Meeting Abstract
Diversity in testudine cranial shape is hypothesized to reflect aspects of ecology and behavior. To investigate the functional links between feeding behavior and the morphology of the Cryptodiran skull, I performed a landmark-based 3D geometric morphometric analysis of cranial form in 12 species representing the phylogenetic and behavioral breadth of the clade. Virtual 3D models were produced from CT scans, and landmark data were collected using the auto3dgm package in the program R. Published data using bulk measures of diet were restructured into proportional categories reflecting an estimate of food-jaw contact and the material properties of food items. Shape data and diet were compared using two-block partial least squares analysis in GeomorphR, which returned a high correlation between the datasets (r=0.85), but was non-significant (p=0.09). A greater proportion of tough vegetative matter is associated with dorsoventral compression of the caudal skull; trochlear and articular surfaces that are perpendicular to the long axis of the skull; a vertically oriented anterior adductor chamber that alters the orientation of the adductor mandibulae externus tendon; and a concave labial margin. In contrast, hard animal matter is associated with a caudal skull that increases in height caudally; a more caudally inclined anterior adductor chamber; a laterally oriented trochlear and articular surface; a smoothly convex labial margin; and a more pointed and elongate squamosal eminence. This analysis has uncovered sources of variation in anatomical details that may vary predictably with diet beyond the external head dimensions discovered in previous analyses.
