7 - Patterns of dental variation and evolution in prairie dogs, genus Cynomys

Summary

Prairie dogs are large, distinctive ground squirrels of the genus Cynomys that occur today on the Great Plains and on high plateaus and basins of the Rocky Mountains from southern Saskatchewan to northern Mexico. Two subgenera (Cynomys and Leucocrossuromys) and five extant species currently are recognized (Pizzimenti, 1975). The members of the two subgenera are referred to as black-tails and white-tails, respectively, designations that will be used in this chapter. The genus extends from the late Pliocene (late Blancan) to the Recent, but the record is best known for the late Pleistocene (late Irvingtonian and Rancholabrean) and Recent. The fossil record of the genus was recently reviewed (Goodwin, 1990).

The purpose of this chapter is to document patterns of morphological variation in several characters of fossil and Recent prairie dogs and to consider the tempo, mode, and causes of evolution as inferred from these patterns. The patterns that are treated include temporal variations in measures of dental size and “shape,” in sample variability of measures of size, and in frequency of a nonmetric character, as well as latest Pleistocene (late Rancholabrean) geographic variations in measures of size and shape.

Materials and methods

Variables

This study was restricted to lower jaws and dentitions because relatively large sample sizes are available in the fossil record for these elements. Ten measurements originally were obtained: length of the lower alveolar row (MDALV); individual lengths of P₄-M₃; trigonid and talonid widths of P₄; and trigonid widths of M₁-M₃.