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Most scientists believe that sharks came into existence around 400 million years ago (200 million years before the dinosaurs) and descended from a small leaf shaped fish that had no eyes, fins or bones. Ancestral fish evolved and diverged into the two main groups seen today; Osteichthyes (bony fish) and Chondrichthyes (cartilaginous fish).
The fossil record documents over 3,000 types of shark and their relatives, however 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 are its teeth, dermal denticles and fin spines. Although from a single tooth scientists can tell what the shark fed on and even identify the species.
The fossil records of sharks are abundant and diverse. Some fossil species that lived over 150 million years ago are identical to sharks that exist today. One of the earliest known species is the Cladoselache, which lived about 350 million years ago, like many other early sharks their mouth was located at the front of their snout. The Megamouth Shark, Frilled Shark, Angelshark and devil rays still have this today, whereas most sharks have evolved a mouth under their snout. One fossil tooth belonging to the Megalodon Shark (ancestor of the White Shark), was recorded at 17cm suggesting an enormous predator as long as two buses!
Sharks have either shared or solely owned the position at the top of the marine food chain for over 400 million years. Massive marine reptiles, such as Mosasaurs and Plesiosaurs, briefly joined them as apex predators but sharks are the only group to have survived to modern day.
There are four periods that make up the entire history of planet Earth:
This began with the evolution of the Earth 4.6 billion years ago and is categorised by a complete lack of animal life.
THE PALEOZOIC (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 a number of 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 these species.
THE MESOZOIC (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 where all modern shark families and the skates and rays first evolved.
THE CENOZOIC (65 million years ago - present day)
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. Following the fall of the great marine reptiles at the end of the Mesozoic, only modern sharks and toothed whales (such as the Killer Whale) remained at the top of the food chain.
Despite miraculously surviving five mass extinctions, many species of shark are currently under threat and need our help. Find out how you can help by visiting our Get Involved page.
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