Palaeontologists have found a 400 million-year-old coelacanth fossil fin, which they say, fills the shrinking evolutionary gap between fins and limbs.
Washington, Aug 2 : Palaeontologists have found a 400 million-year-old coelacanth fossil fin, which they say, fills the shrinking evolutionary gap between fins and limbs.
University of Chicago scientists, who have described the finding in a paper in the July/August 2007 issue of Evolution and Development, say the fossil pattern is similar to the branching arrangement still embedded in the fins of paddlefishes, sturgeons and sharks.
"This ends intense debate about the primitive pattern for lobed fins, which involves the ancestry of all limbs, including our own," said author Michael Coates, Ph.D., associate professor of organismal biology and anatomy at Chicago.
"To understand the developmental evolution of the limbs of tetrapods [four-limbed vertebrates], we shouldn't be looking at the fins of our nearest living fish relatives-lungfishes and coelacanths-because they're far too specialized," he said.
"Part of the reason why this is an interesting discovery is that people think of coelacanths animals as archetypal living fossils. But it's a common misconception. If you look deep in the fossil record to the first members of that group, they are really different and very diverse," added Matt Friedman, evolutionary biology graduate student at Chicago and lead author of the paper.
Until now, many biologists have looked at lungfish as a primitive model of the evolution of tetrapods.
But, according to Friedman, both lungfish and coelacanth - the two living groups of close fish relatives of tetrapods - acquired many of the same specializations independently of one another.
"They give this perception that maybe those are general characters, but we can show with fossils like this one that they've actually developed specializations in tandem," Friedman said.
"With this fossil, we have a conservative pattern in a close relative of tetrapods that is actually conserved in other fish groups outside of this immediate group. Not only does this fossil bridge the gap between primitive ray-finned fish and limbed animals like Tiktaalik roseae, the new data forces scientists to reassess the characteristics of the coelacanths," he said.
ANI