Dsungaripterus, Young, 1964

Pêgas, Rodrigo V, Costa, Fabiana R & Kellner, Alexander W A, 2021, Reconstruction of the adductor chamber and predicted bite force in pterodactyloids (Pterosauria), Zoological Journal of the Linnean Society 193 (2), pp. 602-602 : 602-

Dsungaripterus

D. weii exhibits an enlarged upper temporal fossa and temporal region overall, which indicate a highly enlarged temporal adductor musculature. This is consistent with exerting high bite forces. The specialized teeth of D. weii have been interpreted as a specialization for crushing shells ( Young, 1964; Wellnhofer, 1991). We found this taxon to bear relatively high absolute bite forces and the highest bite force quotient of all analysed taxa, as well as high mechanical advantages similar to those of Th. sethi . The absolute bite force values found for the posterior teeth of D. weii (185 N) and the palatal keel apex of Th. sethi (219 N) are close to the bite force of 209 N measured for the mollusc-crushing horn shark Heterodontus francisci (Girard, 1855) ( Huber et al., 2005) . We thus interpret our estimations to provide support for the hypothesis of durophagy for D. weii .

PTEROSAUR MANDIBLES: SHAPE AND FUNCTION

Following the results presented above, we argue that differences in the biomechanical performance of pterosaur jaws (mechanical advantage of the jaw adductor muscles, bite force, BFQ) are related to feeding styles. Still, these type of data are not unambiguous and must be interpreted in a comprehensive way, taking into consideration other ecomorphological data, such as tooth morphologies (as in the cases with Dsungaripterus and anhanguerids, with their specialized teeth) and even wing shape and limb proportions, which may influence lifestyle and therefore constrain feeding habits (as mentioned above for Thalassodromeus and azhdarchoids in general). In this way, a question remains: how do these functional signals relate to jaw shape? Concerning morphological variation of pterosaur mandibles in lateral view, Navarro et al. (2018) concluded that there was no clear segregation of feeding ecologies throughout the morphospace, with a limited functional signal. Jaw shape variability was mostly explained by two major components: orientation in lateral view (dorsally curved, straight or ventrally curved) and depth of the jaw (mostly influenced by sagittal crests). This means these two trends were responsible for most of the variation seen in pterosaur jaw shape in lateral view. The influence of sagittal crests in jaw shape variation suggests sociosexual function as a strong driver of pterosaur mandibular evolution ( Navarro et al., 2018). However, due to much scatter in ecological groups throughout the morphospace, neither component seems to relate strongly to a particular feeding ecology ( Navarro et al., 2018). We suggest this could be partially explained by similar jaw shapes possibly presenting discrepant biomechanical performance. For example: in the PC2 vs. PC1 plots of the shape analysis by Navarro et al. (2018), the mandibles of Dsungaripterus and Pteranodon fall relatively close; and yet, we demonstrated above that they present distinct biomechanical properties. In fact, with regards to bite force, factors such as adductor muscle proportions, position and inclination will directly affect, respectively, the CSA, the outlever, and the angle of action of the adductor muscles. These features impact bite force and mechanical advantage, and yet are not accounted for by mandible morphometry in lateral view; the same is true for other data such as tooth morphology. We wonder if finer details of jaw shape variation could capture stronger biomechanical signals, which may be worthy of further investigation.