Tesserae ultrastructure and ontogeny

Summary
The tiled outer layer of shark and ray skeletons is a natural composite of mineralized polygonal tiles (tesserae) and collagen fiber bundles, the complex and finescale 3d arrangements of which have made characterization difficult. Using high-resolution materials characterization techniques (e.g. qBEI, µCT, SRµCT) we show that tesserae exhibit great heterogeneity in mineral density, with distinct hypermineralized structural features appearing to function in load bearing, abrasive resistance and energy dissipation (e.g. at crack tips). We examine the ultrastructure of these mineralized features across ontogeny to understand how they function in skeletal performance, but also how they come to exceed mineral content and tissue stiffness of mammalian bone.