype SMNS 91415 is poorly preserved in this region). However, it is only in Lemmysuchus and Machimosaurus that the jugal is extremely elongate, it anteriorly extends and reaches the anterior end of the lacrimal. The postorbital-jugal or quadratojugal-jugal contacts cannot be seen clearly in NHMUK PV R 3168, as the specimen is crushed in those areas. In LPP.M.21, the postorbital-jugal contact is anteroposteriorly straight (Fig. 8A, B). The quadratojugal-jugal contact is not clear in either NHMUK PV R 3168 or LPP.M.21. Nasals: The nasals (Figs 1, 2, 3A, C) are large triangular bones exposed on the dorsal surface of the posterior rostrum and orbital area. Both nasals (in NHMUK PV R 3168) are missing their anterior and posterior regions. The nasal anterior processes extend past the third maxillary tooth. Deformation, due to an embedded tooth previously mentioned from another animal (which is circular and has left a striated impression behind), obscures the view of the anterior region of the nasal anterior processes. The nasals have a little ornamentation, consisting of faint ridges. There is a faint internasal midline suture on the anterior rostrum; further posteriorly there is no internasal suture, suggesting the nasals are partially or completely fused. This is seen in NHMUK PV R 3168 as well as LPP.M.21 (Fig. 8A, B), NOTNH FS3361 (Fig. 10A, B) and PETMG 39 (Fig. 4A, B). Both nasals form the beginning of a dorsally directed ‘dome’ towards the medial contact with the frontal. PETMG 39 (Figs 4, 5) and NOTNH FS3361 (Fig. 10) show the beginning of the ‘dome’ in the anterior nasals (as the posterior nasals are not preserved in NOTNH FS3361). In LPP.M.21 (Fig. 8A, B), it is not clear if the nasals are convex (due to dorsoventral crushing, although this could be an ontogenetic feature), and the nasal anterior processes are approximately one-third of the posterior rostrum and have well-developed near-parallel suture contacts with the maxillae. Prefrontals: The prefrontals (Figs 1, 2) are slightly sub-circular in dorsal view and form the anteromedial border of the orbits. The prefrontal contacts the nasal medially and the lacrimal laterally. The frontal-prefrontal contact cannot be clearly seen even in the better preserved PETMG R39 due to breaks in this area (Figs 4–6). In LPP.M.21 (and to some extent on the right side in NOTNH FS3361), the prefrontal contacts the frontal posteromedially at a straight angle (Figs. 8A, B). The prefrontals are well developed and tear-shaped (Figs. 8A, B, 10). Lacrimals: The lacrimals are better preserved in PETMG R39 (Figs 4–6) and LPP.M.21 (Fig. 8A, B) than in NHMUK PV R 3168 (Figs 1, 2) even though the medial and posterior margins are not preserved well. The lacrimals are large and triangular as in other teleosaurid taxa (Andrews, 1909, 1913) and constitute most of the anterior-lateral border of the orbits. Andrews (1913) reported paired openings ~5–7 cm anterior to the lacrimal in NHMUK PV R 3168 that he considered to be antorbital fenestrae, describing them as no more than 5 cm in length and longer than wide (Andrews, 1913). PETMG R39 (Figs 4–6), NOTNH FS3361 (Fig. 10) and LPP.M.21 (Fig. 8A, B) show that L. obtusidens did not have antorbital fenestrae. As such, we interpret these ‘openings’ in NHMUK PV R 3168 to be cracks caused by compression. Frontal: The frontal (Figs 1, 2, 3A, C) is a large and deep (dorsoventrally thickened) bone with no evidence of a midline suture. The anterior region slightly slopes anteriorly in conjunction with the posterior nasal and descends posteriorly, giving it a ‘domed’ appearance (Figs 2, 3A, C). The anterior process is not preserved; however, it is well preserved in LPP.M.21 (Fig. 8A, B), showing that it is as short as in most other teleosaurids (e.g. S. leedsi; see Andrews, 1913). The frontal contributes to the posteromedial border of the orbits (Figs 1, 2) and is well seen in LPP.M.21 (Fig. 8A, B). The frontal forms a straight vertical contact with the postorbital in dorsal view and forms the anterior medial borders of the supratemporal fenestrae. The ornamentation on the frontal does not differ from other OCF teleosaurids and consists of pronounced irregular ridges radiating from the centre of the bone. Postorbitals: The large, robust postorbitals (Figs 1, 3A, C) form the lateral and part of the posteroventral border of the orbits. In lateral view, the dorsoventral suture of the postorbital contacts the squamosal and the left postorbital strongly contacts the frontal and forms the posterior margin of the orbit. Because both postorbitals are broken, the postorbital bars are not preserved in NHMUK PV R 3168. In LPP.M.21, the postorbital bar is similar to other OCF teleosaurids (Fig. 8A, B). It forms the posterior margin of the orbit, is slightly anteroposteriorly thickened and of standard mediolateral length. Parietal: The unornamented parietal (Figs 1, 2, 3A, C) is a single bone with no trace of a midline suture that contributes to the medial and posterior borders of the supratemporal fenestrae. Dorsally the parietal does not overhang the occipital condyle. The parietal bar is relatively thin and anteroposteriorly elongated. The posterior region of the parietal is anteriorly concave. In LPP.M.21, there is little to no ornamentation on the parietal (Fig. 8A, B). Squamosals: The squamosals (Figs 2, 3B, D) are large, anteroposteriorly elongate, L-shaped bones and are well preserved in LPP.M.21 (Fig. 8A, B). The squamosal forms the posterolateral border of the supratemporal fenestrae and its posterolateral surface is concave. It contacts the quadrate posteroventrally in lateral view. The squamosal bar is robust and anteriorly contacts the postorbital bar (together forming the supratemporal arch). In NHMUK PV R 3168, the left squamosal is distorted and flattened due to poor preservation. Quadrates: The quadrates (Figs 1, 3B, D) are large, robust and are strongly sutured to the squamosals and quadratojugals. The anterodorsal region of the quadrate contacts the squamosal and quadratojugal while the posteroventral margin articulates with the angular (=jaw joint) and medially contacts the exoccipital. The posteroventral lateral and medial hemicondyles are approximately the same size and length. They are both elongated mediolaterally, are oval in shape and have rounded posterior edges. In occipital view, the hemicondyles posteriorly extend further than the exoccipitals. The right quadrate is well preserved while the left quadrate is not. In LPP.M.21, the quadrates are large and mediolaterally expanded in ventral view (Fig. 8C, D). Quadratojugals: The quadratojugals are dorsally and ventrally compressed and are not visible in dorsal view. The posterior region of the quadratojugal is expanded mediolaterally to accommodate the quadrate and extends slightly further than the outermost tip of the quadrate. Ectopterygoids: Only the right ectopterygoid is preserved in NHMUK PV R 3168. Anteriorly it contacts with the maxilla. The contact with the pterygoids and palatines cannot clearly be seen. The dorsal surface of the ectopterygoid is slightly concave. The right ectopterygoid is preserved in LPP.M.21 and curves ventromedially (Fig. 8A, B). Supraoccipital: The supraoccipital is positioned ventral to the parietal and is only visible in occipital view (Fig. 3B, D). The ventral edge is not triangular but curved so it appears as two ‘lobes’ (Fig. 3). A large nuchal crest (Fig. 3B, D) is situated directly in the middle of the supraoccipital. Exoccipital: The exoccipitals make up the majority of the occipital surface of the cranium. The right side has been medially compressed and the dorsal rim curves medially, while the left side tilts dorsally and flares mediolaterally. The exoccipitals are dorsally expanded above the foramen magnum, as in M. buffetauti and M. mosae (Hua, 1999; Martin & Vincent, 2013). Laterally, the exoccipitals descend rapidly, so in occipital view, they appear almost box-like. The exoccipitals contribute to the occipital condyle. The paraoccipital processes are small and the lateral wings are elongate and robust. The foramen for cranial nerve XII is small and parallel to the foramen magnum (Fig. 3B, D). Basioccipital: The basioccipital contributes to the ventral region of the foramen magnum and