New earliest Paleocene (Puercan) periptychid ‘condylarths’ from the Great Divide Basin, Wyoming, USA

Abstract

An earliest Paleocene (Puercan) locality in the China Butte Member of the Fort Union Formation in the Great Divide Basin (GDB) of Wyoming contains a diverse mammalian faunal assemblage, including a number of ‘condylarth’ taxa. From UCM locality 2011035, we describe three new periptychid ‘condylarths’ and report first occurrences of Maiorana noctiluca, Ampliconus antoni and Conacodon harbourae from the GDB. The new genus and species Miniconus jeanninae is characterized by a ridge-like metaconid and incipient paraconid on p4, and a molar parastylid. Based on its similarity to M. jeanninae and differences from other species of Oxyacodon, O. archibaldi is placed within the new genus Miniconus. A second new genus and species Beornus honeyi is characterized by its large size with inflated premolars and molars, and small molar paraconid. A new species of Conacodon, C. hettingeri, is similar to other species of Conacodon but differs in its m3 morphology. To examine the relationships of the three new GDB taxa to each other and to other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed using 28 Puercan periptychid and arctocyonid taxa as well as the eutherian outgroup taxon Procerberus formicarum and 64 dental characters. The resulting strict consensus tree of 210 steps confirms that the three new species from the GDB fall within Periptychidae. Beornus honeyi forms a polytomy with Mithrandir gillianus and Hemithlaeus kowalevskianus. Conacodon hettingeri is recovered as the basal member of a clade that includes the other species of Conacodon. Miniconus jeanninae is the sister to M. archibaldi. Additionally, the early Puercan Mimatuta spp. and Maiorana noctiluca fall within the Arctocyonidae, supporting the phylogenetic placement of these taxa by other recent analyses. The occurrence of the three new periptychids in the GDB indicates that mammalian diversity is higher than previously suggested for the early Puercan.

http://zoobank.org/urn:lsid:zoobank.org.pub:4F31F461-814D-4C4A-99A9-3D7ED5D6701C

Keywords:

• Periptychidae
• Condylarthra
• Paleocene
• Puercan mammals
• Great Divide Basin

Acknowledgements

Without the tremendous collecting and mapping efforts by James and Jeannine Honey as well as Malcolm McKenna, and the mapping by James Honey and Robert Hettinger, this window into a new early Puercan fauna in the GDB would not exist. Jeannine Honey provided valuable historical insight and logistical assistance with recent fossil collecting by the UCM. More recent fieldwork associated with this study (in the summers of 2017–2019) was funded by a grant awarded to JJE by the David B. Jones Foundation and a permit from Wyoming Game and Fish. Travel grants awarded to MRA from the Department of Geological Sciences, Graduate School, and United Government of Graduate Students (UGGS) at the University of Colorado at Boulder allowed presentation of the preliminary results at the Geological Society of America (GSA) Rocky Mountain and Cordilleran Joint Section Meeting (2018) and GSA Annual Meeting (2018). UCM Vertebrate Paleontology collections managers Toni Culver (retired) and Jacob Van Veldhuizen provided access to the UCM specimens. We thank Deane Bowers and Virginia Scott in the UCM’s Entomology Section who provided access to an imaging station for photography of the specimens. Thomas Williamson (NMMNH) provided access to the collections at the New Mexico Museum of Natural History. We thank Christy McCain, Benjamin Burger and Leilani Arthurs who provided support and advice throughout the course of the study, a portion of which formed part of the master’s thesis research of MA. We thank reviewers Don Lofgren and Sarah Shelley whose comments and advice considerably improved the manuscript, and we thank the editors Drs Thomas Halliday and Zerina Johanson for their comments and suggestions.

Supplemental material

Supplemental material for this article can be accessed here: https://doi.org/10.1080/14772019.2021.1924301.

Associate Editor: Thomas Halliday