Paleontologists have unearthed a remarkably well-preserved snake fossil in Brazil, challenging existing theories about the lifestyle of early snakes and intensifying a long-standing debate over whether their ancestors were burrowers, swimmers, or surface dwellers. Their findings were published in the journal Nature.
“Snakes are essentially highly modified lizards,” said study co-author Roy Ebel from Museums Victoria Research Institute. “During the age of dinosaurs, one lineage of lizards shed their limbs and elongated their bodies. The big question is why. For over a century, different ideas have competed against each other.”
One theory proposes that the first snakes inhabited bodies of water, evolving a long, legless body adapted for swimming, much like an eel.
A second hypothesis suggests they lived on the land surface, among leaf litter and vegetation, where shortened limbs might have aided movement through dense ground cover.
A third view contends they moved underground, losing their limbs and elongating their bodies to adopt a burrowing lifestyle, tunneling head-first like modern blind snakes.
The challenge is that the evidence relies on a very limited fossil record. Fewer than ten skeletons of early snakes from that era are known.
In their study, Ebel and his colleagues examined an exceptionally well-preserved skull and postcranial material from a previously unknown species of primitive snake.
This reptile, named Tametara mirim, lived in what is now Brazil during the Late Cretaceous period, approximately 85 to 75 million years ago.
The fossil was discovered in 2020 in a quarry near the city of Presidente Prudente in the Brazilian state of São Paulo.
This specimen is the first articulated snake fossil from Brazil and one of the few three-dimensionally preserved snake fossils from the Mesozoic era worldwide.
A distinctive feature of the Tametara mirim skull is its extraordinary level of detail, preserved to the present day.
Using high-resolution computed tomography, paleontologists reconstructed the animal’s brain, cranial nerves, and inner ear with unprecedented clarity, creating what they describe as the most complete picture to date of brain anatomy in a primitive snake.
The reconstruction results showed that the shape of the snake’s brain does not resemble that of any other early snake, nor any living snake, indicating far greater diversity in brain structure—and likely in sensory abilities—over the course of snake evolution than previously recognized by scientists.
Ebel and his co-authors compared the brain data with an analysis of the fossil’s bone microstructure—a method that determines an animal’s lifestyle based on the density and thickness of its skeleton.
Both lines of evidence independently pointed to the same conclusion: Tametara mirim was a burrowing animal.
“In animals that burrow head-first, the bone at the top of the skull becomes denser and thicker,” said Ebel. “This trait has evolved independently in numerous lineages of burrowing lizards. We hypothesize that it reinforces the skull, protecting it from the strain of being used as a digging tool.”
“Tametara mirim shows exactly this combination of features. In fact, based on our lifestyle reconstruction, the fossil ranks among the most specialized head-first burrowing creatures, and it differs significantly from lizards and snakes with a more generalist lifestyle,” he added. “But the top of the skull wasn’t our only evidence. We also digitally recreated its brain cavity—this is the most detailed reconstruction of its kind ever performed for any ancient snake.”
This cavity would have closely matched the shape of the living animal’s brain. Reduced optic centers and a simplified forebrain structure point in the same direction as the bones: underground.
The study’s findings stood in sharp contrast to a similar analysis of Dinilysia patagonica, the oldest snake from Argentina and one of the best-known Cretaceous snake fossils, whose brain shape and bone structure instead pointed to a non-burrowing, surface-dwelling lifestyle.
Taken together, these two fossils suggest that early snake lineages were not ecologically uniform.
Rather than descending from a single ancestor with one fixed lifestyle, snakes appear to have branched early, adopting burrowing, terrestrial, and even marine forms, with different lineages adapting repeatedly over tens of millions of years before modern snake groups emerged.
“For the two oldest snakes we can study in such detail, their brains differed more from each other than those of most living snake lineages. Dinilysia patagonica was not a burrowing snake. It lived on the surface,” said Ebel. “Their brains suggest how differently these two animals perceived the world around them.”
Tametara mirim had poor vision, typical of creatures that spend their entire lives in darkness. Dinilysia patagonica, on the other hand, had sensory organs adapted for open terrain. At the dawn of their history, snakes were already tuning their senses to entirely different habitats.
The findings add to a small but growing collection of well-preserved Cretaceous snake fossils that paleontologists are using to solve one of the toughest puzzles in vertebrate evolution: how a lizard-like ancestor gave rise to the elongated, legless body plan seen in more than 4,200 living snake species today.
“Our results provide quantitative, multi-system evidence for a burrowing lifestyle in a primitive snake, resolving a long-standing debate that was previously addressed mainly through qualitative analysis or isolated anatomical data,” the researchers concluded. “More broadly, they emphasize that snake origins were shaped not by a single ecological pathway, but by parallel and overlapping experiments with burrowing and other lifestyles, highlighting the ecological breadth underlying one of the most dramatic transformations in body plan in vertebrate evolution.”
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