`Humans evolved from a prehistoric shark`

Last Updated: Thursday, June 14, 2012 - 19:04

London: 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.

A re-analysis of the fish braincase dating back to 290 million years shows it was an early member of the modern gnathostomes (jaw bearing animals) that include a range of vertebrates from fishes, birds, reptiles, mammals and humans, the Daily Mail reported.

Acanthodes, a Greek word for `spiny`, existed before the split between the earliest sharks and the first bony fishes - the lineage that would eventually include human beings and its fossils have been found in Europe, North America and Australia.

As compared to the other spiny sharks Acanthodes was relatively large, measuring a foot long. It had gills instead of teeth, large eyes and lived on plankton.

"Unexpectedly, Acanthodes turns out to be the best view we have of conditions in the last common ancestor of bony fishes and sharks," Professor Michael Coates, a biologist at the University of Chicago, said.

"Our work is telling us the earliest bony fishes looked pretty much like sharks, and not vice versa. What we might think of as shark space is, in fact, general modern jawed vertebrate space," Coates said.

Cartilaginous fish, which today include sharks, rays, and ratfish, diverged from the bony fishes more than 420 million years ago. But little is known about what the last common ancestor of humans, manta rays and great white sharks looked like.

The acanthodians died out about 250 million years ago and generally left behind only tiny scales and elaborate suits of fin spines.

"They are much better than scales, teeth or fin spines, which, on their own, tend to deliver a confusing signal of evolutionary relationships," Coates said.

The study found acanthodians as a whole, including the earliest members of humans` own deep evolutionary past, appear to cluster with ancient sharks.

This new revision of the lineage of early jawed vertebrates will allow paleontologists to dig into deeper mysteries, including how the body plan of these ancient species transformed over the transition from jawless to jawed fishes.

PTI



First Published: Thursday, June 14, 2012 - 18:48

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