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Unpublished results of fragmentary fossils found in Late Cretaceous sediments in northern Patagonia indicate that sphenodontians other than Priosphenodon were still alive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.
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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