A newly described fossil from Brazil, Tametara mirim, and a reanalysis of Dinilysia reveal strikingly different brains and lifestyles, challenging the idea that snakes followed a single evolutionary path.
How snakes lost their legs is one of the long-running puzzles of evolutionary biology. One camp has argued that limbless bodies first evolved for burrowing, as legs became a hindrance underground. Another has proposed that snakes arose in water, where a long, flexible body is an asset for swimming. A new fossil suggests both camps may be partly right.
In a study published in Nature, an international team describes a new species of early snake, Tametara mirim, from rocks in southeastern Brazil dated to about 80 million years ago. Together with a reanalysis of another ancient snake, the find indicates that early snakes were already experimenting with very different ways of life.
“Our findings show that early snakes had already achieved remarkable ecological and morphological diversity by the Late Cretaceous, around 80 million years ago,” said Tiago R. Simões, an assistant professor at Princeton University and the study’s lead author.
An exceptional skeleton
Snakes are highly modified lizards, and today there are more than 4,000 living species. But their early history is poorly documented, because snake skeletons are delicate and rarely preserved intact.
Tametara mirim is an exception. Found in the Adamantina Formation, deposits that have also yielded sauropod dinosaurs and ancient birds, it is one of the best-preserved fossil snake skeletons known.
The researchers used computed tomography, a form of X-ray scanning, and a technique called cinematic 3D rendering to reconstruct the snake’s skull and vertebrae in detail. They also reconstructed its endocast, a model of the space the brain occupied inside the skull.
The oldest known snake fossils date to roughly the middle of the Jurassic period, more than 160 million years ago, though many are fragmentary. Some fossil snakes from the Cretaceous, such as Najash rionegrina from Argentina, still had small hind limbs, offering glimpses of the transition from lizard-like ancestors.
Two snakes, two brains
The team compared Tametara with Dinilysia patagonica, a fossil snake from Argentina. Their brains turned out to be very different.
Dinilysia patagonica, which lived around 85 million years ago, has long been a key species in studies of snake evolution because its skull is relatively well preserved. Earlier analyses debated whether it burrowed, swam or lived on the surface. The new brain and bone evidence supports a life on the ground.
“The two had strikingly different brain shapes, both from each other and from most other snakes studied,” said Nicolas Di-Poï, a research director at the University of Helsinki and one of the study’s senior authors. “Brain shape and bone microstructure pointed to the same conclusion: Tametara was adapted to burrowing, Dinilysia to life on the ground.”
Bone microstructure, the internal architecture of bone visible under magnification, can reveal how an animal lived. Burrowers, ground dwellers and swimmers tend to have characteristically different bone density and structure.
Simone Macrì, a postdoctoral researcher at the University of Helsinki, said the brain reconstructions were key. “The brain tells a much richer story than the skeleton alone,” Macrì said. “By combining computed tomography-based brain reconstructions with data from living snakes, we could show that early snakes were not simply progressing toward one modern condition but experimenting with different sensory and ecological strategies.”
Underground, on land and at sea
The fossils join evidence from marine sediments, which preserve the remains of early snakes that lived in the sea. Taken together, the findings point to several shifts between burrowing, ground-dwelling and marine lifestyles early in snake evolution.
“Together with evidence from marine sediments, the findings reveal several shifts between burrowing, terrestrial and marine lifestyles in early snake evolution,” Di-Poï said. “Different lineages explored different habitats much earlier than previously thought.”
That challenges the framing of the long debate over snake origins. “This means that early snakes did not follow a single evolutionary pathway,” Macrì said.
Rather than a straight line from one ancestral lifestyle to modern snakes, the picture is of a branching group in which different lineages specialized for different environments early on, much as modern snakes include burrowing blind snakes, tree-dwelling pythons and fully marine sea snakes.
The value of brains
Fossil brains, reconstructed from the cavities they left in skulls, have become an increasingly powerful tool in paleontology. The shape of different brain regions can reveal which senses an animal relied on, such as smell, vision or balance, which in turn hints at its habitat and behavior.
The study, whose senior authors also include Annie Hsiou of the University of São Paulo, does not settle the question of where the very first snakes lived, since Tametara and Dinilysia appeared tens of millions of years after snakes originated. But it shows that by the Late Cretaceous, snakes were already as ecologically inventive as their modern descendants.
Notes
- Simões, T. R., et al. “Exceptional brain and ecological diversity in the earliest snakes.” Nature, 22 July 2026. DOI: 10.1038/s41586-026-10809-9.
- University of Helsinki. “Early snakes explored life underground, on land and at sea.” EurekAlert!, 3 August 2026. https://www.eurekalert.org/news-releases/1138474.
Jasmine Croghan