New mud turtles (Kinosternidae,Kinosternon) from the middle–late Miocene of the United States

KinosternonSpix, 1824, was widespread in xeric to savanna associated paleowetlands across North America during the middle–late Miocene and steadily diversified following its first occurrences in the Hemingfordian. In the middle Miocene,Kinosternon rinconn. sp. occurred in the late Barstovian Cerro Conejo Formation of north central New Mexico, perhaps concurrently withKinosternon pojoaqueBourque 2012a from the Tesuque Formation. Subsequent late Miocene kinosternine fossils indicate that at least three potentially contemporaneous species existed throughout the Clarendonian. These areKinosternon pannekollopsn. sp., from the Ogallala Formation of northern Texas;Kinosternon wakeeniense, n. sp., from the Ogallala Formation of northwestern Kansas and Ash Hollow Formation of south-central Nebraska; andKinosternon notolophusn. sp., from the Alachua and Statenville formations of northern Florida.Kinosternon rinconis phylogenetically nested between theKinosternon flavescens(Agassiz, 1857) group (=PlatythyraAgassiz, 1857) and more derivedKinosternonincluding theKinosternon subrubrum(Lacépède, 1788) group (=ThyrosternumAgassiz, 1857).Kinosternon pannekollopsis recovered on the stem of theK.subrubrumgroup and is the oldest and largest member of that lineage.Kinosternon notolophusis readily differentiated from other MioceneKinosternonin possessing a distinct dorsomedial keel on the nuchal and faint dorsolateral costal carination. TheK.subrubrumgroup probably originated in the late Miocene savannas of the Great Plains and dispersed eastward via the Gulf Coastal Plain. An unnamed kinosternine taxon existed in the coastal plains of the eastern and southeastern United States during the Middle Miocene Climatic Optimum (with fossils from ~18 to 15 Ma), and disappeared from the region coincident with the end of that megathermal event.