Ancient Rodent Species Shed Light on Oldest Grasslands

Scientists have discovered what might be the oldest grasslands by studying two ancient South American rodent fossils.

A team of paleontologists from the American Museum of Natural History, University of California, Santa Barbara, and Case Western Reserve University uncovered the fossils of the two ancient species, including the oldest chinchilla fossil at the Tinguiririca River valley, an area near the border of Chile and Argentina.

These two species are said to be the second-oldest discovered, the first one being a 42 million-year-old rodent species discovered in Peru. The researchers noted that there are unique features between the oldest and the newly discovered South American rodent species, mainly with respect to the teeth.

Experts studied the teeth of the two ancient South American rodents, which lived near the volcanoes-that are now the steep slopes of a river valley-in the Chilean Andes 32.5 million years ago, and found that they had hypsodonty, which is characterized by high-crowned teeth and enamel.

Hypsodonty provides the extra material to chew on gritty material. Hypsodonty is adapted by animals like cows and horses to graze grasses. Based on the grass-ready teeth, the researchers interpreted that the rodent species inhabited grassland plains and ate tough grasses.

"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," John Flynn, Frick Curator of Fossil Mammals and Dean of the Richard Gilder Graduate School at the American Museum of Natural History said in a statement.

The rodents inhabited the grasslands 15 million years before they were formed in other parts of the globe. This evidence shows that the Tinguiririca River valley was once grass plains much before the region's uplift between 15 and 18 million years ago, offering an insight about the world's oldest grasslands.

The study is published in American Museum Novitates.