Re-Evaluation of Compsemys and North American Compsemydids (Testudinata)

Compsemys is an enigmatic turtle first described over 160 years ago. Its taxonomic position has been uncertain, as many of the species placed in the genus have since been removed from it. For the last 30+ years, Compsemys victa has been the only recognized North American fossil species. New fossil specimens collected from the Paleocene in the United States necessitate a re-evaluation of the taxonomy of these turtles and call into question the long-held belief that only one species of Compsemys is valid in North America. Specimens from the Paleocene are far more complete than the holotype of C. victa, and all have been referred to this species based on a similar surface texture. Differences between material from the Cretaceous and Paleocene suggest multiple species of Compsemys are valid. In addition to the genotypic species Compsemys victa, C. puercensis, and C. torrejonensis are both valid species from the Paleocene. Beyond surface sculpturing and texture, features of the carapace and plastron can be used to help differentiate the three species. North American Compsemys survived the Cretaceous–Paleogene mass extinction. Rather than being a monospecific genus, Compsemys diversified in the Paleocene. Not only does this suggest an increase in the diversity of North American compsemydids, but it also leads to the possibility of asymmetric or budding cladogenesis among Compsemys species during the Late Cretaceous and Paleocene, at least in the American Southwest.