Venomous snakes: the insidious venomous syringes used by snakes

Snakes are the only vertebrates that have two teeth transformed into hypodermic needles. They can be used to inject the deadly content of their poison glands into the body of their prey in a targeted manner. Such fangs have developed independently of one another several times and come in two versions: One channel the toxic liquid through a deep channel, the other through a tube. As molecular genetic analyzes show, teeth that form a cannula are found in vipers (

), poisonous snakes (

) and a subfamily of terrestrial

vipers

(

) developed. Vipers have even developed a nifty mechanism that pops the fangs out of a fold of skin as soon as the mouth opens. Folded in again, even teeth of imposing size can be safely stowed in the roof of the mouth.

The common origin of all these lethal injections were teeth with internal folds: where the epithelium of an embryonic tooth first folds, then correspondingly folded dentine is formed.

Biologists working with Alessandro Palci from Flinders University in Adelaide and Aaron LeBlanc from the University of Alberta in Edmonton have discovered that this so-called Plicidentin is not only typical for certain lizards, but also for snakes.

Using micro-computed tomography, they scanned the teeth of 19 different types of snake, which represented a cross-section through the diversity of these reptiles.

Venomous snakes with harmless ancestors

In 18 species, including many non-toxic, they identified teeth with folded dentin. The only species without plicidentine turned out to be an Australian blind snake, which like all blind snakes lives underground and chases small crawling animals like termites. In most snake teeth, however, the crinkled dentin is limited to the area that is anchored in the jaw. The fact that the wrinkles are also microscopic explains why they have been overlooked so far. Larger and longer wrinkles were already known to be a special feature of poisonous teeth.

As Palci and colleagues

explain

in the

, the deep grooves through which a snake tooth passes poison are nothing more than a special form of plicidentin: the epithelium of the embryonic fangs develops, starting at the tip, a special one deep and long fold. Sometimes, however, it is not only the tooth through which snake venom flows into the victim's body that carries such a concise groove. In some venomous snake species, the researchers found individuals who had more teeth than usual in this way. No wonder that poison fangs emerged several times anew in the evolution of snakes and in different places in the dentition.

From the family of the mostly non-poisonous snakes (

), for example, some venomous snakes have emerged that have their fangs far back in the upper jaw.

Because they open their mouths wide, they can still apply their poison effortlessly.

Snakes are also not the only reptiles to have teeth with folded dentin and deep grooves.

The Gila-Krustenechse (

), also called Gila-Monster, even equips all teeth with a concise notch.

In this black and pink patterned reptile that populates arid regions in southwestern North America, the teeth in the lower jaw in particular act as poisonous fangs.

Because crusty lizards have placed their poison glands there instead of in the upper jaw like snakes.

Lethal injection or muscle strength

But what use is pleated dentin if it is not transformed into a lethal injection? Palci and his colleagues used the finite element method to investigate whether it allows the animals to bite more forcefully. It turned out that teeth with Plicidentin neither withstand more pressure nor withstand greater bending forces than without this design. Because the filigree folds increase the area with which the teeth anchor themselves in the jaw, it probably ensures that they sit more firmly

The majority of the approximately 3,600 species of snakes manage without any poisonous teeth. However, of those who rely on poison rather than muscle strength to hunt down their prey, more than 600 species are medically relevant. There are only two types of venomous snakes in this country, and both are under nature protection for good reason: The aspic viper is only found in the southern Black Forest, the less venomous adder is more widespread and is just as native on moist mountain meadows as it is on the edges of forests and in moors. But it has also become so rare that encounters are rare and bites even more rare.