A synthesis of recent paleontological and genetic research provides a more detailed timeline for the origin and diversification of snakes, indicating that the earliest snakes likely lived on land and that the lineage diversified rapidly after evolving key adaptations around 125 million years ago.
Ancestral Habitat and Limb Loss
Evidence from fossils and brain anatomy suggests the earliest snakes lived on land, possibly in sandy environments, with some capacity for burrowing. Fossils from Patagonia, including Najash rionegrina and Dinilysia patagonica (dating to approximately 95–80 million years ago), support this terrestrial origin.
A separate study analyzing an 80-million-year-old fossil snake, Tametara mirim, from São Paulo state, Brazil, found traits consistent with a head-first burrower, including dense skull bones and reduced visual centers. This study also noted that the two oldest snake brains examined were more different from each other than most living snake lineages are. Analysis of the Dinilysia fossil from Argentina indicated it was not a burrower but lived on the surface. According to this research, the earliest snake lineage likely was subterranean, but early snakes quickly diversified into different habitats.
"The two oldest snake brains examined were more different from each other than most living snake lineages are."
Snakes lost their legs between 150 and 125 million years ago. A four-legged fossil from Scotland, Breugnathair elgolensis (described in 2025), may be either a snake ancestor or a lizard with convergent features.
Key Adaptations and Diversification
Snakes developed flexible skulls with movable bones, allowing them to swallow large prey. This adaptation appeared around 125 million years ago and coincided with a diversification of their diet.
The increase in the number of vertebrae improved locomotion across various environments, including land, trees, and water.
There are over 4,000 living species of snakes on six continents and in oceans. They occupy a variety of ecological niches (burrowing, swimming, gliding) and have diverse diets (including slugs, fish, mammals, and other snakes). One researcher noted that snakes account for about one-third of lizard diversity.
Unresolved Questions
- The oldest known snake fossils are from approximately 125 million years ago; no fossils have been found from the estimated earliest snake origins (~160 million years ago).
- The closest living relatives of snakes remain uncertain; candidates include iguanas, Komodo dragons, and extinct mosasaurs.
- The exact timing and mechanism of leg loss is unknown.
Methods
Researchers combined fossil analysis, CT scans of braincases, genomic comparisons (5,400 genes across over 1,000 species), and dietary records to reach these conclusions. Ongoing fossil discoveries and whole-genome sequencing of approximately 100 species are expected to further refine the evolutionary history of snakes.