Resistance of cervical vertebrae in response to muscular stresses in pterosaurs: implications for foraging habits and skeletal pneumatization

The necks of pterosaurs were flexible and provided mobility for a relatively long skull. The varied morphologies and levels of pneumatization of their cervical vertebrae reflected differences in biomechanical behavior. Here, we examined the structural resistance of the cervical vertebrae to infer the most advantageous movements during the foraging behaviors of two pterodactyloid pterosaurs. We also examined the relationship between vertebral resistance and the presence of pneumatic foramina on the bone cortex. For this purpose, we analyzed three-dimensional models of the cervical vertebrae of Anhanguera piscator and Azhdarcho lancicollis , which are hypothesized to be aquatic and terrestrial predators, respectively, and employed Finite Element Analysis (FEA) to assess and quantify the stresses experienced by the vertebrae due to the performance of six different movement scenarios. We observed that the shorter vertebrae at the ends of the neck of both species favored the proliferation of larger stresses in these regions, especially in the posterior cervicals of Anhanguera piscator and in the atlas-axis of Azhdarcho lancicollis , and that their taller neural arches aided in absorbing stress. Larger stresses at the ends of the neck are consistent with the interior trabecular reinforcement of the atlas-axis and posterior cervical vertebrae, suggesting a link between biomechanical behavior and the level of pneumatization. Additionally, mechanical requirements may have also influenced the presence, size, and number of pneumatic foramina on the vertebral cortex, as evidenced by the large lateral foramen in Anhanguera piscator and the smaller and more numerous ones bordering the neural canal in Azhdarcho lancicollis . Our inferences corroborate the differences in foraging strategies hypothesized for anhanguerids and azhdarchids. The absorption of stresses resulting from ventral pitching of the head and neck indicates that the cervical vertebrae were well-adapted for making rapid movements during predatory hunting. However, variations in the height of the neural spine indicate different mechanical behaviors between these species when raising the skull and neck, which could be faster in Anhanguera piscator while more vigorous in Azhdarcho lancicollis .