Weird Lizard Fossil Reveals Clues to Snake Evolution, Experts Say

Scott Norris
for National Geographic News
March 26, 2007

A 95-million-year-old marine lizard with minuscule front legs may shed new light on the evolution of modern reptiles, particularly snakes, scientists have reported.

The fossilized remains of the reptile represent the earliest known example of a lizard evolving toward a limbless state, according to experts who described the new species.

The creature's vestigial, or no longer functional, forelimbs barely protrude from its long, snakelike body.

Although its rear legs were of normal size, researchers said the lizard was probably an eel-like swimmer that spent little time on land.

Michael Caldwell, of the University of Alberta, in Edmonton, led the team that made the discovery. He said the lizard, dubbed Adriosaurus microbrachis or "small-armed Adriosaurus," belongs to the lizard group most closely related to snakes.

Intriguingly, Caldwell noted, the new fossil dates to the same period as fossils of primitive snakes that also retained their hind legs.

"This animal appears to have been aquatic, like the rear-limbed snakes from the Middle East," Caldwell said.

He and Italian paleontologist Allessandro Palci reported the discovery in the March issue of the Journal of Vertebrate Paleontology.

Look, No Hands

Experts believe all lizards and snakes descended from a common reptilian ancestor that walked on four legs and lived on land.

Adriosaurus and early snakes probably evolved their elongated bodies and shortened front legs independently of one another, Caldwell noted.

But the similarities between the two may help explain the evolutionary origin of the snakelike body form.

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