3D Fossil Skull Reveals Oldest Burrowing Snake
One Tiny Skull, One Giant Question
For decades, the oldest snakes were believed to have lived on the surface or in the water. The earliest known snake ancestor, a creature that lived 167 million years ago, was thought to have been somewhat adapted for an underground lifestyle, but not nearly as good at burrowing as later species. Then, in 2020, scientists in southeastern Brazil uncovered a fossil that shattered this assumption.
The fossil belonged to a previously unknown snake species that lived 85 million to 75 million years ago. Researchers named it Tametara mirim, after the words for “adorned” and “small-sized” in the Tupi-Guarani language of Brazil. Its skull, only 20 millimeters in length, was preserved in three dimensions — a rarity for snake fossils, which are typically flattened like pancakes by millions of years of pressure. [1]
This quality of preservation allowed paleobiologist Tiago Simoes of Princeton University to answer questions that are impossible to answer with flattened fossils. Using CT scans, the team reconstructed the snake’s brain anatomy. The shape of snake brains closely matches the inside of their braincase, unlike human brains which float in fluid within the skull. The scans revealed that T. mirim had a poorly developed optic lobe, meaning it probably could not see very well. [1]
But its otic capsule — a bony structure that protects the inner ear — was enlarged. This is a feature often seen in snakes that sense vibrations. The snake also had an unusually thick skull. These features suggest T. mirim lived underground, digging tunnels by butting its head against the dirt. This is the earliest concrete evidence of a fossorial snake — a serpent that burrowed underground.
The Next Step: Finding Fossils That Show Transitions
The discovery of T. mirim suggests that early snakes explored more habitats and lifestyles than previously thought. By the Cretaceous Period, snakes were swimming, slithering, and, in T. mirim’s case, digging. This apparent increase in diversity in the Cretaceous could be because snakes evolved new sensory functions and abilities very quickly, or because they were diverse all along.
Simoes says that finding new fossils with intact braincases could help resolve that debate. To better understand how snakes diversified into all their modern forms, scientists will need to find fossils that show 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,” Simoes says.
The snake family tree probably included many branching lineages with their own unique anatomies and lifestyles. What is clear is that early snake evolution 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 Research Group That Will Test the Replication
The fossil is one of only four snake fossils from the Age of Dinosaurs preserved this well. The researchers, led by Tiago Simoes of Princeton University, published their findings in the journal Nature on July 22. Simoes says the next step is to find more fossils with intact braincases, which could help resolve the debate about early snake diversity.