their early ancestors. The great reptiles, in spite of their eighty-foot length, were small in bulk compared with the biggest existing whales, the size of which has never been surpassed by any animal of any kind.

There are vast numbers of extinct mammals related to existing lions, bears, hyenas, horses, cattle, sheep, goats, antelopes, and other warm-blooded, hairy quad

SKULL OF PALEOMASTODON, A REMOTE
ANCESTOR OF THE ELEPHANT

rupeds. There are many extinct mammals which have no direct representatives in these days. Among the latter the dinoceras, a strange creature the size of a rhinoceros, had three pairs of horns on the top of its head and a pair of huge tusks, produced by the enlargement of the upper canine teeth. Another great animal, known as the titanotherium, resembled a rhinoceros, but had a pair of horns placed side by side on the nose. Characteristic of these and other horned animals of great bulk now extinct is the small brain, the volume of which was far smaller than that of existing great mammals, though the skull in some cases is three feet in length.

The extinct great armadillo of South America, known

as the glyptodon, like the little armadillo of the present day, carried armour formed by bones in the skin. The superiority of the small, surviving form is seen in an improvement which the great one never evolved. The armour is jointed, enabling the animal to roll up into a ball. The megatherium was very like the little sloth of to-day, but was nearly as big as an elephant. Instead of living in trees it stood on the ground and pulled the branches down for food.

The mylodon, which lived at the same time as the megatherium, was not quite so big. It was supposed to be long extinct when a discovery in a vast cave in Patagonia proved that it had survived into quite recent times. In this cave a great piece of skin was found, dry but not decomposed, covered with hair and studded on the inner side with pieces of bone. Further exploration revealed the skeletons of about twenty mylodons, quantities of bones broken by human agency, and stores of dry grass. The most likely conjecture seems to be that the mylodons had been kept there by Indians only a few centuries ago to serve as food.

Australia, cut off from the main stream of mammal evolution, is characterized by its pouched mammals, which elsewhere, with few exceptions, died out as the higher types appeared. Fossil remains show that among the extinct forms were kangaroos twice as big as the present ones, and wombat-like animals as large as a moderate-sized elephant.

Among the extinct predecessors of the elephants we find the mammoth, the mastodon, and other less familiar forms.

The mammoth, which had a much wider range than the elephant of to-day, resembled the Indian elephant,

but was slightly bigger, covered with coarse hair, as are the new-born young of existing elephants, and with tusks displaying a somewhat different curve. Its tusks and teeth are frequently dug up in England, and in North Siberia whole carcasses are found in a frozen condition with the skin, hair, trunk, and soft parts complete.

The mastodon was very like a true elephant, but had slightly different teeth and a longer head and jaw. It

SKELETON OF MAMMOTH

survived into comparatively recent times, and its remains are commonly found in a very complete state in North America. Some of the older species were probably the ancestors from which elephants sprang. One of these has no tusks in the upper jaw, but two huge ones in the lower jaw. An elephant-like creature about the size of a horse appears to be a sort of connecting link between the elephant species and more ordinary mammals. Another smaller skeleton, though undoubtedly that of a member of the elephant stock, had probably no trunk at all and small tooth-like tusks. The cheek teeth of this creature have the few transverse ridges characteristic of those of mastodons. In later elephants the ridges became narrower and

increased greatly in number, the mammoth having twenty-two, and the Indian elephant as many as twenty-seven. This increase in the number of ridges and other peculiarities in the teeth, the development of trunk and tusks, and shortening of face were specialized features produced during the evolution of elephants and leading them farther and farther away from the ordinary mammal type, to which we find the earliest

AN ANCESTOR OF THE HORSE

With four toes on the fore-feet and three toes on the hind-feet

representatives of the stock bear much more resemblance than the later.

The most marked divergence from the typical fivetoed mammal produced during the evolution of the horse is the reduction of the toes to one on each foot. All the horse-like animals probably sprang from an extinct stock which had five toes on each foot. A considerable step in the evolution of the modern horse was made by a little creature known as eohippus, which is only eleven inches high. This has four toes in front and three behind. In later beds we find horses which had three well-developed toes on each foot, each with a hoof resting on the ground. Then we have a horse with three toes on each foot, but the side toes are small and

do not reach the ground and are evidently on their way to disappearing. Present-day horses occasionally 'throw back' to their three-toed ancestors by being born with these small side toes. Twelve stages have been recognized showing the gradual evolution of the modern horse. Besides the main line of descent which produced existing horses and zebras there were several side branches which became extinct. Accompanying the development of the special peculiarity of one-toed feet we find other changes of structure taking place in the horse by which it became better fitted for its environment. The neck grew longer, enabling the animal to graze on short grass; limbs became adapted for swifter motion and the teeth for more efficient chewing, and the general improvement in organization was accompanied, as often, by great increase in size.

Man, the crown of mammal evolution, dominates this earth more completely than any other animal that has ever existed. The most important human fossil remains take us back some 150,000 years, and show that man was at that date living in Europe in a savage state with the mammoth, cave-hyena, cave-lion, woolly rhinoceros, reindeer, and bison.