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Could ancient fish with legs be our evolutionary missing link?

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Could it be possible that hind legs evolved from legs? According to The Huffington Post on Tuesday, the closest known relative of the ancestors of limbed animals such as humans likely evolved the foundation for rear legs even before the move to land.

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Paleontologists led by Prof Neil Shubin from the University of Chicago have discovered unique fossils of Tiktaalik roseae – the most compelling example yet of a creature that was at the cusp of the fish-tetrapod transition.

Until now, the only specimens of Tiktaalik researchers had examined were of its front portions. To find out more about the fish, researchers investigated additional blocks of rock recovered from the dig site where Tiktaalik was discovered.

Scientists investigated fossils of a 375-million-year-old fish known as Tiktaalik roseae, discovered in 2004 in northern Canada's Ellesmere Island. Possessing a broad flat head and sharp teeth, Tiktaalik resembled a cross between a fish and a crocodile, growing to a length of 9 feet (2.7 meters) as it hunted for prey in shallow freshwater.

Corresponding author of the study Doctor Neil Shubin, of the University of Chicago, said: 'Previous theories, based on the best available data, propose that a shift occurred from 'front-wheel drive' locomotion in fish to more of a 'four-wheel drive' in tetrapods.

'But it looks like this shift actually began to happen in fish, not in limbed animals.'

Tiktaalik roseae lived in Devonian period around 375 million years ago. It was a predator with sharp teeth, a crocodile-like head and a flattened body. The animal looked like a cross between a fish and a crocodile, growing up to a length of 9 feet as it hunted in shallow freshwater environments.

“It’s reasonable to suppose with those big fin rays that Tiktaalik roseae used its hind fins to swim like a paddle. But it’s possible it could walk with them as well. African lungfish living today have similarly large pelves, and we showed in 2011 that they walk underwater on the bottom,” Prof Shubin said.

Shubin cautioned that Tiktaalik is not the ancestor of all limbed vertebrates. It is currently the closest known relative, "but not the sole, direct ancestor," he said. "It is more like our closest cousin."

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