Fossil Box Turtles (Terrapene) from Central North America, and Box Turtles of Eastern Mexico

Abstract

Aftonian of the Pleistocene in Kansas. Only two fossil specimens of Terrapene ornata ornata were examined. Both were from New Mexico, one from a Wisconsin and one from a post-Wisconsin deposit. Most of the fossil box turtles from the central United States are referred to Terrapene carolina. The oldest specimens are from pre-Sangamon deposits of Texas and Kansas and are identified as T. carolina putnami. A number of the fossils are of Sangamon and early Wisconsin age and are identified as Terrapene carolina putnami x triunguis. The majority of the fossils are of late Wisconsin age and are identified as T. carolina triunguis, which occupies most of the central U. S. today. It is suggested that at times during the Pliocene and Pleistocene conditions comparable to those of the modern Gulf Coastal Plain extended as far inland as Kansas, New Mexico, and eastern Mexico, and that this broad coastal plain area was occupied by a single subspecies, T. carolina putnami. Climatic fluctuations and associated environmental changes during the Pleistocene ultimately led to the differentiation of putnami into T. carolina major in the southeast and T. carolina triunguis in the west. In Mexico, T. carolina putnami, or forms intermediate between putnami and triunguis, gave rise to T. carolina mexicana (formerly T. m. mexicana), T. carolina yucatana (formerly T. m. yucatana), and T. coahuila. T. carolina mexicana has a restricted distribution in southeastern Mexico and it is morphologically close to T. carolina triunguis. Texas fossils of late Wisconsin times indicate that the isolation of mexicana and triunguis is a relatively recent occurrence. T. carolina yucatana is restricted in distribution to the Yucatan Peninsula and it is morphologically close to T. carolina major. It is suggested that yucatana reached the Yucatan Peninsula during a glacial state of the Pleistocene when sea levels were low and a coastal plain was exposed between the present gulf coast and the mountains. The isolation of yucatana occurred prior to that of mexicana, and yucatana is somewhat closer to the older putnami stock than is mexicana. T. coahuila is restricted in distribution to a bolson in central Coahuila where it maintains an aquatic existence. Its distinct morphology may be attributed either to isolation from putnami at a time earlier than the other turtles were isolated or to a higher evolutionary rate as a result of rigorous selective pressure.