34-Million-Year-Old Snake Found in Wyoming Rewrites Our Understanding of Evolution

A small fossil snake may hold outsized clues about snake evolution, behavior, and an ancient ecosystem that looked nothing like today’s.

A newly identified fossil snake from Wyoming is rewriting scientists’ understanding of snake evolution. The species, named Hibernophis breithaupti, lived about 34 million years ago and may represent an early branch of Booidea, the broader group that includes modern boas and pythons.

This discovery is notable not only for the snake itself, but also for the unexpected way it was uncovered. Researchers studied four fossils from the White River Formation in Converse County, Wyoming. Three came from a single rock block, and two of those were visible on the surface. A third was hidden inside the rock and only detected later through CT scanning. A fourth specimen came from a nearby site in the same formation.

Rare Fossils Reveal a More Complete Snake

Fossil snakes are usually known from isolated vertebrae, which can tell researchers only so much. Here, the team could examine skulls, jaws, vertebrae, and other parts of the skeleton in remarkable detail. That allowed them to identify a new genus and species rather than trying to force the fossils into older, poorly defined categories based mostly on loose vertebrae.

The new snake was small, likely burrowing, and appears to have been part of an ancient North American snake fauna that looked very different from today’s. Before more modern snake groups rose to dominance, constricting snakes were a major part of North America’s ecosystems. Hibernophis helps fill in that earlier world and suggests the continent may have played a bigger role in the early evolution of boa-like snakes than scientists once thought.

An intriguing behavioral possibility

The snakes were preserved curled together in what appears to have been a burrow, which could make this the oldest known evidence of snakes hibernating in groups. If confirmed, this would push back the evolutionary origins of complex social or survival behaviors in snakes by tens of millions of years. That idea cannot be proven with complete certainty, but it fits the arrangement of the specimens and echoes a behavior still seen in living snakes.

“Modern garter snakes are famous for gathering by the thousands to hibernate together in dens and burrows,” says Michael Caldwell, a U of A paleontologist who co-led the research along with his former graduate student Jasmine Croghan, and collaborators from Australia and Brazil. “They do this to conserve heat through the effect created by the ball of hibernating animals. It’s fascinating to see possible evidence of such social behavior or hibernation dating back 34 million years.”

The anatomy tells a more complex story. Hibernophis shows traits of early booid snakes, along with features seen in Charinaidae, suggesting it may lie near a key evolutionary split. Its uncertain placement makes it especially valuable, capturing an early stage in the evolution of boa-like snakes.

Rather than fitting neatly into existing categories, it reveals that snake evolution was likely more gradual and branching than previously thought. Together, these fossils provide important new insight into how modern boa-like snakes first emerged and diversified.

Reference: “Morphology and systematics of a new fossil snake from the early Rupelian (Oligocene) White River Formation, Wyoming” by Jasmine A Croghan, Alessandro Palci, Silvio Onary, Michael S Y Lee and Michael W Caldwell, 19 June 2024, Zoological Journal of the Linnean Society.
DOI: 10.1093/zoolinnean/zlae073

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