Early Mammals Had Social Lives, Too

Early Mammals Had Social Lives, Too
Chipmunk-like animals that lived among the dinos appear to have been social creatures, which suggests that sociality arose in mammals earlier than scientists thought. Christopher Intagliata reports.

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. These things 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 little 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 and Evolution. [Lucas N. Weaver et al, Early mammalian social behaviour revealed by multituberculates from a dinosaur nesting site]

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 is mammals living during time of dinos were mostly solitary rat-like creatures scuttling in the night under dinos. And so the fact we’re finding these multituberculate mammals—a totally unrelated group of mammals—exhibiting social behavior means this was probably not uncommon under these early mesozoic mammals. And it changes the narrative that sociality as somehow unique to placental mammals.” 

Even today, social behavior is relatively rare among mammals. But these findings suggest the need for company in some mammalian species is an ancient evolutionary invention.

—Christopher Intagliata

[The above text is a transcript of this podcast.]

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