Phylogenetic placement of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar: implications for allotherian relationships

ABSTRACT

The phylogenetic position of Gondwanatheria within Mammaliaformes has historically been controversial. The well-preserved skeleton of Adalatherium hui from the Late Cretaceous of Madagascar offers a unique opportunity to address this issue, based on morphological data from the whole skeleton. Gondwanatheria were, until recently, known only from fragmentary dental and mandibular material, as well as a single cranium. The holotype of A. hui provides the first postcranial skeleton for gondwanatherians and substantially increases the amount of character data available to score. We sampled 530 characters and 84 cynodonts (including 34 taxa historically affiliated with Allotheria) to test the phylogenetic relationships of Gondwanatheria and Allotheria using parsimony, undated Bayesian, and tip-dated Bayesian methods. We tested three lower dental formulae for Adalatherium, because its postcanines are distinctly different from those of other mammaliaforms and cannot readily be homologized with any known dental pattern. In all analyses, Adalatherium is recovered within Gondwanatheria, most frequently outside of Sudamericidae or Ferugliotheriidae, which is congruent with establishment of the family Adalatheriidae. The different dental coding schemes do not greatly impact the position of Adalatherium, although there are differences in character optimization. In all analyses, Gondwanatheria are placed within Allotheria, either as sister to Multituberculata, nested within Multituberculata, or as sister to Cifelliodon (and Euharamiyida), or in a polytomy with other allotherians. The composition of Allotheria varies in our analyses. The haramiyidans Haramiyavia and Thomasia are placed outside of Allotheria in the parsimony and tip-dated Bayesian analyses, but in a polytomy with other allotherians in the undated Bayesian analyses.

ACKNOWLEDGMENTS

For access to comparative material (specimens, casts, 3D prints, or CT data sets), we thank the following curators/colleagues and collections managers: R. Asher, J. Clack, M. Lowe, and R. O’Meara (University Museum of Zoology, Cambridge); S. Bi (Indiana University of Pennsylvania and Yunnan University); P. Brewer and J. Hooker (Natural History Museum, London); Ł. Fostowicz (Polish Academy of Sciences); J. Galkin, J. Meng, and E. Westwig (American Museum of Natural History); A. Huttenlocker (University of Southern California); P. Gill (University of Bristol); C. Jin, H. Wang, and Y. Wang (Institute of Vertebrate Paleontology and Paleoanthropology); T. Lyson (Denver Museum of Nature & Science); T. Martin (University of Bonn); Q.-J. Meng (Beijing Natural History Museum); Z.-X. Luo (University of Chicago); and C. Zhou (Paleontological Museum of Liaoning). We also extend our sincere gratitude to our colleagues Q.-J. Meng (Beijing Museum of Natural History) and Z.-X. Luo (University of Chicago), who organized the 2018 International Symposium on Mesozoic Mammal Evolution, and made available numerous critically important specimens of Mesozoic mammals, in part through the generosity of the curators and collection managers of many other institutions in China. Finally, we thank E. Panciroli and an anonymous reviewer for their comments on the manuscript.

For funding, we gratefully acknowledge the National Science Foundation (grants DEB-1501497 to S.H.; DEB-1654949 to J.R.W.; EAR-1122642, EAR-1528273, and EAR-1664432 to D.W.K.) and the Agencia de Promoción Científica y Tecnológica, Argentina (grant PICT-2016-3682 to G.W.R.).