Sharks have definitely evolved since the Devonian, although they’re basic design has enabled them to survive without changing much. The first true shark, Cladoselache, came around 380 million years ago, in the VERY late Devonian. It was unlike most sharks because of its weaker jaw. During the Carboniferous period, when Cladoselache was around, sharks were the most abundant the earth would ever see. It is composed of 45 families of sharks, compared to the 40 that we have today. The most peculiar, Helicoprion,  had a spiral shaped jaw that was lined with dozens of teeth. These types of sharks were successful, surviving until the Permian, where geological and environmental changes brought on by volcanic activity led to the extinction of 95% of the marine life. Then new sharks evolved, called the hybodonts. They too, were successful enough to survive for ages, or more specifically, the Age of Dinosaurs. They reigned supreme until that massive extinction, where the neoselachians took the throne. Around that time, a truly amazing shark evolved. It had jaws that were so wide it could swallow a cow. A reconstruction of those jaws can be seen at the American Museum of Natural History in New York. Its name was Megalodon. Different size estimates put it at around 60 feet long! It had an insatiable appetite for anything it came across, such as dolphins, whales, and even other sharks! You can find a lot more on Megalodon on my Famous Sharks Page. Eventually, Megalodon went extinct, and modern sharks started to take power. Overall, sharks have a long and interesting history.

Image credit: Nobumichi Tamura/Stocktrek Images

Cladoselache swimming through the carboniferous seas.

Helicoprion was the strangest shark of all time because of its peculiar jaw

image credit: James St. John

The Megalodon had truly humongous jaws!

Image credit: American museum of Natural History