When describing the architecture and ultrastructure of animal skeletons, introductory biology, anatomy and histology textbooks typically focus on the few bone and cartilage types prevalent in humans. In reality, cartilage and bone are far more diverse in the animal kingdom, particularly within fishes, where cartilage and bone types exist that are characterized by features that are anomalous or even pathological in human skeletons. Here, we discuss the curious and complex architectures of fish bone and shark and ray cartilage, highlighting similarities and differences with their mammalian skeletal tissue counterparts. By synthesizing older anatomical literature with recent high-resolution structural and materials characterization work, we frame emerging pictures of form-function relationships in these tissues and of the evolution and true diversity of cartilage and bone.

To understand the true scope of variation of vertebrate skeletal tissues, with regard to structure, composition, and mechanics, it is important to look beyond the limited number of the often-used model species and sample vertebrates as broadly as possible. By examining evolutionary alternatives to mammalian bone, we can expand and reframe our understanding of form-function relationships in vertebrate skeletal tissues and the factors that drove their evolution. In 'The Multiscale Architectures of Fish Bone and Tessellated Cartilage and Their Relation to Function' (Seidel R, Jayasankar AK, Shahar R & Dean MN (2019). In: Architectured Materials in Nature and Engineering (pp. 329-353). Springer, Cham.) we discuss the two major mineralized tissue types of fishes: the bone of bony fishes and the tessellated cartilage of sharks and rays.