A new slider turtle (Testudines: Emydidae: Deirochelyinae: ) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines.

(Testudines: Emydidae) represents one of the most well-known turtle genera today. The evolution of , while being heavily documented with fossil representatives, is not well understood. Numerous fossils from the late Hemphillian Gray Fossil Site (GFS) in northeastern Tennessee help to elucidate its evolution. The fossil at the GFS represent a new species. The new taxon, , is described, and currently represents the most thoroughly described fossil emydid species known. A phylogenetic analysis, including 31 species, focusing on the subfamily Deirochelyinae is performed that includes the new fossil species, along with numerous other modern and fossil deirochelyine species, representing the first phylogenetic analysis published that includes several fossil deirochelyines. The phylogenetic analysis, utilizing morphological evidence, provides monophyletic clades of all modern deirochelyines, including , , , , , and . A strict consensus tree finds the recently described fossil species to be part of a clade of + . Three fossil taxa, including one previously referred to () and two to ( and ) are found to form a clade with modern , with sister to the other members of the clade. is found to be part of a basal polytomy with in relation to other deirochelyine taxa. Two fossil taxa previously referred to ( and ) form a paraphyly with the modern and , and may be referable to distinct genera. Additionally, fossil taxa previously attributed to (, , , and ) and are found to form a clade separate from clades of northern and southern species, potentially suggesting a distinct lineage of with no modern survivors. Hypotheses of phylogenetic relationships mostly agree between the present study and previous ones, although the inclusion of fossil taxa provides further clues to the evolution of parts of the Deirochelyinae. The inclusion of more fossil taxa and characters may help resolve the placement of some taxa, and further elucidate the evolution of these New World turtles.