These snakes, which lived around 38 million years ago, provide an unprecedented look into the social lives of long-extinct reptiles.

This small space, used by animals to keep warm during winter, offered a unique glimpse into the behavior of these ancient reptiles. The fossils were found nestled together, suggesting a social behavior previously unknown in the fossil record.

“Of the almost 15,000 different kinds of reptile species alive today, none of them hibernate in the way that garter snakes do,” said study co-author Michael Caldwell.

“Here, we’ve got three really lovely specimens in one burrow, which gives us the information we need to investigate the origins and evolutionary history of an enigmatic group of living, burrowing snakes,” Caldwell said.

“We find early dogs and cats, and saber-toothed relatives of cats that aren’t the same saber-tooths of the mammoth and mastodon,” Caldwell said. “Early bunny rabbits, all kinds of lizards, turtles, big-bodied mammals, early chameleons. The White River stuff is just amazing.”

Researchers discovered the fossils in the White River Formation in 1976 and first noted their clustering behavior in a 1986 study. Thanks to modern technology, researchers are able to take a closer look at the fossils for the first time.

Caldwell noted, “They can’t regulate their body temperature, so they need to find a way to conserve as much heat as they can through the winter.”

Modern snakes still exhibit this behavior, as thousands of garter snakes in cold climates have been discovered living together in holes.

The team suspects that a small flood caught the snakes while they were in a winter den, quickly trapping and encasing them in fine sandy mudstone.

“Finding the whole snake? That’s rare,” Caldwell said, highlighting the significance of this discovery.

Caldwell explained, “We learn quite a bit more about boidae evolution in the broad sense. It seems that they probably started out as relatively small-bodied snakes.”

This size difference helps researchers understand how this ancient species grew and developed.

Most reptiles today do not hibernate in groups, making this find particularly intriguing. It opens new avenues for research into the survival strategies of ancient reptiles.

This circumstance allowed the snakes to be fossilized in a near-complete state, providing a rare opportunity for paleontologists to study their anatomy in complete detail.

This discovery adds a new dimension to our understanding of reptilian social structures and how they may have evolved over millions of years.

Understanding the social and hibernation habits of Hibernophis breithaupti can help scientists make connections to the survival strategies of contemporary species.

Anacondas and boa constrictors, both large snakes, typically inhabit South America and are part of the snake family.

A burrowing mammal carved out a burrow where the snakes were found. This indicates that the snakes did not mind sharing space with other animals.

“They’re small-bodied night feeders that are rather secretive and spend a lot of time hiding in the sand, so very few people see them. They’re common in the pet trade if you’re into a rubber boa that stays buried in the sand in your terrarium all day, which I’m not.”

Further studies could reveal more about the environmental conditions that shaped the lives of these fascinating creatures 38 million years ago.

“That’s how we found the third specimen,” Caldwell said. “It was inside the block and wasn’t clearly visible on the surface since it’s slightly below the other two.”

However, the discovery leads to more questions for the team: “Could this be a parent and a couple of young ones? Or is it possible that we’ve got a fright response and they’ve all ended up in a burrow together in the midst of a volcanic ash event? Or were they preparing for a cold weather season? We don’t know.”

“Every good answer just rattles a whole series of questions even harder,” Caldwell said. “Are there more specimens of Hibernophis? What would that have to say about the hypotheses that we’ve put forward in this recent publication? How does new material and new information change what we think we know about the interrelationships of these animals with all other birds and snakes, both fossil and living?

“There are hundreds, if not thousands, of specimens hiding away in museum collections that have never been examined,” he said. “The next places to go are out into the field and down into museum collections. Several places have good White River Formation collections. We need to see if there’s anything in those collections that’s been missed.”