A perfectly preserved fossilized snake burrow is evidence that the reptiles were social animals for almost 40 million years, says a new study co-authored by a University of Alberta paleontologist.
Modern snakes are known to congregate in burrows for a variety of reasons, including breeding and surviving cold temperatures by huddling together to maintain body temperature. But new research on a fossil found nearly 50 years ago offers a rare glimpse into the deep roots of this behavior.
“We certainly expect this in mammals, but we don’t look for it in the fossil record of reptiles,” said Michael Caldwell, a professor at the University of Alberta and co-author of a new paper published in the journal Zoological Journal of the Linnean Society.
The fossil in question is the 1976 discovery of three “beautiful, conjoined” specimens of boa constrictors found together in a Wyoming burrow. The fossil has not been properly studied until now.
Caldwell said the find was rare. Scientists are typically limited to studying isolated fossilized snake vertebrae, “and we don’t know what part of the snake they came from.”
In contrast, these fossilized snakes had almost completely preserved spines and skulls.
Scientists speculate that the Wyoming burrow may have flooded, filled with sediment, and fossilized three snakes there, said Jasmine Croghan, a clinical professor at Oklahoma State University Health Sciences Center and the paper’s first author.
Croghan said a fourth snake fossil was found nearby.
“Whether they are hibernating or just fleeing the volcanic ash storm because they are terrified, which is possible, we really don’t know,” Caldwell said.
“But we have evidence that at least they were willing to spend time together when they died.”
Although the authors of this paper do not believe they were the first to discover the first fossil evidence of social behavior in snakes, Caldwell says the discovery is still remarkable.
“That’s another really cool part to me, just the idea that we have almost 40 million years of evidence that shows social behavior in reptiles.”
In Alberta, rattlesnakes, grass snakes, and garter snakes often hibernate in groups.
“Most snakes will seek shelter in an accessible place underground—like a burrow, usually dug by something else. So they tend to be quite dependent on mammals, and maybe turtles or tortoises, so they may have burrows that they can access,” Croghan said.
James Gardner, a curator at the Royal Tyrrell Museum in Drumheller, Alberta, who specializes in fossil amphibians and reptiles, said he was “comfortable with the hypothesis that this was a natural accumulation of many individuals — probably in a burrow” put forward in the paper.
“This fossil shows us that at least 38 million years ago, snakes used burrows – either to escape the heat or the cold. [or] as a place of refuge, which is a behavior we see in modern snakes in similar environments,” Gardner said.
Gardner said the fact that the fossil was found nearly 50 years ago places some limitations on the data that can be obtained from it. There likely is little recorded information about it, he added, including the local geology of the site.
Gardner said tracing the fossil back to where it was found could yield even more finds.
“There may have been more fossilized snake skeletons coiled in the burrow.”
