Quantitative imaging supports that endoskeletal mineralization in sharks is an adaptive trait

Modern sharks (Selachimorpha) exhibit a broad suite of adaptations that enable them to inhabit diverse marine environments. Notably, their cartilaginous endoskeleton displays varying degrees of mineralization, potentially reflecting adaptations for buoyancy, locomotion, and feeding. Here, quantitative computed tomography was applied to assess endoskeletal mineralization in representatives from all nine orders of sharks spanning 26 out of 35 families. Our findings reveal that skeletal mineralization is highly variable between species and is more closely associated with ecological factors such as depth distribution, than with phylogenetic relationship. We find that deeper-dwelling species generally exhibit lower degrees of mineralization, suggesting adaptations for buoyancy regulation and energy conservation. Our study provides insight into the variation of skeletal mineralization in the ecology and evolution of sharks.