Snake legs it straight out of Eden

Michelangelo seems to have got it at least partly right, when in the Sistine Chapel he depicted the snake in the Garden of Eden as having arms.

Except for one detail: the last things snakes lost was their legs, according to scientists who reckon they have found a 97-million-year-old missing link.

If the details are confirmed of the fossilised skeleton, which was found, appropriately enough, 20km north of Jerusalem, then it may answer one of evolution's great unsolved mysteries: how did lizards lose their limbs and become snakes?

The suggestion is that the most primitive ancestor of the snake, called Pachyrhachis problematicus, evolved during the Cretaceous period between 136 and 165 million years ago.

It had a pelvis and tiny but well-formed hind limbs, which would fit with the fact that modern-day boa constrictors have traces of a pelvic girdle, and even have limited vestiges of back legs.

Michael Caldwell, of Alberta University, Edmonton, and Michael Lee, of Sydney University, reckon that Pachyr- hachis problematicus may have lived in the sea before its descendants moved onto dry land.

Because snake skeletons are delicate structures, they tend not to form clear fossils, leading to gaps in the evolutionary table.

"The search for the origin of snakes has proved to be a thorn in the side of vertebrate paleontologists," commented Nicholas Fraser, of the Virginia Museum of Natural History.

The appropriately-named Pachyrhachis problematicus was originally classed as a snake, and then as a lizard, when it was discovered 20 years ago.

But the Canadian and Australian fossil hunters, who report their work today in the science journal Nature, found new evidence that Pachyrhachis problematicus is really the most primitive snake. It has a snake-like head, a long, slender body, no forelimbs but well-developed hind limbs.

They further claim that snakes are related to a group of lizards which include the present-day monitors, such as the Komodo Dragon, from Asia.

This group includes several kinds of extinct sea-lizard, which may be the distant ancestors of snakes. Best known of these are the mosasaurs, giant sea monsters that died out at the same time as dinosaurs, 65 million years ago.