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March 16, 2000


Snake Fossil - see the tiny leg bones?

DALLAS (SMU) — Researchers from Southern Methodist University have described an intriguing new species of fossil snake with legs that was found in a limestone quarry north of Jerusalem.

In a paper published in the March 17 issue of the journal Science, SMU paleontologist Louis Jacobs and several international co-authors say the fossil snake is important because it provides new information on the evolution of snakes.

The fossil snake, which lived 95 million years ago, is named Haasiophis terrasanctus after a Hebrew University professor named George Haas who obtained it from quarry workers more than 20 years ago. The well-preserved fossil sat largely unstudied in storage until Mike Polcyn, an SMU graduate student in paleontology, brought back pictures of it and other undescribed specimens that he took while on a business trip to Israel in 1996.

"We immediately decided we needed to go back and organize a joint project to research and publish on this unique location and the animals preserved there," Polcyn said.

Haasiophis is a little over a meter long and has hind legs about 2 cm long that extend all the way to the toe bones. Its head and lower jaws are intact.

"It is extremely rare to find a fossil snake head preserved because they usually get spread and scattered," Jacobs said.

Louis Jacobs searching for fossils

Haasiophis is the second limbed snake to come from the limestone quarry near the villages of 'Ein Yabrud, north of Jerusalem. George Haas published a description of the first limbed snake, Pachyrachis problematicus, in 1979, but at the time he placed it not as a snake but as a marine lizard known as a dolichosaur. Some scientists believe Pachyrachis represents the most primitive snake known and provides evidence of a link between mosasaurs – giant swimming lizards of the Cretaceous Period – and true snakes.

In the past 20 years, however, researchers have developed more quantitative methods of evaluating relationships between species based on unique anatomical details. The analysis of the head and jaws of Haasiophis presented in the Science article places it closer to more advanced terrestrial snakes such as boas and pythons and suggests that neither Pachyrachis nor Haasiophis has anything to do with snake origins.

"As a result of this analysis, it seems less likely that snakes evolved from mosasaurs," Jacobs said.

Scientists believe snakes evolved from a group of lizards prior to 100 million years ago. During the evolutionary process, their headbones changed, they developed long bodies with specialized vertebra and muscles, and they lost their legs.

Jacobs said analysis of Haasiophis indicates that snake feeding apparatus, body form and locomotor pattern all evolved before the hind legs were lost.

"The fact Haasiophis had legs means that either snakes lost their legs more than once or they re-evolved them," Jacobs said. He speculates that the tiny legs on Haasiophis were somehow used in reproduction and stimulation, much like the spurs on anacondas are used today. They are too small in relation to the reptile’s whole body to have helped it move.

Analysis of Haasiophis also adds to the debate over whether snakes originated on land or in the sea. Haasiophis lived in the sea, and Jacobs believes it may represent the first invasion of the sea by snakes.

A large view of the entire snake fossil

During the Cretaceous Period, the area that includes the Middle East was a shallow sea with patches of reef and limestone deposition, much like the modern-day Bahamian reef. At one point about 95 million years ago, the sea level fell, making a quiet area on this limestone shelf. Animals washed into the area and fell to the bottom. With no scavengers to eat the bodies, they eventually fossilized within the limestone. Paleontologists also have found fossils of sharks, turtles, primitive mosasaurs and plants in the 'Ein Yabrud quarry.

Rocks in the Dallas/Fort Worth area are similar in age to those at 'Ein Yabrud, suggesting that limbed snakes such as Haasiophis could once have lived in Texas.

"It’s not beyond possibility," Jacobs said.

Lou Jacobs with a dinosaur skeleton at the Dallas Museum of Natural History

Jacobs is a professor of Geological Sciences in SMU’s Dedman College and president of SMU’s Institute for the Study of Earth and Man. Most recently he has served as director ad interim of the Dallas Museum of Natural History. He has conducted extensive field research in Pakistan, Mexico, Kenya, Cameroon, Malawi and Yemen, as well as in Texas and other parts of the United States. He is the author of Lone Star Dinosaurs (1995), Cretaceous Airport (1993) and Quest for the African Dinosaur: Ancient Roots of the Modern World (1993), as well as numerous scientific papers.

Co-authors with Jacobs and Polcyn on the March 17 Science paper include Eitan Tchernov of Hebrew University, Olivier Rieppel of the Field Museum in Chicago and Hussam Zaher of the Universidade de Sao Paulo in Brazil. Tchernov and Rieppel were both students of George Haas.

Reporters may contact: Ellen Mayou
SMU Public Affairs
(214) 768-7659