The three abundant and conspicuous beasts, all three typical of the great mammalian fauna which was contemporary with the prehistoric human hunters, and all three common to all the continents on which this great mammalian fauna was found, were the lion—using the name to cover several species of huge horse-killing and man-killing cats; the elephant, including several totally different species, among them the mammoth and mastodon; and the horse, including numerous widely different species. Together with these three universally distributed animals were many others belonging to types confined to certain of the continents. Rhinoceros were found in Europe, Asia, and Africa (they had once flourished in North America but had died out long before man appeared on the globe). Camels were found in Asia, in South America, and especially in North America, which was their centre of abundance and the place where they had developed. Wild oxen were found in all the continents except South America; deer everywhere except in true Africa, zoogeographical Africa, Africa south of the Sahara. The pigs of the Old World were replaced by the entirely different peccaries of the New World. Sheep, goats, and goat-antelopes lived in Eurasia and North America. Most of the groups of big ruminants commonly called "antelopes" are now confined to Africa; but it appears that formerly various representatives of them reached America. The giraffe through this period was purely African; the hippopotamus has retreated to Africa, although in the period we are considering its range extended to Eurasia. In South America were many extraordinary creatures totally different from one another, including ground-sloths as big as elephants. Two or three outlying representatives of the ground-sloths had wandered into North America; but elsewhere there were no animals in any way resembling them. The horse, the lion, and the elephant were the three striking representatives of this vast and varied fauna which were common to all five continents.
The North American fauna of this type reached its height about the time—extending over many scores of thousands of years—when successive ice ages alternated with long stretches of temperate or subtropical climate throughout the northern hemisphere. During the period when this great North American fauna flourished hunter-savages of archaic type lived amid, and partly on, the great game of Europe. But, as far as we know, men did not come to America until after, or at the very end of, the time when these huge grass-eaters and twig-eaters, and the huge flesh-eaters which preyed on them, vanished from the earth, owing to causes which in most cases we cannot as yet even guess.
Much the most striking and interesting collection of the remains of this wonderful fauna is to be found near one of our big cities. On the outskirts of Los Angeles, in southern California, are asphalt deposits springing from petroleum beds in the shales below. The oil seeping up to the surface has formed shallow, spread-out pools and, occasionally, deep pits covered with water. In part of the area these pits and pools of tar have existed for scores of thousands or hundreds of thousands of years, since far back in the Pleistocene. They then acted as very dangerous and efficient mammal traps and bird traps—and now continue so to act, for the small mammals and the birds of the neighborhood still wander into them, get caught in the sticky substance, and die, as I have myself seen. Moreover the tar serves as a preservative of the bones of the creatures that thus perish. In consequence some of the ancient pits and pools are filled with immense masses of the well-preserved bones of the strange creatures that were smothered in them ages ago.
Nowhere else is there any such assemblage of remains giving such a nearly complete picture of the fauna of a given region at a given time. A striking peculiarity is that the skeletons of the flesh-eaters far surpass in number the skeletons of the plant-eaters. This is something almost unique, for of course predatory animals are of necessity much less numerous than the animals on which they prey. The reversal in this case of the usual proportions between the skeletal remains of herbivorous and carnivorous beasts and birds is due to the character of the deposits. The tar round the edges of the pools or pits hardens, becomes covered with dust, and looks like solid earth; and water often stands in the tar pits after rain, while at night the shallow pools of fresh tar look like water. Evidently the big grazing or browsing beasts now and then wandered out on the hard asphalt next the solid ground, and suddenly became mired in the soft tar beyond. Probably the pits in which water stood served as traps year after year as the thirsty herds sought drink. Then each dead or dying animal became itself a lure for all kinds of flesh-eating beasts and birds, which in their turn were entrapped in the sticky mass. In similar manner, thirty years ago on the Little Missouri, I have known a grizzly bear, a couple of timber-wolves, and several coyotes to be attracted to the carcass of a steer which had bogged down in the springtime beside an alkali pool.
Another result of the peculiar conditions under which the skeletons accumulated is that an unusually large number of very old, very young, and maimed or crippled creatures were entrapped. Doubtless animals in full vigor were more apt to work themselves free at the moment when they found they were caught in the tar; and, moreover, a wolf or sabretooth which was weakened by age or by wounds received in encounter with its rivals, or with some formidable quarry, and which therefore found its usual prey difficult to catch, would be apt to hang around places where carcasses, or living creatures still feebly struggling, offered themselves to ravenous appetites.
