In very rare cases, an exceptional fossil is found that provides an exceptional view of the evolution of a group of organisms.
This time it's a beautifully preserved skull of an ancient 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 longstanding questions about the origin of snakes, such as how they lost their limbs and evolved their highly specialized skulls.
History of fossils
Najash rionegrina is named after the biblical snake Nahash (in Hebrew for snake) and the province of Rio Negro in Argentina where fossils were discovered.
The fossils of Najash are about 95 million years old and were first described in by Nature by a fragmentary skull and partial skeleton of the body that retained healthy hind limbs.
This excavated snake with hind limbs has aroused great media interest as it has followed previous reports of fossil sea snakes with hind limbs, what made Najjash unique was that it was a land snake living in the desert, not a water snake living in the ocean.
In addition, the fossils were not flattened flat by the weight of the proper sediments, i. and so they are preserved in three dimensions, unlike fossil sea snakes.
Unfortunately, the first description of Najash relies on a very fragmentary skull. Snake evolution scientists have been left wondering what the head of these ancient animals might look like.
From their shared anatomy, we know that snakes have evolved from lizards. We also know that snake skulls have been key to their successful and highly specialized feeding adaptations. The new Najash fossil skulls would be very informative about the model of the evolution of the snake skull.
The New Discovery
It was a hot day in February 2013, when Fernando Garberolio, then a paleontology student from Universidad de Buenos Aires, embarked on his first flight to the paleontological zone of La Bouitreña in the Arctic La Paitretraña .
With him were two paleontologists: Sebastian Apestegua, of the Universidad Maimunides, and Guillermo Ruggie of the University of Louisville.
The search for fossil vertebrates is an act of patient, diligent discovery. It requires you to be close to the ground, scanning the grains of sand, pebbles, rocks and sediment for signs of bone. You should take each piece, inspect it carefully, put it down and then repeat it hour after hour.
At La Buitrera, you are burned by the hot sun, filled with driving and frozen by the frosty Andean winds. 
Up: Student Fernando Garberoglio and paleontologist Sebastian Apestegreía work , Argentina.
But it's all worth it. Especially when, as happened with Garberolio, he finally raised a pebble just a few inches long to find a small, ancient, bony face staring at him.
"I found a snake skull!"
Rugger asked himself to inspect the fossil and discovered that to his surprise Garberolio was right – there is a nearly complete, 3D-preserved snake skull 95 million years old.
It has been 13 years since the name of Najash and seven years since the inauguration of Fernando. Today the long hunt has given away a treasure trove of new skulls and skeletons to Najash of the rich in fossil sites in La Bouitrera.
Evolution of the skull
It has been a long-standing hypothesis that snakes evolved from a blind, burrowing lizard precursor. A group of small, small-horned worms known as scolecofids have long been considered the most primitive living snakes.
The new Nadjash fossil material shows that the skulls of the ancestry of ancient serpents were not anything like the scolecofid serpents. Instead, Najash and his appearance had large mouths with sharp teeth and some of the movable skull joints that are characteristic of most modern snakes.
However, they still retain some bony features of the skulls of the more typical lizards.
In evolutionary terms, Najash tells us that snakes evolve to the skull motility needed to absorb fairly large prey, a remarkable feature of many modern snakes.
Critical information is also preserved in the bone-to-bone details stored in these new fossils of Najash . For example, for a very long time, the stick-like bone behind the eyes of modern serpents – called the South – was considered the equivalent of the postorbital bone of their ancestral lizards.
The idea was that the South was absent in all snakes, fossil and modern.
The new skull of Najash shows strongly that this is not correct. The bone under the orbit in Najash has the same shape, position and connections as the L-shaped south of the more typical lizards.
This indicates that the lower lane of the south has been lost through the evolution of the snake, i. leaving behind a scepter-like scepter in modern snakes. It is the postorbital bone that is lost, not the jugal.
These new instances of Najash are an excellent example of the predictive power of science. Hypotheses, such as the presence of the south in snakes, may be supported by the discovery of new data that meet these predictions. What results is that the old hypothesis is fake and the new one is tested.
In short, the skull of Najash tells us that the ancestral snakes were very similar to some of their close lizards, like lizards with big heads with big heads like Komodo dragons. This is indeed a far cry from the idea that snakes could have evolved from small, blind, worm-like small ancestors; there are no known fossils of ancient serpents that look like all primitive ones, with small horns of scolecofids. Evolutionary Biology, Flinders University.
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