A squirrel-like animal in the tree branches above would have been a familiar sight to some dinosaurs, researchers have learned. Newly discovered fossils indicate that mammals have been around since "at least" the late Triassic period, an expert says, though he acknowledges that his claim—which suggests mammals appeared some 208 million years back—could be "contentious," given that other experts put their appearance millions of years later. Researchers were already aware of a group of animals known as haramiyids, which lived in China some 160 million years ago, during the Jurassic period. But the animals have been mysterious, National Geographic reports.
Just last year, experts revealed the first complete haramiyid skeleton; in the new study, they describe six more, representing three species. The finds have indicated that the creatures were indeed mammals; the three bones in their middle ears were a big clue, Reuters reports. Sporting long fingers and thin bodies, they likely "spent even more time in the trees than squirrels," study leader Jin Meng, of the American Museum of Natural History in New York, tells Reuters. And they're contributing to a more varied picture of early mammals, who "walked on the ground; they also swam, dug to burrow, and glided in the forests," Meng tells National Geographic. (Our picture of dinosaurs is expanding, too: For instance, it seems they had babysitters.)