is slightly wider than tall. The occipital condyle is larger and more circular than the foramen magnum. In ventral view (LPP.M.21), two well-developed and slightly anteroposteriorly elongated basioccipital tuberosities are visible, with the left one being larger due to variable preservation (Fig. 8C, D). Pterygoid: The right pterygoid wing is present in the holotype (NHMUK PV R 3168), but it is poorly preserved; it is unclear how complete the pterygoid wing is in this specimen without access to the palatal view. The left pterygoid is similarly broken but the lateral pterygoid wing is accessible laterodorsally. It is large and elongated craniocaudally and lateromedially. The dorsal surface of the wing is concave and the posterior region curves anteromedially, possibly due to breakage. In ventral view (LPP.M.21), the pterygoid is thin and elongated and contributes to the medial and posterior borders of the sub-orbital fenestrae, which are tear-shaped (thin anteriorly, wide and slightly rounded posteriorly) (Fig. 8). In LPP.M.21, the anterior process of the pterygoid articulates with the palatines (Fig. 8C, D). Palatines: All information from the palatines comes from LPP.M.21 and PETMG R39. The palatines (Fig. 8C, D) are dorsoventrally thin, elongate bones and are similar in form to other teleosaurids, such as S. leedsi (NHMUK PV R 3806) (Andrews, 1913). In LPP.M.21, the anterior regions of both palatines are not preserved and both posterior regions are slightly deformed; however, PETMG R39 preserves the anterior palatines that are slightly rounded, have small anterior processes and articulate with the posterior processes of the maxillae (Fig. 4C, D). The palatines contact one another along the skull midline until posteriorly they are separated by the anterior process of the pterygoid. The anterior extensions of the palatine are nearly parallel to the maxillary tooth row, similar to M. buffetauti (Martin & Vincent, 2013). Basisphenoid: The anterior surface of the basisphenoid (LPP.M.21) is deformed (Fig. 8C, D). This structure has two elongated posterolaterally directed processes and comes into posterior contact with the quadrate. Other elements: The proötic and laterosphenoid are not visible in dorsal or ventral views, and as a result we could not properly describe these bones. Mandible: The mandible of NHMUK PV R 3168 is diagenetically deformed and attached to the cranium so that the dorsal surface is not visible. The mandibular symphysis measures ~58 cm, contributing ~42.3% of the entire length (Young et al., 2015a). Among other specimens, only a short segment of the right mandibular ramus in PETMG R39 is preserved and it clearly shows the contact among the dentary, angular and splenials to be posterior to the mandibular symphysis on the ventral side. The majority of the mandible is also preserved in LPP.M.21, as the posterior-most areas are missing. Our mandibular description refers to the holotype (NHMUK PV R 3168) unless otherwise specified. Dentary: The dentary (Figs 1, 2, 3A, C) is a long major element of the lateral surface of the lower jaw, as in the majority of crocodylomorphs. The anterior end of the dentary is spatulate and laterally enlarged as in Machimosaurus (Young et al., 2014a). There are ~29 (possibly one or two more alveoli) alveoli per dentary (at least 25 alveoli per dentary in LPP.M.21) of which ~22–24 are adjacent to the mandibular symphysis (Andrews, 1913; Young et al., 2015a). Many of the teeth are missing but those still in situ are well preserved and complete. The four anterior-most teeth are elevated dorsally when compared to the rest of the tooth row, as normally seen in teleosaurids such as S. leedsi (Andrews, 1913). The dentition is strongly heterodont compared to other teleosaurids; the teeth in the anterior region are large and have a higher crown base to length ratio, whereas the posterior crowns are characterised by a lower ratio. The interalveolar distance is generally smaller than half the alveolar length but always longer than a quarter of the alveolar length. Surangular and angular: The surangular (Fig. 2) is thin and posteriorly elongated in lateral view. The surangular, in conjunction with the angular and articular bones, is anteroposteriorly elongated and forms a distinctive ‘V’ shape. The anterior region of each surangular gradually terminates near the last alveolus of the dentary. The posterior margin of the surangular is rounded and it bounds a small mandibular fenestra. The angular (Fig. 2) is elongate and occupies a more extensive area than the surangular in lateral view. The angular is more robust than the surangular with a strong dorsal curvature (Fig. 2) which articulates with the retroarticular process of the articular. The dorsal and the ventral surfaces of the angular are not viewable in NHMUK PV R 3168. The prearticulars, which are supposed to be present (Andrews, 1913), are not seen. Articular: The anterior region of the articular of NHMUK PV R 3168 is hidden by the quadrate and surrounding bones. The retroarticular process is, however, extremely elongate and triangular-shaped in dorsal view and it bears a strongly pronounced anteroposterior keel, which separates the medial and lateral grooves. Both grooves are concave, in particular the lateral ones. The posterior end of the retroarticular process is slightly rounded, concave and curves dorsolaterally. The glenoid fossa is large and faces mediodorsally. Splenial: All of the information on the splenial comes from LPP.M.21. Only the anterior regions of these bones are preserved. The splenial (Fig. 9) is situated medially and is mediolaterally thinner in width than the dentaries. Both splenials begin at approximately the 15th mandibular alveoli in the dentaries. While the coronoids are not preserved, the sulci where they are hosted are. They participate with the mandibular symphysis, and the anterior extension begins at approximately the 21st alveoli of the dentaries and continue parallel, and eventually past, the tooth row. Dentition: As discussed above, the dentition of NHMUK PV R 3168 is both heterodont and serrated (with both true and false denticles; Young et al., 2015a). The holotype has 33 isolated teeth, as well as in situ teeth: ~29 in each dentary, 4 per premaxilla and ~29 (possibly more) per maxilla (verified by LPP.M.21). The teeth (Fig. 12A–D) are conical, robust, single-cusped and bicarinate, as in Machimosaurus (Martin & Vincent, 2013; Young et al., 2015a, b; Foffa et al., 2015;,Fanti et al., 2016). They have a blunt apex in comparison to other Steneosaurus species (Andrews, 1913). The enamel is thinner towards the base of the crown and becomes progressively thicker towards the apex (Fig. 12A–D), much like in Machimosaurus (Young & Steel, 2014). Figure 12. View largeDownload slide Isolated tooth crowns of Lemmysuchus obtusidens (Andrews, 1909) comb. nov. NHMUK PV R 3168 (holotype) in (A) mesial view and (B) lingual close-up view and PETMG R39 (C, D) close-up detailed view of erupting tooth. Isolated tooth crowns referred to Machimosaurini indet.: GPIT/RE/301 [in E (posterior), F (labial), G (anterior), H (lingual) and I (dorsal) views)]; CAMSM J64508 [in J (posterior), K (labial), L (anterior), M (lingual), N (dorsal) views, O (ventral) and P (apex close-up) views]; OUMNH J.14464 [in Q (posterior), R (labial), S (anterior) and T (lingual) views]. Scale bar: (A) 2 cm; (B–T) 1 cm. Figure 12. View largeDownload slide Isolated tooth crowns of Lemmysuchus obtusidens (Andrews, 1909) comb. nov. NHMUK PV R 3168 (holotype) in (A) mesial view and (B) lingual close-up view and PETMG R39 (C, D) close-up detailed view of erupting tooth. Isolated tooth crowns referred to Machimosaurini indet.: GPIT/RE/301 [in E (posterior), F (labial), G (anterior), H (lingual) and I (dorsal) views)]; CAMSM J64508 [in J (posterior), K (labial), L (anterior), M (lingual), N (dorsal) views, O (ventral) and P (apex close-up) views]; OUMNH J.14464 [in Q (posterior), R (labial), S (anterior) and T (lingual) views]. Scale bar: (A) 2 cm; (B–T) 1 cm. There are many protruding apicobasal enamel ridges on these teeth, giving them a ‘wrinkled’ texture. These apicobasal ridges are close to one another and run parallel from the base of the crown to approximately three quarters of