Antler

Antlers are extensions of the skull grown by members of the deer family. They are not true bone structures but they usually grow in symmetrical pairs. In most species, only the male grows antlers with the exception of Caribou and the antlers primarily function in sexual selection as attractions to females and as weapons in fights for control of harems. In many temperate zone species, antlers are shed and regrow each year, while horns are permanent.

Antler comes from the Old French antoillier (see present French : "Andouiller", from ant-, meaning before, oeil, meaning eye and -ier, a suffix indicating an action or state of being) possibly from some form of an unattested Latin word *anteocularis, "before the eye" (and applied to the word for "branch" or "horn").

Antlers are unique to cervids. The ancestors of deer had tusks (long upper canine teeth). Antlers appear to replace tusks; two modern species, the musk deer and the water deer, have tusks and no antlers, the muntjac has small tusks and small antlers, and other deer have full-sized antlers and no tusks.

Antlers are usually found only on males. Only reindeer (known as Caribou in North America) have antlers on the females, and these are normally smaller than those of the males. Nevertheless, fertile from other species of deer have the capacity to produce antlers on occasion, usually due to increased testosterone levels. The "horns" of a pronghorn (which is not a cervid but a giraffoid) meet some of the criteria of antlers, but are not considered true antlers because they contain keratin.

Each antler grows from an attachment point on the skull called a pedicle. While an antler is growing, it is covered with highly vascular skin called velvet, which supplies oxygen and nutrients to the growing bone. Antlers are considered one of the most exaggerated cases of male secondary sexual traits in the animal kingdom, and grow faster than any other mammal bone. Growth occurs at the tip, and is initially cartilage, which is later replaced by bone tissue. Once the antler has achieved its full size, the velvet is lost and the antler's bone dies. This dead bone structure is the mature antler. In most cases, the bone at the base is destroyed by osteoclasts and the antlers fall off at some point. As a result of their fast growth rate, antlers are considered a handicap since there is an immense nutritional demand on deer to re-grow antlers annually, and thus can be honest signals of metabolic efficiency and food gathering capability.

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