Chew on this: All about animal teeth

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Animal skulls have evolved for millions of years to protect vertebrate's brains and sensory organs. Many of an animal's dietary and social patterns can be deduced by examining its skull and teeth.

The structure or shape of a mammal's jaw and teeth, as well as the placement of its eyes, are related to its diet. Mammals are really the only animals that have developed differentiated teeth, most other animals have teeth of only one shape, if they have teeth at all.And, unlike other animals, mammals have only two sets of teeth, the first (often called 'milk teeth') erupts after birth. After puberty, a larger set, with more and bigger teeth to fill larger jawbones, emerges. There are four different types of teeth: Incisors are the front teeth, used for cutting and grasping; Canines are next to incisors and are used for tearing; Premolars, located behind the canines, have sharp edges for crushing food; Molars, the very back teeth, are broad, flat grinders.

Carnivores are meat eaters and have comparatively small, less developed incisors (incisors play a minor role for carnivores such as grooming). The canine teeth are large, long and pointed for piercing and holding prey. Cheek teeth (pre-molars and molars) are sharp and pointed for cutting and tearing flesh. Some of the upper cheek teeth overlap lower teeth, providing a scissor-like shearing action to cut meat. These teeth are referred to as carnassial teeth. With overlapping cheek teeth and long canines, carnivores do not have the ability to move the lower jaw from side to side in a chewing motion. As predators they tend to bite, tear and gulp food without any chewing action. Their teeth tend to be clean and white because they are not stained by plant material.

Herbivores have large, well developed incisors for cutting plant material. Their canines resemble incisors in form and function. (Note: American elk are the only members of the North American deer family that have upper canine teeth. These teeth, found in both males and females are often referred to as "ivory teeth" or "tusk teeth.") Most ruminant (cud chewing) herbivores (deer, sheep, cattle, etc.) do not have upper incisors or canines. Instead, they have a hard upper palate that serves as a "cutting board" for the lower incisors to cut through plant stems. This arrangement permits the rapid ingestion of large amounts of plant material. Ruminant animals often seek cover after eating to regurgitate and chew their cud while watching for predators. Herbivore cheek teeth are large and wide with high, sharp crowns for grinding and chewing plant material. Instead of overlapping, the cheek teeth make surface contact to provide a grinding action. Herbivore teeth are often stained from substances in plants.

Herbivores such as rodents and rabbits tend to have very well-developed flat pre-molars and molars, often with sharp ridges on the tops.Their canines are often non-existent, and their incisors which are used to snip off foliage are often very large.In animals such as rodents, the incisors grow their entire lives, it is only through the action of them hitting together that they are ground down and kept at a reasonable length.Many herbivores have a large space called a diastema between the incisors and the pre-molars/molars through which chewed foliage passes through when swallowing.

Omnivores, with the ability to eat both meat and plants, have a wider choice of food sources than strict carnivores or herbivores. Good examples of omnivores are raccoons, bears, and humans, but one of the most successful omnivore survivors is the coyote. Coyotes are currently found in all the contiguous United States, throughout Canada, north to near the Arctic Circle and south to the Panama Canal. Within this extensive range of climates, this animal is found in remote wilderness and in large urban areas. The characteristics that play a role in this survivability include the combination of being an omnivore that can eat almost anything with excellent senses of sight, hearing and smell.

As might be expected, omnivores have a combination of carnivore and herbivore teeth characteristics. Omnivores have fairly large and well developed incisors for cutting plant material. The canine teeth are long and pointed for killing and holding prey. Cheek teeth are a combination of sharp, scissor-like carnassial teeth for shearing meat, and teeth with more rounded cusps for grinding and crushing plant material. There is surface contact between some upper and lower molars. Omnivores (except some primates) do not have side to side lower jaw movement. Rather than a chewing action, their cheek teeth perform both shearing and crushing actions. Many omnivores are either predominately meat eaters or predominately plant eaters. The cheek teeth of these animals can usually tell us their predominant feeding strategy. For example, the coyote is an omnivore that is predominately a meat eater and has cheek teeth very similar to a carnivore. However, the coyotes' most posterior molars have rounded cusps for grinding and crushing plant material. On the other hand, the black bear is an omnivore that is predominately a plant eater and has cheek teeth more closely resembling those of an herbivore.

The shape of a mammal's jaw can also provide clues to its diet. Herbivores tend to have thick, square lower jaws that help with grinding and crushing tough plant material. The lower jaw of a carnivore is slender and works with the upper teeth like a pair of scissors, slicing and cutting the meat of its prey. These adaptive characteristics have allowed animals to survive in their environment and, as their ecological niche changes, their future generations will change as well.

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