Sharks' answer to bone: how calcified cartilage evolved and its relation to feeding.

Sharks and their relatives (chondrichthyans) have a unique skeleton made entirely of cartilage, unlike other jawed vertebrates. Tessellated calcified cartilage (TCC) provides the skeleton with both flexibility and stiffness, and fossil evidence shows that chondrichthyans developed this innovative tissue in place of bone. Our knowledge of TCC greatly lags behind that of bone and is mainly limited to 2D data. This project will be the first to visualise TCC in 3D in both extinct and extant chondrichthyans using propagation phase-contrast synchrotron microtomography (PPC-SRμCT). Twenty-six specimens will be examined, focusing on the Meckel's cartilage (lower jaw) to observe variations linked to feeding mechanisms. These specimens represent diverse feeding strategies and span 400 million years of evolution. The results will provide new insights into the structure and function of TCC, with implications for evolutionary biology, material science, and medical research on cartilage disorders.