SPECIES OF MAMMALS OF THE PACIFIC AREA 153 The Sumatran Rhinoceros (Rhinoceros HumatranuH) is the smallest of the family and also tlif- most hairy, especially when youn^. This rhinoceros carries two horns, and the folds of the brownish black skin are much less marked. On the mainland it has much the same range as the Javan rhinoceros; on tijf; islands it occurs in Sumatra and Borneo but not in Java. Its habits are very similar to those of the Javan rhinoceros but it prefers the thickest of forest jungle on rough mountainsides. Mud wallows are necessary for the health of this animal, and when found they are a sure indication that rhinoceros are in the vicinity. Like the Javan rhinoceros it has been persistently hunted for its horns and blood, used as medicine by the Chinese, and consequently it is no longer found over much of the country where it once existed. It also is doomed to extinction unless adequate protection is given it. Fig. 68 — Malay Tapir Tapies. Family Tapieid^ This family includes the Old World and New World tapirs. The New World tapirs are found in Central and South America while in the Old World the single species is found from
154 MAMMALS OF THE PACIFIC WORLD Tenasserim south through the Malay Peninsula to Sumatra. The Malay Tapir (Tapirus indicus) is easily recognized by its heavy build, short tail, oval ears, and long snout or proboscis. The head, fore parts, and hind legs are black; the remainder of the rump and the upperpart of the thighs is grayish white. The young at birth are brownish black with spots and streaks of brownish yellow on the back and sides, but they change to the adult color during their first year. An adult may reach the height of three and one-half feet. Tapirs frequent forests ; they live chiefly in swamps and along rivers and are very partial to water. In their native home they are shy and difficult to approach, but in captivity they become very tame.
3 Distribution of Mammals in the Pacific Area The reason for the presence of certain kinds of mammals on one island group, for their absence from another, or the substitution of still other kinds of animals on a third island, must be sought in the interweaving histories of the evolution of the mammals themselves and in the evolution of the topography, climate, vegetation, and other components of their environments.
ORIGIN AND EVOLUTION OF MAMMALS The earliest, most primitive mammals are lineal descendants of peculiar reptile-like creatures whose fossil remains have been found in South Africa and elsewhere. Those first mammals imperceptibly and during the course of very many generations developed away from being actual reptiles. Gradually those basic distinctions by which every mammal today is distinguished from every reptile took form: heat-conserving and regulating mechanisms including hair, sweat glands, special automatic nervous control of the oxidizing processes were progressively developed; milk glands, together with the change from egglaying to bearing of young, were evolved ; alterations took place in the forms and functions of certain bones and muscles adjoining the head and the hinged part of the jaw. During an immensely long period of time these alterations of body parts into different shapes and for new purposes took place ; the descendants of reptiles became mammals.
Those dawn mammals were unlike any living mammals today. 155
156 MAMMALS OF THE PACIFIC WORLD The few fragmentary fossils known indicate that some, at least, were rat-sized creatures, with pointed teeth suitable for eating insects. Yet from those animals or others somewhat like them began not only the genealogical lines leading to the principal modern Orders, but a host of other lines which, figuratively speaking, experimented with themselves for longer or shorter periods of time, and, finding themselves inadequate, died out. The few successful ones became the ancestors of our earliest carnivores, insectivores, bats, hoofed animals, rodents, marsupials, and monotremes. Such relatively modern groups alone concern us here.
That process, involving change of shape and size combined with change of use of parts, has remained continuously operative. The primitive five-toed horse progressively lost its outer toes and became one-toed. Thus during millions of years or even millions of generations a little five-toed mammal gave rise to a large, one-toed horse. At the same time the remaining toes increased in size and strength in order to sustain the weight of the body, for horses were growing bigger. Innumerable other changes in the many parts of all animals, which fitted them for the performance of diverse functions, took place continuously everywhere. This process is generally termed evolution. EVOLUTION OF ENVIRONMENTS Throughout this length of time, when the characteristics of mammals were changing, alterations were taking place also in the earth itself. Slow movements of the earth's crust raised or lowered parts of the surface. Near the sea, uplifts pushed back the ocean and caused islands long separate from the mainland to become joined to it ; or downwarping permitted the waters to flood the land and to convert high ground near the coast into islands. On the continents long-continued earth movements elevated mountain ranges, diverted rivers, or established new rain-collecting areas.
The slowly changing shapes of the land and oceans simulta-
DISTRIBUTION OF MAMMALS 157 neously brought about slowly changing climates. The draining of shallow seas had modifying effects on the temperature and moisture of the air above and around them. The elevation of large mountain ranges, particularly if directed north and south, not only produced colder climates on their own slopes and crests but by altering prevailing winds modified profoundly the rainfall and temperature of the lowlands on either side. The reverse of these processes also took place: The heights of other mountain ranges already elevated were gradually reduced by weathering and erosion, again with the effect of modifying local climates. Such changes take place on islands as well as on continents.
From time to time during the earth's history periods of lower temperatures have, by cumulative effect, resulted in "ice ages," when vast amounts of water from the oceans slowly accumulated as snow or ice at or near the earth's poles. Those huge polar ice-caps — smaller ones exist today on Greenland and Antarctica — ^had, at their greatest development, pronounced climatic effects on the regions near them. The grinding movement of the ice also caused important local changes in the rocks and soils which it overspread.
