MORPHOSPACE OCCUPATION AND BIOMECHANICAL PERFORMANCE OF THE PERIGNATHIC GIRDLE IN JAWED ECHINOIDS

Anatomical structures and behaviors associated with feeding strategies are strongly acted upon by selective pressures, as these morphologies interact directly with an organism’s environment and have significant influence on fitness and survival. Innovations in feeding structures and associated feeding behaviors have been suggested to underlie major adaptive radiations and expansion into new niche spaces across several different clades. In addition to establishing occupation and evolution through morphospace of feeding structures, the associated biomechanical performance of these structures can be quantified for a more holistic exploration of evolution across adaptive landscapes. Here, we present a preliminary analysis of the morpho-functional landscape of the perignathic girdle, the skeletal support structure of the jaw apparatus in crown group jawed echinoids. We implement 3D geometric morphometric techniques, using a combination of anatomical landmarks and surface semi-landmarks, to explore phylo-morphospace of taxonomically and ecologically distinct girdle shapes. We compare biomechanical performance using the distribution of stress along different girdle shapes resulting from simulated applied muscle forces using finite element methods. Finally, we explore ecological breadth of echinoid groups as related to the biomechanical performance of their perignathic girdle shape. We demonstrate notable differences in distribution of stress among girdle shapes and find convergence of girdle morphology in phylogenetically distinct lineages. Weak trends are observed with girdle biomechanical performance and ecological breadth, with ‘weaker’ girdles associated with echinoids that are more environmentally restricted. Results from this pilot dataset highlight the need for a continued comprehensive exploration of the role of perignathic girdle evolution, function, and performance in the post-Paleozoic evolution of crown group echinoids.