Scientists discovered four snakes curled together in a burrow for 38 million years as the volcanic ash preserved their remarkable fossils |

Overview of Hibernophis breithaupti (UW11120 on two blocks), showing holotype (UW-11120-A) and paratype (UW-11120-B) specimens as exposed on the surface. Image Credit: Zoological Journal of the Linnean Society

A snake fossil discovery in Wyoming has given palaeontologists an unusually close look at the lives of these ancient reptiles. Four complete skeletons belonging to a newly recognised species, have helped researchers understand an early member of the ‘boa family’ and the history of small, burrowing snakes in North America. Three of the snakes were preserved together in a burrow-like cast, while a fourth specimen from the same formation provided additional evidence for identifying the species. The fossils date to the early Oligocene, more than 30 million years ago, and were found in the White River Formation. Their preservation is especially important because ancient snakes are usually known from scattered vertebrae rather than complete skeletons. The findings, published in the ‘Zoological Journal of the Linnean Society,’ offer a rare glimpse into snake evolution and possibly ancient communal sheltering behaviour.

What makes these 38-million-year-old snake fossils unique

Fossil snakes are often frustratingly incomplete. Their slender skeletons can break apart and become scattered before fossilisation, leaving researchers with isolated vertebrae rather than a complete animal that can be studied from head to tail. The discovery described is therefore particularly valuable. Researchers examined four fossil snakes belonging to the newly established species ‘Hibernophis Breithaupti.’ Three are part of specimen UW-11120, preserved together in two matching blocks of rock. Two can be seen on the surface, while CT scanning revealed a third snake hidden inside the rock. A fourth specimen, UW-11990, came from a different locality in the same formation.The arrangement of the first three fossils had already attracted attention decades ago. According to the research paper, scientists Brent H. Breithaupt and David Duvall first described them in 1986 and suggested that they could represent a fossil snake hibernaculum, essentially a place where snakes sheltered together. The new study has now provided the detailed anatomical work needed to identify what these animals actually were

Overview of UW-11990, the referred specimen of Hibernophis breithaupti. Image Credit: Zoological Journal of the Linnean Society

How did these ancient snakes become preserved together

The fossils were found in Wyoming’s White River Formation, in rocks dating to the early Oligocene. The study explains that surrounding material is a fine, sandy mudstone and that the sediments were probably deposited during a small flood. The volcanic connection comes from the geology of the wider formation. The study notes that volcanic ash layers elsewhere in the White River Formation have been used to establish a minimum age of about 32 million years for these rocks. The Daily Galaxy describes the preservation as the result of volcanic ash, mud and floodwater working together to bury and protect the snakes. That combination created an unusual fossil record. Instead of being scattered by the environment, the snakes remained sufficiently intact for researchers to study their bones.

Hibernophis Breithaupti and its position in the snake family

The researchers determined that the fossils represented a previously unknown snake and named it Hibernophis Breithaupti. The genus name combines the Latin ‘hibernare,’ meaning to pass the winter, with the Greek word ‘ophis,’ meaning snake. The name reflects the unusual preservation of the four individuals and the earlier suggestion that they may have occupied a shared winter shelter. The study found that Hibernophis could not simply be placed among previously recognised fossil snakes such as Ogmophis and Calamagras. Detailed examination showed differences in the vertebrae and skull, allowing the researchers to establish it as a distinct species. Its position on the snake family tree is also significant. The researchers’ evolutionary analysis places HibernophisBreithaupti as the sister group to all other booids. But another possible position close to some New World ‘erycines’ and ungaliophiines could not be completely ruled out.

Did the snakes really hibernate together

This is perhaps the most intriguing question raised by the fossils, but it requires some caution. The three snakes preserved together were found in an arrangement that resembles a shared shelter or hibernation site. The study records that their unusual preservation had previously been interpreted as a possible fossil hibernaculum. The Daily Galaxy also highlights the comparison with modern garter snakes, which can gather in large numbers inside dens and burrows during cold periods. However, the fossil evidence cannot prove exactly why the snakes were together. The researchers can identify their position and anatomy, but behaviour is much harder to establish millions of years later. The arrangement is therefore best treated as possible evidence of communal sheltering rather than definite proof that the snakes were hibernating.

Analysing snake evolution through these complete fossils

The discovery matters beyond the unusual sight of several snakes preserved together. Complete fossil snakes are rare, meaning that important parts of their anatomy are often missing from the fossil record. These four Hibernophis specimens provide researchers with both skull and body information. The team used detailed anatomical comparisons and CT scans, alongside evolutionary analyses, to determine where the species belonged. The findings also suggest that the early history of ‘boa relatives’ in North America was more complicated than previously shown. Instead of relying mainly on isolated vertebrae, palaeontologists can now examine a much more complete animal. The story of HibernophisBreithaupti is about an unusually preserved moment that survived long enough for modern technology to reveal it. What began as a strange cluster of fossil bones has become evidence for a previously unknown species and a potentially ancient behaviour, offering a rare glimpse into how snakes lived millions of years ago.