A new baenid turtle, Palatobaena knellerorum sp. nov., from the lower Paleocene (Danian) Denver Formation of south-central Colorado, U.S.A.

ABSTRACT

Baenidae are the most diverse clade of turtles from the latest Cretaceous and earliest Paleogene of North America. Palatobaena species have a distinctive cranial bauplan within baenid turtles and we herein describe a new species, P. knellerorum, based on a complete cranium from the lower Paleocene Denver Formation in the Denver Basin, Colorado. Palatobaena knellerorum differs from other Palatobaena species in the extreme degree of its dorsally oriented orbits, as well as the presence of a broad pentagonal midline crest formed by the supraoccipital and parietals. It can be further diagnosed from other species of Palatobaena by the following unique combination of characters: having a broadly rounded cranium, presence of upper temporal emargination that extends well anterior to the otic chamber, a broad exposure of the supraoccipital on the dorsal skull roof, a broadly rounded ‘tongue groove’ between the maxillae and premaxillae, and a deeply emarginated nasal region that exposes the underlying premaxillae in dorsal view. Palatobaena knellerorum most closely resembles the Maastrichtian/Danian taxon Palatobaena cohen and the Danian taxon P. bairdi. A phylogenetic analysis places P. knellerorum as sister to P. bairdi, and these taxa are sister to P. cohen. Palatobaena knellerorum overlaps in time with P. cohen, but the two are separated geographically with P. knellerorum restricted to the Denver Basin and P. cohen restricted to the Williston Basin. Cranial anatomical data and sedimentological data suggest Palatobaena spp. were bottom dwelling turtles living in shallow water environments that used a putative proboscis to prey upon freshwater-shelled invertebrates.

ACKNOWLEDGMENTS

We thank Norwood Properties, City of Colorado Springs, Waste Management, Aztec Family Raceway, J. Hawkins, J. Hilaire, J. Carner, W. Pendleton, the Bishop Family, H. Kunstle for land access; the State of Colorado, Office of the State Archaeologist, for issuing collection permits; S. Milito for discovering the beautiful holotype specimen; J. Englehorn and N. Brandborg for preparation of specimens; R. Hess, S. Milito, Y. Rollot, P. Sullivan, L. Taylor, and K. Weissenburger for field assistance; R. Wicker and the USGS National Unmanned Aircraft Systems team for photography; S. Luallin and L. Dougan for making photogrammetry models provided in the Supplemental Data; A. Atuchin provided artwork used in Fig. 1. K. MacKenzie and N. Neu-Yagle for collections assistance; R. Lavie for assistance with GIS data; B. Snellgrove for logistics; and B. and W. Stevenson for lodging during fieldwork. G. Bever, D. Brinkman, and W. Joyce had numerous insightful comments that helped improve the quality of this manuscript. Funding was provided by The Lisa Levin Appel Family Foundation, M. Cleworth, Lyda Hill Philanthropies, David B. Jones Foundation, M. L. and S. R. Kneller, T. and K. Ryan, and J. R. Tucker as part of the Denver Museum of Nature & Science No Walls Community Initiative, as well as support from the National Science Foundation (NSF-DEB-1947025) to T.R.L.