This 22 November 2019 video says about itself:
On very rare occasions, an exceptional fossil is unearthed that provides an extraordinary glimpse into the evolution of a group of organisms.
This time, it is the beautifully preserved skull of an ancient snake with rear limbs, Najash rionegrina. Our study of this fossil has been published in the journal Science Advances.
This and other new fossils help answer longstanding questions on the origins of snakes, such as how they lost their limbs and evolved their highly specialized skulls.
Najash rionegrina is named after the legged biblical snake Nahash (Hebrew for snake), and the Río Negro Province in Argentina, where the fossils were discovered. Fossils of Najash are about 95 million years old, and were first described in Nature from a fragmentary skull and partial body skeleton that preserved robust rear limbs.
This rear-limbed fossil snake garnered a great deal of media interest as it followed earlier reports of fossil marine snakes with rear limbs. What made Najash unique was that it was a terrestrial snake living in a desert, not an aquatic snake living in the ocean. In addition, the fossils were not compressed flat by the weight of overlying sediments, and so they were preserved in three dimensions, unlike the fossil marine snakes.
Unfortunately, that first description of Najash relied on a very fragmentary skull. Scholars of snake evolution were left to guess at what the head of these ancient animals might have looked like.
We know from their shared anatomy that snakes evolved from lizards. We also know that the skulls of snakes have been key to their successful and highly specialized feeding adaptations. New Najash fossil skulls would be highly informative on the pattern of snake skull evolution.
The new discovery
It was a hot day in February of 2013 when Fernando Garberoglio, then an undergraduate palaeontology student from the Universidad de Buenos Aires, went on his first field trip to the La Buitrera Paleontological Area in northern Patagonia, Argentina. With him were two palaeontologists: Sebastián Apesteguía, from the Universidad Maimónides, and Guillermo Rougier, from the University of Louisville.
Looking for fossil vertebrates is an act of patient, painstaking discovery. It requires you to be close to the ground, scanning the grit, pebbles, rocks and sediments for a sign of bone. You must pick up each piece, inspect it closely, put it down and then repeat, hour after hour. At La Buitrera, you are scorched by the hot sun, pelted by driving rain and frozen by chilly Andean winds.
But it’s all worth it. Particularly when, as happened to Garberoglio, he finally picked up a pebble, only a few centimetres long, to find a small, ancient, bony face staring back at him.
From the University of Alberta in Canada:
An ancient snake’s cheekbone sheds light on evolution of modern snake skulls
100-million-year old legged snake fossil provides critical insight into how the heads of modern snakes evolved
November 20, 2019
New research from a collaboration between Argentinian and University of Alberta 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 — also known as a jugal bone — that has all but disappeared in their modern descendants.
“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 Fernando Garberoglio, from the Fundación Azara at Universidad Maimónides, in Buenos Aires, Argentina and lead author on the study. “The 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.”
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.
“This research revolutionizes our understanding of the jugal bone in snake and non-snake lizards,” said Michael Caldwell, professor in the Department of Biological Sciences and Earth and Atmospheric Sciences, and 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 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.
“This research is critical to understanding the evolution of the skulls of modern and ancient snakes,” added Caldwell.
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