Turtles of the Aguja and Javelina formations, Upper Cretaceous (Campanian – Maastrichtian), west Texas

Freshwater turtles of the Aguja and Javelina formations include Basilemys, Adocus, Compsemys, and Aspideretoides which are widely distributed and have long ranges throughout Campanian-Maastrichtian strata in the Western Interior of North America. Several species with restricted ranges are however documented for the first time, including Neurankylus baueri, Denazinemys nodosa, and Thescelus rapiens. Fragmentary specimens also record an unidentified baenid, likely kinosternoids and chelydrids, and three trionychids other than cf. Aspideretoides spp. Specimens attributed to Neurankylus baueri are among the largest known. A Neurankylus specimen from the Javelina Formation likely represents a distinct unnamed late Maastrichtian species. Thescelus rapiens is reported for the first time outside of New Mexico. Denazinemys occurs throughout the Upper Cretaceous section, with the most complete specimens attributed to D. nodosa. The Denazinemys lineage was restricted to the southern part of the Western Interior throughout its history, and survived into late Maastrichtian time only in Texas. The Campanian turtle fauna is allied with those of northern Mexico, New Mexico, and Utah in the presence of bothremydids along with the baenids N. baueri, D. nodosa, and T. rapiens; together these comprise a distinct ‘southern’ Campanian assemblage. Maastrichtian turtles comprise a lower diversity fauna of mostly cosmopolitan taxa, as is also the case in correlative strata in New Mexico and Utah. This may reflect drier inland habitats represented in these ‘southern’ deposits, compared to coastal habitats that hosted a diverse endemic turtle fauna at northern sites bordering the remnant interior seaway at the end of Cretaceous time.