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The greater evolutionary history of Cynomys (prairie dog, Rodentia, Sciuridae) has been established. Earliest members are recorded from the late Blancan Land Mammal age, Late Pliocene. The fossil history for Cynomys is well reconstructed for the Great Plains of the USA and Canada. However, it is insufficiently studied for the arid Southwest and almost entirely unknown for adjacent northern Mexico. This paper reports on the remains of Cynomys recovered from the paleontological site of La Playa, northern Sonora, Mexico. Two species of Cynomys live today in Mexico in disjunct, likely relictual locations, Cynomys ludovicianus and Cynomys mexicanus. The distribution of prairie dogs today does not include the region of La Playa: the closest population lives about 150 km north and east in northeastern-most Sonora and adjacent Arizona. The identification criteria presented here indicate that the black-tailed prairie dog, C. ludovicianus, inhabited the valley bottom now exposed as the La Playa fossil deposits. The description of this species from La Playa represents the first report of Rancholabrean prairie dogs from Sonora. Its recovery from the extremely low elevations of northern Sonora indicates that a different climatic regime was in operation during the Late Pleistocene resulting in local vegetation and soil types considerably different from those recorded there today. The late Wisconsinan Glacial climate supported herbivores that cannot inhabit the area today. |
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