Meeting Abstract
Lamniform sharks vary widely in morphology and feeding niche, however, the functional morphology of their jaws is difficult to study due to their large size, rarity, and pelagic habit. To determine whether, and how, skeletal structure and performance vary with ecology, we created a custom analysis module for CT data to quantify aspects of structure of the jaw skeleton from all 15 members of Lamniformes. The module provides a customizable and slice-wise analysis of jaw structure, outputting shape-based descriptors relating to skeletal function, e.g. second moment of area, mineralized cross-sectional area, cortical wall thickness, and the anatomical orientation of each cross-section’s major axis. These parameters help describe the contribution of jaw shape to skeletal bending and torsion resistance, while also localizing regions of reinforcement (e.g. higher wall thickness) and the likely predominant orientation of loading (based on distribution of material). Our results suggest diet-specific structural organization in the jaws, but also broad consistencies across the closely related lamniforms. The mineralized tissue of the jaws is arranged in such a way as to resist flexion ~5–20 times better than if it were a solid rod of similar length. The anterior tooth-bearing ends of both upper and lower jaws are rounder in cross-section implying higher torsion resistance, whereas the posterior ends (near the jaw joint and adductor muscle insertions) are extremely narrow, suggesting high, but anisotropic, resistance to flexion and a more uniform loading direction. These data suggest that skeletal geometry in sharks may be organized in predictable ways, as in bone, to resist dominant loading regimes. Furthermore, our CT data provide new anatomical insights, such as previously undescribed gaps in the mineralization layer near the jaw joints.
