The new rodent species indicate that there was explosive diversification on South America when it was an island continent, before the formation of the Isthmus of Panama about 3.5 million years ago.
Eoviscaccia frassinettii, which is related to the modern chinchilla, and, Andemys termasi, related to a lesser-known group that includes the agoutis, a group of short-tailed rat-like species also native to South and Central America, belong to what originally was an exclusively South American group of rodents called caviomorphs.
Caviomorph rodents include the New World porcupines, capybara, guinea pig, and many others. Based on the fossil record and evolutionary relationships, the ancestors of these animals are thought to have come to South America from Africa on rafts of debris. Once on the massive island, caviomorphs diversified into some of the unique species we see today.
"The island continent of South America represented a land of evolutionary opportunity for the ancestors of chinchillas and other caviomorph rodents," said co-author Darin Croft of Case Western Reserve University in Cleveland. "These remarkable rodents came to fill an amazing variety of ecological niches and today are among the most characteristic Neotropical mammals."
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American Museum of Natural History