There’s a fossil sitting in a museum somewhere that’s making paleontologists look foolish. Not in a mean way, but in that humbling scientific way where you realize you’ve been confidently wrong for 160 years.
The specimen is Najash rionegrina, an ancient rear-limbed snake from Argentina that lived nearly 100 million years ago. When researchers finally got a good look inside its skull using micro-CT scanning, they discovered something that upended decades of assumptions about where snakes came from and how they got to where they are today.
The findings, published in Science Advances in 2019, revealed that Najash still had a cheekbone, or jugal bone, a feature that has almost vanished in modern snakes. That might sound like a small detail. It’s not. That one bone helped scientists realize they’d been misunderstanding snake anatomy for generations.
The Burrower Theory Was Wrong
For a long time, the leading idea was that snakes evolved from small burrowing ancestors. It made intuitive sense. Burrow deep enough underground, lose your limbs because they’re useless in tight spaces, and eventually you’ve got yourself a snake.
Except Najash suggests something completely different.
According to Fernando Garberoglio, lead author on the study and researcher at the Fundación Azara at Universidad Maimónides in Buenos Aires, “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.” The fossils showed that early snakes held onto their hindlimbs for a long time before becoming the mostly limbless creatures we see today.
This wasn’t just a minor correction. This was a whole new picture of snake origins. Bigger bodies. Bigger mouths. Different hunting strategies. A different lifestyle entirely.
Unlocking Hidden Details with Technology
The breakthrough wouldn’t have been possible without micro-CT scanning, a technique that let researchers see inside the fossil without cracking it open. They could trace the paths of nerves and blood vessels, reconstruct bones buried deep in the rock, and examine anatomical details that would otherwise remain hidden.
What they found resolved something that had been nagging at paleontologists. The jugal bone in snakes and their relatives had been misunderstood for so long that the confusion had calcified into textbooks. Michael Caldwell, a professor in the Department of Biological Sciences and Earth and Atmospheric Sciences and co-author on the study, didn’t mince words about it: “After 160 years of getting it wrong, this paper corrects this very important feature based not on guesswork, but on empirical evidence.”
That’s the kind of correction that careers are built on.
The Plot Gets Stranger
Here’s where it gets interesting. Research published after 2019 hasn’t settled the snake question so much as made it messier.
In 2020, paleontologists found Boipeba tayasuensis, a blind snake from Brazil that pushed the blind snake fossil record deeper into dinosaur times. These early blind snakes were larger than their modern cousins, topping 1 meter in length. The finding suggested that early snake diversity in Gondwana was bigger and more varied than anyone expected.
Then 2023 threw another curveball. A study in Science Advances reconstructed the brains of living squamates and fossil snakes, suggesting that the ancestor of crown snakes might have been adapted for burrowing while also hunting opportunistically. Not purely a burrower, not purely a surface hunter. Both, depending on the situation.
And just last year, a Nature study described a Middle Jurassic squamate from Scotland with this weird mix of lizard-like and snake-like traits. Early squamate evolution, it turns out, involved massive anatomical experimentation and convergent evolution.
Rather than neatly settling the debate, these discoveries revealed something more important: snake origins were complex. Different branches of the snake family tree preserved different clues about evolution. The story wasn’t a straight line from point A to point B.
Why Najash Still Matters
Despite all the recent discoveries, Najash remains special. It captures a moment in time when snakes were literally in the process of becoming snakes. They had hindlimbs but were losing them. They had more lizard-like skulls but were modifying them. They hadn’t yet fully acquired the body plan of their modern descendants.
That combination, that transitional state, is exactly what makes the fossil valuable. Najash doesn’t just show us an ancient snake. It shows us an ancient snake in the middle of reinventing itself.
The deeper paleontologists dig, the more they realize that evolution rarely moves in the clean, linear paths we imagine. Sometimes it meanders. Sometimes it backtracks. Sometimes an organism becomes both smaller and larger, both more specialized and more opportunistic, all at different times in different lineages. The real story of how snakes evolved isn’t one answer. It’s dozens of answers, all happening at once across different species, different continents, different millions of years.
And that’s a much more interesting puzzle to solve.
