Two views of the same "Petrodus", a dermal denticle
from the skin of ancient sharks. The petrodi consists of a round base that
is larger at the top than at the bottom and a cone shaped upper section.
The base was located within the skin and the upper section protruded through
the skin. petrodi consist of trabecular dentine beneath a very thin layer
of orthodentine. These denticles formed a sort of skin armor that
helped protect the shark. When they were originally named they were
assumed to be from a single species of shark, but we now know that they
occur on a large number of species. therefore, the name "Petrodus
patelliformis" is no longer considered correct. (Nomina Dubia)
This is a picture of several samples of "Petrodi" or dermal denticles from the skin of ancient sharks.
Approximate Age: 310-312 million