Tuesday 23 September, 2014

Research suggests humans evolved from prehistoric sharks

Published On: Thu, Jun 14th, 2012 | Evolution | By BioNews

Believe it or not – humans evolved from a prehistoric shark that populated the seas more than 300 million years ago, according to scientists.

The ancient fish called Acanthodes bronni was the original father of all jawed vertebrates on Earth – including humans. A re-analysis of a braincase dating back 290 million years shows it was an early member of the modern gnathostomes, ‘jaw-mouths’ that include tens of thousands of living vertebrates ranging from fish to birds, reptiles, mammals and humans.

Acanthodes, Greek for ‘spiny’, existed before the split between the earliest sharks and the first bony fishes – the lineage that would include human beings. Fossils have been found in Europe, North America and Australia.

Compared with other spiny sharks it was larger, measuring a foot long. It had gills instead of teeth, large eyes and lived on plankton, the journal Nature reports.

The Daily Mail quotes Michael Coates, professor of biology at the University of Chicago, as saying, “Unexpectedly, Acanthodes turns out to be the best view we have of conditions in the last common ancestor of bony fishes and sharks.”

“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,” added Coates.

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. But armed with new data on what the earliest sharks and bony fishes looked like, the researchers re-examined fossils of Acanthodes bronni, the best-preserved species.

The analysis of the sample combined with recent scans of skulls from early sharks and bony fishes led the researchers to a surprising reassessment of what Acanthodes bronni tells us about the history of jawed vertebrates.

“For the first time, we could look inside the head of Acanthodes, and describe it within this whole new context. The more we looked at it, the more similarities we found with sharks,” said Coates.

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

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