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Eitan Tchernov
There are many stories about the origin of snakes
 real 28k

Friday, 17 March, 2000, 12:43 GMT
Discovery challenges snake origins
Snake Science
The limb could have acted as a claw
By BBC News Online science editor Dr David Whitehouse

The view that snakes originally evolved from sea-living lizards may have to be rethought, say scientists who have analysed a fossil serpent with legs.

The creature was found in 95-million-year-old sedimentary rock near Jerusalem. The well-preserved specimen, called Haasiophis terrasanctus, is the second, legged snake species to come from this particular site at Ein Yabrud.

We can't exclude the possibility that limbs in snakes were lost not just once in the beginning, but several times throughout their history

Dr Olivier Rieppel
It was from studies of the first species, called Pachyrhachis problematicus, that researchers got the idea that modern snakes might have descended from giant swimming lizards from the Cretaceous period (144-65 million years ago) called mosasaurs. Pachyrhachis was viewed as an intermediate step, displaying features that lay somewhere in between those of the marine creatures and today's snakes.

But the better detail in the new fossil challenges this theory, claim Dr Olivier Rieppel, of the Field Museum in Chicago, and Professor Eitan Tchernov, of the Hebrew University of Jerusalem.

Their research not only suggests that Haasiophis and Pachyrhachis were closely related, but that the two creatures were actually quite advanced. They do not easily fit into our existing theories on the origins of snakes.

Massive gape

The scientists looked closely at skull features, which are remarkably similar to boas and pythons. These modern snakes have a distinctively mobile skull structure that allows them to nearly unhinge their jaw in a formidable gape. This allows them to eat very large prey. The two fossil snakes look as though they had a similar ability.
Snake Science
The skull of H. terrasanctus viewed from above and below
"We went back and looked very carefully at the skulls of Pachyrhachis, Haasiophis, and lizards like mosasaurs, looking at features like the braincase, the dentition, and the joint in the middle of the lower jaw," says Dr Rieppel.

"The better preservation of Haasiophis allowed us to use its anatomy as a guide, and gave us the background to see just how much these fossils looked like advanced snakes."

And both snakes appear to have unsnake-like hind limbs which researchers speculate have evolved more than once during the snake's evolution.

Scientists suggest that the snakes with advanced skull design regained hindlimbs that were lost by evolution.

Use of claw

"We know of at least 62 lizard and snake lineages that have undergone some degree of limb reduction," Dr Rieppel says. "Since our fossil record of snakes is very poor, we can't exclude the possibility that limbs in snakes were lost not just once in the beginning, but several times throughout their history."

Dr Rieppel says that after studying the new fossils it is difficult to tell how the legs themselves might have been used, since they are too small in relation to the animal's whole body to have been of any use for movement.

Modern pythons have a rudimentary hindlimb, usually little more than a "claw" of cartilage tipped with bone that they use during mating and occasional fighting, and it is possible that the Haasiophis leg served a similar purpose.

The researchers conclude that Haasiophis and Pachyrhachis are not related to primitive mosasaurs. Dr Rieppel says he believes the ancestors of modern snakes were burrowing lizards that lived on land. However, he acknowledges that the West Bank fossils do not provide clear answers to the question.

Professor Tchernov told the BBC that a new project would start shortly to uncover as much material as possible from the rich and well preserved Ein Yabrud site.

"We hope we will come out with other sensational finds," he said. "Because this is very close to Jerusalem, we have this kind of Holy Spirit around this geological section which somehow is associated with the history of snakes."

The research is reported in the journal Science.

Snake Science
The specimen sat in a drawer for some years

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04 Nov 99 | Sci/Tech
Oldest fossil fish caught
16 Dec 99 | Sci/Tech
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