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.

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 biome...

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Frugivorous mammals play a key role in forest regeneration by dispersing seeds yet their effectiveness can vary with landscape disturbance and the native or exotic status of the plant species. In the ...

The characterization of soil mite (Acari) communities traditionally follows morphological identifications of specimens extracted from soil, which is a highly laborious and time-consuming process. Meta...

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The evolution of marine mammals in South America includes unique and extinct lineages found nowhere else in the world, such as the walrus-convergent whale Odobenocetops and multiple aquatic sloth spec...

Clitellata is a major annelid clade comprising oligochaetes (e.g., earthworms) and hirudineans (e.g., leeches). Due to their scant fossil record, the origins of clitellates, particularly Hirudinea, are poorly known. Here, we describe the first leech body fossil, Macromyzon siluricus, gen. et sp. nov., from the Brandon Bridge Formation (Waukesha Lagerstätte). This fossil, which is preserved in exceptional detail, possesses several hirudinean soft-tissue synapomorphies–including a large sucker at the posterior end and sub-divided segments–and phylogenetic analyses resolve Macromyzon siluricus as a stem leech. Its age, 437.5–436.5 Ma, is consistent with early age estimates for the origin of clitellates, and predates molecular-clock-based estimates of hirudinidan origins by at least 200 million years. These findings suggest that the earliest true leeches were marine and that, contrary to prevailing hypotheses, were unlikely to have fed on vertebrate blood.