Sunday, December 16, 2007

Andean Highlands In Chile Yield Ancient South American Armored Mammal Fossil


ScienceDaily (Dec. 14, 2007) — A paleontological dig in Chile at an altitude of more than 14,000 feet in the Andes has yielded fossils of an 18-million-year-old armored mammal. It appears to be one of the most primitive members of a family of extinct mammals known as "glyptodonts," a group closely related to the modern-day armadillo.
Darin Croft from Case Western Reserve University, John Flynn from the American Museum of Natural History and Andre R. Wyss from the University of California Santa Barbara report the discovery and describe the mammal in the Journal of Vertebrate Paleontology.
Researchers have named the animal, Parapropalaehoplophorus septentrionalis. They derived the first part of the name from the new mammal's resemblance to a slightly younger animal from Argentina (Propalaehoplophorus). Septentrionalis means northern in Latin.
The newly discovered animal lived in the early Miocene epoch about 18 million years ago and its family went extinct about the time humans arrived in the New World.
P. septentrionalis is a member of the glyptodonts, a large group of extinct animals that lived almost exclusively in South America. (A few species reached North America several million years ago when the two continents were reconnected by the Panamanian land bridge.) They are recognized for their thick shells of hardened and immovable bony plates and their large, grooved teeth. But unlike their modern day armadillo relatives (who have thinner shells with movable plates and smaller, simple teeth), these animals could grow to the size of a small car and weigh as much at two tons.
According to Croft, the new species was relatively small for a glyptodont and is the first one found in Chile. "It would have looked like a cross between a tortoise and an armadillo, but of course is much more closely related to armadillos," he said. He described P. septentrionalis as roughly the size of an African spurred tortoise, which is less than three feet long and weighs about 200 pounds.
The glyptodont was reconstructed from fossils of the jaw, shell, leg and backbone. These were compared with other known glyptodonts and with close glyptodont relatives. "These different skeletal parts all gave the same answer -- this was a new species of glyptodont that had a greater number of primitive features than any other species," said Croft.
"When we collected the fossil, we had no idea that it would turn out to be a new species. We knew that it would be an important specimen, given its completeness, but it was only after cleaning it and carefully studying it that we realized how unusual it was," Croft said.
The P. septentrionalis fossil was found during a field expedition in 2004 to the Salar de Surire region. This area has yielded the Chucal fauna, the collective name given to the 18 fossil animal species from the region. This fauna includes armored mammals (armadillos and their relatives), marsupials (relatives of the opossum), rodents, frogs and many ungulates (hoofed animals).
Finding the new species was no easy task as the researchers encountered the thin air at the high altitude, scarce water and temperatures that plummeted as night fell. But these are not the conditions under which the glyptodont lived. According to Flynn from the American Museum of Natural History in New York City, "Our studies and plant work elsewhere on the Altiplano suggest that the region was at much lower elevation when these fossils lived, giving us new insights into the timing and rate of uplift of the high Andes."
Flynn added that Chucal, at more than 14,000 feet above sea level, is the highest elevation vertebrate fossil site in the Western Hemisphere. The highest site in the world is much younger and is found in the Tibetan Plateau at an altitude of more than 15,000 feet.
Like other glyptodonts, P. septentrionalis probably spent a lot of its time grazing on ground vegetation in open areas, much like cows do today. This interpretation is supported by the presence of many other open habitat mammals at Chucal and the presence of plant fossils typical of such environments.
A detailed description of the new mammal is found in the article, "A New Basal Glyptodontid and other Xenarthra of the Early Miocene Chucal Fauna, Northern Chile." The research was undertaken in collaboration with the Field Museum of Natural History in Chicago and the Museo Nacional de Historia Natural and the Consejo de Monumentos Nacionales in Santiago, Chile. Research support came from the National Geographic Society, the National Science Foundation, and FONDECYT Chile.
Adapted from materials provided by Case Western Reserve University.

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