Washington, July 05: The baffling mystery of how animals crawled onto land, scientists hope, will soon be solved by the rediscovery of a fishy four-legged fossil in Scotland, reported the `New Scientist` journal.
A possible animal `bridge` was always a necessity for paleontologists to demystify the critical evolutionary gap between 335 million and 365 million years ago when aquatic animals first made it out of the water.
The new creature, a type of tetrapod, is the only intact skeleton from this time period ever unearthed. It resembles an ungainly crocodile with a whip-like tail and the three-foot long amphibian had the sensory apparatus of a fish, but limbs and feet adapted for life on solid ground, the report adds.
About 345 million years old, this one-of-a-kind fossil has been dubbed Pederpes, meaning rock crawler. "It`s by far the earliest leg that looks like it could have been used on land," says Jennifer Clack, University Museum of Zoology in Cambridge, UK.
From this time gap, previously only a few fragments of tetrapod legs and shoulders had been found in Canada. Before the gap, tetrapods had evolved limbs for paddling, but not walking.
Immediately after the gap, they were running all over the land. Pederpes could help scientists comprehend exactly how the change happened, says paleontologist Robert Carroll of McGill University. "It`s giving us an idea of what changes were made in what sequence and over what period of time," he says. It could also help scientists to understand the interrelationships of all the land vertebrates that followed, he adds.
Collected in 1971, the fossil discovery was a stroke of luck, says Clack. Misidentified as a type of fish called a rhizodont, it was relegated to the basement of the Hunterian Museum in Glasgow where it lay there for 25 years until one of Clack`s graduate students picked it up while trawling for rhizodonts for his dissertation work. When he brought it back to Cambridge, Clack saw immediately that it was in fact an early tetrapod.
"When we combined it with the date, it was like finding the Holy Grail," she says.