A fossil found in Argentina is changing how scientists see the origins of snakes. The remains of __Najash rionegrina__ show that early ones still had hind limbs and kept skull bones that are missing in modern species. Dating back nearly 100 million years, this specimen sheds light on a stage of evolution that has long been unclear.
It shows that reptiles did not become fully limbless all at once, but went through a gradual transformation. For years, the early history of snakes has been hard to piece together because of limited fossils. Many ideas were built on incomplete evidence, leaving open questions about how their bodies and skulls evolved.
A Snake That Still Had Legs And A More Complete Skull
The fossil of Najash rionegrina clearly shows hind limbs, confirming that early snakes kept these features longer than previously thought. The 2019 study in Science Advancesdescribes it as a species where limb reduction was still in progress.
“Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes,” the authors wrote.
Another key detail is the jugal bone, or cheekbone, visible in the skull. This bone is almost completely absent in living snakes. Its presence in Najash clears up a long-standing misunderstanding. Co-author Michael Caldwellpointed out that this corrects more than a century of confusion about this reptile skull anatomy.
“This research revolutionizes our understanding of the jugal bone in snake and non-snake lizards,” he said. “After 160 years of getting it wrong, this paper corrects this very important feature based not on guesswork, but on empirical evidence.”
Scans Reveal What The Rock Was Hiding
To study the fossil without damaging it, researchers used micro-CT scanning. This method allowed them to rebuild the skull in detail and see structures hidden inside the rock, including nerve channels and blood vessel pathways.
The team explains that these scans revealed features that had been missed or misread before. They also helped clarify how certain skull bones weregradually reduced or lost over time, leading to the flexible skulls seen in modern cold-blooded animals.
The Origins Just Got More Complicated
The anatomy of Najash challenges the idea that silent predator started out as small burrowing animals. Lead authorFernando Garberoglioinstead describes ancestors that were larger-bodied with wide mouths.
“Our findings support the idea that the ancestors of modern snakes were big-bodied and big-mouthed — instead of small burrowing forms as previously thought,” he explained. “The study also reveals that early snakes retained their hindlimbs for an extended period of time before the origin of modern snakes which are for the most part, completely limbless.”
Later findings support this more complex view. Fossils like __Boipeba tayasuensis__ show that some early blind snakes could grow to over one meter long. Another study suggests early ones mixed burrowing habits with more flexible behavior, rather than sticking to one lifestyle. Taken together, these discoveries show that their evolution followed several paths at once. Najash rionegrina still stands out as one of the clearest examples of that transition in progress.
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