Fossil records suggest that at one point in history, there were more than 3,000 types of sharks and their relatives. Sharks managed to survive during extinction events when the ocean lost its oxygen – including the die off during the Cretaceous period, when many other large species were wiped out.
While much of life became extinct during the End-Cretaceous extinction event, including all non-avian dinosaurs, sharks once again persisted.
Sharks have survived many mass extinction during their presence of 450 million years on Earth. Scientists believe that their ability to repair damaged DNA has helped them survive over the years. Their presence on the planet over millions of years have earned them the title of living fossil.
Sharks Have Survived Four Mass Extinctions, But Now, They're Endangered. They're older than the dinosaurs, they've survived four mass extinctions, and yet today, in the wake of climate change, pollution, and commercial fishing, sharks are endangered.
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.
Land walking is a more recent trend for the epaulette sharks, as only younger members of the species have been recorded doing it. Utilizing their fins as leg-like appendages, the sharks search for prey in reef regions where other sharks can not tread.
Scientists credit Triops cancriformis as the oldest animal species. Other species may not be quite so old, but the natural histories of the species are similar.
“It's a great mystery,” Elizabeth Sibert, a paleobiologist and oceanographer at Yale University, told Science News. “Sharks have been around for 400 million years. They've been through hell and back. And yet this event wiped out (up to) 90% of them.”
Nevertheless, a handful of sharks die of old age or at least get so old that they lose their faculties until they can no longer feed or compete for food. Some may starve to death due to a loss of vision, while others may struggle to fend off disease as the result of a weakened immune system.
And if they were to disappear, the repercussions on ocean food webs would ultimately affect humans, too. "Fisheries may collapse, with artisanal fishers being the likely most affected, and popular tourism destinations which rely on sharks to attract tourists will also suffer greatly," Bortoluzzi said.
Birds: Birds are the only dinosaurs to survive the mass extinction event 65 million years ago.
Because sharks have been around and at the top of their game for so long, they have evolved so their DNA can repair itself and is more tolerant to damage. "Genome instability is a very important issue in many serious human diseases," says study co-leader Dr Mahmood Shivji.
Even though megalodons and dinosaurs are both extinct, they never coexisted. The dinosaurs died out about 66 million years ago. Megalodons came later. The oldest megalodon fossils are from the Miocene Epoch, which began 23 million years ago.
Internet rumors persist that modern-day megalodons exist – that they still swim around in today's oceans. But that's not true. Megalodons are extinct. They died out about 3.5 million years ago.
However, this just isn't the case. Sharks do not attack people for fun or for revenge, therefore we cannot treat sharks like we would a human villain committing a crime. In other words, there is no one to punish.
Instead, these sharks rely on obligate ram ventilation, a way of breathing that requires sharks to swim with their mouths open. The faster they swim, the more water is pushed through their gills. If they stop swimming, they stop receiving oxygen. They move or die.
So, while most sharks will be 100% fine if they stop swimming, a few iconic species such as great white sharks, whale sharks, hammerheads and mako sharks would suffocate without forward motion or a strong current flowing towards their mouths.
In a significant development in evolutionary studies, scientists have found that human beings evolved from a prehistoric shark which existed more than 300 million years ago. According to a new research, primitive fish named Acanthodes bronni was the common ancestor of all jawed vertebrates on Earth - including humans.
The global population of sharks and rays has crashed by more than 70% in the past 50 years, researchers have determined for the first time, with massive ongoing losses pushing many species towards extinction.
Sharks have roamed the world's oceans for hundreds of millions of years. In that time, many species have barely changed. But some strange sharks are still evolving—and have even learned to walk.
Coelacanth – 410 MYA
The oldest Coelacanth fossils are only 410 million years old, predating dinosaurs, trees, and sharks by a large margin. They were originally considered to have gone extinct 66 million years ago but were found off the coast of South Africa.
That said, two mammals that have undergone the fewest evolutionary shifts are the platypus and the opossum, says Samantha Hopkins, associate professor of geology at the University of Oregon.
However, because jellyfish are soft-bodied and almost all water, jellyfish fossils are incredibly rare. Of those that do exist, the oldest-known jellyfish fossils, found in Utah, date to 505 million years ago and have enough detail to show clear relationships with some modern species of jellyfish.