August 31, 2005

First land animals may have shuffled not walked

LONDON (Reuters) - The first four-limbed animals on land may not have hopped or waddled but rather shuffled like modern-day caterpillars, according to new research published in the science journal Nature.

Scientists from Uppsala University in Sweden and McGill University in Canada came to these conclusions after studying the fossils of the Ichthyostega -- a four-legged fish that lived around 360 million years ago.

They noted that the construction of the creature's backbone ruled out wriggling in a fish-like side-to-side motion, but instead suggested a ripple-like forwards movement.

The creature would have used its hind legs to pull its tail forward, arching the spine as it did so. It would then have smoothed out the arch by using its forelegs to pull the front section forward, the scientists wrote.

"Two gaits seem theoretically possible: 'walking' with diagonally synchronized limb movements and rigid elevated trunk; and a bilaterally symmetrical 'shuffling' or 'inchworm' movement," they said, adding that more research was needed.

"Ichthyostega appears to be an early and ultimately unsuccessful attempt at adapting the tetrapod body plan for terrestrial locomotion, divergent but not very remote from the lineage that ... ultimately gave rise to all living tetrapods," the scientists wrote.