Shark Evolution

Most scientists believe that sharks came into existence around 400 million years ago. That's 200 million years before the dinosaurs!

It's thought that they descended from a small leaf-shaped fish that had no eyes, fins or bones. These fish then evolved into the 2 main groups of fish seen today. Bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes – the sharks, skates, rays and chimaera).

The fossil record documents over 3,000 shark species. Yet it's likely many more existed but disappeared without trace. After death, a shark’s skeleton rots away due to it being made of cartilage instead of bone. So, usually the only remains they leave behind are their teeth, dermal denticles and fin spines. But we can tell a lot from a single tooth. From this, scientists can tell what the shark fed on and even identify the species it belonged to.

Shark fossil records are abundant and diverse. They show that some species, living over 150 million years ago, were identical to those existing today. One of the earliest known species was the Cladoselache. Like many other early sharks their mouth was located at the front of their snout. A trait that the Megamouth Shark, Frilled Shark, Angelshark and devil rays still have today.

One fossil tooth, belonging to a Megalodon Shark, measures a massive 17cm in length. Indicating that this enormous predator was as long as two buses! The massive Megalodon is an ancestor of today's infamous White Shark.

Sharks have always dominated the top of the marine food chain. For a brief time they were joined by other huge marine reptiles, such as Mosasaurs and Plesiosaurs. Yet sharks are the only group to have survived to modern day.

The entire history of our planet can be broken down into 4 stages:

THE PRECAMBRIAN SUPEREON

This began with the evolution of the Earth 4.6 billion years ago. It's categorised by a complete lack of animal life.

THE PALEOZOIC ERA (545-250 million years ago)

This period saw the evolution of life from single celled organisms to bony fish and sharks. A rapid increase in the number of shark species occurred during this time. In an age called the Carboniferous some sharks evolved weird and crazy appendages. None of the sharks that lived in the Paleozoic are around today. But all modern day sharks evolved from them.

THE MESOZOIC ERA (250-65 million years ago)

Some of the sharks from the Paleozoic period survived into the Mesozoic. During the Jurassic period there was another rapid increase in the number of shark species. This is when all modern shark families and the skates and rays first evolved. The end of the Mesozoic saw the fall of the great marine reptiles.

THE CENOZOIC ERA (65 million years ago - present day)

Modern sharks and toothed whales (such as the Killer Whale) continued to flourish at the top of the food chain. Hammerheads were the last of the modern shark families to evolve, and did so in the Cenozoic. Their evolution date is estimated at between 50 and 35 million years ago.

Despite surviving 5 mass extinctions, today, many shark species are threatened with extinction. Pressure form damaging human activities means that sharks are now one of the most threatened groups of animals on the planet.

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