The evolution of snakes has intrigued scientists for years because they knew that these complex vertebrates had limbs and have adapted over time to live without them dramatically.
But a limited fossil record did not reflect how this transition has occurred since snakes first appeared during the Middle Jurassic period, 163 to 174 million years ago.
Over the years, theories have suggested that these limbs were only a transitional phase before snakes quickly adapted to their present limbless form.
But newly discovered and well-preserved snake fossils, particularly snake skulls, suggest that they had hind legs for an extended period, according to a new study published Wednesday in the journal. Scientific advances.
Najash rionegrina was a type of early snake with hind limbs. The researchers found eight skulls, including one that was almost perfectly intact, and other fossils in the paleontological area of La Buitrera in northern Patagonia, Argentina.
Najash had more primitive features similar to lizards, such as a cheekbone, and snake-like features, including the lack of a bony bow that connects from the skull to the cheekbone. It also had something intermediate between snakes and lizards, as part of a jaw joint.
This cheekbone, also called the jugal bone, existed in these early snakes nearly 100 million years ago, but is not apparent in modern snakes.
"Our findings support the idea that the ancestors of modern snakes were large and large – rather than small excavating forms as previously thought," said Fernando Garberoglio in a statement, principal author of the Fundación Azara at Universidad Maimónides in Buenos Aires, Argentina.
"The study also reveals that primitive snakes retained their hind limbs for a long period of time before the origin of modern snakes, which are most often completely limbless."
Nor did the snake have a series of bony ridges, which had long been thought to be a defining feature of the "snake."
For 70 million years, Najash snakes have successfully and stably lived on their hind legs. This suggests that the hind limbs were useful for snakes and were not part of a transitional phase before they adapted to live without them.
Light microscopy and computed tomography allowed researchers to see Najash in 3D and better understand the early stages of evolution that led to modern snakes. This also provided researchers with a closer look at the pathways to nerves and blood vessels in the snake's skeleton.
"This research revolutionizes our understanding of the jugal bone in snake and non-snake lizards," said Michael Caldwell, co-author and professor at the University of Alberta. "After 160 years of mistakes, this article corrects this very important feature based not on assumptions, but on empirical evidence."
Overall, his research provided an in-depth view of the snake's body plan. Due to the lack of forelimbs, researchers believe they disappeared long before the hind limbs.
"This research is critical to understanding the evolution of modern and ancient snake skulls," Caldwell said.
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