the entire tooth. At the apex, the ridges are considerably shorter and are organized in the typical anastomosed pattern that has been described for other members of Machimosaurini (Young et al., 2014a, 2015a; Jouve et al., 2016). Teeth with blunter apices are situated in the middle and posterior regions of the tooth row and those with sharper apices are near the anterior. The teeth have true denticles and false denticles (Young et al., 2015a), although the latter cannot be seen clearly with the naked eye. True denticles are situated on the carina and false denticles are formed via interactions between the carina and enamel ridges (Young et al., 2015a). Postcranial skeleton: vertebral column and ribs: Most of the vertebral column of NHMUK PV R 3168 is preserved, so our description of vertebrae is based on this specimen unless otherwise specified. The first (atlas) and second (axis) vertebrae are fused together, forming the well-developed ‘complex’ (Fig. 13A) that is common in teleosaurids (Andrews, 1913; Martin & Vincent, 2013). The axis neural arch is not present and the odontoid and intercentrum are not distinct from one another due to the degree of atlas–axis fusion. The lateral surfaces of the axis are concave and have large protruding regions for the parapophyses. There are no diapophyses present behind the odontoid process on the axis, which is slightly larger than the atlas. Figure 13. View largeDownload slide Atlas–axis complex (A), cervical rib (B) and proximal thoracic rib (C) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Note there are no axial diapophyses and that the odontoid and intercentrum cannot clearly be distinguished. Atlas–axis complex is in lateral view, cervical rib is in ventral view, thoracic rib is in medial view. Refer to main text for the abbreviations list. Scale bar: 5 cm. Figure 13. View largeDownload slide Atlas–axis complex (A), cervical rib (B) and proximal thoracic rib (C) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Note there are no axial diapophyses and that the odontoid and intercentrum cannot clearly be distinguished. Atlas–axis complex is in lateral view, cervical rib is in ventral view, thoracic rib is in medial view. Refer to main text for the abbreviations list. Scale bar: 5 cm. The centra of the remaining six cervical vertebrae are amphicoelous, slightly longer in width than height, and have sub-circular anterior and posterior articular surfaces. There is a small notch in the middle of the dorsal margin of the centrum that is visible in anterior view. In lateral view, the centra are slightly spool-shaped with concave ventral margins similar to Machimosaurus (Martin & Vincent, 2013). The prezygapophyses are slightly anterior to the centrum edge, with the anterior articular facets facing ventrally and curving inwards. The postzygapophyses extend laterally just above the base of the neural spine. The posterior articular facets face dorsally and the transverse processes are laterally wide. The neural spine is rectangular and nearly as tall as the centrum. Only one complete cervical rib is preserved. It is T-shaped in dorsal view and has a distinct dorsomedial curvature (Fig. 13B). Both the tubercular and capitular processes of this rib are rounded, and its tubercular is larger than the capitular. The distal area behind the processes is short and does not extend posteriorly while the area in front is considerably more elongated. Fourteen robust thoracic vertebrae are preserved in NHMUK PV R 3168 although only one is complete. The centra (Fig. 14) are massive and appear spool-shaped in ventral view. The articular surfaces are amphicoelous and oval (slightly taller in length than wide). The neural spine is short and broad, and not as tall as the centrum. The transverse processes are long and wide and are positioned approximately at the centre of the neural arch. They are broadened anteroposteriorly, with rounded proximal ends (Fig. 14). There is a second projection on the transverse process, separated from the vertebral body by a small concavity. This projection is small, circular and laterally faced. Figure 14. View largeDownload slide Dorsal vertebra of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in (A) anterior, (B) left lateral, (C) posterior, (D) right lateral, (E) dorsal and (F) ventral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 14. View largeDownload slide Dorsal vertebra of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in (A) anterior, (B) left lateral, (C) posterior, (D) right lateral, (E) dorsal and (F) ventral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. The dorsal ribs (Fig. 13C) are dichocephalous and have robust heads and bodies. The capitulum of these ribs is proximodistally lengthened and dorsally rounded (Fig. 13C) and each neck is elongated, separating the capitulum from the tuberculum. The articular facets are flat and separated from the top of the tuberculum. The tuberculum is a small nodule located in the middle of the rib body. The articular facet and tuberculum are both laterally shifted so that they are nearly situated on the lateral edge of the body. The costal groove is deep and runs from the ventral tuberculum to near the end of the rib body, disrupting an otherwise sub-circular cross-section. The sternal end of the rib is anteroposteriorly flat, straight and thin in width. There are three sacral vertebrae (Fig. 15) (Andrews, 1913). The first two are true sacral vertebrae and the first caudal vertebra acts as a pseudo-sacral, as it looks and functions as a third sacral. This ‘third’ sacral has large, mediolaterally expanding transverse processes and an expanded lateral iliac attachment area, much like the two true sacrals. The neural spines are short and robust and the sacral ribs curve and contact one another (Andrews, 1913). The anterior margin of the posterior area of the second sacral vertebra (Fig. 15B, D) has a large, expanded projecting flange. The presence of a ‘third’ sacral vertebra is an autapomorphy shared by L. obtusidens and Machimosaurus spp. within Thalattosuchia (Young et al., 2014a). Figure 15. View largeDownload slide Sacral vertebrae of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in correct anatomical order. (A) Anterior, (B) dorsal, (C) posterior, (D) left lateral and (E) right lateral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 15. View largeDownload slide Sacral vertebrae of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, in correct anatomical order. (A) Anterior, (B) dorsal, (C) posterior, (D) left lateral and (E) right lateral views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Only 21 caudal vertebrae are preserved. However, it is likely that the total caudal vertebral count is similar to that of S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701), of around 36–38 (Andrews, 1913) or even higher (as in S. edwardsi PETMG R275). The caudal vertebrae become increasingly thinner and smaller from anterior to posterior. The typical posterior caudal vertebral centrum is thin, taller than wide and strongly hourglass-shaped. The neural spines are thin, tall and higher than the centrum. Shoulder girdle and fore-limb: No coracoids are preserved. The scapula (Fig. 16A, B) is of the typical thalattosuchian type similar to S. leedsi (NHMUK PV R 3806) (Andrews, 1909, 1913), being an elongate bone with a slender body. The proximal and distal regions extend mediolaterally, with the distal end being slightly larger. The scapular glenoid fossa (Fig. 16B) is half-moon shaped. The proximal region of the humerus (Fig. 16C, D) is poorly preserved, so the deltopectoral crest and proximal head cannot be properly described. However, the proximal edge of the humeral head appears to be slightly curved, as seen in other OCF teleosaurids such as S. leedsi (NHMUK PV R 3806). The shaft of the humerus is straight and the distal end is rounded. There is a concave, oval (Andrews, 1913) depression in the middle of the distal end of the humerus in lateral view (Fig. 16D). The ulna is similar in shape to other Callovian teleosaurids such as S. leedsi (Andrews, 1913). The proximal region is slightly deformed and fractured. The radius is a squat, straight bone and is unornamented. Figure 16. View largeDownload slide Scapula (A, B) and humerus (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Scapula in (A) lateral and (B) medial views; humerus in medial (C) and lateral (D) views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 16. View largeDownload slide Scapula (A, B) and humerus (C, D) of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Scapula in (A) lateral and (B) medial views; humerus in medial (C) and lateral (D) views. