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Snake Skulls in a Nutshell – Legged relatives of chalk and the development of their skulls to the present day

Snake Skulls in a Nutshell

Contemporary reptiles are still considered by many to be strange cold-blooded creatures with a strange hostile expression in beaded eyes, they are wrongly seen in this way, but in this respect, snakes (Ophidia) stand out. Although they were initially perceived by the human race as creatures from which we should learn, were bearers of knowledge and culture, after the turn of the era they saw themselves as an image of eternal evil stemming from their administration in the Christian world. One way or another, snakes do not change anything in terms of their evolution, which has until recently been shrouded in mystery in the form of controversial findings and not very clear developments with other reptile groups. Only the reclassification and reinterpretation of some fossils and new findings showed their first representatives as Scincomorpha-like reptiles with short limbs and a strong body. A few days ago, a paleontological group of Argentine and Canadian paleontologists published a study on another aspect of their anatomy – the jaw structure and their ability to open extremely.

Previously, the beginnings of snakes as a group were put on the territory of Israel and Argentina, because it was here that the paleontologists uncovered the oldest and most primitive fossils of the group. Today we know that their origins are geographically and temporally distant, but just the Argentinean representative species Najash rionegrina focused on the study of the development of snake skulls to modern form. Credit: Raúl Goméz, taken from the Sci-News website

Candeleros Formation in Argentina – today a dry and sunny piece of South American pampas would not be much different from its Cretaceous counterpart, except for the absence of grasses and a large number of angiosperms. These were probably not as common as 90 million years ago. Probably the most famous representatives of the fauna of this geological formation are the large carcharodontosaurids of the genus Giganotosaurus and sauropods like Andesaurus and Limaysaurus. Under their feet, a two-foot-long Najash snake would have disappeared, but for paleontologists, it had become an eye-catching object of interest. When formally described in 2006, he confirmed the hypothesis of the evolution of snakes and their ancestors from reptile species that lived in a greedy way of life.

However, vertebrate paleontology has progressed since then in terms of the development of snakes. In the last 5 to 7 years, the fossils of these reptiles from Western Europe, the Midwest of the United States, and some other places in the world have been discovered and reclassified, so we learn more about their pedigree more than a long time since the first primitive snakes were discovered. Hypotheses about possible other evolutionary origins of snakes as a group have also been raised, but this paper will deal with the actual development of the morphology of these animals – the skull.

The paleontologist Fernando Garberoglio of the Universidad Maimónides, Buenos Aires, Argentina, who is also the lead author of the study, has focused on the study of the skull and archaic features of snakes who no longer share current species in the South American primitive serpent from the Candeleros Formation. Probably not by chance, because Najash is evolutionarily quite close to the ancestors of the “true snakes” (Serpentes), and moreover, the paleontologists have heard that it also has the best preserved three-dimensional skull among extinct basal snakes.

It was clear from the outset that this genus of snake would not stand out from the generally accepted model of the evolution of snake ancestors – scientists agreed and confirmed that it was a burrowing species with a number of differently visible archaic features such as stunted hind legs. At the same time, they confirm the assumption that the evolutionary ancestors of snakes were predators at the time of their creation, sometimes reaching considerable size (family Madtsoiidae) and having a large head for eating prey.

However, the genus Najash possesses one essential feature that modern snakes lack today, the so-called jugular bone. This bone is found, for example, in contemporary lizards and crocodiles under the orbits, merged with the cheekbone in mammals, but is absent in snakes and is probably related to greater skull flexibility in prey eating. He owns some elastic joints like today’s species, but the rest of the skull lacks and probably due to the presence of the jugular bone.

But there are other peculiarities on the skull. The presence of the jugular bone resembles the current lizard (Varanoidea) or other lizards, as does the construction of his middle ear. This is about halfway between lizards and snakes, at least from an external anatomical point of view. In addition, the entire skull was richly covered with blood vessels and nerves, as shown by computer microtomography.

Co-author of the study, prof. Michael Caldwell of the University of Alberta, pointed out that the study provides clear evidence of the evolutionary direction with contemporary snakes at the end of it, which gradually lost the jugular bone and this allowed the skull more flexibility. Modern snakes and Najash share the ancestor who owned it, but the ancestors of today’s elongated, reptilian, tongue-like reptiles prefer to eat more prey than themselves.

According to the paleontological team, this is another conclusion they have made. The South American snake from the Candeleros Formation, according to their interpretation, represents a separate morphotype of developmentally not very dependent snakes, who retained the limbs and shape of some bones due to the evolutionary success of that morphotype. They could therefore adapt to life in water, on land and underground. This completes the study.

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