The Serpent's Tale: How Snakes Lost Their Legs and Conquered the World

A 2025 review in the Annual Review of Ecology, Evolution, and Systematics synthesizes the latest evidence on snake evolution, revealing a story of dramatic adaptation, lost limbs, and rapid diversification.

Origins in the Sand

The earliest snakes likely lived on land, possibly in sandy environments, with some ability to burrow. This conclusion is drawn from evidence ranging from brain anatomy to fossils like Najash rionegrina and Dinilysia patagonica, both unearthed in Patagonia and dating to roughly 95–80 million years ago. These findings challenge older theories of an aquatic origin for all snakes.

"The current consensus is that early aquatic snakes entered water from land." — Tiago Simões, Princeton University

The Great Leg Loss

Snakes lost their legs between 150–125 million years ago. A remarkable four-legged fossil from Scotland, Breugnathair elgolensis (described in 2025), may represent a snake ancestor—or a lizard with convergent features. The exact timing and mechanism of leg loss remain a mystery, but genomic comparisons across 1,000+ species have identified genes linked to limb loss and fasting tolerance (including a missing ghrelin gene).

"Despite lacking limbs and the ability to chew, snakes are among the most successful animals." — Marc Tollis, Northern Arizona University

Jaw-Dropping Adaptations

Snakes developed flexible skulls with movable bones, enabling them to swallow large prey. This adaptation appeared around 125 million years ago, coinciding with a major dietary diversification. Combined with body elongation—driven by an increased number of vertebrae—snakes improved their locomotion on land, in trees, and in water.

A Modern Success Story

Over 4,000 living species now occupy six continents and oceans. Snakes fill an extraordinary range of niches: burrowing, swimming, and even gliding. Their diets are equally diverse, spanning slugs, fish, mammals, and other snakes.

"Snakes account for about one-third of lizard diversity." — Alex Pyron, George Washington University

Unresolved Mysteries

Despite major advances, key questions remain:

• The oldest snake fossils (~160 million years) are still missing; the earliest known fossils date to only ~125 million years ago.
• The closest living relatives of snakes remain uncertain; candidates include iguanas, Komodo dragons, and extinct mosasaurs.
• Blind snakes are too specialized to represent the ancestral snake form, according to Catie Strong (Harvard University).

Looking Ahead

Ongoing fossil discoveries and whole-genome sequencing of ~100 species are expected to refine snake evolutionary history. The field is poised for rapid progress, with new specimens and molecular data promising to fill in the gaps of this serpentine saga.