dermal denticle (oscicle)
Petrodus sp. - dermal denticle
General abundance: Common
Denticles typically have a broad basal plate and a highly sculptured crown.
These denticles formed an overlapping skin armor that protected the sharks. These denticles are called Petrodus. At one time they were assumed to be from a single species of shark, but they have been found associated with a number of different species. The shape of denticles varies from species to species and can be used in identification. "Petrodus patelliformis" is no longer considered correct.
Denticles are often termed placoid ("plate-like") scales in older texts, most biologists today prefer the more descriptive phrase, dermal denticles (literally, "tiny skin teeth").
Hand book of Paleoichthyology Volume 3A, Chondrichthys I
Phylum Chordata (sharks & bony fish)