Common ancestor of sharks and humans existed 440 million years ago, study reports

Avatar By Joseph Scalise | 3 years ago

Though humans and sharks are incredibly different creatures, both shared a common ancestor roughly 440 million years ago, a recent study published in the journal Royal Society B: Biological Sciences reports.

This discovery comes from a group of researchers at the University of Chicago, who analyzed fossils from a shark that lived during the Devonian period. That age is when four-legged animals first began to move onto land, and looking at the specimen allowed the team to determine that sharks and the ancestors of humans split sometime during the Silurian period, which took place 443 million to 416 million years ago.

Scientists first discovered the ancient shark — known as Gladbachus adentatus — in 2001. However, though it had already been described, the group in the recent study decided to take another look because of its age, unique anatomy, and preservation.

Most shark fossils are simply a mix of tiny scales and teeth. However, the 2.6-foot-long G. adentatus has an articulated skeleton, meaning that its bones are still in place. The remains suggest the species had a wide mouth and splayed-out gills.

“The body is preserved as a sheet of prickly scales,” said lead author Michael Coates, a professor in the Department of Organismal Biology and Anatomy at the University of Chicago, according to Live Science. “The skeleton of the head has a very course grain to it, almost like the pattern of tree bark.”

G. adentatus is one of the earliest known sharks on record. After analyzing it with a high-resolution computed tomography scan, researchers discovered that the ancient fish represents the tip of a branch from the base of the shark family tree. As a result, it gives new insight into early shark diversity and sheds more light on how the predators developed over time.

Not only does this new information show that at least 440 million years have passed since humans and sharks shared a common ancestor, but it also reveals that several early shark lineages converged on what scientists now recognize as classic shark-like features, such as having a long throat with multiple gill slits.

Researchers used to believe multiple gill slots were a primitive feature, but the new study shows they are not.

“These serial gill slits represent an early specialization, and, we argue, this specialization is for filter feeding, somewhat like a modern basking shark,” Coates noted.

The team plans to further study the ancient specimen to see what else they can unearth about the ancient fish. Shark evolution is a mystery, and studies such as this one help researchers better understand the changes the species went through over the years.