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Pelvic girdle and hind-limb: The ischium (Fig. 17A, B) is squat and robust and only preserved in NHMUK PV R 3168. The two proximal articulation processes are divided by a small yet deep oval notch. The smaller process has a circular proximal head while the larger process is posterolaterally curved. A large protruding ridge runs proximodistally in line with the second proximal process. Two small, sub-circular ‘bumps’, presumably for muscle attachment, are present ~10 cm from the posterior edge. These are not as prominent in other teleosaurids, such as S. leedsi. The ischial blade (Fig. 17A, B) is large, expanded and thick, with the posteroventral, sub-square border. The anterior flange is thin and broken. Figure 17. View largeDownload slide Pelvis of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Ischium in (A) medial and (B) lateral views, ilium in (C) medial and (D) lateral views and pubis in (E) medial and (F) lateral views. Note that the acetabulum (D) is weakly concave and that the supraacetabular crest (D) is greatly reduced, and the pubic boot (E, F) is missing. Also, the medial and lateral sides of the ilium are not completely prepared. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 17. View largeDownload slide Pelvis of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. Ischium in (A) medial and (B) lateral views, ilium in (C) medial and (D) lateral views and pubis in (E) medial and (F) lateral views. Note that the acetabulum (D) is weakly concave and that the supraacetabular crest (D) is greatly reduced, and the pubic boot (E, F) is missing. Also, the medial and lateral sides of the ilium are not completely prepared. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Both NHMUK PV R 3168 and PETMG R39 preserve an ilium. However, in the latter specimen, it is still articulated with the sacrum and femoral head, is missing the anterior side and is still partially covered in matrix. Conversely, the NHMUK PV R 3168 ilia (Fig. 17C, D) are well preserved, square-shaped and compact. The anterior-facing vertical outer rim has a slight sub-horizontal curvature (Fig. 17C, D). The medial attachment points of the sacral ribs are faint (Fig. 17C) so that it is difficult to tell the anterior iliac facet and posterior iliac facet apart from one another (Fig. 17C). The acetabular depression (or acetabular notch) is a smooth U-shaped arch in lateral view (Fig. 17C) and is halfway through the ventral articulating points with the pubis and ischium. The anterior articulation facet in front of the incision is larger than that of the posterior articulation facet and extends ventrally. The supraacetabular crest (Fig. 17D) is poorly developed, as is the shallow acetabulum (Fig. 17D). The preacetabular (=anterior process) (Fig. 17D) is shortened (with respect to other thalattosuchians) and well rounded and curves laterally. The majority of one pubis is preserved in NHMUK PV R 3168 (Fig. 17E, F) but the pubic boot is missing. Conversely, the ventral part of the pubis is possibly preserved in matrix in PETMG 39 (PETMG R31) (Fig. 24D). The body and distal region of the neck of the NHMUK PV R 3168 pubis are deformed into curving medially. The anterodistal pubic plate is expanded and rounded along the ventral rim (Fig. 17E, F). All the information on the hind-limb comes from NHMK PV R 3168. The femur (Fig. 18) is slender and long, with a weak sigmoidal curvature throughout the shaft, which is typical of many teleosaurids (Andrews, 1909, 1913). The proximal head (Fig. 18) extends medially into the acetabulum while the anterior region of the femoral head is ventrally curved. There is a large concavity on the posterolateral surface of the head. The posterior margin of the head is rugose, and this rugosity continues down through the neck of the femur. In dorsal view, the head is circular to sub-circular, with an expanded posteromedial tuber. The ‘fourth trochanter’ (i.e. no true process, just the rugose area mentioned before) is small compared to other Callovian teleosaurids and is situated on the medial neck of the femur (Fig. 18). The two posterodistal condyles – medial (greater) and lateral (lesser) – are clearly visible with the medial condyle being slightly larger (Fig. 18). Figure 18. View largeDownload slide Femur of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) medial and (B) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. Figure 18. View largeDownload slide Femur of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) medial and (B) lateral views. Refer to the main text for the abbreviations list. Scale bar: 10 cm. The tibia (Fig. 19) is a robust bone with the proximal end being larger than the distal end. In dorsal view, the proximal end is heart-shaped. The tibial tuberosity (Fig. 19A, C) is large and projects posterodistally. In lateral view, it is directed ventrally at a sharply obtuse angle (Fig. 19C). The medial side of the tibial neck is slightly concave, while the lateral side is flat (Andrews, 1913). The distal end is rounded, although it is obstructed by the distal area of the fibula. The fibula (Fig. 19) is an elongate, slender and straight bone, with only the distal half preserved. It is slightly smaller in width (Fig. 19A) than the tibia. Figure 19. View largeDownload slide Tibia of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) posterior, (B) anterior and (C) lateral views. Note the anterior deflection of the proximal region. Refer to the main text for the abbreviations list. Note the distal area of the fibula attached to the tibia. Scale bar: 5 cm. Figure 19. View largeDownload slide Tibia of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype in (A) posterior, (B) anterior and (C) lateral views. Note the anterior deflection of the proximal region. Refer to the main text for the abbreviations list. Note the distal area of the fibula attached to the tibia. Scale bar: 5 cm. There are three ankles bones (Fig. 20): the calcaneum (Fig. 20A–D), astragalus (Fig. 20E–G) and cuboid (Fig. 20H, I). They are all robust and large, with well-developed articulation surfaces. Excluding the clear difference in the large size, the three ankle bones resemble those of other teleosaurids (Andrews, 1913). All metacarpal and metatarsal fragments are slender, as are four complete phalanges (all relatively the same length). Figure 20. View largeDownload slide Ankle of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, including the calcaneum (A–D), astragalus (E–G) and cuboid (H, I). Calcaneum in (A) right dorsolateral, (B) anterior, (C) left dorsolateral and (D) posterior views; astragalus in (E) dorsal, (F) ventral and (G) posterior views; cuboid in (H) dorsal and (I) ventral views. Scale bar: 5 cm. Figure 20. View largeDownload slide Ankle of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype, including the calcaneum (A–D), astragalus (E–G) and cuboid (H, I). Calcaneum in (A) right dorsolateral, (B) anterior, (C) left dorsolateral and (D) posterior views; astragalus in (E) dorsal, (F) ventral and (G) posterior views; cuboid in (H) dorsal and (I) ventral views. Scale bar: 5 cm. Osteoderms: Fifty-six dorsal, mostly unarticulated osteoderms are present in NHMUK PV R 3168. Smaller osteoderms are box-shaped (Fig. 21C), whereas larger ones are elongate and oval (Fig. 21A, B). A prominent anteroposteriorly directed keel is present (Fig. 21A), being more pronounced in larger osteoderms. The pits on the dorsal surface of larger osteoderms (Fig. 21A) are oval, elongate, deep and spaced apart. They radiate outwards from the centre of the keel in a ‘starburst’ pattern. The pits generally become larger further from the centre of the osteoderms. Some pits merge with one another along the outermost lateral margins of the osteoderms. The ventral surfaces of all osteoderms are smooth and unaltered. Figure 21. View largeDownload slide A–C, dorsal osteoderms of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. All are in dorsal view. Note the characteristic ornamentation pattern, with elongated pits radiating from the centre of the keel. