Dental morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the LATE Cretaceous of Madagascar

ABSTRACT

The dentition in the only known specimen of Adalatherium hui, a gondwanatherian mammal from the Late Cretaceous of Madagascar, is markedly different from that of any previously known mammaliaform, extinct or extant. The two preserved upper incisors and single lower incisor of Adalatherium are each very large, open-rooted, and bear a restricted band of enamel. A shallow-rooted, rudimentary upper canine is present. The upper postcanine dentition is composed of a small, simple, two-rooted tooth mesially and four large, multiple-rooted (five roots or more) teeth distally. The latter are quadrangular in outline, each with four major cusps and three perimetric ridges bordering a central valley that opens buccally. There are four lower postcanines, also with four major cusps each. The first postcanine has two roots, but the following ones each have (or likely had) at least four. The two distal lower postcanines bear a prominent mesiobuccal basin. The cusps and other topographic features of the postcanines cannot be unambiguously homologized with those of other known mammaliaforms. Diastemata are present in the upper dentition between the incisors and canines and between the canines and postcanines, and in the lower dentition between the incisors and postcanines. Adalatherium, like several gondwanatherians from the Late Cretaceous and Paleogene of Argentina, retains relatively plesiomorphic, ‘normal’ radial enamel (i.e., single-layered schmelzmuster, non-decussating small prisms, interprismatic matrix anastomosing around prisms). This stands in contrast to the modified radial enamel found in other gondwanatherians from the Late Cretaceous of India and Madagascar, which exhibit prominent interrow sheets of interprismatic matrix.

ACKNOWLEDGMENTS

We sincerely thank R. Fox (University of Alberta), Meng Jin (American Museum of Natural History), E. C. Kirk (University of Texas, Austin), and J. Wible (Carnegie Museum of Natural History) for discussions of tooth morphology and homologies; V. Heisey (Stony Brook University) for initial mechanical preparation of UA 9030 and J. Alicea (Denver Museum of Nature & Science) for additional preparation of alveoli; J. Diehm and B. Reuther (Avonix Imaging) for µCT scanning and data set reconstruction; R. Schellhorn (Universität Bonn) and M. Hata (Ohio University) for 3D prints of reconstructed tooth models; various members of the Stony Brook University Department of Radiology for assistance with secondary scanning of enlarged prototyped materials; O. Dülfer, P. Göddertz, and G. Oleschinski (Universität Bonn) for technical assistance with scanning electron microscopy; G. Daggett (Denver Museum of Nature & Science) for specimen photography (Fig. 6); L. Betti-Nash (Stony Brook University) for executing the drawings and arranging figures; an anonymous reviewer whose comments improved the manuscript; and the National Science Foundation (grants EAR-9706302, EAR-1123642, EAR-1528273, EAR-1664432 to D.W.K.), National Geographic Society (grants 6400-99, 6940-00 to D.W.K.), and the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (grant PICT-2016-3682 to G.W.R.) for financial support.