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Lecture 8

BIO2242: Textbook summary - Lecture 8

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Mammals Mammalian teeth became differentiated to perform specialized functions such as cutting, seizing, gnawing, tearing, grinding, and chewing. Teeth differentiated in this manner are called heterodont. Mammalian dentition is differentiated into 4 types: incisors, with simple crowns and sharp edges, used mainly for snipping or biting; canines, with long conical crowns, specialized for piercing; premolars and molars with compressed crowns and one or more cusps, suited for shearing, slicing, crushing, or grinding. Unlike most other vertebrates, mammals do not continuously replace their teeth throughout their lives. Most mammals grow just teo sets of teeth: a temporary set, called deciduous, or milk, teeth, which is replaced by a permanent set when the skull has grown large enough to accommodate a full set. Only incisors, canines, and premolars are deciduous; molars are never replaced and the single permanent set must last a lifetime. The feeding, or trophic, apparatus of a mammal – teeth and jaws, tongue, and digestive tract – is adapted to its particular feeding habits. Insectivorous mammals, such as shrews, moles, anteaters, and most bats, are usually small. They feed on insects, as well as a variety of other small invertebrates. Insectivores eat little fibrous vegetable matter that requires prolonged fermentation, so their intestinal tract tends to be short. Insectivorous mammals have teeth with pointed cusps, permitting them to puncture the exoskeleton or skin of prey. Because many omnivores and carnivores also consume insects, the insectivorous diet is distinctive mainly by its lack of plant materials and vertebrates. Herbivorous mammals, which feed on grasses and other vegetation, form two groups: browsers and grazers, including ungulates (hooved mammals including horses, deer, antelope, cattle, sheep, and goats); and gnawers, including many rodents, and rabbits and hares. In herbivores, canines are absent or reduced in size, whereas molars and premolars, which are adapted for grinding, are broad and usually high-crowned. Rodents, such as beavers, have chisel-sharp incisors that grow throughout life and must be worn away to keep pace with their continual growth. Herbivorous mammals have a number of adaptations for processing their fibrous diet of plant food. Cellulose, the structural carbohydrate of p
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