Zebras and canines
Because of their vegetarian diet, zebras have no use for the killing-sharp canine teeth so essential to carnivores. These canines, however, are quite developed in male zebra … and quite useful too.
Reader Marie Shatkovsky queried the following description in Wild 19 winter 2012: “Most zebra stallions live in bachelor groups where they often display their rank through orderly fighting that includes displays of the canines.”
Canines are synonymous with piercing and killing, hence their importance to meat-eating mammals. So it seems a bit odd to learn that herbivores need such teeth at all. But teeth are not only used for eating.
Teeth in mammals
It was many millions of years ago, in the Mesozoic era, when major changes occurred in the teeth and jaws of mammals. Teeth became specialised to perform various functions ranging from seizing and cutting to tearing and grinding.
There are four types of teeth in mammals:
• Incisors with sharp edges for snipping and biting
• Canines with long conical crowns for piercing (often reduced or missing in herbivores)
• Premolars with compressed crowns for shearing, slicing, crushing and grinding
• Molars with compressed crowns for shearing, slicing, crushing and grinding
Unlike their reptilian friends, mammals do not continuously replace their teeth throughout their lives. Deciduous (or milk) teeth are replaced only once; these include the incisors, canines and premolars. Molars, on the other hand, are never replaced and are the only permanent set which must last the lifetime.
Related to the domestic horse, zebras are grazers. They have strong upper and lower incisors for cropping grasses. Their molars are adapted for grinding with a broader and higher crown useful when processing silicate-rich grasses. A zebra’s canine teeth are reduced in size and, like all herbivores, do not play a prominent role in food gathering and processing.
Teeth are the only form of sexual dimorphism (difference between the sexes) in zebras. Male zebra have spade-shaped canines, which they use in rivalry fights with other stallions.
A male wild boar also has modified canines, just like male zebras, which are quite pronounced and used as weapons. In other mammals other teeth have become specialised. The tusks of elephants, for example, are modified upper incisors used for defence, attack and rooting.
Integrated Principles of Zoology (thirteenth edition). Hickman, Roberts, Larson, l’Anson, Eisenhour. 2006. MsGraw-Hill. p604-605, 693-694.
Posted on: November 26, 2012, 11:17 AM
Posted on: November 26, 2012, 11:19 AM