A new dermatemydid (Testudines, Kinosternoidea) from the Paleocene-Eocene Thermal Maximum, Willwood Formation, southeastern Bighorn Basin, Wyoming

Abstract

<div><p>ABSTRACT</p><p><i>Gomphochelys nanus</i>, new genus and species, is described from the earliest Wasatchian (biohorizon Wa 0; ∼55.8 Ma) of the southeastern Bighorn Basin, Washakie County, Wyoming. The new taxon represents the only known dermatemydid from the Paleocene–Eocene Thermal Maximum (PETM) interval and extends the lineage back from previous records by approximately 2 million years. <i>Gomphochelys nanus</i> has a thick tricarinate carapace and differs from other dermatemydids in attaining a smaller adult body size, having reduced plastral features, a posteriorly situated gular–humeral sulcus, an acarinate pygal, and thick shortened peripherals. Reexamination of previously described fossil dermatemydids suggests that the taxa <i>Baptemys tricarinata</i> and <i>Kallistira costilata</i> are junior synonyms of the middle–late Wasatchian <i>Notomorpha garmanii</i>, and <i>Baptemys fluviatilis</i> is likely a junior synonym of <i>Baptemys wyomingensis</i>. <i>Gomphochelys nanus</i> is a stem dermatemydid that is similar to <i>N. garmanii</i> but differs in possessing symplesiomorphies with the Late Cretaceous–Paleocene genera <i>Agomphus</i> and <i>Hoplochelys</i>. Aspects of shell morphology suggest that <i>G. nanus</i> was a commensurate swimmer and bottom-walker like extant <i>Dermatemys</i> and <i>Staurotypus</i>. The presence of a dermatemydid (a tropically distributed clade) in the southeastern Bighorn Basin during the PETM (when global temperatures increased by 5°C–10°C over a period of ∼60 ky) further supports the hypothesis that climate was megathermal in the region during this interval and is consistent with previously documented geographic range changes in both plants and animals. Dermatemydids disappear from the fossil record at the end of the PETM and don't reemerge until the next warming event, Eocene Thermal Maximum 2.</p><p>http://zoobank.org/urn:lsid:zoobank.org:pub:19A98079-5CAD-4BC5-8C21-2810AA576D98 </p><p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP</p></div