Abstract

The complete skeleton of a fossil mud turtle, Kinosternon pojoaque, n. sp., is described from the late Barstovian Rodent Pocket, San Ildefonso Locality of Santa Fe County, New Mexico. The new species represents the oldest member of the Kinosternon flavescens group and suggests that this clade first evolved in the southwestern United States, which, along with northern Mexico, is the center of diversity for these turtles today. The new taxon exhibits plastral characters that suggest phylogenetic affinities with Kinosternon angustipons, Kinosternon dunni, Kinosternon herrerai, Kinosternon hirtipes, and Kinosternon sonoriense and is interpreted here as an example of a morphological intermediate between the clade composed of these taxa and the flavescens group. The new fossil, along with other Miocene Kinosternon fossils from New Mexico, provides evidence that the flavescens clade likely diverged from other southwestern, Central, and South American Kinosternon by at least the late Barstovian, 14.3–13.3 million years ago.