'Prehistoric fish extinction allowed humans to evolve'

If it had not occurred, humans and their ancestors may not have evolved, or could have evolved very differently, said researchers from the University of Chicago.

According to them, key features shared by all modern mammals, birds and reptiles -- such as five-digit limbs -- originated when life re-emerged after the mass extinction, the Daily Mail reported

"Everything was hit, the extinction was global," said lead researcher Lauren Sallan.
"It reset vertebrate diversity in every single environment, both freshwater and marine, and created a completely different world."

The Devonian Period, which stretched from 416 to 359 million years ago, is also known as the Age of Fishes. A broad array of species filled the oceans, rivers and lakes, but most were unlike any alive today, the researchers said.

Armoured placoderms, such as monstrous 30-foot carnivore Dunkeosteus, and lobe-finned fishes similar to modern lungfish dominated the waters, while ray-finned fishes, sharks and four-limbed tetrapods were in the minority.

But the picture changed abruptly with the traumatic Hangenberg extinction.
"There's some sort of pinch at the end of the Devonian," said Prof Michael Coates, from the University of Chicago.

"It's as if the roles persist, but the players change: the cast is transformed dramatically.
"Something happened that almost wiped the slate clean and, of the few stragglers that made it through, a handful then re-radiate spectacularly."

According to the scientists, new fossil finds and analytical techniques brought to light the full impact of the Hangenberg event.

However, what happened to trigger the mass extinction still remains an unsolved mystery. Many believe that substantial glacier formation at the end of the Devonian would have dramatically affected sea levels.

The first appearance of forest-like environments may also have produced atmospheric changes with catastrophic consequences for life.

"It is a pivotal episode that shaped modern vertebrate biodiversity," said Professor Coates.

"We are only now beginning to place that important event in the history of life and the history of the planet, which we weren't able to do before."

The research is published in the journal Proceedings of the National Academy of Sciences.