Sharks are hardly newbies on our planet. As a group, they have existed for at least 450 million years , surviving four of the "big five" mass extinctions, including the catastrophe that wiped out the nonavian dinosaurs 66 million years ago at the end of the Cretaceous period.
Sharks are close relatives of skates, rays and chimeras, all of which belong to a group of fish known as the chondrichthyes, which are distinct in that most of their skeleton is made of cartilage rather than bone. Gene expression studies in skates have shown their adaptability when the waters they inhabit change several degrees in temperature. For example, a population of winter skate living in the southern Gulf of St.
This versatility likely underpins sharks longevity as a group, said Gavin Naylor, director of the Florida Program for Shark Research. For instance, sharks are found in different parts of the water column — living in deep oceans, shallow seas and even rivers — and can gobble up an array of food, including plankton, fish, crabs, seals and even whales, according to the Natural History Museum in London.
"Sharks have been able to deal with climatic changes in the past fairly well, but the biggest challenge to the world's sharks and rays today is overfishing," Naylor said."There are no clever tricks that these animals can resort to to contend with being fished out of the water."—Why do turtles live so long?"The effects of pollution, contaminants and habitat loss also likely factor into their loss in some places," Lowe added.