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.)