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 21. View largeDownload slide A–C, dorsal osteoderms of Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype. All are in dorsal view. Note the characteristic ornamentation pattern, with elongated pits radiating from the centre of the keel. Refer to the main text for the abbreviations list. Scale bar: 5 cm. DISCUSSION Specimens previously referred to ‘Steneosaurus’ obtusidens Andrews (1913) referred two large, but very incomplete, specimens to ‘S.’ obtusidens: NHMUK PV R 3169 and NHMUK PV R 3898. The former comprises one scapula, right coracoid, left ulna, one radius, right ilium, femora, pubes, tibiae, a fibula, five carpal/tarsal bones, one hyoid, three tracheal rings, five osteoderms and numerous teeth and fragmentary elements. Nine characteristics differentiate NHMUK PV R 3169 from L. obtusidens: The tibial tuberosity is not angled as in L. obtusidens (NHMUK PV R 3168). Instead it is directed almost 180° horizontally, similar to S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701 and PETMG R178) (Fig. 23A–C). While the femur of NHMUK PV R 3169 is long and gracile, somewhat similar to L. obtusidens (NHMUK PV R 3168), it is slightly smaller in length and width (possibly from a smaller individual; Fig. 24A–C). In dorsal view, the femoral head is larger and more triangular than that of L. obtusidens (NHMUK PV R 3168), due to an enlarged posteromedial tuber (Fig. 24A–C). This is somewhat similar to the condition seen in the metriorhynchid Tyrannoneustes lythrodectikos (GLAHM V1145; Young et al., 2013). The greater femoral condyle of the NHMUK PV R 3169 is much larger than the lesser condyle (Fig. 25A–C), as opposed to L. obtusidens (NHMUK PV R 3168) in which the greater condyle is only slightly larger than the lesser condyle. The ilium has a slender, elongate anterior process, as opposed to the short, stubby anterior process of L. obtusidens (NHMUK PV R 3168) (Fig. 24D–F). The ilium has only two sacral rib articulation surfaces, and these are large and well developed. In L. obtusidens (NHMUK PV R 3168), the ilia have three poorly developed sacral rib articulation surfaces (Fig. 24D–F). The acetabulum is deep, and the anterior-most ridge of the ilium is vertical, whereas in L. obtusidens (NHMUK PV R 3168), the acetabulum is poorly concave (see Fig. 17D). The anterodistal rim if the pubic plate is straighter and sub-square, whereas in L. obtusidens (NHMUK PV R 3168), the pubic plate rim is rounded and circular. The osteoderms of NHMUK PV R 3169 are an enigma. Out of the five osteoderms preserved, two have a dorsal pitting pattern similar to that of L. obtusidens (NHMUK PV R 3168). These pits are elongated and radiate out from the centre of the keel. The other three are similar with those seen in S. edwardsi (NHMUK PV R 3701 and PETMG R178). The pits are not elongated and occur in a random arrangement (Fig. 23D–F). Thus, we can conclude that NHMUK PV R 3169 is not L. obtusidens and is morphologically more similar to S. edwardsi (NHMUK PV R 3701) or S. leedsi (NHMUK PV R 3806). Figure 22. View largeDownload slide Comparative photographs of (A) Steneosaurus heberti (MNHN.F 1890-13), (B) Steneosaurus edwardsi (PETMG 178) and (C) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., showing the dorsoposterior curvature of the retroarticular process. Comparative photographs of (D) S. heberti (MNHN.F 1890-13) holotype, (E) S. edwardsi (NHMUK PV R 2865), (F) L. obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype and (G) Machimosaurus buffetauti (SMNS 91415), showing the absence of antorbital fenestrae. Figure 22. View largeDownload slide Comparative photographs of (A) Steneosaurus heberti (MNHN.F 1890-13), (B) Steneosaurus edwardsi (PETMG 178) and (C) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., showing the dorsoposterior curvature of the retroarticular process. Comparative photographs of (D) S. heberti (MNHN.F 1890-13) holotype, (E) S. edwardsi (NHMUK PV R 2865), (F) L. obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168, holotype and (G) Machimosaurus buffetauti (SMNS 91415), showing the absence of antorbital fenestrae. Figure 23. View largeDownload slide Comparative line drawings of the tibiae in posterior (left) and lateral (right) views of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) NHMUK PV R 3169 and (C) Steneosaurus edwardsi (PETMG R178); comparative line drawings of the dorsal osteoderms in dorsal view of (D) L. obtusidens holotype (NHMUK PV R 3168), (E) NHMUK PV R 3169 and (F) S. edwardsi (PETMG R178). Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 23. View largeDownload slide Comparative line drawings of the tibiae in posterior (left) and lateral (right) views of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) NHMUK PV R 3169 and (C) Steneosaurus edwardsi (PETMG R178); comparative line drawings of the dorsal osteoderms in dorsal view of (D) L. obtusidens holotype (NHMUK PV R 3168), (E) NHMUK PV R 3169 and (F) S. edwardsi (PETMG R178). Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 24. View largeDownload slide Comparative line drawings of the femora in medial view of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and Steneosaurus edwardsi [(B) NHMUK PV R 3898; (C) PETMG R178]; comparative line drawings of the ilia in medial view of (D) L. obtusidens holotype (NHMUK PV R 3168) and S. edwardsi [(E) NHMUK PV R 3898; (F) PETMG R178]. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 24. View largeDownload slide Comparative line drawings of the femora in medial view of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and Steneosaurus edwardsi [(B) NHMUK PV R 3898; (C) PETMG R178]; comparative line drawings of the ilia in medial view of (D) L. obtusidens holotype (NHMUK PV R 3168) and S. edwardsi [(E) NHMUK PV R 3898; (F) PETMG R178]. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 25. View largeDownload slide Four articulated vertebrae of PETMG R39, referred to Lemmysuchus obtusidens (Andrews (1909)comb. nov., in (A) left and (B) right lateral views. Five articulated vertebrae (two dorsal, three sacral), incomplete ilium, femur and pubis (ischium?) of PETMG R31, which is thought to correspond to PETMG R39, in (C) left and (D) right lateral views. Scale bar: 10 cm. Figure 25. View largeDownload slide Four articulated vertebrae of PETMG R39, referred to Lemmysuchus obtusidens (Andrews (1909)comb. nov., in (A) left and (B) right lateral views. Five articulated vertebrae (two dorsal, three sacral), incomplete ilium, femur and pubis (ischium?) of PETMG R31, which is thought to correspond to PETMG R39, in (C) left and (D) right lateral views. Scale bar: 10 cm. Andrews’ (1913) second L. obtusidens referred specimen, NHMUK PV R 3898, consists of an ilium, ischium and femur. All three bones are very large and robust. However, the features in these bones differ vastly from those seen in the L. obtusidens holotype (NHMUK PV R 3168). The ilium of NHMUK PV R 3898 has: (1) an elongate and slender anterior process, (2) a pronounced supraacetabular crest and (3) a strongly concave acetabulum (Fig. 23E; see Johnson et al., 2015). This differs from the L. obtusidens (NHMUK PV R 3168) ilium, which has a short anterior process, a greatly reduced supraacetabular crest, and a shallow acetabulum (Fig. 25D). The ischium of NHMUK PV R 3898 has a sub-triangular posteroventral margin of the ischial blade (Johnson et al., 2015), as opposed to the broad, sub-square posteroventral margin in L. obtusidens (NHMUK PV R 3168). As Johnson et al. (2015) showed, these morphologies exclude NHMUK PV R 3898 from L. obtusidens and demonstrate that it in fact pertains to S. edwardsi. Two additional specimens from the Peterborough Member of the OCF are here referred to as L. obtusidens: PETMG R39 and PETMG R178. The first specimen, PETMG R39, is a partial skull (Figs 4–6) and partial mandible (only preserving the anterior end of the mandibular symphyseal region) (Fig. 7), four articulated dorsal vertebrae (Fig. 