This week’s entry focuses on snakes, creatures that have caused an intense hate from human beings since ancient times. One of the main reasons why snakes are so deeply rooted in the human mind is the posed by the fact that some species are venomous, possessing venomous glands which open through ducts into grooved or hollow teeth. Although most species are harmless to human being, these animals still give the shivers to more than one.
Venomous fangs appeared as a modification of maxillary teeth. Depending on the level of specialization in both the jaw and these fangs, each species of snake may be classified into one of four different groups.
AGLYPH (lacking grooves)
Aglyphous snakes have the most primitive condition in which teeth are solid, without grooves or specialized venom-injecting fangs. This is the less specialized dentition, which is found in many snake families, from the great boas and pythons to the primitive blind snakes from the infraorder Scolecophidia, and even in some members of the great Colubridae family. Teeth usually have the same size and morphology. This type of dentition is usually linked with non-venomous species, although a few aglyphous snakes do have venom yet most are nonlethal to human beings.
OPISTHOGLYPH (rearward grooves)
These snakes posses venom which is injected with specialized fangs found at the posterior end of the maxilla, which are backward-oriented and grooved so that toxins are canalized to the tip of the tooth. To correctly inject venom, these snakes must hold their prey and move it to the rear of the mouth, a pretty arduous task if the prey is of a considerable size.
This type of dentition is found in various species into the large Colubridae family, in which it has evolved twice independently.
Even though most opisthoglyphous snakes are harmless to humans (because fangs are found at the back of their mouths, and these snakes aren’t usually very big) some species are lethal to humans, like the “boomslang” (Dispholidus typus) and the bird snakes (Thelotornis sp.) which bite with the mouth wide open (up to 170 degrees to insert their venomous fangs firmly) and generate powerful haemotoxins against which no efficient antitoxin has been developed yet. Haemotoxins are toxins which destroy red blood cells collapsing the circulatory system and provoking severe necrosis to the other tissues.
PROTEROGLYPH (forward grooved)
Proteroglyphous species have venomous fangs at the front of their mouth and these aren’t usually very long. That’s why these snakes must apply pressure on their bite long enough to inject the necessary venom into their prey.
This kind of teeth is characteristic of the Elapidae family, which includes cobras and sea snakes. The members of this family have venoms most of which consist in neurotoxin (toxins that destroy the nervous system), and are amongst the most venomous of all vertebrates.
Also, some elapids of the Naja genre are known as spitting cobras, because their anterior fangs are modified and present orifices which allow them to spray their venom with the contraction of muscles of their venomous gland.
SOLENOGLYPH (pipe grooved)
This is the most evolved form and it is exclusively found in the members of the Viperidae family. In these species the maxilla is extremely reduced and serves as the support to a pair of hollow fangs which can make up to half the skull’s length.
These fangs are usually folded against the roof of the mouth but can articulate with the rest of the cranium when the mouth is opened up to 180 degrees to bite. This allows vipers to penetrate their fangs deeper into their prey and inject large quantities of venom, which being usually less powerful than the one of proteroglyphous snakes, in large quantities can be lethal.
Intern taxonomy of the different snake groups is based on many different anatomic characteristics. The classification presented here only refers to the dentition and jaw structure, and that may not be directly correlated to the evolutionary relationships between different families. For example, inside the Colubridae family (family which includes two-thirds of the extant snake species), we can find species with aglyphous, opisthoglyphous and proteroglyphous dentitions, even though the proteroglyph type is characteristic of the Elapidae family, where it has evolved independently.
The following sources have been consulted in the elaboration of this entry:
- Cover photo: Siddhesh Chafekar.