THE ANISOTROPIC MECHANICAL PROPERTIES AND MORPHOLOGY OF ELASMOBRANCH SKIN

The goal of these studies was to quantify mechanical properties of elasmobranch (sharks and batoids) skin to understand the functional relationships between mechanics and morphology, and how these correspond to differences in swimming and ecology. I relate mechanical behaviors with morphological structures to elucidate the underlying contributions of the skin toward elasmobranch skin mechanics. I mechanically tested skin in uniaxial tension to failure to assess the tensile strain at maximum load (extensibility), ultimate tensile strength, Young’s Modulus of elasticity (stiffness), and toughness among diverse groups of elasmobranchs. Across three chapters, I compare mechanical behaviors of the skin among species of sharks and batoids (separately) among body regions, and between sexes and axes of stress (longitudinal and hoop). Among 20 shark species, I quantified mechanical properties among ecomorphotypes and ontogenetically (across three maturity stages) and found that mechanical behaviors increase ontogenetically and are governed by two different underlying trends (maturity and ecomorphology). I found that shark skin oriented in the hoop direction was stronger and stiffer compared to skin oriented longitudinally, as hoop-oriented skin maintains internal volume and hydrostatic pressure by resisting deformation. Shark skin oriented longitudinally was more extensible, allowing for increased stretchability anteroposterior as a shark’s body undulates along the longitudinal axis. Dermal denticles (placoid scales), tooth-like structures of enameloid and dentine, are rooted in the stratum compactum layer of the dermis, embedded in a collagen fiber network.