Fin to limb
A modern-day coelacanth fish
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Wednesday, 01, Aug 2007 02:09
A 400 million-year-old fossil has helped scientists to fill in part of the gap in knowledge about how limbs evolved from fins.
The fossil of a fin from the coelacanth fish was excavated from Paleozoic sediments at Beartooth Butte in northern Wyoming, US.
People have dubbed the fish 'old four-legs' because of its limb-like fins, and after it was first discovered suggestions were made that it would use its fins to walk around the seabed.
Researchers now know it hovers just above the seafloor using an organ in its nose to detect living things in the mud.
Scientists from the University of Chicago say the fossil shows that the ancestral pattern of fins resembles the pattern in the fins of primitive living ray-finned fishes.
"This ends intense debate about the primitive pattern for lobed fins, which involves the ancestry of all limbs, including our own," said author Dr Michael Coates.
Writing in the journal Evolution & Development, the researchers argue that the fossil bridges the gap between primitive ray-finned fish and limbed animals like Tiktaalik roseae, a fish-like creature with four limbs which lived hundreds of millions of years ago.
"If you're going to figure out how limbs evolved, you need to have a good idea about pre-conditions," said the study's lead author Matt Friedman.
"You need to know what the ancestral morphology was. With things like this [fossil], we're beginning to hone in on the primitive conditions of fins that gave rise to limbs later on."