Meeting Abstract
The diet of durophagous turtles impacts the shape and size of the skull, enabling the higher bite forces these species require to access hard-shelled prey. In a recent comparison, the durophagous Malaclemys terrapin was demonstrated to have a larger head relative to body size and therefore greater bite force than the closely related diet generalist, Trachemys scripta. Here, I test the hypothesis that jaw lever mechanics, not just relative head size, differ between the species, contributing to the higher bite force of M. terrapin. Female specimens of both species underwent diceCT, allowing me to digitally dissect the jaw closing musculature. The resultant 3D digital models were used to calculate lever mechanics of the jaws and measure the volumes of the jaw closing musculature. M. terrapin have 155% larger muscles relative to jaw length than T. scripta, which is indicative of a higher bite force capability even when scale for head size. Surprisingly, the line of action of the major jaw closing musculature differs between the species by less than one degree, indicating that neither is at an advantage for force input into the jaw lever system. The out-lever of the jaw was 4% larger in M. terrapin while the in-lever was 6% longer in T. scripta, suggesting that the mechanical advantage of the jaws is in fact higher in T. scripta. These results support that T. scripta possesses a mechanically more advantageous jaw system, but that the overall greater muscle volume relative to head size in M. terrapin is a major contributer to the observed differences in bite force between these species. Whether muscle architecture lends additional influence to the bite force capabilities of M. terrapin remains to be explored.
