Susanne Rourke, age 11, of Cleveland, Ohio, for her question:

DO A DEER'S ANTLERS SERVE A PURPOSE?

Deer is the common name for a large family of hoofed mammals that are usually characterized by bony, often branching antlers that are shed and regenerated annually. The antlers are used to slash territorial markings on trees or bushes, to make threatening displays and to combat other males.

Usually the fighting of deer is stylized and harmless, but occasionally males of large species lock antlers and die of exhaustion or starvation.

Unlike the hollow, permanent horns of other ruminants, the antlers of deer are solid and bony. Except in the caribou, antlers form only on males, and their growth is controlled by the male sex hormone.

Arising from the frontal bones and nourished by a highly vascularized, fine haired skin, called velvet, antlers complete their growth within a few months. Circulation is then cut otf and the resulting dead skin is sloughed off as the animal rubs its antlers against trees.

Because of their often cumbersome size and the great amount of calcium needed for their growth, antlers can be considered a natural extravagance.

Moose antlers reach a width of six feet and a weight of 44 pounds and the extinct giant fallow deer Megalosaurus had antlers with a spread of more than 10 feet.

Deer forage on twigs, leaves, bark and buds of bushes and saplings, and on grasses and other plants, feeding most actively at twilight. Tne female gives birth once a year, usually to one or two fawns. The gestation period lasts from 160 days in musk deer to 10 months in roe deer. Fawns are kept hidden in thickets, camouflaged by their usually dappled markings.

In the United States, where deer now have few natural predators, they often overbrowse their territory and may die of starvation, especially during winters of deep snow. Hunting seasons are adjusted to keep such populations within limits.

The most abundant deer populations occur in mixed wooded and open land, although the animals also live in swamps, on mountains and on treeless northern tundras.

Deer species range in size from the European elk, or moose, which may reach a shoulder height of seven feet, to the South American pudu, which is 13 inches high at the shoulder.

The first true deer appeared in the lower Pliocene epoch, dating to about 10 million years ago.

Deer commonly have lithe, compact bodies and long, powerful legs suited for rugged woodland terrain. They are also excellent swimmers.

A deer's lower cheek teeth have crescent ridges of enamel, which allows it to grind a wide variety of vegetation. The animal is a ruminant, or cud chewer, and has a four chambered stomach.

The musk deer and the Chinese water deer do not have antlers. Instead, they have bearing upper canines that have developed into tusks.