ENVIRONMENT OF THE TITANOTHEKES 



129 



Thus far all examples of T. bairdi [Elasmognathus] have been 

 found exclusively on the Atlantic side of the Isthmus [of 

 Panama], and north of the Chagres River. Their favorite 

 haunts appear to be in the hills lying at the back of Sion Hill 

 and the adjoining stations of the Panama Railway. It is only 

 during the rainj' season that they seem to seek the lowlands, 

 for it is only in that season they are captured. 



Similarly Tapirus {Elasmognathus) dowi was found 

 in the highlands of Guatemala, Nicaragua, and Costa 

 Rica. 



3. The opposite extreme from mountain-living 

 habits is furnished by the typical South American 

 tapir (T. terrestris), which inhabits the forest districts 

 of Brazil, Paraguay, and the northern part of Argen- 

 tina. This species is fond of gamboling in the water 

 and rolling in soft mud and swims and dives like a 

 capybara; it is not improbable that it may also walk 

 along the beds of shallow rivers and lakes, as was 

 observed to be the habit of a specimen of the Malayan 

 tapir (Tapirus indicus). In Brazil, in districts remote 

 from cultivation, the food of the tapir is composed 

 largely of palm leaves, but at certain seasons of the 

 year these animals subsist almost exclusively on 

 fallen fruits, and in some districts swampy grasses 

 and water plants form their chief food. 



VERTICAL GEOGRAPHIC RANGE OF QUADRUPEDS 



The rhinoceroses as a group have a wide vertical 

 geographic distribution, ranging from sea level to the 

 snow belt. The black rhinoceros, although it prefers 

 the lower grassy plains, is found also on the high 

 plateaus near the glaciers of Mount Kenya. (Gregory, 

 1898, op. cit., p. 263. '') As above noted, the tapirs 

 as a group range from sea level to the snow belt, 

 8,000 feet above sea level. Some species are exclu- 

 sively low-level forms {T. terrestris); others range 

 from sea level well up into the mountains {T. iairdi); 

 still others inhabit the higher Andes {T. pinchaque). 

 The elephants also enjoy a wide vertical range; 

 Elephas (Loxodonta) africanus is said to ascend and 

 descend steep places with wonderful facility, and 

 t footprints of the modern Asiatic elephants have been 

 seen among the eternal snows of the highest mountains 

 (Pohlig, 1891.1, p. 328). 



VERTICAL GEOGRAPHIC RANGE OF THE TITANOTHERES 



Thus, judging by analogy with the other Perisso- 

 dactyla and from what we know to be true also of the 

 horses, it is probable that the titanotheres enjoyed a 

 considerable vertical geographic range in the Rocky 

 Mountain region in Eocene time and that this may 

 have entered into the causation of their local adaptive 

 radiation. 



TEN CHIEF HABITAT ZONES OF MAMMALS 



Wide climatic and physiographic differences, if 

 concentrated in a geographically restricted area, 

 facilitate local adaptive radiation. For example, 



" Gregory inadvertently attributes this range to the white rhinoceros. 



grassy meadows favorable to shrubs bring grazers and 

 browsers together. That much more extreme con- 

 trasts are by no means unnatural is shown along the 

 coasts of Mexico, where there is an abrupt transition 

 from an extremely moist, warm lowland to a dry, . 

 cool upland. Similarly abrupt transitions are ob- 

 served in parts of the Andes and the Himalayas. 



It is consequently not difficult to account for the 

 fact that seven or eight different phyla of titanotheres 

 lived together in southern Wyoming and northern 

 Utah in middle and upper Eocene time, for the entire 

 region was varied and rnountainous. 



The life zones of mammals have been set forth 

 admirably by Kobelt (1902.1) and should be studied in 

 connection with the vegetation zones of Schimper 

 (1903.1). Some mammals are strictly confined to 

 their typical habitat zones — that is, they are intensely 

 localized. Certain antelopes, such as Tragelaphus 

 angasi, the inyala (Stevenson-Hamilton, 1912.1, p. 

 135), probably feed upon only a single plant and are 

 limited in range to its distribution. Many Herbivora, 

 such as elephants, rhinoceroses, and horses, are very 

 plastic and have great diversity of habitat in the 

 course of the change in seasons and under varying 

 conditions of competition. 



Life zones are defined by land and water, by mois- 

 ture and aridity, by depression and elevation, by low 

 and high temperature, by the distribution of insects, 

 and especially by the presence of vegetation adapted 

 to grazing or browsing. Life zones are therefore de- 

 fined sharply in some places and feebly in others. 

 The ten zones discriminated are described below. 



1 . Mountain or alpine liaiitat. — High mountains and 

 mountain ranges with the snow and timber lines at 

 altitudes of 6,000 to 12,000 feet or more. Thinly 

 forested or tundra-like lands, adapted both to grazing 

 and browsing ungulates having relatively short limbs 

 and feet adapted to climbing. The Artiodactyla are 

 represented by many forms, some of which range far 

 above timber line, including goats (Capra), rupi- 

 caprines {Rupicapra, NemorJiaedus, Oreamnos), moun- 

 tain sheep (Ovis), vicunas {Lama vicunna) at certain 

 seasons, Pudu deer {Pudua). The Perissodactyla that 

 invade these high forest zones are only certain tapirs 

 of the Andes {Tapirus pinchaque and T. roulini). 



2. Mountain forest habitat. — Lower mountain ranges 

 and foothills, dry or well watered, well wooded, with 

 river valleys. This zone includes the dry tropical 

 woodlands (such as those of India), which are favorable 

 to the larger ungulates; also the tropical rain forests 

 (Asia, Africa, North America), generally unfavorable 

 to large ungulates. In Asia the especial habitat of 

 many deer, bovines, antelope, browsing perissodactyls, 

 such as Rhinoceros sondaicus of Java, typically a forest 

 dweller, R. {Dicerorhinus) sumatrensis of Sumatra. 

 In the northern latitudes of North America, the typical 

 home of the deer {Odocoileus), moose {Alces), wapiti 