25A, B), an osteoderm fragment, sacrum and some isolated bone fragments (Fig. 25C, D). Parts of this specimen have been referred to PETMG R31, another specimen that it has been constantly mixed and stored with. However, a specimen registration entry mentions that PETMG R31 ‘fits with R39’. Nevertheless, the preservation and texture of the bones and the matrix are identical in both specimens, which importantly also share autapomorphies of L. obtusidens. Based on these lines of evidence, we consider PETMG R39 and PETMG R31 belonging to the same individual and both pertain to L. obtusidens. The skull of PETMG R39 (Figs 4–6) includes the nasals, posterior maxillae, jugal and anterior orbit. Several alveoli are visible on both lateral sides of the maxillae. The alveoli are separated by variable interalveolar spaces (always fewer than one alveolus length but longer than half) and most teeth are still in situ. Two erupting teeth show the typical Machimosaurini crown ornamentation. This specimen is referable to L. obtusidens due to the following features: (1) closure of the antorbital fenestrae; (2) there is a slight beginning of a ‘dome’ near the posterior section of the nasals; (3) the teeth have blunt apices, denticles and the characteristic Machimosaurini enamel ornamentation pattern and (4) an extreme anteroposterior elongation of the jugal. PETMG R31 consists of five articulated vertebrae (two complete dorsal, two complete and one incomplete sacral), incomplete ilium, femur and pubis (or ischium?) (Fig. 25C, D). The sacral vertebrae largely resemble the L. obtusidens holotype (NHMUK PV R 3168). Although the posterior-most vertebra is incomplete, one of its ribs is partially preserved, and there is little doubt that it is a sacral rib due to its shape and dimension, with an expanded flange. The fragmentary status of the specimen and abundant matrix around the bones does not allow direct comparison of other elements. Thus, PETMG R31 pertains to Lemmysuchus based on the presence of three sacral vertebrae, and the fact that it likely belongs with PETMG R39. The second specimen, PETMG R178, represents a nearly complete skeleton. However, it lacks characteristics seen in the L. obtusidens holotype (NHMUK PV R 3168). The dorsal rim of larger cervical ribs does not curve dorsomedially. The shape and position of the tuberculum in the dorsal ribs is similar to S. edwardsi (NHMUK PV R 3701), whereas L. obtusidens (NHMUK PV R 3168) displays a more medial position of the tuberculum. The ilium has a deep well-developed acetabulum and an elongate, slender anterior process, which differs from the shallow acetabulum and the proportionally shorter anterior process seen in L. obtusidens (NHMUK PV R 3168) (Fig. 24D, E). The ischium is gracile and the posteroventral margin of the ischial blade is sub-triangular in shape, which differs from the robust ischium with a square-shaped posteroventral ischial blade of L. obtusidens (NHMUK PV R 3168). The proximal tibia is not strongly deflected anteriorly as in L. obtusidens (NHMUK PV R 3168) and Machimosaurus (Hua, 1999). The skull of PETMG R178 lacks the strongly convex (‘domed’) nasals seen in L. obtusidens (NHMUK PV R 3168 and PETMG R39), although this may be due to preservation. The dorsal osteoderm ornamentation differs from that seen in L. obtusidens (NHMUK PV R 3168). The pitting pattern is random, as seen in S. edwardsi (NHMUK PV R 3701). Thus, PETMG R178 is not referable to L. obtusidens and is more morphologically similar to S. edwardsi. Hua et al. (1994) described a fragmentary skeleton from the upper Callovian of Villers-sur-Mer, Calvados, France, and referred it to ‘S.’ obtusidens. It was the first non-English specimen referred to L. obtusidens. However, comparing the figures from Hua et al. (1994) with the L. obtusidens holotype (NHMUK PV R 3168) shows that the ischium, ilium and dorsal osteoderms do not match. In the French specimen, the ilium anterior process is much more elongated and slender than that seen in the Lemmysuchus holotype (NHMUK PV R 3168). The supraacetabular crest is pronounced, the acetabular depression is strongly concave and the posterior margin of the ischial blade is sub-triangular. The osteoderm (Hua et al., 1994; fig. 1a) lacks the ‘starburst’ pattern of pits. As with PETMG R178, this specimen more closely resembles S. edwardsi than L. obtusidens. Foffa et al. (2015) described an incomplete mandible (DORCM G3939), which preserves the symphyseal region up to approximately the 19th alveoli (alveoli one and two are missing). Due to the incompleteness of its preservation, the lower jaw could not be confidently assigned to a taxon but was referred to ‘S.’ cf. obtusidens. It is difficult to determine for certainty whether DORCM G3939 is L. obtusidens, as so little of it is preserved; however, the high symphyseal tooth count, the Meckelian groove not being exposed on the dorsal surface of the splenials, the blunt tooth apices, the anastomosed apical enamel ornamentation, presence of denticles and deep reception pits place it within Machimosaurini. If this specimen does belong to L. obtusidens, it expands the stratigraphic range of this taxon into the early Oxfordian. Comparison with other OCF teleosaurids Lemmysuchus obtusidens (NHMUK PV R 3168, PETMG R39) has numerous teleosaurid apomorphies including: a laterally expanded premaxilla and anterior dentary, and a relatively small frontal (Andrews, 1913). However, L. obtusidens has a number of autapomorphies, particularly in the postcranial skeleton (Tables 1 and 2). Table 1. Comparison of cranial characters between Lemmysuchus obtusidens and selected specimens of other teleosaurids Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  SMNS 91415, Martin & Vincent (2013), Young et al. (2014a)   MNHN.F 1890-13  MNHN.F RJN 118, NHMUK PV R 3701, PETMG R178  NHMUK PV R 3806  PETMG R39 (+ PETMG R31)  LPP.M.21  Antorbital fenestrae  Absent  Absent  Absent  Absent  Present  Nasal dorsal surface  Strongly convex  Slightly convex  Slightly convex  Slightly convex  Slightly convex  Frontal ornamentation  Yes: large circular pits  Yes: well-developed pits/ridges  Yes: ridges  Yes: circular pits  Yes: ridges  Supratemporal fenestra shape  Rectangular (anteroposteriorly elongated)  Rectangular (anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Occipital tuberosities  Yes: pronounced  Yes: pronounced  Yes: pronounced  No  No  Nuchal crest  Pronounced  Reduced  Reduced  Small  Small  Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  SMNS 91415, Martin & Vincent (2013), Young et al. (2014a)   MNHN.F 1890-13  MNHN.F RJN 118, NHMUK PV R 3701, PETMG R178  NHMUK PV R 3806  PETMG R39 (+ PETMG R31)  LPP.M.21  Antorbital fenestrae  Absent  Absent  Absent  Absent  Present  Nasal dorsal surface  Strongly convex  Slightly convex  Slightly convex  Slightly convex  Slightly convex  Frontal ornamentation  Yes: large circular pits  Yes: well-developed pits/ridges  Yes: ridges  Yes: circular pits  Yes: ridges  Supratemporal fenestra shape  Rectangular (anteroposteriorly elongated)  Rectangular (anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Parallelogram (slightly anteroposteriorly elongated)  Occipital tuberosities  Yes: pronounced  Yes: pronounced  Yes: pronounced  No  No  Nuchal crest  Pronounced  Reduced  Reduced  Small  Small  View Large Table 2. Comparison of postcranial characters between Lemmysuchus obtusidens and selected specimens of other teleosaurids Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti and M. mosae, Young et al. (2014a)  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  MNHN.F 1890-13  NHMUK PV R 3701  NHMUK PV R 3806  PETMG R39 (PETMG R31)  PETMG R178  Ilium  Short anterior process; shallow acetabulum; faint supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long slender process, deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Ischium  Broad ischial blade; sub-square posteroventral margin  Somewhat broad ischial blade; sub- square posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Number of sacral vertebrae  3 (2 true, 1 pseudo)  3  2  2  2  Femur  Sub-triangular head (dorsal view); medial condyle slightly larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; slightly sigmoidal  Triangular to ‘kidney-bean’ shaped