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Journal of Mammalian Evolution

, Volume 20, Issue 2, pp 83–114 | Cite as

Postcranial Analysis of a Carnivoran-Like Archaic Ungulate: The Case of Arctocyon primaevus (Arctocyonidae, Mammalia) from the Late Paleocene of France

  • Christine ArgotEmail author
Original Paper

Abstract

The postcranial skeleton of the late Paleocene Arctocyon primaevus is described based on a sub-complete associated specimen. A comparison with arboreal or scansorial and fossorial extant taxa shows that on the forelimb, several features suggest arboreal capabilities, including the development of abductors and adductors, the development of digital flexors, which allows grasping/manipulative ability, as well as the highly mobile articulations, the convex ulna, and the pentadactyl, plantigrade foot. In contrast with the highly mobile joints of the limbs, Arctocyon had a rigid posterior thoracic area, characterized by revolute zygapophyses unknown in extant mammals. The morphology of the most anterior caudal vertebra indicates that the tail was long, powerful, muscular, and rigid at its base, and that it played an important role in locomotion. The morphology of the hind limb is congruent with that of the forelimb, the development of the adductors, flexors, and rotators of the mobile hip joint being emphasized. Although the femoral trochlea is longer and better defined than in highly arboreal taxa, Arctocyon probably moved in a controlled fashion. A comparison with South American borhyaenoids shows that Arctocyon is morphologically more similar to some predator-like Miocene metatherians than to any living mammal. It represents an interesting mix between Prothylacinus and Borhyaena in overall size and proportions, and shows a development of crests and processes of the humerus similar to those of Prothylacinus. Arctocyonidae, which evolved towards incipient saber-toothed canines combined with cheek teeth compatible with an omnivorous diet, and which show a postcranium that is morphologically more similar to carnivorans than to ungulates, represent a mosaic of features that is of particular interest in the evolution of mammals.

Keywords

Arctocyonidae Borhyaenoids Carnivora Functional morphology Paleocene Postcranium 

Notes

Acknowledgments

I thank the editor John R. Wible, Kenneth D. Rose, and an anonymous reviewer for providing numerous comments that improved the text. I also thank Philippe Loubry for all the photographs illustrating this paper, Charlène Letenneur for Figs. 18, 19 and 20 and the prothylacinid drawings in Fig. 21, Sophie Fernandez for arctocyonid drawings in Fig. 21, Cécile Colin-Fromont and Luc Vivès for access to extant specimens, and Vincent Pernègre for restoration of the axis, the second thoracic vertebra, and a humerus of the sub-complete specimen of A. primaevus.

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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Département Histoire de la Terre, CR2PMuséum national d’Histoire naturelle, UMR 7207 du MNHN-CNRSParisFrance

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