Snakes of the World - Part 8
Snakes of the World - Part 8
Snake fangs image courtsey: tigerhomes.org
Snakes and their Teeth
The very word “snake” reminds about the dreaded poison-fangs they possess and create terror in the listener. But there are more to snake’s teeth than just poison. They tell more about the evolutionary status of snakes and are helpful to herpetologists (people who deal with reptiles. Gk, herpetos = reptiles) in the process of classifying them
Snakes are carnivorous (animal which feeds on other animals. Latin carn = flesh + vorus = feeding) and they swallow the prey as such, this make the role of teeth in chewing limited, yet being curved backwards they keep the prey from rushing out. Fangs got evolved from ordinary teeth and present only in poisonous varieties (only ten percent of snakes are poisonous). Some snakes have well developed teeth others have only reduced ones but all snakes have teeth.
Teeth are found on maxillary, palatine, pterygoid and mandibualr (bones which constitutes the upper and lower jaws) bones and rarely on the pre-maxilla. There are no pits (sockets) for the teeth in snakes as in higher group of animals but simply joined to the bone. The teeth are periodically shed (as the next row is ready to take charge). The removed teeth leave only slight markings on the bones.
Main changes due to evolution have taken place on the maxillary-bones; hence its value to taxonomy (Science of classification of living things, Greek taxis = arrangement + nomia = distribution) is more pronounced than any other any other bones of the jaws. Its shape and its position with regard to other bones of the arch are useful. Knowing the exact count of the of teeth is important, and to do this the maxilla or the entire arch may have to be separated from the body, cleaned, and dried to ascertain the impressions of shed teeth.
In most cases as every alternate tooth having shed, the jaw appears, to possess only half the real number. Snakes are blessed with a succession of teeth, the new rows wait in the gum ready to take charge. Replacement teeth in different stages of development can be observed, sometimes as many as three or four sets wait in vertical series one by one.
Aglypha (pain toothed)
Snakes are divided mainly in to three based on the structure of their teeth, they are 1- solid toothed, 2- groove-toothed, and 3- canliculate-toothed. Solid teeth (aglyphous, French, a =nil + glyph = groove) occur in all the primitive snakes, more than half of the members of family Colubridae belong to this group. Three sub-groups
1. Acrochordinae (Mostly aquatic ex Natrix)
2. Colubrinae (typical snakes) and
3. Rhachiodontinae (egg-eating snakes)
The Opisthoglypha (Gk, opisthen = behind) or back-fanged.
They have grooved teeth confined to the last two or three maxillary teeth usually larger than the others. The grooves occur on the external or antero-external surface of the teeth; and vary considerably among species. The difference may be so small and may require magnification for identification. It is connected with the ducts to the poison gland. (Three sub-families 1-Homalopsinae aquatic snakes 2- Dipsadomorphinae; majority are arboreal 3- Elachistodontinae – those with rudimentary teeth)
The front-fanged Proteroglypha (Greek, proteros = front)
(Elapidae, the cobra family) and solenoglypha (Vipers).
Front fanged ones are generally very poisonous. In Protero glypha (protero = front) the canal has been evolved from the grooved condition by its extension in to the tooth. This connection made by decalcifying the tooth, when the filling disappears and groove is reinstated. The Cobra in fact is not much different from the opisthoglypha.
Solenoglypha (Gk solen = channel-toothed)
In vipers the poison fangs are fixed on a vertically movable maxillary bone hence the large fangs can be raised for use and folded after it. Here the union is more rigid and irrevocable. These all suggest that Elapidae and Viperidae that both not only evolved separately but Vipers are the forerunners in the process. When a cluster of 3 to 4 rows are in the reserve for Viperidae; Elapidae has only one or two.
As there is no direct attachment between the poison duct to the fang (When it reaches the base of the fang it expands in to a small cavity in the fold of the gum overlying the opening into the canal), the loss of the tooth therefore, does not injure the duct and venom-supply to the next tooth made before the old is shed.
It is a pity to state that there is no single external character to identify a poisonous snake from a harmless one as the fangs alone establish this feature, which is not easily identifiable. Species like Callophis have fangs which are extremely small and requires a magnifying glass to identify them. Teeth of snakes are important not only as they are the only mark to reveal the venomous nature of snakes but also as the prominent story tellers about the evolutionary stages snakes traversed to reach the present status occupied by them.
To be continued...