Printer Friendly

Retelling the tale of the two-legged snake.

In 1978, the late geologist George Haas, working near Jerusalem, found the fossil of a sinuous, meter-long creature with two stubby rear legs. He called it a lizard. When Michael W. Caldwell and Michael S.Y. Lee reexamined the bones recently, they came to a different conclusion.

"It's the missing link between the snake and the lizard," says Lee, a paleontologist at the University of Sydney in Australia. The reclassification challenges the dominant theory that snakes evolved solely from burrowing lizards, since the Israeli fossil represents an aquatic creature. The two scientists posit in the April 17 Nature that modern snakes descended from giant sea lizards called mosasaurs, which became extinct with the dinosaurs.

Caldwell and Lee did a bone-by-bone comparison between the 97-million-year-old fossil, Pachyrhachis problematicus, and other animals. The fossil resembles a snake in that it has mobile jaws and a narrow skull that fully encloses the brain. The fossil's an kles have two distinct bones that in land lizards are fused.

Both the fossil and the mosasaurs have a pelvic girdle and tiny rear limbs. Some living snakes, such as the boa constrictor, contain traces of a pelvis and bony knobs that could be the vestiges of limbs. Even though the fossil's centimeters-long rear legs are fully formed, they were probably too small to serve any purpose, suggesting that over generations the creatures were slowly losing their legs.

Caldwell, a paleontologist at the Field Museum in Chicago, says it's conceivable that two lines of snakes developed, one from burrowing lizards and another from aquatic lizards. For now, he considers both evolutionary theories equally plausible, but he su spects that as scientists find more fossils, the weight of the evidence will tip toward a marine origin. Only two P. problematicus fossils have been found, both by Haas and both in the same location. The other one has a crushed skull and pelvis.

Nicholas C. Fraser of the Virginia Museum of Natural History in Martinsville agrees that the reexamined fossil more closely resembles a snake than a lizard. He also says that Lee and Caldwell's argument for a marine origin is persuasive but not conclusive . The link between the early snake and the mosasaurs may be coincidental, he warns. For example, species like bats and pterosaurs share many features, but they evolved independently.
COPYRIGHT 1997 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1997, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Pachyrhachis problematicus fossil indicates snakes may have evolved from giant sea lizards called mosasaurs rather than from borrowing lizards
Author:Smaglik, Paul
Publication:Science News
Article Type:Brief Article
Date:Apr 19, 1997
Words:384
Previous Article:From sun to Earth: tracking a new storm.
Next Article:Oldest fossil ape may be human ancestor.
Topics:


Related Articles
Leaping lizards and male impersonators: are there hidden messages? By imitating male mating behavior, all-female lizard species apparently enhance...
Schism in the house of reptiles.
Lizards flash colors people can't see.
Return of the tuatara: a relict from the age of dinosaurs gets a human assist.
Neglected elders.
Turtle genes upset reptilian family tree.
Fossil gets a leg up on snake family tree.
Herpin' around: Thought it just took a little water to make these critters happy? Biologists say it takes trees to make frogs sing and snakes slither.
Flying snakes glide through the treetops. (Slithering on Air).
Scaly surprises: go behind the scenes of a museum exhibition to learn about scaly lizards and snakes.

Terms of use | Privacy policy | Copyright © 2020 Farlex, Inc. | Feedback | For webmasters