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

Abstract

Trachemys(Testudines: Emydidae) represents one of the most well-known turtle genera today. The evolution ofTrachemys, 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 fossilTrachemysat the GFS represent a new species. The new taxon,Trachemys haugrudi, 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, includingChrysemys,Deirochelys,Pseudemys,Malaclemys,Graptemys, andTrachemys. A strict consensus tree finds the recently described fossil speciesGraptemys kernerito be part of a clade ofGraptemys+Malaclemys. Three fossil taxa, including one previously referred toPseudemys(Pseudemys caelata) and two toDeirochelys(Deirochelys carriandDeirochelys floridana) are found to form a clade with modernDeirochelys reticularia reticularia, withD. floridanasister to the other members of the clade.Chrysemysis found to be part of a basal polytomy withDeirochelysin relation to other deirochelyine taxa. Two fossil taxa previously referred toChrysemys(Chrysemys timidaandChrysemys williamsi) form a paraphyly with the modernChrysemys picta pictaandDeirochelys, and may be referable to distinct genera. Additionally, fossil taxa previously attributed toTrachemys(Trachemys hillii,Trachemys idahoensis,Trachemys inflata, andTrachemys platymarginata) andT. haugrudiare found to form a clade separate from clades of northern and southernTrachemysspecies, potentially suggesting a distinct lineage ofTrachemyswith 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.