Around 38 million years ago, three small snakes slithered into a burrow seeking shelter from an apocalypse blanketing their world in volcanic ash. They never escaped, becoming entombed in the spot where they sought sanctuary in what would far into their future become Wyoming.

The misfortune of the small snakes has become a boon for paleontologists. New research published by a team from the University of Alberta has gained critical insight into the elusive history of prehistoric snakes.

“We’ve never had a good fossil record of these snakes,” said Michael Caldwell, a professor in the Department of Biological Sciences at the University of Alberta in Edmonton, Canada. “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.”

White River Wyoming

The White River Formation is a layer of rock deposited during the Paleogene Period. Caldwell described it as a time of weird mammals and widespread volcanic activity in North America.

“The rocks of the White River Formation are 38 million years old, give or take a week or two,” he said. “It’s white because the sediments are heavily dominated by volcanic ash mixed with sand and fine-grained silt. Volcanic ash events were continual and caused several disasters.”

The fossils from the White River Formation are legendary. Large and small mammals, birds, amphibians and reptiles are immaculately preserved in the ash-dominated rock.

“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.”

There are legendary exposures of the White River Formation in Wyoming, particularly around Douglas. That’s where the University of Wyoming was excavating in 1976, when researchers found the three small snakes that are leaving a big impact.

Breithaupt’s Hibernating Snake

The fossilized snakes were collected with several other White River fossils during UW’s 1976 field project in Douglas. Aside from a 1997 paper written by paleontologist Brent Breithaupt, the UW Geological Museum’s collection manager at the time, the snakes haven’t garnered much attention until recently.

“I was talking with Brent, and he offered me the opportunity to work on the material in the early 2000s,” Caldwell said. “It took me a while to find a grad student to put on the project, and then it took us a while to get the paper written once she had graduated.”

That grad student, Jasmine Croghan, is the lead author of the paper describing the Wyoming White River snakes. The new species was called Hibernophis breithaupti, honoring Breithaupt and his original hypotheses about the unique discovery.

“Brent’s paper interpreted them as a hibernating assemblage of snakes,” Caldwell said. “That’s why we named them Hibernophis, the hibernating snake.”

A Den Of Beautiful Snakes

When describing a new species of prehistoric animal, the Holy Grail for paleontologists is a complete specimen.

Croghan, Caldwell and the other scientists studying the White River snakes had four of them, all nearly perfect skeletons to study, all collected near Douglas.

Snakes from the White River Formation aren’t well-known in the fossil record. Paleontologists have acquired most of their knowledge on their biology and evolutionary history from isolated fragments or individual bones.

“There are millions of isolated snake vertebrae in museum collections around the world, but very few articulated snakes,” he said. “As terrifying and robust as a snake might appear, they’re not held together very tightly. When they die, their bits and pieces wash about and they become disarticulated very easily.”

Caldwell said the three snakes found in the burrow, and a fourth specimen found nearby, are the most complete specimens of their kind ever found in the White River Formation.

“This particular trio of snakes are beautifully preserved,” he said. “We have almost everything in the anatomy of these little snakes, from the tips of their noses to the tips of their tails. They’re only missing the very tip of the tail, but everything else is there.”

Caldwell explained that “without going into the gory details about snake bony anatomy,” that Hibernophis is a kind of rubber boa, a smaller member of the boid family of snakes, which includes anacondas and boa constrictors.

While boids were and are widespread throughout the Americas, their evolutionary history remained an enigma until the discovery of Hibernophis. Wyoming’s White River snakes have provided critical insight into their evolutionary story.

Boid Behavior

While the anatomy and evolutionary significance of Hibernophis is exciting, the discovery revealed equally exciting information on the behavior of the 38-million-year-old snake. Caldwell said the preservation of three snakes in one burrow is significant.

“We have something that we never find in the fossil record,” he said. “Here we have three of these little rubber boas all curled up together in this ancient mammal burrow. One of them is substantially larger than the other two, so you can put on your natural history hat and start imagining what this could be.”

Whatever it was that drove the snakes into the burrow, which had been dug by a burrowing mammal, the snakes didn’t mind sharing the same space.

“We don’t know why they were there, but they were comfortable being together wherever they were,” he said. “Which means there is social behavior of snakes preserved in the fossil record.”

There’s a modern precedent for this behavior in snakes. Thousands of garter snakes in cold climates have been found living together in holes, entering a prolonged stupor while surviving from their collective body heat in what’s called a hibernaculum.

The three Hibernophis specimens may have perished in their hibernaculum, but more research would be needed to prove this. Regardless, Caldwell said the discovery is a rare and exciting instance of prehistoric behavior preserved in the fossil record.

“Most people think of reptiles as dim-witted, cold-blooded, not very social and with no maternal care,” he said. “The usual non-mammal analogies. 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.”

Rediscovering Discoveries

The four specimens of Hibernophis breithaupti are in the collections of the UW Geological Museum. Caldwell and the other scientists briefly took the fossils to the University of Alberta for research and then to Austin, Texas, for a micro-CT scan.

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

A major scientific discovery usually raises more questions than it answers. Thanks to the discovery of Hibernophis, Caldwell anticipates a flurry of scientific inquiries will be pursued.

“Every good answer just rattles a whole series of questions even harder,” he 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?

“You end up with more questions to ask from every answer that you put forward.”

For Caldwell, another major takeaway from the study of Hibernophis was its “rediscovery” in the collections of the UW Geological Museum. He believes more future paleontological discoveries will come from already-excavated fossils sitting on the dusty shelves of museums.

“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.”

Yesterday And Today

While these Hibernophis died in an ash-filled burrow 38 million years ago, their boid descendants survived into the present day. Rubber boas are everywhere in Wyoming, although they can be hard to find.

“These boas alive today are part of that same radiation as are these fossil ones,” he said. “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.”

The anatomy and behavior of Wyoming’s modern-day boids might shed more insight into the world of their prehistoric ancestors preserved in the White River Formation. Hibernophis has established itself as another jewel in the ornate crown of Wyoming paleontological discoveries.

“With Hibernophis, we fill in a science gap and get some insights on prehistoric snake behavior,” Caldwell said. “It’s a great story and three really lovely specimens.”

Andrew Rossi can be reached at arossi@cowboystatedaily.com.