head (dorsal view); medial condyle much larger than lateral condyle; slightly sigmoidal  Triangular head (dorsal view); medial condyle much larger than lateral condyle; sigmoidal  Tibial tuberosity  Sharply angled  Sharply angled  Horizontal  Horizontal  Horizontal  Characteristics  Lemmysuchus obtusidens  Machimosaurus buffetauti and M. mosae, Young et al. (2014a)  Steneosaurus heberti  Steneosaurus edwardsi  Steneosaurus leedsi  NHMUK PV R 3168  MNHN.F 1890-13  NHMUK PV R 3701  NHMUK PV R 3806  PETMG R39 (PETMG R31)  PETMG R178  Ilium  Short anterior process; shallow acetabulum; faint supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Long slender process, deep acetabulum; well-developed supraacetabular crest  Long anterior process; deep acetabulum; well-developed supraacetabular crest  Ischium  Broad ischial blade; sub-square posteroventral margin  Somewhat broad ischial blade; sub- square posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Slender ischial blade; sub-triangular posteroventral margin  Number of sacral vertebrae  3 (2 true, 1 pseudo)  3  2  2  2  Femur  Sub-triangular head (dorsal view); medial condyle slightly larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; sigmoidal  Triangular head (dorsal view); medial condyle larger than lateral condyle; slightly sigmoidal  Triangular to ‘kidney-bean’ shaped head (dorsal view); medial condyle much larger than lateral condyle; slightly sigmoidal  Triangular head (dorsal view); medial condyle much larger than lateral condyle; sigmoidal  Tibial tuberosity  Sharply angled  Sharply angled  Horizontal  Horizontal  Horizontal  View Large Andrews (1913) recognized some of these autapomorphies: (1) three sacral vertebrae; (2) blunt, heavily ornamented teeth and (3) a unique osteoderm pattern (however, points 1 and 2 are now recognized as characters shared with Machimosaurus, see Diagnosis and Discussion; Young et al., 2014a, 2015a; Jouve et al., 2016). While Andrews (1913) gave a generally good description of the skull, we disagree with some of his observations regarding the antorbital fenestrae, lacrimal and sacral vertebrae. These autapomorphies readily distinguish it from two common OCF teleosaurids, S. leedsi and S. edwardsi. The skull of L. obtusidens (NHMUK PV R 3168) is marked similar to Machimosaurus (Table 1; see Krebs, 1967; Buffetaut, 1982a; Martin & Vincent, 2013; Young et al., 2014a; Fanti et al., 2016) in being large and robust. This is opposite of S. leedsi (NHMUK PV R 3806), which has a slender skull. Steneosaurus edwardsi (NHMUK PV R 3701, PETMG R178) has a large skull similar to L. obtusidens (NHMUK PV R 3168), with some specimens of S. edwardsi being even larger than the L. obtusidens holotype. Both S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) lack the dorsoventrally deep ‘domed’ nasals-frontal as seen in L. obtusidens (NHMUK PV R 3168). The supratemporal fossae in L. obtusidens (NHMUK PV R 3168) extend further anteriorly along the frontal than those of S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701). The articular, surangular and angular bones of L. obtusidens (NHMUK PV R 3168) are more elongated anteroposteriorly than lateromedially, giving them a combined ‘V’ shape. This differs in comparison to S. edwardsi (NHMUK PV R3 701), in which the three bones are not elongated anteroposteriorly. Steneosaurus leedsi (NHMUK PV R 3806) displays the same shape and anteroposterior elongation as L. obtusidens (NHMUK PV R 3168), although it is smaller and slenderer. The Meckelian groove is not excavated on the dorsal surface of the symphyseal splenial in L. obtusidens (NHMUK PV R 3168) (Fig. 26E), which it shares with M. mosae neotype (Fig. 26F), S. edwardsi (NHMUK PV R 3701) (Fig. 26C) and S. hulkei (NHMUK PV R 2074) (Fig. 26D). Other thalattosuchians, such as S. leedsi (NHM UK PV R 3806, NHMUK PV R 3320) (Fig. 26A, B), have the Meckelian groove deeply excavated on the dorsal surface of the splenial. As mentioned before, L. obtusidens (PETMG R39) lacks any evidence of antorbital fenestrae (contraAndrews, 1913), the condition shared with S. edwardsi (PETMG R178), Machimosaurus, and S. heberti (MNHN.F 1890-13). Small, slit-like fenestrae are present in S. leedsi (NHMUKPV R 3806). The teeth of S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) are more elongate and slender than those of L. obtusidens (NHMUK PV R 3168) and have pointed apices continuously throughout the maxillae and dentaries, as well as lacking an anastomosed apical pattern. Figure 26. View largeDownload slide Comparative photographs of Steneosaurus leedsi (A) NHMUK PV R 3806; (B) NHMUK PV R 3220, (C) Steneosaurus edwardsi (NHMUK PV R 3701), (D) Steneosaurus hulkei (NHMUK PV R 2074), (E) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168) and (F) Machimosaurus mosae (taken from Young et al. 2014a, fig. 19), showing the shallow vs. deep excavation of the Meckelian groove. Note that (A–B) are much more deeply excavated and exposed than (C–F). Scale bar: 10 cm. Figure 26. View largeDownload slide Comparative photographs of Steneosaurus leedsi (A) NHMUK PV R 3806; (B) NHMUK PV R 3220, (C) Steneosaurus edwardsi (NHMUK PV R 3701), (D) Steneosaurus hulkei (NHMUK PV R 2074), (E) Lemmysuchus obtusidens (Andrews, 1909) comb. nov., NHMUK PV R 3168) and (F) Machimosaurus mosae (taken from Young et al. 2014a, fig. 19), showing the shallow vs. deep excavation of the Meckelian groove. Note that (A–B) are much more deeply excavated and exposed than (C–F). Scale bar: 10 cm. Aside from the osteoderms and sacral vertebrae, Andrews (1913) largely neglected to describe the postcranial skeleton. Herein, we have shown the postcrania of L. obtusidens to be distinctive (Table 2). One striking difference found in L. obtusidens (NHMUK PV R 3168) is the absence of axial diapophyses. These processes are present in S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701). Steneosaurus bollensis, however, also lacks the axial diapophyses (see Westphal, 1962). The two primordial sacrals in L. obtusidens (NHMUK PV R 3168) are similar in form to S. leedsi (NMHUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The anterior projecting flange on the second sacral vertebra is seen in S. leedsi (NHMUK PV R 3806), although it is much smaller and does not extend anteriorly (Fig. 27B) as in L. obtusidens (NHMUK PV R 3168) (Fig. 27A). The cervical rib of L. obtusidens (NHMUK PV R 3168) (Fig. 28A) has a distinct medial curvature in the dorsal rim. The cervical ribs of S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) both have straight, T-shaped dorsal rims (Fig. 28B–D). The area posterior to the tubercular and capitular processes of the cervical rib is also shorter than the anterior area in L. obtusidens (NHMUK PV R 3168), whereas in S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806), they are more elongated (Fig. 28) and are approximately the same length. Figure 27. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and (B) Steneosaurus leedsi (NHMUK PV R 3806) articulated sacral vertebrae. Note that the anterior projecting flange on the second sacral vertebra in S. leedsi (B) does not extend anteriorly and is small. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 27. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and (B) Steneosaurus leedsi (NHMUK PV R 3806) articulated sacral vertebrae. Note that the anterior projecting flange on the second sacral vertebra in S. leedsi (B) does not extend anteriorly and is small. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 28. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701); (D) PETMG R178, cervical ribs. Scale bar: 5 cm. Figure 28. