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New research from a collaboration between Argentinian and University of Alberta and 麻豆AV palaeontologists adds a new piece to the puzzle of snake evolution.

The researchers examined a strikingly well-preserved fossil of the rear-limbed snake Najash rionegrina, found in Argentina. The study shows that nearly 100 million years ago, these legged snakes still had a cheekbone鈥攁lso known as a jugal bone鈥攖hat has all but disappeared in their modern descendants.

鈥淥ur findings support the idea that the ancestors of modern snakes were big-bodied and big-mouthed鈥� instead of small burrowing forms as previously thought,鈥� explained Fernando Garberoglio, from the Fundaci贸n Azara at Universidad Maim贸nides, in Buenos Aires, Argentina and lead author on the study. 鈥淭he study also reveals 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.鈥�

For decades, paleontologists' understanding of snake evolution was hampered by the limited fossil record. The new fossils presented in this study are crucial for reconstructing the early steps in the evolutionary history of modern snakes.

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鈥淭his research revolutionizes our understanding of the jugal bone in snake and non-snake lizards,鈥� said Michael Caldwell, professor in the Department of Biological Sciences and Earth and Atmospheric Sciences at University of Alberta, and a co-author on the study. 鈥淎fter 160 years of getting it wrong, this paper corrects this very important feature based not on guesswork, but on empirical evidence.鈥�

The nearly 100 million year old fossil snakes described in this study, found in Northern Patagonia, are closely related to an ancient lineage of snakes 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 the skull structures within the specimen, examining the pathways of nerves and blood vessels as well as the skeletal structure that would be otherwise impossible to see without damaging the fossil.

鈥淭his research is critical to understanding the evolution of the skulls of modern and ancient snakes,鈥� added Caldwell. 鈥淭he high level of imaging tools we used allowed us to peer deep into these early snake skulls and solve a lot of mysteries. Perhaps most exciting for me is the resulting evolutionary trees that suggest legged snakes were not just transitional forms, but persisted for nearly 100 million years!鈥� stated , Canada Research Chair in Vertebrate Palaeontology at 麻豆AV.

The paper, 鈥淣ew Skulls and Skeletons of the Cretaceous Legged Snake Najash, and the Evolution of the Modern Snake Body Plan,鈥� will be published in (doi: 10.1126/sciadv.aax5833).

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