They can be found, swimming slowly, throughout the cold, deep waters of the North Atlantic. With this leisurely pace of life and sluggish growth rate, the sharks were thought to live for a long time. But until now, determining any ages was difficult. For some fish, scientists are able to examine ear bones called otoliths, which when sectioned, show a pattern of concentric rings that scientists can count as they would the rings in a tree.
Sharks are harder, but some species, such as the Great White, have calcified tissue that grows in layers on their back bones, that can also be used to age the animals. However the team found a clever way of working out the age. So we can isolate the tissue that formed when the shark was a pup, and do radiocarbon dating. The team looked at 28 sharks, most of which had died after being caught in fishing nets as by-catch.
Using this technique, they established that the largest shark - a 5m-long female - was extremely ancient. Because radiocarbon dating does not produce exact dates, they believe that she could have been as "young" as or as old as But she was most likely somewhere in the middle, so about years old. Fossil teeth show that the asteroid strike at the end of the Cretaceous killed off many of the largest species of shark. Only the smallest and deep-water species that fed primarily on fish survived.
Sharks soon began to increase in size once again, and continued to evolve larger forms throughout the Palaeogene 66 to 23 million years ago.
It was during this time that Otodus obliquus , the ancestor to megalodon Otodus megalodon , appeared. Despite what many might think, megalodon is not related to great white sharks. In fact it may have been in competition with the great white shark's ancestors, which evolved during the Middle Eocene 45 million years ago from broad-toothed mako sharks.
There are at least eight different species of hammerhead shark, and while fossil teeth evidence suggests that their ancestors may have existed 45 million years ago, molecular data points to a much more recent appearance during the Neogene which began 23 million years ago.
The strange shape of their head is thought to mainly help in electroreception the detection of naturally occurring electric fields or currents as they hunt for prey. It may also improve their vision, enhance their swimming and refine their ability to smell. Since the End-Cretaceous mass extinction, sharks have come to dominate the oceans once again, returning to the role of apex predator along with large marine mammals.
Because most of the skeleton of sharks is made from soft cartilage, it takes special conditions for this to preserve. The teeth, however, are made from a much tougher material known as dentin, which is harder and denser even than bone.
While this enables a powerful bite, it also increases the chance that the teeth will fossilise as they are less likely to decompose. The other reason is simply numbers. Rather than having just a few sets of teeth that last all their life, sharks are continually producing new teeth.
As an older one breaks or wears down, it simply falls out of the front of the mouth and onto the sea floor, as a new tooth takes its place. Depending on species and diet, over its entire lifetime a shark can produce between 20, and 40, teeth.
This means that there is a much greater chance that a shark tooth will be preserved and turned into a fossil. Not only are the teeth the most common part of sharks to be found, they're one of the most common fossils of any organism. There is no single reason sharks survived all five major extinction events - all had different causes and different groups of sharks pulled through each one.
One general theme, however, seems to be the survival of deep-water species and the dietary generalist. It is possible that shark diversity may also have played an important role. Emma explains, 'I think it is safe to say that it is partly because sharks are able to exploit different parts of the water column - from deep, dark oceans to shallow seas, and even river systems. They eat a wide variety of food, such as plankton, fish, crabs, seals and whales.
This diversity means that sharks as a group are more likely to survive if things in the oceans change. One thing we do know, according to Devine, is that female Greenland sharks might not reach sexual maturity until years old. To put that into perspective, the person widely considered to be the oldest human to have ever lived, Jeanne Calment, died at the age of , having outlived her own grandchildren.
A Greenland shark born on the same day as Calment would still have been awaiting shark puberty when she died. Cameron is a contributing writer covering life sciences for Live Science. He holds a master's degree in animal behavior from Western Carolina University and teaches at the University of Northern Colorado. Live Science. Environment COP26 nears conclusion with mixed signals and frustration. Environment Planet Possible India bets its energy future on solar—in ways both small and big.
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