A new box turtle from the Miocene/Pliocene boundary (latest Hemphillian) of Oklahoma and a refined chronology of box turtle diversification

Abstract

A near complete shell from the Hemphillian 4 (Miocene/Pliocene boundary) Buis Ranch local fauna of Beaver County, Oklahoma, represents a fossil box turtle. An anterior contact of neural III and neural V with costal III and costal V only, respectively, presence of a small contact between the suprapygal and eleventh peripherals, development of a thin peripheral lip for articulation with the posterior plastral lobe, placement of the vertebral III/IV sulcus on neural VII, presence of two anterior musk duct glands, a rounded posterior plastral lobe, an elongate shell outline, and a complete neural series diagnose the fossil as a new species,Terrapene parornatan. sp. A phylogenetic analysis of fossil box turtles placesT. parornataalong the phylogenetic stem of the extant taxonT. ornata. The holotype of ‘Terrapene longinsulae’ cannot be distinguished fromTerrapene ornataand is therefore synonymized. Finally, ‘Terrapene’cornerilacks characters of crown groupTerrapeneand may therefore represent a stem box turtle. The provenance of the holotype of ‘Terrapene longinsulae’ is more poorly known than previously recognized and this specimen may originate from Kansas or Nebraska and be early Miocene to late Pleistocene in age.Terrapene parornatais therefore the oldest demonstrable representative of crown groupTerrapene(ca. 5.3–4.6 Ma). ‘Terrapene’cornerifrom the late Barstovian of Nebraska and fragmentary material from the middle Barstovian of Nebraska by contrast are the oldest representative of theTerrapenelineage (ca. 14.5–11.5 Ma). A review of morphological characters related to shell kinesis reveals that most are highly correlated. The results of the phylogenetic analysis converge upon those of molecular data when these correlated characters are omitted from the analysis.