Fossil of animal that devoured baby dinosaur may help unravel the origin of snakes


Fossils of a snake that perhaps devoured baby dinosaurs 70 million years ago may be the missing clue to how snakes acquired the ability to swallow proportionately very large prey in one go.

The first steps in the process appear to have involved minor modifications to the back of the skull, which would also help to understand how the snake lineage separated from other reptiles.

The keystone of a new study on the topic is the Sanajeh indicus, found, as its scientific name suggests, in western India. The animal was originally described in 2010, but a new fossilized specimen preserves cranial structures that provide important information about the origins of snakes’ so-called macrostomia.

The term, derived from Greek words with the literal meaning of “big mouth”, refers not only to the proportionately huge mouth opening of many of these critters but also to specialized movements that help them swallow large victims.

These peculiar macrostomia movements depend on a number of specializations in the structure of the reptile skull, including the posterior cranial region, the roof of the mouth (or palate), and the junction between the snout and the rest of the mouth. Not all modern snakes are capable of this type of feat, but the most well-known to the public, such as boa constrictors, rattlesnakes and pythons, can do it.

The new work on Sanajeh, which also includes an extensive comparative analysis involving other extinct and modern snakes, is in the specialized journal Zoological Journal of the Linnean Society. The work is signed by a pair of Brazilians —Hussam Zaher, from the USP Museum of Zoology, and Felipe Grazziotin, from the Butantan Institute—, along with Jeffrey Mantilla, from the University of Michigan (USA), and Dhananjay Mohabey, from the University of Nagpur. , in India.

Zaher, one of the leading experts on the early stages of snake evolution during the Age of Dinosaurs, says that the Indian species most likely still had small but functional hind legs, although these pieces of the animal’s skeleton did not become fossilized.

The legs, which make clear the kinship relationship between these animals and the ancient lizards from which they descend, are present in other primitive snakes, such as the najash rionegrina, which Zaher described along with colleagues from Argentina. The fossils of Sanajeh they were found in the nests of sauropod dinosaurs — quadrupedal, herbivorous, long-necked giants. As the cubs were tiny compared to their parents, it makes sense to imagine that the Sanajeh prey them.

The USP researcher explains that the data on the origins of macrostomia are relevant to a broader discussion on the emergence of snakes as a whole. This is a debate that basically pits the sea against land – on the one hand, some researchers argue that snakes descend from a group of aquatic reptiles, the mosasaurs (marine lizards), while other scientists, including , argue that a terrestrial and fossorial origin (ie living in burrows in the ground) is the most suitable scenario.

It turns out that the macrostomia came to be used as one of the trump cards of those who defend the aquatic origin of snakes, since mosasaurs also had this characteristic. Some species of snakes with legs from the Age of Dinosaurs, which had marine habits and had macrostomia, were also cited as an argument in favor of this idea.

The new data on the Sanajeh, however, contradict this hypothesis by showing that the first cranial modifications that would eventually allow the emergence of macrostomia in snakes did not follow the same steps in mosasaurs. It would therefore have been a process of convergent evolution—roughly, like the flight of birds and bats, which produced similar results without one group descending from the other.

In snakes of very primitive anatomy, such as the Indian species, these first steps involved alterations that produced a more closed braincase. “In addition Sanajeh and other similar snakes have a mandible with an internal joint and have already lost the fixed connection that existed between the premaxillary [o osso da frente na parte de cima da boca, mais ou menos abaixo do nariz em humanos] and jaw,” says Zaher. “Basically, they are intermediate elements between snakes and lizards.”

These mouth “hinges” may have given a first boost to the ability to face very large prey. But two important elements were still missing for the macrostomia itself. One of them is the mobility of the palatal region (the roof of the mouth). “At this point, the Sanajeh It has characteristics of a lizard”, highlights the researcher. The other is the mobile junction between the snout and the rest of the snakes skull. It is with the help of these diverse areas with mobility that most of the current species are able to push proportionally large prey into the gullet.

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