An early bothremydid (Testudines, Pleurodira) from the Late Cretaceous (Cenomanian) of Utah, North America.

Walter G Joyce,James I Kirkland,Tyler R Lyson

doi:10.7717/peerj.2502

Walter G Joyce, James I Kirkland + Show 1 more

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https://doi.org/10.7717/peerj.2502

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Abstract

BackgroundBothremydidae is a clade of extinct pleurodiran turtles known from the Cretaceous to Paleogene of Africa, Europe, India, Madagascar, and North and South America. The group is most diverse during the Late Cretaceous to Paleogene of Africa. Little is known, however, about the early evolution of the group.MethodsWe here figure and describe a fossil turtle from early Late Cretaceous deposits exposed at MacFarlane Mine in Cedar Canyon, southwestern Utah, USA. The sediments associated with the new turtle are utilized to infer its stratigraphic provenience and the depositional settings in which it was deposited. The fossil is compared to previously described fossil pleurodires, integrated into a modified phylogenetic analysis of pelomedusoid turtles, and the biogeography of bothremydid turtles is reassessed. In light of the novel phylogenetic hypotheses, six previously established taxon names are converted to phylogenetically defined clade names to aid communication.ResultsThe new fossil turtle can be inferred with confidence to have originated from a brackish water facies within the late Cenomanian Culver Coal Zone of the Naturita Formation. The fossil can be distinguished from all other previously described pleurodires and is therefore designated as a new taxon, Paiutemys tibert gen. et. sp. nov. Phylogenetic analysis places the new taxon as sister to the European Polysternon provinciale, Foxemys trabanti and Foxemys mechinorum at the base of Bothremydinae. Biogeographic analysis suggests that bothremydids originated as continental turtles in Gondwana, but that bothremydines adapted to near-shore marine conditions and therefore should be seen as having a circum-Atlantic distribution.

Highlights

Bothremydidae is an extinct clade of pelomedusoid turtles
We explore the phylogenetic position of Paiutemys tibert gen. et sp. nov. by integrating the new turtle into the phylogenetic analysis of Gaffney, Tong & Meylan (2006), which was developed to investigate the relationships of pan-pelomedusoid turtles, bothremydids
Our phylogenetic analyses (Fig. 5) place UMNH VP26151within the internested clades Pleurodira, Pelomedusoides, Bothremydidae, and Bothremydinae based on a substantial list of characters

Summary

Introduction

Bothremydidae is an extinct clade of pelomedusoid turtles. The group was originally known from rare fossil material from the Late Cretaceous to Paleogene of North America (see Hay, 1908 for summary), but more recent efforts yielded a surprising diversity of fossil forms ranging from the Early Cretaceous to Paleogene of North and South America, Europe, Africa, India, and Madagascar, most recently summarized by Gaffney, Tong & Meylan (2006). Paiutemys tibert is distinguished from other representatives of Bothremydinae by the following combination of characters: presence of a nuchal notch (otherwise present in Chedighaii barberi, Foxemys trabanti Rabi, Tong & Botfalvai, 2012, ‘‘Podocnemis’’ parva Haas, 1978a, Polysternon provinciale (Matheron, 1869), and Rosasia soutoi Carrington da Costa, 1940), lack of an overlap of the pectoral onto the entoplastron ( present in Rosasia soutoi), lack of a pectoral overlap onto the epiplastra (broadly present among many other bothremydids), reduction of the anterior plastral lobe (otherwise present in ‘‘Podocnemis’’ parva, Foxemys spp., Elochelys spp., and Polysternon provinciale), and the apomorphic presence of a contact of the axillary buttress with costal II and of a surface sculpture consisting of a combination of fine striations in the central parts of the shell and fine polygons along the margins.

Results

Conclusion