Ancient snake fossil with legs rewrites reptile evolution history

A remarkable fossil discovered in Argentina is reshaping our understanding of snake evolution. Named Najash rionegrina, this ancient creature had well-developed hips and hindlimbs—features rarely seen in snakes today. The find challenges long-held assumptions about how and where these reptiles first evolved.

Najash rionegrina was unearthed in Patagonia's Cretaceous sediments, dating back around 95 million years. Unlike many early snake fossils found in marine rocks, this specimen came from terrestrial deposits, suggesting snakes may have originated on land rather than in water.

The fossil's most striking feature is its pelvis and functional hindlimbs, which extended beyond the ribcage. These were not mere vestigial spurs like those seen in some modern boas and pythons but fully formed limbs, indicating they played an active role in movement. This discovery supports the idea that snakes once had a much broader range of body structures before losing their limbs over time.

A 2019 study using CT scans revealed even more about Najash. Its skull displayed a mix of lizard-like and snake-like traits, reinforcing its position as one of the most basal branches of Serpentes. Researchers believe leg loss in snakes happened gradually, with hindlimbs disappearing long after forelimbs had already vanished.

The significance of Najash lies in its well-preserved skeleton, particularly its articulated hindlimbs and sacrum—features absent in nearly all other fossil snakes. This provides strong evidence that snakes evolved from limbed lizards living on land, contradicting earlier theories of an aquatic origin.

The discovery of Najash rionegrina offers concrete proof that early snakes were far more diverse in form than previously thought. Its terrestrial origins and well-developed limbs suggest a complex evolutionary journey before snakes became the limbless creatures we recognise today. The fossil remains a key piece in unravelling the mystery of snake ancestry.