(Lat.: Megaloceros giganteus)

Among the largest deer ever known, this animal was up to 3.5 meters long, 2.1 meters tall at the shoulders, and its antlers spanned as much as 3.6 meters between from tip to tip. The antlers alone could weigh as much as 40 kilograms. Only the males had antlers, which they shed once a year. They lived in open fields and became extinct after the last ice-age (about 8,000 years ago). The reason is obvious: They need the open fields, because they can't move in the forest.

Antlers of the Irish Elk

These enormous structures are credited by some authorities with being responsible for the extinction of the Irish elk. The burden of their great weight and size, together with the metabolic load of funding their manufacture, severely reducing the male animals' fitness. (A difficult argument, apparently, to square with evolutionary theory.)

The elk's antlers showed, particularly dramatically, the positive allometry seen in horn-like structures generally. (Larger animals have disproportionately larger antlers; the effect being both inter-and intra-specific.) By the hypothesis of the previous paragraph: the mysterious force producing positive allometry killed the elk.

Another effect tending to make the antlers of this massive animal large is the association between cold temperatures and the size of horn-like structures. The colder the climate the larger the structure. An example is the great, curving tusks of the mammoth.

In water, low temperature gigantism is a well known phenomenon. Two theories are advanced: Oxygen, O2, is more soluble in colder water, more available to the animals. The larger animal has the geometric problem that the surface area of its gas exchange surfaces increases as the square of its linear dimensions while its bulk, and therefore O2 demands increases as the cube. This difficulty is mitigated by more plentiful oxygen. Another argument is that an animal's intrinsic metabolism is lowered by cold and so the same amount of food may fund a larger animal. This reasoning, in particular, has many, huge assumptions.

(See: Bergman's Rule.)

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