An exquisitely preserved skeleton of Eoarctos vorax (nov. gen. et sp.) from Fitterer Ranch, North Dakota (early Oligocene) and systematics and phylogeny of North American early arctoids (Carnivora, Caniformia)

ABSTRACT

An exquisitely preserved male skeleton of an early arctoid, Eoarctos vorax new genus and species, provides a unique window into the origin and early divergence of Carnivora. Recovered from the Fitterer Ranch locality in the early Oligocene (Orellan to Whitneyan North American Land Mammal ages) Brule Formation of southwestern North Dakota (∼32 Ma), the new arctoid offers an opportunity to evaluate the fundamental relationships of the caniform (dog-like) carnivorans. Eoarctos vorax possesses a suite of plesiomorphic characters inherited from its miacid ancestors, making it an ideal model for ancestral arctoids. We present a comprehensive treatment of E. vorax, combining traditional description with photographic documentation, microCT, laser scans, and photogrammetry. Showing its plesiomorphic morphology, Eoarctos vorax is scansorial, somewhat like a modern raccoon, retaining the ability to climb trees and lacking cursorial adaptations present in the early canid Hesperocyon. However, E. vorax shows clear signs of durophagous cranio-dental morphology, presumably for an obligatory diet of mollusks, with frequent damage to shell-crushing premolars, plus associated dental infections. We review several other key North American early arctoids and present total-evidence (nuclear DNA and discrete morphological characters) Bayesian and parsimony analyses of Caniformia phylogeny, including extinct stem taxa plus a living member of all modern families. We recognize an endemic North American ursoid clade, Subparictidae, which includes Eoarctos vorax. We demonstrate the importance of North America as an early cradle of evolution for caniform carnivorans, including early precursors of Canidae, Amphicyonidae, Ursidae, and Pinnipedia.

ACKNOWLEDGMENTS

This project spans generations of vertebrate paleontologists. We thank the numerous collectors in the Frick Laboratory, unsung heroes of a collection unsurpassed in scope and magnitude. C. Frick’s passion in mammalian carnivorans was a key driver in the accumulation of the magnificent Frick Collection. Through this collection were the interests of RJE and RHT first met and this project initially conceived.

We would like to thank the Fitterer family for giving paleontologists access to their lands over the last 75 years and for their donation of thousands of important fossil specimens. These specimens have been used in numerous studies and have proven to be invaluable to our understanding of vertebrae evolution and biostratigraphy. This volume would not have been possible without the fossils collected from their property. Several of the referred specimens of Eoarctos vorax were collected by volunteers on the North Dakota Geological Survey’s Public Fossil Digs, contributing to our knowledge of this new taxon.

We are in debt to B. Barnes from the North Dakota Geological Survey for her superb illustrations published in the frontispiece of this volume and Fig. 35. We greatly appreciate the artistic interpretation of Eoarctos by M. Hallett. We thank A. Henrici from Carnegie Museum of Natural History for arranging photography of the holotype of Subparictis montanus and D. Pagnac from South Dakota School of Mines and Technology for providing photos of the holotype of Subparictis dakotensis. E. Cirot kindly provided her Master’s thesis and Ph.D. dissertation that contain unpublished material of Amphicynodon important in this volume.

We wish to thank S. Tetradis for providing access to the SkyScan scanner and to A. Soundia for performing the microCT scans at the UCLA School of Dentistry, Section of Oral and Maxillofacial Radiology. D. Pagnac and C. Cranor of South Dakota School of Mines and Technology provided photos of specimens under their care. R. Paterson provided the original data matrix file of his published phylogeny of pinnipeds. We thank A. Zwingenberger, School of Veterinary Medicine, University of California, Davis for providing images used to assist in the digital reconstruction. We also thank D. Griffon and Jin Yu, College of Veterinary Medicine, Western University of Health Sciences, Pomona, CA, for sharing dog CT scans to assist us in our reconstruction.

The senior author would like to thank his wife, Y. Song, for her patience and understanding during the long gestation period of this project. She also helped in Photoshop treatments of images.

We thank the following museum curators and collections managers for access to collections under their care: J. Meng, J. Flynn, C. Mehling, R. O'Leary, and J. Galkin of the American Museum of Natural History; K. C. Beard, D. Miao, and M. Sims of University of Kansas Museum of Natural History; G. Corner, R. Secord, and S. Tucker of University of Nebraska State Museum; J. Eberle and J. Van Veldhuizen of University of Colorado Museum; A. C. Henrici of Carnegie Museum of Natural History; K. Bell, J. Dines, V. Rhue, J. Hook, and S. McLeod of Natural History Museum of Los Angeles County; C. Norris and M. Fox of Peabody Museum of Natural History at Yale University; G. Rössner of Staatliche Naturwissenschaftliche Sammlungen Bayerns—Bayerische Staatssammlung für Paläontologie und Geologie; B. Simpson of the Field Museum of Natural History; S. Shelton of South Dakota School of Mines and Technology. We thank M. Wolsan for permission to photograph several European musteloid specimens on loan to him, N. Rybczynski for providing 3D scan images of Puijila, and R. Paterson of Carleton University for providing a data matrix of his published phylogeny of pinnipeds. We thank D. Boyer of Duke University for pointing out errors in our wrist assembly of Eoarctos. A. Zdinak of Natural History Museum of Los Angeles County made molds and casts of relevant specimens as well as minor repairs on the holotype.

We greatly appreciate two reviewers, O. Bertrand and T. Smith (especially the former), for their time and efforts in making detailed suggestions and criticisms that greatly improved this manuscript. We also thank Journal of Vertebrate Paleontology Memoir Editor P. M. O’Connor for his guidance and stewardship, as well as for his numerous editorial suggestions, Staff editor J. Harris for pointing out formatting issues, and editorial staff, A. López-Arbarello, M. D’Emic, and D. Ruiz Ramoni, for other editorial improvements.

Travels by XW and software for digital 3D models were supported by grants from National Science Foundation (EAR-1227212, 1949742), Deutsche Forschungsgemeinschaft, and Natural History Museum of Los Angeles County.

SUPPLEMENTARY FILES AND 3D MODELS

Online Supplementary File 1, nexus dataset for MrBayes analysis.

Online Supplementary File 2, total evidence data matrix for TNT analysis.

Online Supplementary File 3, Additional notes on articulated skeleton.

All 3D models in this study may be downloaded from https://www.morphosource.org/concern/biological_specimens/000375779 (for original CT scans, photogrammetry and laser scans of individual bones, and articulated 3D models in PLY format) and from https://doi.org/10.5281/zenodo.5534654 (for segmentations in Avizo program files). Table 6 provides MorphoSource and Zenodo media IDs and DOI links for individual bones and articulated models.