In such a position the animal would
have been capable not only of browsing among the higher branches of
trees, but of defending itself against the carnivorous dinosaurs by
using its relatively short but heavy front limbs to ward off attacks.
There are also indications of aquatic habits in some of the giant
dinosaurs which render it probable that a considerable part of their
life was led in the water. One of these indications is the backward
position of the nostrils. Many, but not all, water-living mammals and
reptiles have the nostrils on top of the head, in order to breathe
more readily when the head is partly immersed. Another fact of note,
although perhaps less conclusive, is the fitness of the tail for use
while moving about in the water, if not in rapid swimming.
The great tail, measuring from twenty-eight to thirty feet, was one of
the most remarkable structures in these animals, and undoubtedly
served a great variety of purposes, propelling while in the water,
balancing and supporting and defending while on land. In _Diplodocus_
it was most perfectly developed from its muscular base to its delicate
and whip-like tip, perhaps for all these functions.
_The Three Kinds of Giant Dinosaurs._ It is very remarkable that three
distinct kinds of these great dinosaurs lived at the same time in the
same general region, as proved by the fact that their remains are
freely commingled in the quarry.
What were the differences in food and habits, in structure and in
gait, which prevented that direct and active competition between like
types in the struggle for existence which in the course of nature
always leads to the extermination of one or the other type? In the
last three years we have discovered very considerable differences of
structure which make it appear that these animals, while of the same
or nearly the same linear dimensions, did not enter into direct
competition either for food or for territory.
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