A remarkably preserved fossil from Argentina is helping scientists clarify the picture of snake evolution. is of sample Najash RionegrinaAn ancient hind-limbed snake that lived about 100 million years ago. Its skull shows that these early snakes still had a cheekbone, also called a jugal bone, a feature that has almost completely disappeared in living snakes. The 2019 study added an important piece to the fossil record that had long been too scarce to clearly explain the early stages of snake evolution.
The findings also challenged a popular old idea about snake origins. Instead of starting out as small burrow diggers, from the evidence Nazash The ancestors of modern snakes were pointed to as large-bodied animals with wide mouths. Fossils also show that early snakes held on to their hind limbs for long periods of time, before the emergence of most of today’s limbless snakes.
“Our findings support the idea that the ancestors of modern snakes were large-bodied and large-mouthed, rather than small-billed forms, as previously thought,” said study lead author Fernando Garberoglio of the Fundación Azara of the Universidad Maimonides in Buenos Aires, Argentina. “The study also shows that early snakes retained their hind limbs long before the origin of modern snakes, which are, for the most part, completely limbless.”
Detail of a skull hidden inside a 100 million year old fossil
The snake fossils described in the study come from northern Patagonia and are closely related to the ancient southern lineage that lived on the continent of Gondwana. Researchers say this group appears to be one of only a few unusual snakes alive today. The team used micro-computed tomography (micro-CT) scanning to look inside the specimen without damaging it. This allowed them to reconstruct the skull in extraordinary detail, including the pathways of nerves and blood vessels as well as the bones buried inside the rock.
That level of detail helped resolve a long-running physiological debate. Scientists had misunderstood the jugal bone in snakes and snake relatives for generations, and Nazash The fossils gave them direct evidence to set the record straight. The study authors argued that these new skulls and skeletons clarified the sequence of bone loss that ultimately led to the formation of the highly specialized skulls of modern snakes.
“This research revolutionizes our understanding of the jugular bone in snakes and non-snake lizards,” said study co-author Michael Caldwell, professor in the Department of Biological Sciences and Earth and Atmospheric Sciences. “After 160 years of being wrong, this paper corrects this important feature not on the basis of conjecture, but on empirical evidence.”
“This research is important for understanding the evolution of the skulls of modern and ancient snakes,” Caldwell said.
The paper, “New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan,” was published. science advancement In 2019.
Later studies added more twists to the snake’s origin story
Research published after 2019 Nazash The paper has made the story even more interesting. In 2020, Paleontologists have described Boipeba tayasuensisA Late Cretaceous blind snake from Brazil. That fossil extended the record of blind snakes deeper into the age of dinosaurs and suggested that some early blind snakes were much larger than their living relatives, reaching lengths of up to 1 meter. The discovery supports the idea that parts of early snake evolution in Gondwana were more diverse and often larger-bodied than previously thought.
Then, in 2023, another science advancement Study By reconstructing the brains of living squamates and fossil snakes, snake origins were viewed from a completely different angle. That work suggested an ancestor of crown snakes, meaning that the group that gave rise to living snakes would have been adapted to burrowing, exhibiting opportunistic behavior. Rather than neatly settling the debate, the results revealed that snake origins were likely complex, with different branches of the snake family tree preserving different clues about the evolution of body size, habitat, and feeding style.
one 2025 Nature Study Even more context was added by describing a Middle Jurassic squamate from Scotland with an amazing mix of lizard-like and snake-like traits. The authors found that early squamate evolution involved a lot of physical experimentation and convergent evolution, which helps explain why the story of early snakes is so difficult to unravel from fossils alone.
Why Nazash still matters
Even with those later discoveries, Nazash remains one of the clearest windows into a critical stage of snake evolution. It captures a moment when snakes’ hind limbs were still present, yet in some cases still had lizard-like skulls intact, and they had not yet fully acquired the body plan seen in their modern descendants. That combination is what makes the fossil so valuable. It doesn’t just show an ancient snake. It depicts an ancient snake in a state of infection.
The University of Alberta described the work as part of the Faculty of Science’s broader mission as a leading center for research and teaching with a focus on advancing knowledge through classroom, laboratory and field research.