The Courtship of Animals

by W. P. Pycraft

In the now extinct Sabre-toothed Tiger the upper canines were of enormous length, and it is not improbable that they, on this account, exceeded the bounds of usefulness; that, while as weapons of offence they may have proved exceedingly effective, yet they hampered the animal when feeding. In many ways one is reminded by these weapons of the huge tusks of the Walrus. These are blunt-pointed, and are said to be used very largely for digging up the large clams and other burrowing shell-fish on which this animal mainly feeds. They are also used as levers to drag the huge body out of the water on to the ice. As fighting weapons they are formidable, and the wounds they inflict are sometimes serious. The polygamous habits of this huge creature may account for the fact that they are so much larger in the males, wherein they may attain a length of thirty inches, and a weight of eight pounds a-piece.

In connection with the monstrous tusks of the Sabre-toothed Tiger there is a point which so far seems never to have attracted the attention it deserves. And this concerns two small flanges of bone which project from the lower border of the end of the lower jaw. In themselves they are unimportant: they lie, it is to be noticed, parallel with the points of the great upper teeth which descend on either side of them. Their full significance is not apparent till we turn to the skull of another extinct animal of quite another type—the huge Dinoceros, one of the Ungulates. This animal was also armed with an enormous pair of tusks, which also, when the mouth was closed, descended on either side of a flange. In this case, however, the flange was developed to such an extent that its free edge descended to the level of the point of the tusk, thus affording it protection against injury. The really striking feature of this curious down-growth is not apparent till an attempt is made to explain its presence. What determined its growth? It seems to furnish us with another of the many instances which are to be found of the correlation of growth between unrelated parts, for there is apparently no traceable connection between the growth of this pair of teeth in the upper jaw and the development of the flanges of the lower border of the jaw which are embraced by these teeth. In the Sabre-toothed Tiger the inciting cause to this flange growth, whatever it may have been, seems to have been much weaker than in the case of Dinoceros.

Naturally one asks, can the whole thing be explained by the theory of Kinetogenesis promulgated years ago by Cope? That is to say, are these curious down-growths the result of a response to a stimulus set up in the lower jaw by constant lateral blows dealt by the tusks against the side of the jaw during the lateral movements of the jaw when feeding or ruminating? Such movements in an Ungulate would be frequent and constant: hence perhaps the more striking result. On account of the scissor-like action of the jaws in the Sabre-tooth such lateral movements were far less extensive, and less powerful. But though this explanation sounds plausible, it presents many difficulties. In the first place it seems to commit one to the admission that the responses of the Somatoplasm during the life of the individual are transmitted to the germ-plasm: that, in short, the characters acquired by the individual during its lifetime are transmitted to its offspring. And there are insuperable difficulties in the way of such a theory. Yet, it must be admitted, it is no less difficult to believe that this correlation of growth is due solely to fortuitous variation, for one cannot really conceive of a variation of this kind taking place in two such different structures independently. Such a conception would have been less difficult if the case of Dinoceros alone were known to us. We could have supposed that, somehow, the lower jaw started to produce its flange just as the teeth began to develop an excess of growth which carried their points beyond the level of the jaw. But the Sabre-tooth shows that the tusks had assumed a growth relatively exaggerated as in Dinoceros, and yet the flange never attained to more than feeble development. We cannot rest content with the theory that the flange is due to the constant stimulus of blows struck against this region of the jaw during the lateral movements which take place when feeding. Were these animals alive to-day it could be tested by extracting the tusks during infancy, when, the stimulus being removed, the flanges should not appear.

There are yet other aspects of the skull of Dinoceros which may well be considered here. The first concerns the excessive armature of horns, there being no less than three pairs supported on massive bony cores; and the second the ridiculously small brain cavity which is proportionately smaller than that of any other known mammal, recent or fossil. This poverty of brain-power was probably one, if not the chief, factor among the causes which brought about the extinction of this strange beast. Even more formidable horns were borne by the extinct Arsinoetherium. But this animal did not display the double armature of horns and tusks.

Among the Carnivora monogamy is the rule, though the Lion is occasionally polygamous. But the Eared-seals (Otaria), or Sea-lions, and Sea-bears afford a striking example of polygamous species and of the ferocity they display when sexually excited. These animals, moreover, are capable of the most astonishing powers of endurance and vitality, exceeding indeed that of all other mammals. Since the habits of the Northern Fur-seal (Otaria ursina) have been more carefully studied than those of any others, it may serve as a sample of the rest.

Living for the greater part of the year in the open sea, the old bulls—animals of six or seven years old—are the first to seek the “rookeries,” or breeding grounds, taking up their territory a full month before the cows arrive. Later, the younger bulls appear, and the more daring endeavour to force their way through the ranks of those who have already taken up positions. This often leads to fighting, but more usually nothing further than “bluffing” is indulged in, though it is commonly supposed that very severe engagements take place. This seems, however, to be only occasionally true. In due course, generally about the second week in June, the cows begin to arrive, at first in straggling numbers, but soon the main body puts in an appearance, and before the end of the month many thousands of both sexes are crowded along the foreshore. But yet, contrary to the generally accepted belief, no serious fighting takes place. The bulls quietly seize the females as they arrive. It would seem that the first arrival serves as a focus of attraction for all later comers landing in the vicinity. The bull holding the most advantageous post—that is to say, that nearest the best landing-place—starts the collection and, unintentionally, the distribution of the cows. Having seized the first arrival, he places her by his side. As the later females arrive he gives each a most cordial welcome, and then proceeds to round up his harem. But soon he has more wives than he can continue to control. Do what he will, he cannot be in two places at once; and thus it is that in rushing off to chastise some covetous neighbour, one or more bulls on the opposite side of his harem proceed to make captures from his horde. And this system of abduction goes on over the whole rookery till all the cows have been appropriated, leaving a crowd of envious bachelors in the background who have not yet developed either courage or strength to secure mates for themselves.

Plate 13.

Photo by New York Zoological Society, from “The Living Animals of the World.”

CALIFORNIAN SEA-LIONS, OR EARED SEALS.