Rare 3D Fossil Reveals Early Snake Lived Underground

An 85-million-year-old snake fossil discovered in southeastern Brazil is providing the earliest concrete evidence of a fossorial, or burrowing, lifestyle in ancient serpents. Published July 22 in the journal Nature, the specimen—named Tametara mirim—retains a three-dimensional braincase. In the fossil record, pressure typically flattens remains, making this preservation exceptionally rare.

CT Scans Expose Subterranean Skull Design

Paleobiologist Tiago Simões of Princeton University notes that this level of preservation allows scientists to examine specific anatomical features that are usually lost. By using CT scans to reconstruct the brain anatomy, researchers determined that the snake likely spent its life underground, digging tunnels by butting its head against the dirt.

Inner Ear Adaptations Reveal Vibration-Based Hunting

The fossilized skull, measuring only 20 millimeters in length, reveals a specialized sensory profile suited for a subterranean environment. While the snake possessed a poorly developed optic lobe, suggesting limited vision, it featured an enlarged otic capsule. This bony structure, which protects the inner ear, is a hallmark of snakes that sense vibrations.

The physical structure of the skull further supports this burrowing hypothesis. The bone is unusually thick, providing the structural integrity necessary for pushing through compacted soil. This discovery challenges previous assumptions about early snake evolution, indicating that the lineage was already diversifying into specialized ecological niches during the Cretaceous Period.

Branching Lineages Rewrite the Cretaceous Family Tree

The discovery of Tametara mirim highlights that early snake evolution was more complex than previously understood. Paleontologist Michael Caldwell of the University of Alberta in Edmonton, Canada, who was not involved in the research, observes that the ancient snake family tree likely included many branching lineages with their own unique anatomies and lifestyles.

While the exact environment of the first snake ancestors remains a subject of ongoing debate, the evidence suggests a shift in lifestyle capabilities over millions of years. The earliest known snake ancestor, dating back 167 million years, may have been somewhat adapted for an underground lifestyle, though was not nearly as good at burrowing as Tametara mirim.

The Hunt for Intact Braincases Continues

The transition from surface-dwelling to specialized environments, such as underground or aquatic habitats, occurred gradually rather than instantaneously. Researchers suggest that the 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.

Finding additional fossils with intact braincases could help resolve that debate. By studying these endpoints of a very long evolutionary history, scientists aim to better understand the lineage that led to the diverse range of snakes observed today.