An international team of paleontologists has discovered two ancient species of South American rodents, including the oldest chinchilla, a discovery that substantiates what might be the earliest grasslands in the world.
The two new species lived near a chain of volcanoes about 32.5 million years ago in what are now the steep slopes of a river valley in the Chilean Andes. Studies of the teeth of the ancient chinchilla support evidence from other species in the concurrent fauna indicating that the animals inhabited an open and dry environment 15 million years before grasslands emerged 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 Dr John Flynn, Frick Curator of Fossil Mammals and dean of the Richard Gilder Graduate School at the American Museum of Natural History, who is a co-author of a paper published in the journal American Museum Novitates.
The team has explored the fossil history preserved in the Chilean Andes for the past 25 years. In the Tinguiririca River valley, an area near the border of Chile and Argentina once thought to be inhospitable to fossils because of the dominance of volcanic rocks, the researchers have uncovered hundreds of specimens, including the two newly named species of early South American rodents.
The new specimens – Andemys termasi, for which the genus name means “mouse of the Andes” and the species name refers to the nearby town of Termas del Flaco, and Eoviscaccia frassinettii, named for the late Daniel Frassinetti, who was a longtime collaborator and head of paleontology at Chile’s National Museum of Natural History—are the second-oldest rodents ever discovered in South America. The oldest are recently discovered 41-million-year-old rodents from Peru. The new species are distinguished from the older rodents by many features 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 Dr Ornella Bertrand.
Hypsodonty, the quality of having high-crowned teeth, is a trait that emerged in multiple kinds of animals, such as horses, goats, and cows. Hypsodonty is generally interpreted as an adaption that arose in response to the spread of grassy environments.
The age of the fossils and the high-crowned teeth of the new chinchilla and many other mammals in the same fauna suggest to researchers that the mountainous Tinguiririca River valley was a grassy plain at the time the debris from a volcanic eruption buried them. This means that the Chilean Andes supported plains environments some 15 million years before such ecosystems are known on other continents.
“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 co-author Dr André Wyss of the University of California in Santa Barbara.
Bibliographic information: Bertrand, Ornella C.; Flynn, John J. (John Joseph), 1955-; Croft, Darin A.; Wyss, André R. 2012. Two new taxa (Caviomorpha, Rodentia) from the early Oligocene Tinguiririca fauna (Chile). American Museum novitates, no. 3750