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Fossilized Teeth Point To World’s Oldest Grasslands In Chilean Andes

July 25, 2012
Image Caption: This is a reconstruction of Mesoprocta hypsodus, an extinct, 13-million-year-old Bolivian relative of the new dasyproctid rodent Andemys termasi from Chile. Credit: V. Simeonovski & D.A. Croft

Brett Smith for redOrbit.com – Your Universe Online

Two newly discovered and ancient rodent species, including the earliest known chinchilla, may have lived in the world´s oldest grasslands about 32.5 million years ago.

The discovery and subsequent analysis of the teeth by an international team of researchers, which was published in the journal American Museum Novitates, supports previously collected evidence indicating that these animals once inhabited an open and dry environment 15 million years before grasslands appeared elsewhere in the world.

“The new chinchilla fossil provides important new evidence that early rodents joined other South American mammals in evolving ways to cope with an abrasive diet long before horses, sheep and other mammal groups on other continents ℠invented´ similar adaptations for making their teeth wear out more slowly while eating tough grasses,” said the paper´s co-author John Flynn, of the American Museum of Natural History.

The new specimens were named Andemys termasi, or “mouse of the Andes”, and Eoviscaccia frassinettii, after the late paleontologist Daniel Frassinetti, a longtime collaborator and head of paleontology at Chile´s National Museum of Natural History. The fossils represent the second-oldest rodents ever found in South America.

Discovered in the Tinguiririca River Valley in the Chilean Andes, the new species are distinguished because of the form and function of their teeth.

“The Tinguiririca chinchilla replicates a dental pattern appearing in many other South American herbivores such as Notoungulates — hooved animals that are now extinct — at that time. This pattern is called hypsodonty,” said lead author Ornella Bertrand from the Institut des Sciences de l´Ã‰volution.

Hypsodonty is generally attributed to species adapting to a primarily grass-based diet. The high-crowned teeth of an animal with hypsodont dentition have enamel that extends below the gum line to guard against the extra wear generated from these animals´ eating habits. Cows, goats, and horses are modern day examples of these kinds of animals.

Because of the hypsodonty found in the new chinchilla along with other mammals in the same fauna, the researchers concluded that the mountainous Tinguiririca River terrain was a grassy plain until debris from erupting nearby volcanoes changed the contours of the region. These Chilean grasslands would predate other such ecosystems on the planet by 15 million years.

Discovery of the new species points to an extreme diversification on South America before the development of the Isthmus of Panama about 3.5 million years ago.

“In addition to being preserved in unusual volcanically derived sediments, the new rodent species are notable for coming from what is assuredly one of the most spectacularly scenic and rugged sequences of fossil mammal localities in the world,” said study co-author André Wyss of the University of California in Santa Barbara.

In their quest to flesh out the fossil history of South America, members of the team have scoured the Chilean Andes for the past 25 years. The Tinguiririca River valley, an area near the border of Chile and Argentina, was originally thought to be inhospitable to fossils because of the prevalence of volcanic rock. However, the researchers have uncovered hundreds of specimens over the course of their study.


Source: Brett Smith for redOrbit.com - Your Universe Online



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