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Ancient, Lizard-Like Reptile Discovered

John Roach
for National Geographic News
October 8, 2003
 
A pair of Argentine paleontologists have discovered numerous 90-million-year-old fossils of a new type of sphenodontian—an ancient lizard-like reptile thought to have gone extinct about 120 million years ago except for a few relicts that live today in New Zealand, the tuatara.

The fossils, including several well-preserved skulls, were found in the red sandstone cliffs of the La Buitrera fossil quarry in northwestern Patagonia, about 800 miles (1,300 kilometers) east of Buenos Aires.

The new species, Priosphenodon avelasi, had a blunt head, a sharp eagle-like beak, long arms, and wielded square claws. It was about three feet (one meter) long and weighed an estimated 33 pounds (15 kilograms), making it bigger than any known terrestrial sphenodontian.


The Argentine paleontologists say the discovery of Priosphenodon helps fill a gap in the fossil record between the Early Cretaceous sphenodontians and their living relatives in New Zealand.

"Priosphenodon was not a minor component in the terrestrial faunas of South America," said Sebastián Apesteguía, a vertebrate paleontologist at the Argentine Museum of Natural History in Buenos Aires. "It is the most abundant species of the fossil assemblage."

Other bones collected at La Buitrera (The Vulture Cage) include crocodiles, snakes, and additional remains of one of the largest carnivorous dinosaurs that ever evolved: an eight-ton, 12-foot (3.7-meter) tall, meat-eating, dagger-toothed creature named Giganotosaurus.

Apesteguía and his colleague Fernando Novas, also at the Argentine Museum of Natural History, report on their discovery in the October 9 issue of Nature.

Robert Carroll, a vertebrate paleontologist at McGill University in Montreal, Canada, said the discovery of Priosphenodon raises broad questions about why this group of sphenodontians was so successful in the Cretaceous.

"There is a lot to be learned from South America of vertebrates of all groups," he said.

New Lessons

Before this discovery, scientists believed that the wide appearance of lizards and snakes in the Early Cretaceous fossil record (about 120 million years ago) signified a change that caused sphenodontians to become much less diverse.

"The history was apparently distinct during the Cretaceous of South America," said Apesteguía. "Although the record is still patchy, South American lizards lived with sphenodontians as a minor component of a crocodile-dominated fauna."

South America is part of an ancient landmass known as Gondwana, which separated from the super-continent Pangaea about 230 million years ago and formed South America, Africa, Antarctica, Australia, and peninsular India.

Apesteguía and Novas conclude in their paper that sphenodontians apparently persisted longer on Gondwana than other parts of the world, such as North America.

"The supposed replacement of sphenodontians by lizards was delayed in South America at least until some moment between the end of the Cretaceous and the beginnings of the Tertiary," said Apesteguía.

Unpublished results of fragmentary fossils found in Late Cretaceous sediments in northern Patagonia indicate that sphenodontians other than Priosphenodon were still alive in South America as late as 65 million years ago.

"This is important because it's supporting [the view] that South American sphenodontids were still diverse even until the end of the Cretaceous period," said Apesteguía.

At some point, the researchers do not know exactly when, an unknown factor allowed lizards and snakes to rise to dominance in South America, relegating the sphenodontids to the relic tuataras in isolated New Zealand.

Ancient Forest

The red sandstone cliffs of La Buitrera today break up an otherwise arid, desolate steppe covered in thorny scrubs raked by a wind that fills the air with a scent of thyme, mint, and oregano, said Apesteguía.

Ñandus, foxes, rodents, goats, and horses roam the plain as vultures circle overhead. Summertime temperatures routinely soar above 104 degrees Fahrenheit (40 degrees Celsius) and snows blanket the region in winter.

The cliffs are a reminder that a giant, lazy river sluiced through the prairie as it coursed west to the Pacific, a passage since blocked by the rise of the Andes.

According to the paleontologists, some 90 million years ago the steppe was carpeted in forest and dotted with ephemeral lakes that formed during wet seasons. Sphenodontians, terrestrial crocodiles, snakes, and small mammals roamed in the shadows of dinosaurs.

"Sphenodontians and other small species that died along the river valley were commonly entombed by sudden floodings, being swept a couple of miles downstream together with isolated bones and teeth of large dinosaurs to be finally dumped on a bank that became hard, brown-reddish sedimentary rock along the ages," said Apesteguía.

Today, the 130-foot (40-meter) tall sandstone cliffs are considered South America's equivalent of China's Gobi for the amount and quality of fossil discoveries they have yielded in the past decade. The discoveries, say paleontologists, are helping to rewrite the landmass' history.

"There is a lot of South America and not a lot of South American paleontologists," said Carroll. "The global significance is there is an awful lot more to find that we had no suspicion of whatsoever."

The fossil was found by Sebastian Apesteguía, leading a team of paleontology students as part of another project organized by Fernando Novas. They received the help of the local Avelas, Pincheira, and Salinas families, as well as the Cerro Policia town community, Rio Negro Province. The project was supported by the Agencia de Promocion Cientifica y Tecnologica, The Jurassic Foundation, and the National Geographic Society.
 

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