The largest predaceous
quadrupeds living today are the lion and tiger. The bears although
some of them are much larger, are not generally carnivorous, except
for the polar bear, which is partly aquatic, preying chiefly upon
seals and fish. There are indeed carnivorous whales of gigantic size,
but no very large land carnivore. There were, it is true, during the
Tertiary and Pleistocene, lions and other carnivores considerably
larger than the living species. But none of them attained the size of
their largest herbivorous contemporaries, or even approached it. Among
the dinosaurs on the other hand we find that--setting aside
Brontosaurus and its allies as aquatic--the predaceous kinds equalled
or exceeded the largest of the herbivorous sorts. The difference is
striking, and it does not seem likely that it is merely accidental.
The explanation lies probably in the fact that the large herbivorous
mammals are much more intelligent and active, and would be able to use
their weapons of defense so as to defy the attacks of relatively slow
moving giant beasts of prey, as they do also the more active but less
powerful assaults of smaller ones. The elephant or the rhinoceros is
in fact practically immune from the attacks of carnivora, and would
still be so were the carnivora to increase in size. The large modern
carnivora prey upon herbivores of medium or smaller size, which they
are active enough to surprise or run down. Carnivora of much larger
size would be too slow and heavy in movements to catch small prey,
while the larger herbivores by intelligent use of their defensive
weapons could still fend them off successfully.
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