Snakes Evolved on Land, New Fossil Find Suggests

Nicholas Bakalar
for National Geographic News
April 19, 2006

An ancient snake with hips connected to its spine might be proof that slithery serpents originated on land, not in the water, a new fossil find reveals.

The fossil snake—which has a primitive pelvis and robust, functional legs outside the ribcage—dates from about 90 million years ago.

Sebastian Apesteguía, a researcher with the Argentine Museum of Natural Science, says the new fossil is not the oldest snake fossil ever found. Older marine snakes have been unearthed in North Africa and Eastern Europe.

But the species, named Najash rionegrina, is the earliest limbed snake ever found in a fully terrestrial deposit, he says.

N. rionegrina was discovered in Argentina's Rio Negro province, about 700 miles (1,130 kilometers) southwest of Buenos Aires (see map).

Apesteguía and colleague Hussam Zaher, of the Zoological Museum of the University of São Paulo in Brazil, describe the find in tomorrow's issue of the journal Nature.

Land or Water?

Many living snakes, such as pythons, have the vestiges of legs that are not attached to the backbone and simply hang from the body.

(See a related photo of a python that burst after trying to eat an alligator in the Florida Everglades.)

By contrast, Apesteguía said, "In Najash the hip was connected to the vertebrae, so it has a sacrum. No other known fossil or extant snake is so primitive as to retain this feature."

The sacrum is the bony structure that connects the spine to the hips in vertebrates, including humans.

The animal's sacral region would have made its legs well suited to digging or crawling, the researchers say, giving weight to a land-based origin for snakes.

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