Craniofacial morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar

ABSTRACT

The cranium of Adalatherium hui, as represented in the holotype and only specimen (UA 9030), is only the second known for any gondwanatherian mammal, the other being that of the sudamericid Vintana sertichi. Both Adalatherium and Vintana were recovered from the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar. UA 9030 is the most complete specimen of a gondwanatherian yet known and includes, in addition to the cranium, both lower jaws and a complete postcranial skeleton. Aside from Adalatherium and Vintana, gondwanatherians are otherwise represented only by isolated teeth and lower jaw fragments, belonging to eight monotypic genera from Late Cretaceous and Paleogene horizons of Madagascar, the Indian subcontinent, Africa, South America, and the Antarctic Peninsula. Although the anterior part of the cranium is very well preserved in UA 9030, the posterior part is not. Nonetheless, comparable parts of the crania of Adalatherium and Vintana indicate some level of common ancestry through possession of several synapomorphies, primarily related to the bony composition, articular relationships, and features of the snout region. Overprinted on this shared morphology are a host of autapomorphic features in each genus, some unique among mammaliaforms and some convergent upon therian mammals. The cranium of Adalatherium is compared with the crania of other mammaliamorphs, particularly those of allotherians or purported allotherians (i.e., haramiyidans, euharamiyidans, multituberculates, Cifelliodon, and Megaconus). Particular emphasis is placed on several recently described forms: the enigmatic Cifelliodon from the Early Cretaceous of Utah and several new taxa of euharamiyidans from the Late Jurassic of China.

ACKNOWLEDGMENTS

We thank V. Heisey (Stony Brook University) for mechanical preparation of the cranium of UA 9030, T. Salerno (Stony Brook University) for performing the lion’s share of the digital segmentation, L. Dougan and A. Tecza (Digital Research Laboratory, Denver Museum of Nature & Science) for assistance in digitally investigating obscure structures, M. Colbert (University of Texas at Austin) for µCT imaging, G. Jiang (Denver Museum of Nature & Science) for photography, and L. Betti-Nash for artwork. We appreciate discussions with J. Clark, J. Hopson, A. Huttenlocker, A. Martinelli, C. Kammerer, and E. Panciroli concerning details of cynodont cranial anatomy and are additionally grateful to Clark, Kammerer, Martinelli, and Panciroli for photographs of the crania of various nonmammalian cynodonts and to Huttenlocker for µCT data files on the cranium of Cifelliodon. We are also grateful to J. Schultz and L. Weaver for reviewing this chapter and for their constructive criticism, which improved the manuscript considerably. This research was supported by funding from the National Science Foundation (EAR-1528273 and EAR-1664432 to D.W.K., DEB-1501497 to S.H., and DEB-1654949 to J.R.W.) and the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (grant PICT-2016-3682 to G.W.R.).