How Did Some Reptiles Lose Their Limbs to Become Snakes? An 80-Million-Year-Old Fossil Helps Uncover the Winding Evolutionary History

An ancient snake dating to roughly 80 million years ago is adding a new twist to one of evolution’s enduring questions: how did reptiles with legs become the limbless animals that move across the ground today? The fossil points toward a creature that probably spent much of its time below the surface, digging or moving through underground spaces. Yet evidence from another snake of approximately the same age suggests a different way of life, one closer to the open ground. Together, the findings indicate that the earliest snakes may not fit a single environmental origin story.

Snakes are instantly recognizable for their long bodies, missing limbs and remarkable flexibility. Those features are so familiar that it can be easy to overlook how unusual they are among reptiles. Scientists generally view snakes as descendants of lizard-like ancestors, but the path from a four-limbed reptile to a highly elongated, limbless animal remains difficult to reconstruct. Fossils are scarce, and the surviving specimens often preserve only part of the body or provide limited clues about how an animal lived.

The newly described ancient species offers one such clue. Its anatomy has led researchers to conclude that it was likely adapted to life underground. Burrowing would have presented very different demands from moving across exposed terrain or swimming through water. A narrow body could help an animal push through soil, enter tight spaces and navigate tunnels, while limbs might become less useful or even obstructive in those conditions. The fossil does not settle every question about snake origins, but it strengthens the case that underground habitats were important for at least some early forms.

At the same time, a separate snake from a similar period appears to have occupied the surface rather than a subterranean setting. That contrast matters because it challenges the idea that all early snakes evolved through one shared habitat. Instead of a single lineage following one ecological route, different snake groups may have been adapting to distinct surroundings at around the same point in deep history. The new research therefore shifts attention from finding one definitive birthplace for snakes to understanding a potentially more varied evolutionary landscape.

For decades, the leading possibilities have centered on three settings: water, land and the underground world. Each proposal offers an explanation for why a lizard ancestor might gradually lose its legs and develop a longer body. An aquatic origin could favor streamlined movement; a surface-based origin could reflect changes in locomotion or hunting; and a burrowing origin could reward a compact, tunnel-ready shape. The problem is not a shortage of hypotheses. It is the limited fossil record available to test them against one another.

The story unfolded during the Mesozoic Era, the vast span commonly called the age of dinosaurs. It extended from about 245 million to 65 million years ago and ended after the asteroid impact associated with a mass extinction. Somewhere within that interval, one branch of lizard relatives underwent an extraordinary transformation. Its body became increasingly stretched, its limbs disappeared, and its descendants eventually gave rise to the diverse snakes known today. The underlying evolutionary question is not merely when this change occurred, but what pressures made it advantageous.

That question is especially challenging because anatomy alone can point in more than one direction. A long, flexible body can serve an animal in soil, under vegetation, through narrow rock openings or in water. Features that appear suited to one lifestyle may also prove useful in another. Researchers must therefore compare skeletal details with the geological setting of a fossil and with patterns seen across living reptiles. An 80-million-year-old specimen can provide a valuable data point, but it cannot by itself describe every stage between early lizards and modern snakes.

The emerging picture is less tidy than a single origin in a single habitat, but potentially more realistic. If early snake relatives occupied different environments, the loss of limbs may have been linked to several ecological paths rather than one universal cause. That possibility would help explain why the evidence has been difficult to align behind a single theory. It also means future discoveries will be important not simply for adding older fossils to museum collections, but for revealing where those animals lived and how their bodies functioned.

What comes next depends on whether additional fossils can preserve the traits and environmental context needed to compare early snake lineages more closely. Researchers will be watching for specimens that clarify body shape, limb reduction and habitat, particularly from periods close to the major changes in snake anatomy. For now, the newly identified burrowing species and its surface-dwelling contemporary offer a caution against oversimplification: the winding route to modern snakes may have passed through more than one kind of world.

Source: Smithsonian Magazine