'Walking' lungfish's evolution clue

The new detailed study of lungfish locomotion shows they commonly use their thin, limb-like rear fins to raise their body up and propel it forward.

Lungfish demonstrate both "bounding" motion, where both limbs moved at once, and "walking", marked by alternating limbs.

Such abilities were previously thought to have originated in early tetrapods, the first limbed land-dwellers.

Scientists now think they may have developed much longer ago, with the ancestors of the lungfish.

The US research also raises the possibility that fish, not land animals, left some of the fossil tracks long believed to have been produced by early tetrapods.

"In a number of these trackways, the animals alternate their limbs, which suggested that they must have been made by tetrapods walking on a solid substrate," said lead scientist Dr Melina Hale, from the University of Chicago. "We've found that aquatic animals with fundamentally different morphologies and that aren't tetrapods could potentially make very similar track patterns."

The research is reported today in the journal Proceedings of the National Academy of Sciences.
It suggests that many of the developments necessary for the transition from water to land may have occurred long before early tetrapods took their first steps.

Lobe-finned ancestors of lungfish could have evolved hindlimb propulsion and the ability to walk millions of years before toed limbs and land-dwelling animals appeared.

"This shows us - pardon the pun - the steps that are involved in the origin of walking," said co-author Professor Neil Shubin, also from the University of Chicago.

"If you showed me the skeleton of this creature and asked me to make a bet on whether it walks or not, I would have bet it couldn't. Their fins seem like the furthest thing from walking appendages possible. But it shows what's possible in an aquatic medium where you don't have to support yourself with gravity."

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