Today's sharks are descended from relatives that swam alongside dinosaurs in prehistoric times. It lived just after the dinosaurs, 23 million years ago, and only went extinct 2.6 million years ago.
Competition from other predators of marine mammals, such as macropredatory sperm whales which appeared in the Miocene, and killer whales and great white sharks in the Pliocene, may have also contributed to the decline and extinction of megalodon.
Sharks are among Earth's most ancient creatures. First evolving over 455 million years ago, sharks are far more ancient than the first dinosaurs, insects, mammals or even trees.
Like today's largest sharks, megalodon also faced competition from a giant whale that hunted the same prey. Its name was Livyatan, and it was a ferocious competitor to megalodon. Livyatan was about the same size as the massive shark, weighing an estimated 100,000 pounds and reaching up to 57 feet in length.
What's the biggest shark?
Until 2014, scientists believed that great whites only lived to around 25 – 30 years. However, new findings show that great white sharks may live up to 70 years, decades longer than the previous estimates. Scientists now believe that great white sharks take much longer to mature and age similar to humans.
The earliest fossil evidence for sharks or their ancestors are a few scales dating to 450 million years ago, during the Late Ordovician Period. Analysis of living sharks, rays and chimaeras suggests that by around 420 million years ago, the chimaeras had already split from the rest of the group.
They even managed to survive during times when the ocean lost its oxygen - including one such event in the Cretaceous period, when many other, larger, species died out. As a refuge, sharks moved deeper underwater, says Bird. And while there, they had another cunning trick. Some evolved the ability to glow in the dark.
The oldest confirmed shark scales were found in Siberia from a shark that lived 420 million years ago during the Silurian Period, and the oldest teeth found are from the Devonian Period, some 400 million years ago. Based on these fossils, more than 2,000 species of fossil sharks have been described.
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. After death, a shark's skeleton rots away due to it being made of cartilage instead of bone.
about 530 million years ago
One way to survive in an ocean full of other predators is to be fast. So many sharks are built for speed. Shark skin is made up of tiny V-shaped scales called dermal denticles, because they resemble teeth more than fish scales. These skin denticles decrease drag in the water and help sharks glide more quietly.
How many years ago was the Devonian period?
419.2 (+/- 3.2) million years ago - 358.9 (+/- 0.4) million years ago
This decline has occurred largely due to destructive and unsustainable fishing techniques.
Sharks have a tongue referred to as a basihyal. The basihyal is a small, thick piece of cartilage located on the floor of the mouth of sharks and other fishes. It appears to be useless for most sharks with the exception of the cookiecutter shark.
We need to protect these apex predators before they disappear and their absence wreaks havoc on our ecosystems. It averages out to two to three sharks killed every second, over 11,000 every hour, over a hundred million every year.
They died out at the end of the Permian, 251 million years ago, killed by the end Permian mass extinction event that removed over 90% of all species on Earth. They were very diverse for much of the Palaeozoic, and today trilobite fossils are found all over the world.
Sharks don't feed their young with milk, neither do they have hair or lungs. Sharks are cold-blooded, whereas mammals are warm blooded. This all means that sharks definitely aren't mammals!
