Intraspecific Variation in the Cranial Feeding Mechanism of Turtles of the Genus Trionyx (Reptilia, Testudines, Trionychidae)

and time. Variation in the jaws of T. ferox is shown to be co-existent with variation in 1) other skull features which are presumed to be part of the cranial feeding mechanism, 2) the rhamphotheca or beak, 3) jaw musculature, and 4) feeding habits. In T. ferox, females attain larger size and show more extreme variation in cranial form and diet than males; however the allometric trends are common to both sexes. The relative development of the different features of the cranial feeding mechanism does not reflect a highly integrated structural system. There is no evidence of sexual dimorphism (sensu stricto) nor is there a high correlation between individual skull form and specific food, items. Such a loosely correlated system indicates low selection pressures regarding trophic specialization; individual homeostasis would appear to be a sufficient adaptive strategy.