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701); (D) PETMG R178, cervical ribs. Scale bar: 5 cm. There are three features seen in the dorsal ribs of L. obtusidens (NHMUK PV R 3168) in conjunction with S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) (Fig. 29): Both the tuberculum and articular facet are shifted onto the medial edge of the rib in L. obtusidens (NHMUK PV R 3168), as described before. The position of these articular surfaces in L. obtusidens (NHMUK PV R 3168) could be due to either the massive size of the ribs causing the tuberculum to shift medially or are solely due to deformation. In S. leedsi (NHMUK PV R 3806), the tuberculum and articular surface are situated directly in the middle of the rib and are small. In S. edwardsi (NHMUK PV R 3701), the tuberculum is also situated medially, but closer to the lateromedial edge of the rib. The proximal head of the ribs in L. obtusidens (NHMUK PV R 3168) and S. edwardsi (NHMUK PV R 3701) are elongated proximodistally and are rectangular in dorsal view. In medial view, the dorsal edges of the two specimens appear curved. In S. leedsi (NHMUK PV R 3806), the rib head is as long as it is wide. It is flat and circular in dorsal view and straight in medial view. The sternal rib end is flat in L. obtusidens (NHMUK PV R 3168) and S. edwardsi (NHMUK PV R 3701), while in S. leedsi (NHMUK PV R 3806), it is more rounded, similar to metriorhynchids (Wilkinson et al., 2008). Figure 29. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701) dorsal ribs. Refer to the main text for the abbreviations list. Scale bar: 5 cm. Figure 29. View largeDownload slide Comparative line drawings of (A) Lemmysuchus obtusidens holotype (NHMUK PV R 3168), (B) Steneosaurus leedsi (NHMUK PV R 3806) and (C) Steneosaurus edwardsi (NHMUK PV R 3701) dorsal ribs. Refer to the main text for the abbreviations list. Scale bar: 5 cm. There is also a combination of six pelvic and hind-limb characteristics that readily distinguishes L. obtusidens from S. leedsi and S. edwardsi (Table 2). These characteristics were not noted by Andrews (1909, 1913) and are here listed for the first time: The iliac anterior process in L. obtusidens is short and squat, as opposed to the elongate, slightly thinner processes S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The poorly developed sacral rib attachment areas and acetabulum of L. obtusidens (NHMUK PV R 3168) differs from S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) in that in L. obtusidens, they are both poorly developed (possibly due to preservation). The posteroventral margin of the ischial plate in L. obtusidens (NHMUK PV R 3168) is sub-square in shape, and is not as blunt or widened as seen in metriorhynchids (e.g. Wilkinson et al., 2008), but is broader than the sub-triangular posterior margin seen in S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701) (Andrews, 1913). The anterodistal rim of the pubic plate is curved in a circular fashion, much like that seen in S. leedsi (NHMUK PV R 3806). This differs from S. edwardsi (NHMUK PV R 3701), in that the anterodistal pubic plate rim is straight and square-like with a sharp anterodistal edge. The sigmoidal curvature of the L. obtusidens (NHMUK PV R 3168) femur is most similar to S. leedsi (NHMUK PV R 3806) in being weak. In S. edwardsi (NHMUK PV R 3701, NHMUK PV R 3898), the curvature throughout the femur is strongly pronounced (Johnson et al., 2015). In L. obtusidens (NHMUK PV R 3168), there is a distinctive sharply angled tibial tuberosity that is shared with Machimosaurus (Hua, 1999). In S. leedsi (NHMUK PV R 3806) and S. edwardsi (NHMUK PV R 3701), the tibial tuberosity is horizontal and shows no angle. The dorsal surface ‘starburst’ osteoderm ornamentation of L. obtusidens (NHMUK PV R 3168) differs from the ornamentations seen in S. edwardsi (NHMUK PV R 3701) and S. leedsi (NHMUK PV R 3806) (Fig. 23D– F). In S. edwardsi (NHMUK PV R 3701 and PETMG R178), the majority of pits are circular in shape and are not as deep as L. obtusidens (NHMUK PV R 3168). The pits are closely packed together and are distributed in a random pattern, as opposed to the ‘starburst’ pattern in L. obtusidens (NHMUK PV R 3168). In S. leedsi (NHMUK PV R 3806), the majority of the pits are circular, with some being oval in shape. The pits radiate outwards in a sub-circular fashion and are closely packed together, which differs from L. obtusidens (NMHUK PV R 3168). Andrews (1909, 1913) described the postcranial material (not including the dorsal osteoderms) of L. obtusidens as so similar ‘to that of S. durobrivensis [that] special description is unnecessary.’ However, here we have shown that not only is the postcrania of L. obtusidens distinct, but there were at least two different postcranial morphotypes among OCF teleosaurids. A robust, stockier morphotype was represented by Lemmysuchus (i.e. stout ilia and tibiae, broad ischial blade, large centra and three sacral vertebrae), and a slenderer morphotype was represented by S. leedsi and S. edwardsi (with a gracile ilia, tibiae, and ischial blade, smaller centra, and two sacral vertebrae). These differences may reflect habitat partitioning among sympatric teleosaurids, with L. obtusidens suggested as being more terrestrial, and/or living in higher energy environments. Body length The basicranial length of the L. obtusidens holotype (NHMUK PV R 3168) is ~1.16 m. The vertebral column is not completely preserved. There is one dorsal and one cervical vertebra missing, and the majority of the caudal region is missing. Using the Young et al. (2016b), basicranial length vs. body length equations yields a total body length estimate of between 556.995 and 558.173 cm. Using the femoral length vs. body length equations yields a total body length estimate of between 575.742 ad 582.3 cm. Young et al. (2016b) found femoral-based estimates to be the more reliable than cranial-based estimates, thus a body length of ~5.8 m seems likely for L. obtusidens. Lemmysuchus obtusidens has long been considered to be the largest teleosaurid in the OCF (see Andrews, 1913; Young et al., 2015a). However, as noted above, the largest specimen previously referred to L. obtusidens (NHMUK PV R 3898) has recently been re-assigned to S. edwardsi (Johnson et al., 2015). Young et al. (2016b) found NHMUK PV R 3898 to be between 659.51 and 666.66 cm using the femoral-based equations. Thus, S. edwardsi is the largest known crocodylomorph of the Middle Jurassic. CONCLUSIONS Here, we re-describe the holotype of ‘S.’ obtusidens (NHMUK PV R 3168), demonstrate that it is indeed a valid species and establish a new monotypic genus, Lemmysuchus, for the taxon. It has five autapomorphies and shares nine synapomorphies with Machimosaurus, thus supporting Machimosaurini (Lemmysuchus + Machimosaurus) (Young et al., 2015b; Jouve et al., 2016). This suite of characteristics falsifies the hypothesis that L. obtusidens is a subjective junior synonym of S. edwardsi. Additionally, L. obtusidens lacks eight of the Machimosaurus autapomorphies (including three premaxillary alveoli, a considerably smaller medial hemicondyle and variable presence of carinae) listed by Young et al. (2014a), thus falsifying the hypothesis that L. obtusidens is a subjective junior synonym of M. hugii. Moreover, most specimens previously referred to L. obtusidens are herein considered to pertain to other taxa. We conclude that only three specimens can reliably be referred to L. obtusidens: a nearly complete skull (LPP.M.21) from the E. coronatum ammonite Zone of Migné-les-Lourdines, France; an incomplete skull with associated postcranial elements from the OCF of England (PETMG R39) and a partial rostrum thought to be from the OCF (NOTNH FS3361). As such, L. obtusidens was a somewhat rare taxon in the Callovian of Europe, currently known only from England and France. This contrasts with its sister taxon Machimosaurus, which was widespread and common in European and Tethys shallow marine and brackish ecosystems during the Late Jurassic. [Version of Record, published online 07 August 2017; http://zoobank.org/ urn:lsid:zoobank.org:pub:ADB5B0F9-7D9C-48CF-BBB6-1451BA209584] ACKNOWLEDGEMENTS We thank G. Wass (PETMG), P. Tomlinson (DORCM) and M. Riley (CAMSM) for access to collections and their much appreciated assistance and advice; G. Garcia for photographs of LPP.M.21; P. Hurst and K. Webb (NHMUK Image Resources) for photography of the Lemmysuchus obtusidens holotype (NHMUK PV R 3168) and R. Holmes and J. Liston for advice and guidance. MTY received support for his visits to France (FR-TAF-4021) and Germany (DE-TAF-5132) from the SYNTHESYS Project, which is financed by the European Community Research Infrastructure Action, under the FP7 ‘Capacities’ Program. He would like to thank R. Allain (MNHN), R. Schoch (SMNS), D. Vasilyan and M. 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