Rare 3D snake fossil reveals secrets of its unusual lifestyle

The anatomy of the snake’s skull suggests that it lived underground, unlike other early snakes.

An illustration of a prehistoric snake burrowing underground with birds and dinosaurs in the background.

Most snake fossils are two-dimensional. Sandwiched in the rocks, the pressure of millions of years flattens them like a pancake. But in 2020, scientists discovered a particularly well-preserved snake fossil in southeastern Brazil. The snake’s tiny skull – measuring just 20 millimeters long – was in 3D, with its braincase still intact.

The fossil’s well-preserved skull now provides the first concrete evidence of a burrowing snake — a snake that burrowed underground. And it suggests that early snakes explored more habitats and lifestyles than previously thought, researchers report July 22 in Nature.

The fossil belongs to a previously unknown species of snake that lived 85 to 75 million years ago. Researchers named it tametara childafter the words for “ornate” and “small” in the Tupi-Guaraní language of Brazil. It is one of four snake fossils from the dinosaur era that have been so well preserved.

“This quality of preservation allows us to answer questions that you simply can’t answer if you don’t preserve the right body parts,” says paleobiologist Tiago Simões of Princeton University.

The skull and cranial casing (inset) of a new ancient snake species were still intact. The rare discovery allowed scientists to piece together what the snake’s brain would have looked like, details that provided clues about its behavior. Agustin Martinelli

Unlike the human brain, which floats in the fluid of our skull, the shape of the snake’s brain closely matches the interior of its cranial case. Using CT scans, researchers reconstructed T. mirimthe anatomy of the brain. Well-developed brain regions correspond to the senses the snake relied on most.

T. mirim had an underdeveloped optic lobe, so he probably couldn’t see very well. But its otic capsule, a bony structure that protects the inner ear, has been enlarged – a feature often seen in snakes that detect vibrations. He also had an unusually thick skull. These characteristics suggest T. mirim lived underground, digging tunnels by banging their heads against the earth.

The environment in which the snakes appeared remains a mystery. But the first known snake ancestor, who lived 167 million years ago – may have been somewhat adapted for a underground lifestylebut was not as good at digging as T. mirimsays Simões.

During the Cretaceous, snakes swam, slithered and, in T. mirimIt is, digging. Simões says the apparent increase in diversity in the Cretaceous could be because snakes evolved new functions and sensory abilities very quickly or because they were diverse all along. Finding new fossils with intact braincases could help resolve this debate.

What is clear is that the early evolution of snakes was much more complex than previously thought, says Michael Caldwell, a paleontologist at the University of Alberta in Edmonton, Canada, who was not involved in the research. The snake family tree likely included many branching lineages with their own analyses and lifestyles.

To better understand how snakes diversified into all their modern forms, scientists will need to find fossils showing the transitions between different lifestyles. “When organisms become highly specialized for a particular environment, they don’t become so in the blink of an eye,” says Simões. “What we have today is the end point of a very long evolutionary history.”