This is Scientific American's 60-second Science, I'm Christopher Intagliata.Seventy-six million years ago, a group of small mammals huddled in a burrow in what’s now Montana.They were good diggers―most likely furry―and petite.“They could sit comfortably in the palm of your hand.I mean, if you saw them running around today, you’d think it’s a small rodent―a chipmunk or mouse.”Lucas Weaver is a mammal paleobiologist at University of Washington.These subtle creatures didn’t belong to any of the three main mammal groups on the planet today―which are the placental mammals (like us), monotremes (like the platypus) and marsupials (like koalas and kangaroos).Instead they belonged to another, now extinct group called the “multituberculates.”“They have these really bizarre molars with multiple bumps, which is where they get their name. Multituberculate. just means ‘many bumps.’”Weaver and his colleagues have studied the fossilized skulls and skeletons of these animals, dug up in Montana, and they’ve given them a name: Filikomys primaevus (friendly or neighborly mouse).The details are in the journal Nature Ecology & Evolution.Weaver says drought or climate change may have killed the animals, though it’s hard to be sure.But the critters were fossilized together in ways that suggest they sought out each others’ company.That’s a big deal because it’s commonly thought that social behavior didn’t arise in mammals until after the death of the dinosaurs, 10 million years after these small critters hung out together.“The narrative, for decades, has been that mammals living during the time of dinosaurs were mostly solitary ratlike creatures scuttling in the night under dinosaurs.
