TODO check dentin def

Small outgrowths which cover the skin of many cartilaginous fish including sharks. They are similar in structure to teeth, and teeth may have evolved from denticle-like structures in primitive fish.[citation needed] The placoid scales in sharks are formed of dentine with dermal papillae located in the core. These scales develop from the dermal layer of the skin, which is in contrast to the epidermal development seen the in the elasmoid scales of tetrapods. The shape of denticle varies from species to species and can be used in identification. Studies have found that the denticles create tiny vortices that reduce drag to make swimming more efficient. Denticles also allow sharks to swim silently compared to other fish that generate considerable noise when they ply the water[WP][Wikipedia:Dermal_denticle].

uberon

UBERON:0000041

http://purl.obolibrary.org/obo/NCBITaxon_7777

http://purl.obolibrary.org/obo/NCBITaxon_119203

Scales and teeth of sharks are examples of dermal skeletal elements that are still composed of the three ancient components-enamel, dentine, and bone.