Scientists had once thought that sociable mammals only came into being after the dinosaurs became extinct about 66 million years ago. They also thought that sociability occurred mostly in the Placentalia of which humans are part. These mammals carried a foetus in their womb. About 70 percent of mammals today are mostly solitary.
In Montana, USA, palaeontologists have discovered the well preserved, near complete skulls and skeletons of a small mouse-like mammal that lived in burrows underground in groups. Their anatomy – strong legs – indicate that they were burrowing animals. They have named the new species Filikomys primaevus. The name is taken from the Greek filikos meaning friendly or neighbourly. They believe that they lived in groups of up to 5 individuals. They discovered the skeletons of 22 individuals at a dinosaur nest site, Egg Mountain, in western Montana.
Luke Weaver, co-author of the study
It is really powerful, I think, to see just how deeply rooted social interactions are in mammals. Because humans are such social animals, we tend to think that sociality is somehow unique to us, or at least to our close evolutionary relatives, but now we can see that social behaviour goes way further back in the mammalian family tree.
He said it was ironic that the coronavirus is working against sociability at the time when he was writing up a report about ancient sociability.
This new species belongs to a broader group the multituberculates, which existed for 166 million years. They are one of the most ancient mammal groups and have been extinct for 35 million years. The study is published in the journal Nature Ecology & Evolution.