So the evolution of skeletal bone and teeth in vertebrates is super neat.
A lot of people are aware that shark scales are composed of the same material as teeth (pulp core surrounded by a hard enamel coating), but not many seem to know that it’s not just a weird evolutionary coincidence.
Modern fish are descended from placoderms, early jawed vertebrates which had heavy ossified plates covering their bodies. Sharks had bony placoid scales before they ever had teeth—the scales migrated forward and fused into three-pronged structures called odontodes which eventually modified to form true teeth. So teeth are actually scales, in the same way that the inner ear in tetrapods is a homologous feature to the branchial arch-derived spiracle found in most cartilaginous fishes.