A 100-million-year-old snake fossil from Argentina still had hind legs and a cheekbone that vanished in modern snakes.
The fossil shows early snakes kept legs longer than thought
The specimen belongs to Najash rionegrina, a rear-limbed snake that lived during the Cretaceous period in what is now northern Patagonia. Micro-CT scanning revealed the skull retained a jugal bone, a feature nearly absent in today’s snakes, indicating a slower transition to limblessness than earlier models suggested.
Scientists corrected a 160-year misunderstanding of snake skull anatomy
For generations, researchers misidentified the jugal bone in snakes and their relatives, but the Najash fossils provided direct evidence to resolve the debate. Michael Caldwell, a co-author and professor at the University of Alberta, said the findings correct the record based on empirical data rather than guesswork.
The find challenges the idea that snakes evolved from small burrowers
Instead of originating as tiny underground dwellers, the evidence points to larger-bodied ancestors with wide mouths that gradually lost limbs over millions of years. This aligns with a 2019 study that first used Najash fossils to argue against the burrowing-origin hypothesis, adding weight to the revised evolutionary timeline.
Why did snakes lose their legs?
Scientists believe limb loss in snakes was an adaptation to burrowing or swimming lifestyles, where streamlined bodies offered an advantage, though the exact pressures remain under study.
Is Najash rionegrina a direct ancestor of modern snakes?
Researchers say Najash belongs to an ancient southern lineage related to only a few unusual living snakes, but it is not considered a direct ancestor; rather, it represents an early branch that helps clarify the sequence of evolutionary changes.
