Scientists have just discovered the first evidence of social behavior in mammals

How long have mammals been social creatures? At least on the late Cretaceous side of the dinosaur era, according to a new study, which reports the first evidence of the behavior around 10 million years old.

Studying fossils of the small rodent Filikomys primaevus (meaning “young and friendly mouse”) dated to about 75.5 million years ago, paleontologists have uncovered evidence of animals hanging out and living in groups.

We’re not just talking about adults raising their young – the site at Egg Mountain in western Montana shows adults and young animals choosing to dig and nest together, perhaps one of the first social activities of this type in history.

“It’s really powerful, I think, to see how deeply ingrained social interactions are in mammals,” says paleontologist Luke Weaver of the University of Washington.

“Because humans are such social animals, we tend to think that sociability is somehow unique to us, or at least to our closest evolutionary relatives, but we can now see that social behavior goes back much further in the tree. genealogical of mammals “.

“Multituberculates are one of the oldest mammal groups and have been extinct for 35 million years, yet in the late Cretaceous they apparently interacted in groups similar to those seen in modern-day ground squirrels.”

A realistic reconstruction of f first. (Misaki Ouchida)

This type of deliberate social behavior was thought to have developed after the extinction of the dinosaurs 66 million years ago, and primarily in the mammalian class of Placentalia to which humans belong.

Not so, according to these fossils – the type of rock they were found in, how well they were preserved and the traits that f first sharing with modern-day burrow animals all suggest these ancient creatures were happy to relax together.

The researchers could not find any evidence of bite marks on the fossils, so predators are unlikely to put these animals together, and if they were moved by a river flow, the fossils would not be as complete as they are. .

A block of fossils analyzed from Egg Mountain. (Luke Weaver)

“These fossils change the rules of the game,” says paleontologist Gregory Wilson Mantilla. “As paleontologists working to reconstruct the mammalian biology of this time period, we are usually stuck staring at individual teeth and perhaps a jaw that rolled along a river, but here we have more nearly complete skulls and skeletons stored in the exact place where the animals lived.

“We can now credibly see how mammals actually interacted with the dinosaurs and other animals that lived at this time.”

Artistic reconstruction of a social group of f first in a den. (Misaki Ouchida)

Today, about half of placental or placental mammals socialize in this way (global pandemics permitting), and the behavior is also seen in some marsupials such as kangaroos.

Humans come together for all sorts of reasons that go beyond the work of reproducing and raising children, but in evolutionary terms the behavior can help avoid predators, share resources, and keep warm.

It now appears that the behavior started much earlier than we thought. As much of the world continues to struggle with restrictions on group dating, it reminds us that we are social animals at heart, something the research team is well aware of.

“It was insane to finish this article just as stay-at-home orders were taking effect – we’re all doing our best here to socially distance and isolate, and I’m writing about how mammals interacted socially when dinosaurs were still wandering around. Earth! ”Says Weaver.

The research was published in Nature, ecology and evolution.