SWIDERSKI, D.L.: Diversity of patterns of variation in the lower jaw of tree squirrels.

Squirrels have a reputation for being morphologically conservative, and some investigators explicitly argue that most evolution of squirrel morphology can be described by an allometric trend. Most previous morphometric studies of squirrels have used sets of distance measurements. Such studies are predisposed to find evidence of allometric constraints because the measurements are all correlated with size and thus are correlated with each other. Geometric morphometric methods are free of this bias because size and shape are evaluated independently. In this study, I am using geometric methods to examine patterns of variation in the lower jaw of the fox squirrel, Sciurus niger. Analyses of adult variation in two populations indicate that shape features are not highly correlated with each other, or with size, in either population. Comparisons between the populations show that they differ in both size and shape of the jaw. However, the difference in shape is not consistent with extrapolation of juvenile growth from the smaller adult size to the larger adult size. These results indicate that evolution of jaw shape in squirrels may not be as constrained as previous studies suggested.