ENVIRONMENT OF THE TITANOTHERES 



127 



4. Hippotraginae. — Sable and roan antelopes Hippotragus, 

 oryx and addax, distinguished by the presence of horns in both 

 sexes and small rhinarium or bare space on the muzzle. Sable 

 (H. niger) to a great extent, though not entirely, a grass eater. 

 Prefers thin forest country, interspersed with alternate thickets 

 for shade, and open vleis for grazing. Regular drinker, seldom 

 found more than a few hours from water. Gestation period 

 about 270 days. * * * Roan antelope {H. equinus) favors 

 rather upland, rolling country, not too thickly wooded, such 

 as the middle veldt, but when persecuted takes readily to 

 forest or the same environment as the sable antelope. A 

 grass eater, and drinks regularly * * * [Genus Oryx.] The 

 gemisbuck (0. gazella) of South Africa separated from its nearest 

 generic relative (0. beisa) of German East Africa by an interval 

 of 1,500 miles. Fairly numerous in Kalahari Desert, main- 

 taining its security owing to its independence of water, able 

 to quench thirst from moist tubers and roots. Generally found 

 in small troops. The beisa (0. beisa) inhabits the Kilimanjaro 

 district, British East Africa, Somaliland and the Sudan, east of 

 the Nile. Sometimes found in herds of 50. Period of gestation 

 eight and a half to ten months. White oryx (0. leucoryx) is 

 found west of the Nile. Essentially a desert animal and like 

 the gemsbuck apparenth' associates in small parties. [Genus 

 Addax.] The addax [A. nasomacidatus\ distantly related to 

 both oryxes and roan and sable antelopes, pale sandy color. 

 An inhabitant of waterless sandy deserts of northern Africa. 



5. Neotraginae. — Klipspringers {Oreotragus orcotra.gus), like 

 the chamois, prefer small shrubs and grasses growing among the 

 stones. Live on natural moisture of the grass and nightly 

 dews. * * * Oribi (Ourebia) frequents open grass country 

 or plains not too thickly forested. Grass feeders, seldom found 

 any distance from water. Eight species. 



6. Cephalophinae. — Lovers of dense bush and forest of central 

 and southern Africa. Thirty-eight species. Duiker (Cephalo- 

 phus grimmi), solitary animal, fond of bush country. Never 

 far from covert. Mainly browsers. Nibbles leaves and young 

 shoots of various acacias, small shrubs. Grass consumed 

 when. young and fresh. Red duiker (C natalensis), dense 

 forests and bush. Blue duiker (C monticola), essentially a 

 browser, favors shelter or dense covert. 



7. Ceruicaprinae. — Animals of large or medium size. Water 

 buck (Cobus ellipsiprymiius), open forest country, eastern 

 Africa, favor banks of large rivers, prefer succulent herbage, 

 but are partial to rough and broken country, stony hillsides, 

 and vicinity of fairly thick bush; grass feeders. During dry 

 season frequent banks of streams for succulent herbage. 



* * * Sing-sing water buck {Cobus defassa), habits similar 

 to above. * * * The lech we (C. lechwe) is smaller than 

 the water buck. Hoofs elongated and pointed. Frequent 

 great reed swamps and river borders, northern Rhodesia. 

 Next to the situtunga, the most aquatic of all antelopes, stand- 

 ing knee or even belly deep in large shallow lagoons. Come 

 ashore to graze, food consisting of grass and young reeds. 



* * * Gray's water buck (C maria), frequent river bottoms 

 and reedy grass. Stand in shallow water. * * * Puku 

 (C. vardoni), less aquatic than the lechwe, approaching in this 

 respect the water buck — that is, found close to but not in the 

 water. Frequent swampy plains. * * * Uganda cob (C. 

 thomasi), fond of open, rather swampy plains, near rivers or 

 permanent water. Grazes on young shoots of grass. * * * 

 Common reedbuck {Cervicapra arundinum) , lowlands of Natal 

 and Zululand, Transvaal bush country, etc. Favors grassy or 

 reedy valleys near streams or permanent water of some kind. 

 Occasionally met with in thin bush. Food consists entirely of 

 grass. Do not take to water when alarmed. * * * Moun- 

 tain reedbuck {Ceruicapra fulvorufula), lower slopes of hills 

 covered with rocks and loose stones, mingled with scattered 

 bush and long grass. Grass eaters, at night descending from 

 hills to nearest w-ater. Affecting sides rather than tops of 



hills. * * * Bohor reedbuck {Cervicapra redunca),, favor- 

 ing open vleis and bush or swamp land. Like the neighbor- 

 hood of water. * * * Gray rhebuck {Pelea capreolus) , 

 unlike mountain reedbuck, frequent flat tops of the table 

 mountains; common in South Africa as well as higher levels of 

 the ranges. Grass feeders, and descending at night to drink 

 after the manner of the mountain reedbuck. 



[Note vertical physiographic distribution of the genus 

 Cervicapra.] 



CAUSES OF VARIATION AND POLYPHYLY AMONG 

 QUADRUPEDS 



Change of physical environment. — A series of meteoric 

 and biotic changes — that is, changes of season, of 

 climate, or of rainfall, the appearance of new enemies, 

 the introduction of new plants or the crowding out of 

 old ones — will cause a change of food supply, which 

 will cause a change of habitat, which in turn will 

 cause a change of browsing or grazing habits that 

 will affect locomotion — the use of the limbs in the 

 search for food — and modify the form of the hoofs, 

 because of the change of soil. The browsing mountain 

 moose (Alces) of eastern Idaho, for example, has a 

 hoof of very different form from that of the water- 

 living forest moose of Maine. Among the new 

 enemies that may appear are certain insect pests, 

 such as flies or ticks, which may drive quadrupeds 

 away from feeding ranges that are otherwise favorable 

 into regions, perhaps not far distant, where food is 

 scarcer and the general conditions are more adverse, 

 and where, perhaps, the young are exposed to new 

 dangers. 



Such changes may bring about (1) a change of 

 habit or (2) a change in habitat or environment, 

 either of which, as a general law, culminates in (3) 

 change of function, followed by (4) change of struc- 

 ture. (5) A change of function or habit certainly 

 brings about a new "incidence" of selection or new 

 set of causes tending to survival or extinction. 



Change of appetite. — Variations in appetite are un- 

 doubtedly among the chief causes of local divergence. 

 Stevenson-Hamilton (1912.1, pp. 97-158) noted the 

 fastidious choice of food by each of the principal 

 species of African antelopes, and other wild animals are 

 very fastidious and seek an astonishing variety of food 

 in the course of a single season. The predilection for 

 certain kinds of food is very strong, and departures 

 from it lead to adaptive radiation. Similarly Sampson 

 (1905.1) records that the white-tailed deer (Odocoileus 

 virginianus) browse on many kinds of plants in the 

 course of a year. 



Local polyphyly through reunion of phyla. — Animals 

 that have diverged through migration or through 

 geographic segregation or separation may later be 

 brought together in one region. For example, the 

 mule deer {Odocoileus hemionus) and the white-tailed 

 deer (0. virginianus), which have probably evolved in 

 different regions of the United States, are now found 



