An 80-million-year-old snake fossil from Brazil is helping solve the mystery of how lizards lost their limbs and began to slither

Snakes have appeared in myths and stories for as long as people have told them. But ask scientists how snakes lost their legs and evolved into their long, limbless form, and the answer is still not settled.

That may be changing. According to the journal Nature, researchers have described an exceptionally preserved, roughly 80-million-year-old snake fossil from Brazil that offers some of the clearest physical evidence yet about how the earliest snakes actually lived. The fossil, named Tametara mirim, was unearthed in São Paulo state and is only about 17 inches long, but it is already reshaping a debate on snake evolution that has run for more than a century.

The paper reports that the fossil preserves not just the skull but also the braincase and delicate inner-ear anatomy, and the team used high-resolution micro-CT scans to build a 3D reconstruction of the brain. Those scans point to a snake with a poorly developed optic lobe, an enlarged otic capsule and a thickened skull, a combination the authors say fits a burrowing lifestyle rather than a surface hunter.


CT scans of the 20-millimeter skull revealed a poorly developed optic lobe, an enlarged otic capsule and an unusually thick cranium, which the authors say point to a snake that navigated by touch and vibration rather than sight. They also note that Tametara mirim is one of only four dinosaur-age snake fossils preserved well enough to answer questions about early ecology.

How snakes lost their limbs has puzzled scientists for more than a century
Snakes are, in evolutionary terms, a lineage that diverged from lizards. At some point during the age of dinosaurs, one lizard lineage is thought to have lost its limbs and evolved into the tube-like form we recognize today. More than 4,000 snake species live today on every continent except Antarctica, in deserts, forests, and oceans alike.

Scientists have not had enough well-preserved fossils to determine exactly how that transformation happened. For decades, three competing theories about their origin fought it out: they started out swimming in water, they evolved on land, or they began as underground burrowers. With so few well-preserved early snake fossils to work from, scientists could not settle the argument.

Why Tametara mirim stands out
Tametara mirim gives researchers a way to test that debate directly. It is one of only four known snake fossils from the age of dinosaurs preserved well enough to study in this kind of detail, according to Science News. It is also the first articulated snake skeleton found in Brazil, meaning the bones were still connected as they were in life rather than scattered, making it an unusually complete fossil for its age.

The authors say the fossil is only one of four dinosaur-age snake specimens preserved well enough for this level of study, and they used the intact skull to infer its senses and habits. In the paper, Tametara mirim is described as a new stem snake from Brazil with unprecedented detail in the cranial nerves, inner ear and brain anatomy, giving the most integrated reconstruction of early snake neuroanatomy yet.

The fossil’s skull and braincase were still intact, letting researchers reconstruct its brain anatomy from CT scans and infer a subterranean lifestyle. According to the report, the snake lived 85 million to 75 million years ago.

Researchers used high-resolution CT scanning to study the fossil’s skull and reconstruct its brain cavity, producing what the authors call the most detailed reconstruction of an early snake brain to date. Two features stood out. First, the skull bone was unusually dense and thick in the same area where modern head-first burrowing lizards build up bone to handle the strain of digging. Second, the reconstructed brain showed reduced visual centers, a trait expected in an animal that spent its life underground in the dark.

Tiago Simoes, an evolutionary biology professor at Princeton University who led the study, has described snakes as having one of the most extreme body plans of any vertebrate and their origin as one of the biggest unsolved puzzles in vertebrate evolution.

A surprising twist in the story
The picture becomes more complicated. The team ran the same brain analysis on Dinilysia patagonica, a well-known early snake fossil from Argentina, and expected a similar result. Instead, they found the opposite. Both the shape of its brain cavity and the microscopic structure of its bones pointed to a surface-dwelling animal, not a burrower. The two oldest snakes studied in this level of detail turned out to have brains more different from each other than most living snake species.

That finding suggests snakes may not have shared a single ancestral lifestyle. Simoes has suggested that the ancestral condition for snakes probably was not locked into one habitat at all, but instead sat somewhere between burrowing underground and moving around on the surface. In other words, early snakes appear to have diversified into different lifestyles early on rather than following a single evolutionary path.

What scientists still do not know about early snakes
Tametara left no living descendants, so it is a side branch on the snake family tree rather than a direct ancestor of snakes alive today. Because the fossil did not preserve any teeth, researchers cannot say whether it was venomous. Its hip region was also not preserved, though its close Cretaceous relative Najash rionegrina is known to have had well-developed hind limbs. According to Reuters' coverage of the discovery, republished by Yahoo News, the animal lived alongside long-necked, plant-eating dinosaurs, crocodiles, and early birds.

Why snakes lost their legs
This fossil offers a rare close-up look at a stage when the snake body plan was still evolving. It is a reminder that even one of the animal kingdom’s most successful body plans evolved gradually. It branched and diversified across tens of millions of years before settling into the slithering, limbless shape we associate with snakes today.