"There are many instances," says Sir Edward Ray Lankester in his book on _Extinct Animals_, "in which small living animals were represented in the past by gigantic forms very close in structure to the little living beasts, but of much greater size. Hence it is concluded that these particular living animals are the reduced and dwindled representatives of a race of primeval monsters. There is some truth in this, as may be seen from the history of the living sloths and armadillos of South America, as compared with the extinct gigantic sloths and armadillos dug up in that country. But it is a great mistake to conclude from this that it is a law of nature that recent animals are all small and insignificant as compared with their representatives in the past. That is simply not true. Recent horses are bigger than extinct ones; recent elephants are much bigger than their earlier elephantine ancestors. There never has been any creature of any kind--mammal, reptile, bird, or fish--in any geological period we know of, so big as some of the existing whales, the Sperm Whale, the great Rorqual, and the whalebone whales. "It is true that there were enormous reptiles in the past, far larger than any living crocodiles, standing fourteen feet at the loins, and measuring eighty feet from the tip of the snout to the end of the tail; but their bodies did not weigh much more than a big African elephant, and were small compared with whales. So let us be under no illusions as to extinct monsters, and proceed to look at those of South America with simple courage and confidence in our own day." The peculiar productions of South America in the way of animals appear to be the members of the group of mammals called _Edentata_ found nowhere else. When, however, South America, which once was an island, joined on to North America, numbers of animals, mastodons, horses, tigers, and tapirs, emigrated from north to south, and perhaps proved too much for the aboriginal or native beasts. At any rate, all the big South American mammals died out, and now there are left only the small tree sloths, the small armadillos, and the strange-looking ant-eaters. But in quite late geological deposits of South America we find the bones of gigantic armadillos and of gigantic ground sloths, which lasted on till the time when man appeared on the scene. The _Glyptodon_, of which there were several different kinds, was an enormous armadillo as big as an ox. Like their small, puny, modern descendants, they carried on their backs a hard case of bones, something like the shell of a tortoise. The modern armadillo's shell, however, is jointed so that the little animal can roll itself up into a ball, and in this direction, therefore, the armadillo, though it has decreased so much in size, has advanced in adaptability.