Scientists have discovered 375-million-year-old fossils that they say appear to be the missing link in the evolution of fishes to four-legged land animals. Paleontologists report in the current issue of Nature that the newly discovered species had a bizarre mixture of fish and land animal features. Scientists say the discovery ends speculation about what the transitional creature looked like.
Paleontologists discovered the three fossils in the frozen tundra of Canada's Ellesmere Island, near the North Pole.
Scientists named the well-preserved, skeletons tiktaalik, the largest of which is 2.7 meters. The remains of the two other creatures are 0.9 meters.
Until now, paleontologists could only guess that the transitional fish had four limbs, like the evolved land animals known as tetrapods, according to Ted Daeschler of the Academy of Natural Sciences in Philadelphia, a member of the expedition team.
"But we never really had a good transitional form, something that really showed us both fish features, as well as features that appeared in the earliest tetrapods," he said.
Commenting in the journal, Nature, evolutionary biology Professor Per Ahlberg of Uppsala University in Sweden calls the discovery of tiktaalik very exciting, because it fills a frustrating gap in the evolutionary record, and it is a nice fit.
Ahlberg says tiktaalik turns out to look very much as expected.
"I think, if you had seen one of these animals alive, the impression would have been a very peculiar cross between a small crocodile and the fish, sort of like an alligator's head stuck on to a fish body to an extent, or, perhaps, an alligator head and body, but with fish fins rather than front legs and back legs," said Ahlberg. "That is the sort of impression it would have made."
Experts say tiktaalik showed early evidence of fingers and wrists, arms, elbows and shoulders to pull itself out of the water.
They say the creature probably lived most of its life in the water, but could get around well on land, with the anatomical features that were early predecessors of the arms and legs of reptiles, dinosaurs, mammals and eventually humans.
The Academy of Natural Science's Ted Daeschler and colleagues from the University of Chicago and Harvard University plan to return to Ellesmere Island in search of more prehistoric links between water creatures and tetrapods.
"And we have got to go out there and look," he said. "There is no way we will get these answers, unless we put our feet on the ground and our nose to the rock."