How a poisonous snake got its fangs

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Poisonous snakes use poisonous fangs to inject a cocktail of toxins – a special tooth with grooves and channels that guide the poison to the bites. Unique among animals, grooved tubular teeth have repeatedly evolved with snakes.

Our new study announced today in the Bulletin of the Royal Society BR reveals that this was likely caused by a change in the tooth structure that helped attach the snake’s teeth to the socket. In some species, these structures have evolved into grooves that run the length of the tooth and act as convenient conduits for transporting poison.

of nearly 4,000 species About 600 of the snakes are considered “medically important”. That is, it can give bites that require hospital treatment, but most snakes have small tusks and are mildly poisonous. NS Appearance of a light poison It is believed to have occurred before the appearance of the poisonous fangs of the snake.

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

Repeated story of fangs

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

read more: How Snake Fangs Evolve to Perfectly Adapt to Food

So how did the serpent repeatedly evolve syringe-shaped teeth from the simpler tapered teeth of its ancestors?

To answer this question, we looked at snake teeth and their development. We examined 19 species of snakes, including poisonous and non-poisonous snakes and early fossil morphology. We used traditional and advanced methods, such as studying slides under a microscope. microCT scan When biomechanical modeling ..

Snake Tooth Tips: Dental Origami

The roots of almost all snake teeth, with or without poison, were found to be firmly bent 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 “presidentin” from “prica” ​​which means “fold” in Latin. Plicidentine has been found in many extinct animals and a few living species of fish and lizards. The function of these folds is unclear, but one theory is to reduce the chances of your teeth breaking or bending when you chew.

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

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

What is really interesting, whatever the original function of the teeth of the bent snake, is that in a poisonous snake, one of these folds is much larger than the other, and the teeth are stretched out to form a furrow, or poisonous furrow. Is to generate.

read more: Why are some snakes so poisonous?

These long, simple grooves are sometimes found on the teeth of other species, such as poisonous teeth. Monster of Gila, Each tooth has a groove associated with the folds of the preferred pewter. It is important to note that the grooved teeth of the Gila monster can appear in the mouth far from the poison gland, meaning a cut in between. We have also found that some poisonous snakes have grooves in their teeth other than their poisonous snakes. These teeth are not connected to the venom gland.

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

Next, we investigated how the grooved tusks and poison glands of the poisonous snake together evolved into an efficient structure for delivering venom.

Among the ancestors of today’s poisonous species, the presence of poison glands (or their precursors, the modified salivary glands called Dubernoy’s 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 exit of the venom gland, which was more efficient at injecting the venom.

This sophisticated evolutionary process ultimately produces the large syringe-shaped 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 discovery alters simple ancestral characteristics such as dentin preference (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). Displays the method. And that may help explain why snakes, which are unique among all animals, have developed poisonous fangs so often.

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


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