Late-surviving stem mammal links the lowermost
Cretaceous of North America and Gondwana
Adam K. Huttenlocker
*, David M. Grossnickle
, James I. Kirkland
, Julia A. Schultz
& Zhe-Xi Luo
Haramiyida was a successful clade of mammaliaforms, spanning
the Late Triassic period to at least the Late Jurassic period, but
their fossils are scant outside Eurasia and Cretaceous records are
. Here we report, to our knowledge, the first cranium
of a large haramiyidan from the basal Cretaceous of North America.
This cranium possesses an amalgam of stem mammaliaform
plesiomorphies and crown mammalian apomorphies. Moreover, it
shows dental traits that are diagnostic of isolated teeth of supposed
multituberculate affinities from the Cretaceous of Morocco, which
have been assigned to the enigmatic ‘Hahnodontidae’. Exceptional
preservation of this specimen also provides insights into the
evolution of the ancestral mammalian brain. We demonstrate the
haramiyidan affinities of Gondwanan hahnodontid teeth, removing
them from multituberculates, and suggest that hahnodontid
mammaliaforms had a much wider, possibly Pangaean distribution
during the Jurassic–Cretaceous transition.
The ecological expansion of crown Mammalia accelerated in the
wake of extinctions of diverse and disparate archaic mammalia-
morph groups during the mid-Mesozoic
. Haramiyidans represent
one such clade of early mammaliamorphs that show preservation of
notable links between nonmammalian and mammalian structure and
. Their fossils, which were dated to the Late Triassic–
Jurassic, were historically limited to isolated teeth and incomplete
, hindering a more complete understanding of their
radiation. Recent discoveries of articulated skeletal material of eleuth
erodont haramiyidans from the Middle–Upper Jurassic of China
have shed new light on their diversification
, although these fossils
have also sparked new debate over their phylogenetic position
Department of Integrative Anatomical Sciences, University of Southern California, Los Angeles, CA, USA.
Committee on Evolutionary Biology, The University of Chicago, Chicago, IL, USA.
Geological Survey, Salt Lake City, UT, USA.
Natural History Museum of Utah, Salt Lake City, UT, USA.
Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL, USA.
*e-mail: firstname.lastname@example.org; email@example.com
Fig. 1 | Cranium of C. wahkarmoosuch. a–e, Holotype in dorsal (a), left
lateral (b), frontal (c), ventral (d) and occipital (e) views. as, alisphenoid
(epipterygoid); bs, basisphenoid; C, upper canine alveolus; f, frontal;
f i, incisive foramen; f l, lacrimal foramen; g, squamosal glenoid; I
upper incisor alveolus (homologous to second incisor position in earlier
, second upper incisor alveolus (homologous to third
incisor position); j, jugal; l, lacrimal; m, maxilla; n, nasal; o, occipital;
os, orbitosphenoid; p, parietal; p pr, paroccipital process; pal, palatine; PC
in situ posterior upper postcanine (molar); pe, petrosal; pm, premaxilla;
pp, postparietal; pt, pterygoid; sq, squamosal; t, tabular; v, vomer.
108 | NATURE | VOL 558 | 7 JUNE 2018
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