Abstract

The nearly complete skeleton of a mud turtle, Kinosternon skullridgescens, n. sp., is described from Santa Fe County, New Mexico. The specimen was collected from the early middle Miocene, early Barstovian, Skull Ridge Member of the Tesuque Formation (16.0–14.9 Ma) and is one of the oldest and most complete fossil representatives of the genus Kinosternon. Phylogenetically, the new taxon is placed on the stem of the flavescens group in conjunction with the extinct Kinosternon pojoaque from the late Barstovian of New Mexico. In addition to the flavescens group, K. skullridgescens shares morphological similarities with members of the subrubrum group (of North America), as well as with Kinosternon herrerai (from gulf drainages of eastern Mexico). Close proximity of the fossils K. skullridgescens and K. pojoaque to Mexico suggests that a small-plastroned ancestor of the extant taxa K. herrerai, Kinosternon angustipons (from lower Central America), and Kinosternon dunni (from northwestern South America) could have dispersed from North America into Central America by the middle Miocene (Barstovian). Phylogenetic results based on morphology suggest that the taxon Kinosternon steindachneri (formerly Kinosternon subrubrum steindachneri) be reinstated at the species level.