It was found in a stratum between rocks that are 31.5 million and 37.5 million years old, and its teeth are something like those of modern New World porcupines. But some were as small as mice and others as large as rhinos. He adds that fossils found in the past 10 to 15 years in Patagonia and Bolivia also are answering questions about the Eocene and Paleocene. One startling characteristic of the Tinguiririca fossil assemblages is the dominance of species with high-crowned, or hypsodont, teeth. Paleontologists and ecologists traditionally associate hypsodonty with grazers living on a grass diet because tall teeth are better suited to eating abrasive foods.
Grasses tend to contain large amounts of opal phytoliths, which are like sharp glass needles.
If the Tinguiririca animals were grazers, then grasslands may have been part of the local landscape at least 32 million years ago, well before they developed anywhere else. According to MacFadden, who studies hypsodont fossils mainly from the Americas, South American grass eaters from Tinguiririca developed high-crowned teeth 20 million years earlier than did North American grazers. He wants to know what type of grasses early hypsodonts ate to make inferences about paleoclimate. These plants tend to be found in cool areas near water, says MacFadden. Most modern grasses are C4 plants, which use the Hatch-Slack cycle to photosynthesize.