A new species of Chrysemys (Emydidae: Deirochelyinae) from the latest Miocene-Early Pliocene of Tennessee, USA and its implications for the evolution of painted turtles

Chrysemys, commonly known as painted turtles, have the largest native biogeographic range of all North American turtles. The presence of a new species, Chrysemys corniculata sp. nov., in the Late Hemphillian-Early Blancan North American Land Mammal Age (latest Miocene-Early Pliocene) of Tennessee provides further data on the evolution of Chrysemys, deirochelyines and emydids. The new fossil species lies basally in Deirochelyinae and suggests that either Chrysemys represents a basal deirochelyine morphology and is one of the oldest genera in the family, or that similar basal morphologies have evolved multiple times throughout deirochelyine evolution. Its occurrence at the same time as Chrysemys picta, during the Hemphillian-Early Blancan, a time of high biodiversity in emydid turtles, suggests either multiple species of Chrysemys during the Late Hemphillian-Early Blancan (at least one in the mid-west and one farther east), or multiple lineages with basal morphologies during this time. Early fossil deirochelyines occur after the greenhouse conditions of the Eocene and the Mid-Miocene Climatic Optimum. Vicariance led to deirochelyines becoming more speciose, including the occurrence of C. cornicuktta, after the MidMiocene Climatic Optimum, potentially suggesting cooler temperatures aided in the evolution of the subfamily and their speciation during the Hemphillian and into the Early Blancan.