The plant remains in these deposits show that the climate and vegetation were substantially those of California to-day, although in some respects indicating northern rather than southern California. There were cypress-trees of a kind still common farther north, manzanita, juniper, and oaks. Evidently the region was one of open, grassy plains varied with timber belts and groves. It has been said that to support such a fauna the vegetation must have been much more luxuriant than in this region at present. This is probably an error. The great game regions of Africa are those of scanty vegetation. Thick forest holds far less big animal life. Crossing the sunny Athi or Kapiti plains of East Africa, where the few trees are thorny, stunted acacias and the low grass is brown and brittle under the drought, the herds of zebra, hartebeest, wildebeest, and gazelle are a perpetual delight and wonder; and elephant, rhinoceros, and buffalo abounded on them in the days before the white man came. On the Guaso Nyero of the north, and in the Sotik, the country was even drier at the time of my visit, and the character of the vegetation showed how light the normal rainfall was. The land was open, grassy plain, or was thinly covered with thorn scrub, with here and there acacia groves and narrow belts of thicker timber growth along the watercourses, and in the Sotik gnarled gray olives. Yet the game swarmed. We watched the teeming masses come down to drink at the shrunken rivers or at the dwindling ponds beside which our tents were pitched. As the line of the safari walked forward under the brazen sky, while we white men rode at the head with our rifles, the herds of strange and beautiful wild creatures watched us, with ears pricked forward, or stood heedless in the thin shade of the trees, their tails switching ceaselessly at the biting flies. In wealth of numbers, in rich variety and grandeur of species, the magnificent fauna we then saw was not substantially inferior to that which an age before dwelt on the California plains.
This Pleistocene California fauna included many beasts which persisted in the land until our own day. There were cougars, lynxes, timber-wolves, gray foxes, coyotes, bears, pronghorn antelopes and black-tail or white-tail deer nearly, or quite, identical with the modern forms. They were the same animals which I and my fellow ranchmen hunted when, in the early eighties of the last century, our branded cattle were first driven to the Little Missouri. They swarmed on the upper Missouri and the Yellowstone when Lewis and Clark found the bison and wapiti so tame that they would hardly move out of the way, while the grizzly bears slept on the open plains and fearlessly attacked the travellers. But in the Pleistocene, at the time we are considering, the day of these modern creatures had only begun. The contents of the tar-pits show that the animals named above were few in number, compared to the great beasts with which they were associated.
The giant among these Pleistocene giants of California, probably the largest mammal that ever walked the earth, was the huge imperial elephant. This mighty beast stood at least two feet higher than the colossal African elephant of to-day, which itself is bigger than the mammoth, and as big as any other extinct elephant. The curved tusks of the imperial elephant reached a length of sixteen feet. A herd of such mighty beasts must have been an awe-inspiring sight—had there been human eyes to see it. Nor were they the only representatives of their family. A much more archaic type of elephant, the mastodon, flourished beside its gigantic cousin. The mastodon was a relatively squat creature, standing certainly four feet shorter than the imperial elephant, with comparatively small and slightly curved tusks and a flatter head. Enormous numbers of mastodons ranged over what is now the United States, and the adjacent parts of Canada and Mexico. The mastodons represented a stage farther back in the evolutionary line than the true elephants, and in the Old World they died out completely before the latter disappeared even from Europe and Siberia. But in North America, for unknown reasons, they outlasted their more highly developed kinsfolk and rivals, and there is some ground for believing that they did not completely disappear until after the arrival of man on this continent.
The elephant stock developed in the Old World, and it is probable that the true elephants were geologically recent immigrants to America, coming across the land bridge which then connected Alaska and Siberia. In California they encountered the big descendants of other big immigrants, which had reached North America by another temporary land bridge, but from another continent, South America. These were the ground-sloths, giant edentates, which reached an extraordinary development in the southern half of our hemisphere, where distant and diminutive relatives—tree-sloths, ant-eaters, armadillos—still live. The most plentiful of these California ground-sloths, the mylodon, was about the size of a rhinoceros; an unwieldy, slow-moving creature, feeding on plants, and in appearance utterly unlike anything now living.
Together with these great beasts belonging to stocks that in recent geologic time had immigrated hither from the Old World and from the southern half of the New World was another huge beast of remote native ancestry. This was a giant camel, with a neck almost like that of a giraffe. Camels—including llamas—developed in North America. Their evolutionary history certainly stretched through a period of two or three million—perhaps four or five million—years on this continent, reaching back to a little Eocene ancestor no bigger than a jack-rabbit. Yet after living and developing in the land through these untold ages, over a period inconceivably long to our apprehension, the camels completely died out on this continent of their birth, although not until they had sent branches to Asia and South America, where their descendants still survive.