Prediction of Direction of Chewing from Cranial and Dental Characters in Thomomys Pocket Gophers

Three lines of evidence were used independently to predict directionality of chewing in the nine extant species of Thomomys pocket gophers. Cranial morphometrics identified T. bulbivorus and T. bottae as having the broadest (platycephalic morphology) and narrowest (dolichocephalic) skulls, respectively, in the genus. Using Merriam's (1895) skull-shape approach, chewing in T. bulbivorus was predicted to be transverse/oblique, whereas T. bottae was expected to chew propalinally. Orientation of tooth scars and enamel bands suggested that all nine Thomomys species studied chew propalinally. To determine whether skull morphology or dental features were better indicators of directionality of chewing, live specimens of T. bulbivorus and T. bottae were collected and their chewing modes evaluated by external observation and cineradiography both species (and presumably all members of the genus) chew propalinally. Therefore, dental features better reflect masticatory mode than does skull morphology.