On very rare occasions, an exceptional fossil is discovered that provides an excellent insight into the development of a group of organisms.
This time it is the beautifully preserved skull of an antique snake with hind limbs, Najash rionegrina . Our study of this fossil has been published in the journal Science Advances .
This and other new fossils help answer long questions about the origin of the snakes, such as how they lost their limbs and developed their highly specialized skulls.
Najash rionegrina is named after the bony biblical serpent Nahash (Hebrew for serpent) and the Río Negro province of Argentina, where the fossils were discovered. Fossils from Najash are about 95 million years old and were first described in Nature from a fragmentary skull and partial body skeleton that preserved robust hind legs .
This rear part -Limited fossil snake got a great media interest as it followed previous reports on fossil marine snakes with rear limbs . What made Najash unique was that it was a groundworm that lived in a desert, not an aquatic snake that lived in the sea. In addition, the fossils were not compressed flat with the weight of overlying sediment, and so they were preserved in three dimensions, unlike the fossil marine snakes.
Read more: Did snakes evolve from ancient sea snakes?
Unfortunately, the first description of Najash relied on a very fragmentary skull. Snake development researchers were left to guess what the head of these ancient animals may have looked like.
We know from their shared anatomy that snakes evolved from lizards. We also know that snake peel has been the key to their successful and highly specialized feeding adaptations. New Najash fossil shells would be very informative about the pattern of snake skull development.
The new discovery
It was a hot day in February 2013 when Fernando Garberoglio, then a student of paleontology from the Universidad de Buenos Aires, went on his first field trip to La Buitrera Paleontological Area in northern Patagonia, Argentina. With him were two paleontologists: Sebastián Apesteguía, from Universidad Maimónides and Guillermo Rougier, from the University of Louisville.
Searching for fossil vertebrates is an act of patient, careful discovery. It requires you to be close to the ground and scan grains, rocks, rocks and sediments for a sign of bone. You have to pick up every bit, inspect it carefully, put it down and then repeat, hour after hour. At La Buitrera you are burned by the hot sun, peeled by rain and frozen by chilly Andean winds.
But it's worth it. Especially when, just as happened to Garberoglio, he picked up a stone, only a few inches long, to find a small, ancient, bony face staring back at him.
"I found a snake skull!"
Rougier asked to inspect the fossil himself and found that to his surprise, Garberoglio was right – there it was, an almost complete, 95 million year old 3D preserved snake skull.
It has been 13 years since Najash was named, and seven years since Fernando's discovery. Today, the long hunt has produced its reward of a treasure trove of new skulls and skeletons of Najash from the fossil-rich sites at La Buitrera.
A long-standing hypothesis is that snakes evolved from a blind, burrowing lizard ancestor. A group of small, snake-like, small-mouth burrowing snakes, known as scolecophidians have long been considered the most primitive living snakes.
The new Najash fossil material shows that the skulls in this genus of ancient snakes did not resemble those of scolecophidian snakes. Instead, Najash and its kind had large mouths with sharp teeth and some of the mobile skull joints that are typical of most modern snakes. However, they still retained some bony shell heads in more typical lizards.
In evolutionary terms, Najash tells that snakes evolved against the mobility of the scales that are necessary to eat quite large predators, a landmark for many modern snakes.
Critical information is also preserved in the bone-for-bone details preserved in these new fossils from Najash . For example, for a very long time, the rod-like bone that lies behind the eye of modern snakes – called the jugal – was considered to be the equivalent of the postorbital bone of their lizard ancestors. The idea followed that the jugal was absent in all snakes, fossils and modern.
The new skull from Najash finally shows that this is not correct. The leg during the cycle in Najash has the same shape, position and connections as the L-shaped jugal of more typical lizards. This shows that the lower bar of the jugal was lost through snake development, leaving a rod-like jugal in modern snakes. It is the postorbital bone that has been lost, not the jugal.
These new copies from Najash are an excellent example of the predictable power of science. Hypotheses such as the presence of a jugal in snakes can be supported by the discovery of new data that meets these predictions. What happens as a result is that an old hypothesis is falsified and a new one is verified.
Briefly, the skull from Najash tells that parents snakes were very similar to some of their close lizard relatives, such as large bodies, large high lizards like Komodo dragons . This is really a notion that snakes could have evolved from small, blind, worm-like, small mouthed ancestors; no known fossils of ancient snakes resemble all the supposedly primitive, small-mouthed scolecophidians.
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This article was originally published on The Conversation. The publication contributed the article to Live Science Expert Voices: Op-Ed & Insights .