How Snakes Lost Their Limbs and Conquered the World

Losing their limbs may seem like a handicap, yet this very change helped snakes colonise forests, deserts, oceans and underground habitats. New fossils, 3D imaging and genetic studies are showing how these reptiles reshaped their bodies over more than 100 million years.

The earliest snakes most likely evolved on land

Scientists place the emergence of snake ancestors at roughly 160 million years ago, although the oldest fossils still create uncertainty about their original habitat. For decades, researchers have debated whether the first snakes lived in the sea, below ground or on the surface.

Tiago Simões, an evolutionary biologist at Princeton University, notes that ancient fossils have been found in markedly different settings. The leading theory now is that snakes originated on land, possibly in sandy areas where they could travel across the surface while occasionally sheltering in the soil.

Losing limbs made the snake body more efficient

Alex Pyron, an evolutionary biologist at George Washington University, says limb reduction probably took place between 150 million and 125 million years ago. For creatures moving through low vegetation or confined spaces, legs may have impeded movement and caused their bodies to snag on obstacles.

Fossils such as Najash rionegrina, discovered in Patagonia and dated to around 95 million years ago, still retained hind limbs. However, the four-limbed ancestor that would conclusively connect lizards with modern snakes has not yet been identified, leaving a significant gap in the group’s evolutionary record.

What changes transformed snakes?

A major study published in Science in 2024 examined skulls, diets and thousands of genes from snakes and lizards. It found that, around 125 million years ago, snakes underwent rapid changes to their vertebral columns, feeding and head structure.

• Gradual loss of both forelimbs and hind limbs
• Body elongation, producing hundreds of vertebrae
• A skull separated into highly mobile sections
• Jaws able to widen the mouth opening
• Adaptation to highly varied diets and habitats

These changes enabled snakes to move efficiently on the ground, in water and through trees. Frank Burbrink, curator of herpetology at the American Museum of Natural History, says this bodily flexibility allowed the group to adapt quickly whenever new environmental opportunities arose.

Watch the video shared by the Zoomundo YouTube channel, which tells the story of the emergence and evolution of snakes.

A flexible skull expanded feeding opportunities

In snakes, the braincase creates a strong bony enclosure around the brain, while the other bones remain mobile. Michael Caldwell, an evolutionary biologist at the University of Alberta, believes this change may have started even before the limbs disappeared completely.

Elastic ligaments allow sections of the jaws to move apart, while each side of the palate can move independently to guide prey towards the throat. This anatomy lets snakes eat animals far larger than their heads, as well as slugs, fish, snails and even other snakes.

Genetics and fossils may still provide new answers

Genetic evidence has shown that limb loss is associated with reduced activity in a regulatory sequence known as ZRS, which is important in limb development. Studies also suggest that snakes lost the gene linked to producing ghrelin, a hormone associated with hunger, helping them to go for long periods without eating.

Burbrink, Pyron and Simões are sequencing the complete genomes of more than 100 species to reconstruct this history more precisely. Crucial fossils are still missing, but every discovery strengthens one certainty: safeguarding these records is urgent, because every living snake represents the extraordinary outcome of more than 100 million years of evolution.