When did the first shark appear?

As of August 2014, the earliest generally accepted shark fossils are dated to the Silurian period, 400 to 420 million years ago. Finding fossil evidence of sharks is more difficult than for bony fish because shark skeletons do not fossilize well. Modern sharks date back about 100 million years.

There are over 470 species of shark living in modern times. Extinct types range from the 3.3-foot-long Cladoselache to the giant megalodon, a predatory shark that may have reached a length of 67 feet compared to a maximum of about 26 feet for the modern great white shark and 46 feet for the whale shark.