Rodents are known and named for their ever-growing incisors, which they use for gnawing. Yet the back or "cheek" teeth, used for grinding, have a special story to tell in this case: one that focuses on the crown, the portion of the teeth protected by long-wearing enamel. While the Peruvian rodents had cheek teeth with a crown extending only to the gum line, one of the new ancient Chilean rodents has high crowns that extended underneath the gums, enabling it to eat gritty foods like grass.
"The Tinguiririca chinchilla replicates a dental pattern appearing in many other South American herbivores such as Notoungulateshooved animals that are now extinctat that time. This pattern is called hypsodonty," said lead author Ornella Bertrand, who conducted the research through the Museum's Annette Kade Graduate Student Fellowship Program.
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 de
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American Museum of Natural History