Boremys (Testudines, Baenidae) from the latest Cretaceous and early Paleocene of North Dakota: an 11-million-year range extension and an additional K/T survivor

ABSTRACT

For over a century, the baenid turtle Boremys has been recognized as being restricted to the Campanian of North America. Herein we describe new material of Boremys sp. from the Hell Creek Formation (Maastrichtian) and Fort Union Formation (Puercan) of southwestern North Dakota and eastern Montana, increasing the stratigraphic range of this taxon by 11 million years. The material was recovered from the base of the Hell Creek Formation to 14 m above the pollen-calibrated K/T boundary in the basal Fort Union Formation. Most of the specimens consist of isolated shell elements, which are easily misidentified as belonging to a kinosternid or chelydrid turtle, but complete shells are present as well. The presence of Boremys sp. in the Hell Creek formation increases the baenid taxonomic diversity of this particular rock unit to nine and the overall turtle diversity to 20 taxa, and the presence of Boremys sp. in the Fort Union Formation increases the number of baenid lineages that survive the K/T extinction event to eight.

ACKNOWLEDGMENTS

We thank D. Brinkman (TMP), R. Sullivan (SMP), and M. Carrano (USNM) for access to material under their care. Thanks to the East Marmarth Pasture Members, J. Brown and family, and M. Miller for allowing PTRM to collect and curate several of the fossils. Additional referred specimens were collected from public lands managed by the Bureau of Land Management in Montana and North Dakota, the United States Forest Service and Bowman County in North Dakota, and we would like to thank numerous staff members for their assistance with obtaining access. Yvonne Lichtenfelt is thanked for preparation of the PTRM material. Don and K. Wilkening, M. Clark, and numerous PTRM volunteers helped find the described material. Sean Modesto, J. Anquetin, and an anonymous reviewer made several suggestions that improved the manuscript. Don Brinkman furthermore provided us with insightful discussions regarding baenid systematics. Funding for this project was provided by a National Science Foundation Graduate Research Fellowship to T.R.L. and by a grant from the University of Tübingen to W.G.J.

Handling editor: Sean P. Modesto