A tiny fossilized cheekbone in a 100-million-year-old snake skull is shedding new light on how modern snakes evolved.
Paleontologists from Argentina and the University of Alberta examined a well-preserved fossil of the rear-limbed snake Najash rionegrina, found in what is now northern Patagonia in the South American country.
They found that nearly 100 million years ago, the legged snakes still had a cheekbone—also known as a jugal bone—that has all but disappeared in their modern descendants.
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"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," explained the study's lead author, Fernando Garberoglio of the Fundación Azara at Universidad Maimónides in Buenos Aires, Argentina.
"The study also revealed 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," he added.
For decades, paleontologists' understanding of snake evolution was hampered by the limited fossil record. The new fossils described in the study are crucial for reconstructing the evolutionary history of modern snakes.
"This research revolutionizes our understanding of the jugal bone in snake and non-snake lizards," said U of A paleontologist Michael Caldwell, who was a co-author on the study.
"After 160 years of getting it wrong, this paper corrects this very important feature based not on guesswork, but on empirical evidence."
The fossilized snakes are closely related to an ancient lineage that populated the southern hemisphere continents of Gondwana, and appear to be related to only a small number of obscure, modern snakes.
The researchers used micro-computed tomography (micro-CT) scanning to visualize skull structures in the specimen, examining pathways of nerves and blood vessels as well as the skeletal structure that would be otherwise impossible to see without damaging the fossil.
The study, "New Skulls and Skeletons of the Cretaceous Legged Snake Najash, and the Evolution of the Modern Snake Body Plan," was published in Science Advances.
