A new earliest Paleocene (Puercan) arctocyonid mammal from the Fort Union Formation, Great Divide Basin, Wyoming, and its phylogenetic position among early ‘condylarths’

Abstract

A new arctocyonid ‘condylarth’, Sigynorum magnadivisus gen. et sp. nov., is described from a recently discovered earliest Paleocene (early Puercan) fauna from the China Butte Member of the Fort Union Formation in the Great Divide Basin, southern Wyoming. Based on a sample of 18 specimens (including 14 partial dentaries) whose combined dentitions represent the p2, p4 and m1–3, the new taxon appears most similar in size and molar morphology to the early Puercan arctocyonid Oxyprimus erikseni, but differs in its p4 morphology. To examine the relationship between S. magnadivisus and other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed, utilizing 23 taxa (including 21 ‘condylarth’ species and the outgroup taxa Cimolestes and Gypsonictops) and 73 dental characters. The resulting strict consensus tree of 248 steps confirms the close relationship between S. magnadivisus and O. erikseni. Interestingly, our phylogenetic analysis also suggests that Puercan Periptychidae is paraphyletic; the early Puercan periptychids Mimatuta morgoth, Mimatuta minuial, Maiorana noctiluca and Auraria urbana appear more closely allied with arctocyonid and hyopsodontid taxa, while other Puercan periptychids Conacodon spp., Ampliconus browni, Alticonus gazini, Oxyacodon spp. and Mithrandir gillianus fall into a separate monophyletic clade. This analysis is among the first to focus on a large set of Puercan ‘condylarth’ taxa across geographically widespread localities, and, with the addition of the new species from the Great Divide Basin, suggests that diversity among early Puercan ‘condylarths’ is higher than previously recognized.

http://zoobank.org/urn:lsid:zoobank.org:pub:4BF2E9D5-1803-43E9-82FF-EC4723203A87

Keywords:

• Arctocyonidae
• Condylarthra
• Paleocene
• Puercan mammals
• Great Divide Basin
• Wyoming

Acknowledgements

This research would not have been possible without the decades of palaeontological fieldwork performed by the late James Honey and Malcolm McKenna, and the intensive mapping of the Great Divide Basin undertaken by Robert Hettinger and James Honey. Field support was provided to Honey and McKenna by the McKenna family. Our knowledge of the stratigraphy and history of collecting was augmented considerably from discussions with Jeannine Honey, Louis Taylor and Robert Hettinger. Toni Culver facilitated access to specimens and documentation associated with the study locality. We thank Peter Robinson for his many hours of work and instruction in the moulding and casting of specimens for this study. The Entomology section at UCM (Virginia Scott and Katie Wolfson) allowed use of their imaging station for photography of the specimens. Christopher Norris, Daniel Brinkman and Marilyn Fox provided access to the collection at the Yale Peabody Museum of Natural History, use of an imaging station and the loan of a number of specimens for study. William Clemens and Patricia Holroyd hosted the authors at the University of California Museum of Paleontology at Berkeley and loaned specimens for comparative study. Greg Wilson and students at the University of Washington provided additional casts of specimens. Thomas Williamson at the New Mexico Museum of Natural History provided helpful advice and casts of specimens. Jessica Cundiff facilitated access to specimens in the vertebrate palaeontology collection at the Harvard Museum of Comparative Zoology. The members of KM's thesis committee, William Clemens, Patricia Holroyd and Christy McCain, were immensely helpful over the course of the project. Finally, Rodolph Tabuce and an anonymous reviewer provided valuable critiques that improved the manuscript.

Supplemental material

Supplemental material for this article can be accessed at: http://dx.doi.org/10.1080/14772019.2015.1066886