On very rare occasions, a rare fossil is cut which gives a rare glimpse into the evolution of a group of organisms.
At this time, it is the beautifully preserved skull of an ancient snake with its hind limbs, Najash rionegrina . Our study of this fossil was published in the journal Science Advances .
These and other new fossils help answer long-standing questions about the origin of snakes, such as how they lost their limbs and altered their highly specialized skulls.
History of the Fossil
Najash rionegrina is named after the legged biblical snake Nahash (Hebrew for snake), and the Río Negro Province in Argentina, where fossils were discovered.
The 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 the sturdy hind legs branches of the body.
The rear of this fossil snake has garnered much media interest since it followed earlier reports of the fossil sea snakes with hind legs. The creator of Najash is unique in that it is a terrestrial snake that lives in a desert, not an aquatic snake that lives in the ocean.
In addition, fossils are not compressed flat to the weight of overlying sediments, and thus they are preserved in three sizes, unlike fossil marine snakes.
Unfortunately, the first description of Najash rests on a very fragmentary skull. Snake evolution scholars were left to guess what the head of these ancient animals would look like.
We know from their shared anatomy that snakes have sprouted from lizards. We also know that snake skulls are key to their successful and highly skilled adaptation to feeding. The new Najash fossil skulls will be well versed in the evolutionary pattern of skull evolution.
It was a hot day in February of 2013 when Fernando Garberoglio, then an undergraduate palaeontology student from the Universidad de Buenos Aires, went to his first field in the La Buitrera Paleontological Area in northern Patagonia, Argentina.
He was with two palaeontologists: Sebastián Apesteguía, from Universidad Maimónides, and Guillermo Rougier, from the University of Louisville.
Finding febrile vertebrates is a patient gesture, a painful discovery. You need to be close to the ground, scanning grit, rocks, rocks and sediment for a bone signal. You should take each piece, examine it carefully, place it and then repeat, time after time.
In La Buitrera, you are scorched by the hot sun, blown by driving rain and freezing by the strong Andean winds. 
Above: Student Fernando Garberoglio and palaeontologist Sebastian Apesteguía conducting field work northern Patagonia, Argentina.
But it's worth it. Especially if, as happened to Garberoglio, he finally took a thousand stones, only a few centimeters long, to find a small, ancient, bony face staring at him.
"I found a snake's skull!"
Rougier asked to inspect the fossil itself and found that, to his surprise, Garberoglio was right – there, a nearly complete, 95 million year old, 3D retained 3D skull.
It's been 13 years since Najash was named, and it's been seven years since Fernando discovered it. Today, long hunting rewards a wealth of new skulls and skeletons of Najash from fossil-rich sites in La Buitrera.
Evolution of the skull
A long-held hypothesis is that snakes evolved from a blind and persistent ancestor of a lizard. A group of small, worm-like, small-rotating snakes, known as scolecophidians, have long been considered the most primitive snakes ever lived. the line of ancient snakes is nothing like the scolecophidian snake. Instead, Najash and its type have large teeth with sharp teeth and some of the mobile skull bones typical of most modern snakes.
However, they still maintain some bony skull features of the more common lizards.
In evolutionary terms, Najash tells us that snakes are emerging towards the mobility of the skull needed to satisfy the relatively large prey prey, a landmark feature of there are many modern snakes.
Critical information is also preserved on the details of the bones preserved in the new fossils of Najash . For example, for a very long time, the rod-like bone found behind the eyes of modern snakes – called jugals – was thought to resemble the postorbital bone of their lizard ancestors.
The idea that jugal was absent from all snakes, fossils and moderns was followed.
The new skull of Najash shows the conclusion that this is incorrect. The bone under orbit in Najash has the same shape, position and connection as the J-shaped jugal of more common lizards.
It shows that the lower jugal bar was lost through the evolution of the snake, leaving a jugal like modern snakes. It is the postorbital bone that is lost, not the jugal.
These new specimens Najash are a great example of the unpredictable power of science. Hypotheses such as the presence of a jugal in snakes may be supported by the discovery of new data that fulfills predictions. What happens as a result is that an old hypothesis is wrong and a new one is validated.
Briefly, the skull of Najash tells us that the ancestral snakes are very similar to some of their close relatives of the lizard, such as large roots, large heads of lizards like Komodo dragons. It really shouts from the idea that snakes can emerge from small, blind, like worms, small ancestors; there is no known fossil of ancient snakes resembling all of the so-called primitive, little monkey scolecophidians. Evolutionary Biology, Flinders University. Read the original article.