Shark history is known mainly from the preservation ability of their hard
resilient calcium phosphate teeth.
It is unusual to find shark skeletons or impressions in the fossil record
since this would require a low energy, anoxic environment with an extremely
rapid burial rate; otherwise the cartilaginous skeleton would decompose
and the individual apatite (calcium phosphate) minerals which overlay the
cartilaginous skeleton would be transported to another location.
Since some sharks lose teeth at a rate of one every four hours, the number
of recovered fossilized teeth is extremely high.
Shark teeth are the most common vertebrate fossil.
Impression of Palaeobates fin
Spray River Formation, Triassic
Fossil Fish Lake, B.C.
Cat # NMC 9980