The climate affects mammals largely indirectly, through its effect on vegetation. Damp climates favor forests, relatively dry climates lead to spread of grasslands, while desert climates result in the development of leafless water-storing plants which often produce great quantities of seeds after the occasional rains. Few mammals live with equal advantage in these various climates ; in all environments there are species suited to the special conditions of food and shelter. The presence of these is an important factor in keeping out the less well adapted species.
CONTINENTAL AND OCEANIC ISLANDS Two classes of islands are commonly recognized. Continental islands are those which stand on the continental shelf, sepa-
158 MAMMALS OF THE PACIFIC WORLD rated by relatively shallow seas or straits from the mainland and connected with it at various times in the history of the earth. Oceanic islands have never been connected with a continent but are separated from it by water of great depth — more than six hundred feet. They have arisen from the floor of the ocean. In a few cases it is uncertain whether certain islands are continental or oceanic, whether the former connections with the mainland have foundered or whether the island has been pushed up from the bottom of the sea. Examples of continental islands are the Greater Sundas — Sumatra, Java and Borneo — Japan and Formosa, formerly connected with confinental Asia. Similarly, New Guinea was once joined to Australia. The shallow seas now separating such islands from their mainlands were probably dry land during the last ice age. Many mammals which occurred in neighboring areas of the continents were able to spread to the islands without difficulty. At the end of the ice age the gradually rising seas again isolated the islands with the animals which had invaded them. The mammals inhabiting continental islands differ only slightly or not at all from those of the nearby continents ; ancient types of animals, known as "living fossils," are usually absent.
The Luchu and Kurile Islands seem to represent parts of former continental areas that sank. The higher peaks of former coastal ranges were left as islands, cut off from each other and Japan, Formosa, and Kamchatka by deep straits. Movements of the earth's crust have also thrown up great interior mountain ranges on land; in some cases these ridges continue out onto the floor of the ocean. Such plunging mountain ranges as the Aleutians occur, the landward members of which are continental, but the distant peaks have always been separated by deep straits from the mainland.
Celebes, the Moluccas, the Philippines, and Australia may have been parts of an ancient southeastern extension of the Asiatic continent. If this be true, this area must have been
DISTRIBUTION OF MAMMALS 159 broken up in the Age of Reptiles or not later than very early in the Age of Mammals, a hundred million years ago. No indication of such a continental origin of these islands is to be found in the mammals of this area. Similarly, New Zealand has been supposed by some to have been separated from Australia by the sinking of the great area now covered by the Tasman Sea. Oceanic islands, built up from the bottom of the ocean, are of several kinds. Just as on land, the crust of the earth covered by the oceans may be wrinkled and folded. Great underwater ranges of mountains are known, the highest points of which project above the water. In the case of New Caledonia and probably New Zealand, the projecting mountain-tops form large islands and reach high above the ocean level. Other islands are volcanoes, built up by great eruption from the depths. Combinations of mountain range and volcano may explain the arc-like chains of islands, such as that formed by the Palaus, Marianas, and Bonin Islands. Another such arc includes the Solomons and New Hebrides, while the Marshalls, Gilberts, and Ellice Islands suggest a third. If Celebes, the Moluccas, and the Philippines are not remains of an ancient continental mass, they may well be ridges pushed up from the ocean floor. The first two seem to have been revolved like a vast eddy between the masses of southeastern Asia and Australia. Great disturbances of the earth's crust must have occurred in this region ; certain parts have been heaved up, others have sunk. Coral barrier reefs and coral atolls are built on and around volcanic bases throughout the tropical Pacific. In some cases their peculiar shapes are explained by the gradual sinking of the heavy volcanic islands around which they formed. In other cases the change of sea level during the ice age may have been important.
Oceanic islands, even if situated near the continent, harbor relatively few mammals ; but then, their nearness to the mainland is important if winds and water currents are likely to bring them drifting organisms. Often ancient types, "living
160 MAMMALS OF THE PACIFIC WORLD fossils" today, reached favorably situated islands in the distant past. A few bats and hardy, raft-riding mammals often are found on such islands. The remote Pacific islands had no mammals at all until the first men landed.
RANGE AND DISPERSAL OF MAMMALS At all times during the history of the evolution of a species of mammals its environmental conditions have necessarily been generally favorable. For although the environment best suited to a species probably can never exist, neither can markedly unfavorable conditions be long sustained. Similar or even more favorable locations elsewhere may remain unoccupied by that species only because of intervening environmental barriers. Favorable conjunction of animal needs with suitable surroundings may be temporary only. The animal is continuously evolving; the physiography, climate, and vegetation of its habitat are constantly changing. Let us assume a possible case, under which the surface of the land becomes lower, the climate hotter and drier, the character of the vegetation more and more desert-like. Simultaneously with this environmental change, involuntary evolutionary experiments are being conducted by the animal. Some of the products of variation are more suited to the drying habitat, others to a region even more humid than the original one. The former persist and reproduce their kind ; the latter die. Thus an animal species has changed, and, through the selective action of a changing habitat, the changed species survives as a race distinct from the original one.
In a second situation, the environmental conditions at the margin of the range of a particular species of mammal gradually become favorably modified; what before was desert becomes grassland or forest, favorable to the species. Then, the species as a whole can advance, generation by generation, into the now favorable area until stopped by some new barrier. Ad-