Sharks are among the most primitive of fish, first appearing in the fossil record almost 400 million years ago. The shark differs from other fish in that it has no bone in its skeletal structure. Its frame is composed of cartiliginous material. Usually the teeth are the only hard parts found preserved although the occasional vertebra has been found ossified. These early sharks resembled modern sharks but were usually much smaller than many today.

Modern sharks first appeared in the Jurassic some 200 million years ago. Most Jurassic sharks were of moderate size but when the marine reptiles, the mosasaurs and plesiosaurs, died out at the end of the Cretaceous sharks became the dominant predators in the seas. They culminated in the giant of them all. Carcharodon, was a relative of the great white shark which still survives. Great whites today can reach lengths of 20 feet with 3 inch teeth. Carcharodon was over 50 feet in length and had teeth 8 inches long set in jaws that were over 6 feet wide.