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How a poisonous snake got its fangs

Venomous snakes use poisonous fangs to inject a cocktail of toxins-a special tooth with grooves and canals running to guide the poison to bites. Unique among animals, grooved tubular teeth have evolved many times with snakes.

Our new study announced today Bulletin of the Royal Society BReveals that this was probably caused by a change in the tooth structure that helped secure the snake’s teeth to the socket. In certain species, these structures evolved into grooves that run the length of the tooth and acted as convenient conduits for carrying poison.

of Almost 4,000 species About 600 of the snakes are considered “medically important”. That is, it can give bites that need hospital treatment, but more snakes have small tusks and are slightly poisonous. NS Appearance of mild poison It is believed to be before the appearance of the snake’s poisonous fangs.

Poisonous fangs are mainly placed in one of three ways. It is fixed behind the mouth, like a crab-eating water snake, a cat’s eye snake, a twig snake, or a boomslang. Like cobras, coral snakes, many-banded kraits, taipans, and sea snakes, they are fixed in front of the mouth. Or in front of your mouth, you can fold it backwards or sideways, like adders, vipers, rattlesnakes, sword snakes.

Repeated history of fangs

Looking at the evolutionary tree of snakes, it can be inferred that the latest common ancestor of all tusked snakes was probably fangless. This seems to be much more likely than the other methods. Fangs were acquired once and then independently lost in dozens of different snake strains.

read more: How snake fangs evolve to fit food perfectly

So how did the snake repeatedly evolve syringe-like teeth from the simpler conical teeth of its ancestors?

To address this question, we scrutinized snake teeth and how they develop. We examined 19 species of snakes, including both venomous and non-venomous snakes and one early fossil morphology.We used both traditional and state-of-the-art methods, such as studying slides under a microscope. microCT scan When Biomechanical modeling..

Snake Tooth Tips: Dental Origami

It was found that the roots of almost all snake teeth, with or without poison, were firmly folded and wrinkled in cross section (red wrinkles in the figure below).

These folds and wrinkles occur in a layer of teeth called dentin and are known as “prisidentin” from “prica” ​​which means “fold” in Latin. Plicidentine has been found in many extinct animals and a few living fish and lizard species. The function of these folds is not clear, but one theory is to reduce the chances of your teeth breaking or bending when you chew.

However, when I tested this idea using computer simulation with a digital tooth model with and without these creases, I found that it was not.

Snakes, like sharks, change teeth throughout their lives, and there are no deep holes in their teeth. Therefore, the creases believe that increasing the mounting area can improve the initial mounting of new teeth in shallow sockets.

What’s really interesting, regardless of the original function of the folded snake’s teeth, is that in a venomous snake, one of those folds is much larger than the other, and the teeth are stretched up to form a groove, or venomous groove. Is to generate.

read more: Why are some snakes so toxic?

These long single grooves are occasionally found on teeth of other species, such as poisonous ones. Gila monster, Every tooth has a groove associated with the folds of preferred tin. Importantly, the Gila monster’s grooved teeth can occur in the mouth away from the venom gland, meaning a cut between the two. We also found that some venomous snakes have grooves in their teeth other than their venomous snakes. Such teeth are not connected to the venom gland.

Therefore, it was found that grooved teeth can occur throughout the mouth, even if they are far from the venom gland and its canal, and there is a clear relationship between the presence of prefercidentin and the venom groove. This hypothesized that the original condition of the venomous snake, independent of the venomous snake, may have been a random representation of grooves in the teeth as a result of simply enlarged folds of preferred dentin. I did.

Next, we investigated how the venomous snake’s grooved tusks and venom glands evolved together into an efficient structure for delivering venom.

Among the ancestors of today’s poisonous species, the presence of poisonous glands (or their precursors, modified salivary glands called Dubernoy glands) was an important prerequisite for purifying grooved teeth into enlarged poisonous fangs.

Natural selection appears to have favored an increase in size and efficiency, as a grooved tooth appeared near the outlet of the venom gland, which was more effective at injecting the venom.

This sophisticated evolutionary process ultimately produces the large syringe-like fangs found today in snakes such as cobras and vipers, where the ends of the grooves merge to form a needle-like tubular structure.

This finding modifies simple ancestral features such as preferdentin (wrinkles at the base of the tooth that are likely associated with tooth adhesion) and reuses them for a whole new function (groove for poison injection). Shows the method. And this can help explain why snakes, which are unique among all animals, have evolved poisonous fangs so many times.

Author: AlessandroPalci-Postdoctoral Fellow of Evolutionary Biology, Flinders University | Aaron Leblanc-Postdoctoral Fellow of Paleontology, Royal University of London | Olga Panagiotopoulou-Senior Lecturer, Monash University

How a poisonous snake got its fangs

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