This 100 million-year-old snake had hind legs and a lost bone that changes evolution

A 100-million-year-old fossil from Argentina reveals snakes once had hind legs and a cheekbone, challenging long-held theories of their burrowing origins. | Contesto: cronaca

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• This 100 million-year-old snake had hind legs and a lost bone that changes evolution

Contesto

A stunningly preserved fossil unearthed in Argentina is rewriting the evolutionary history of snakes, revealing that the earliest members of the lineage were not small, burrowing creatures but large, wide-mouthed predators that still possessed hind legs and a prominent cheekbone. The specimen, belonging to the species Najash rionegrina and dating back nearly 100 million years, offers the clearest picture yet of a critical transitional phase in snake evolution. Paleontologists describe the find as a missing link that forces a fundamental rethinking of how snakes lost their limbs and adapted to their modern, limbless form. The fossil, discovered in the La Buitrera paleontological site in northern Patagonia, is exceptionally complete, preserving not only the skull and much of the vertebral column but also the hind limbs and a bone in the cheek known as the jugal. This jugal bone, which is virtually absent in living snakes, connects the skull to the jaw joint and is a key feature in lizards. Its presence in Najash rionegrina indicates that early snakes retained a more lizard-like skull structure, contradicting the prevailing hypothesis that snakes evolved from small, fossorial ancestors that lost their legs while adapting to a burrowing lifestyle. Instead, the new evidence suggests that the first snakes were surface-dwelling or semi-aquatic predators that used their hind limbs for grasping prey or during mating. The size and robust construction of the fossil’s skull and jaws point to an animal capable of taking relatively large prey, a feeding strategy that would later be refined in modern snakes through extreme skull kinesis. The presence of a well-developed jugal bone implies that the early snake skull was less flexible than that of today’s species, but still highly effective for a predator of its time. The implications of this discovery extend beyond anatomy. For decades, the debate over snake origins has been split between two competing theories: one that snakes evolved from terrestrial lizards that burrowed, and another that they descended from aquatic reptiles. The Najash rionegrina fossil provides strong support for the terrestrial, non-burrowing model,...

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Categoria: cronaca