124 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



THE EXISTING AFRICAN ANTELOPES 



The polyphyly among the titanotheres and other 

 extinct Perissodactyla presents a marked contrast to 

 the impoverished conditions among tlie existing mem- 

 bers of the same order wlien we consider that in all 

 parts of Asia and Africa only five kinds of existing 

 rhinoceroses can be distinguished by the characters of 

 the skeleton and teeth alone, that only six or eight 

 kinds of horses, asses, and zebras in the same great 

 region can be distinguished by their hard parts, and 

 that, similarly, among the tapirs of Asia and South 

 America only three kinds can be distinguished. This 

 contrast between present monophyly and former poly- 

 phyly is due to the fact that the order Perissodactyla, 

 though formerly a dominant group, is now a declining 

 group. 



In the existing Bovidae, especially those in the groat 

 continent of Africa, we have a parallel to the ancient 

 polyphyly of the titanotheres and other Perissodactyla. 

 The Bovidae is a family that includes the cattle and 

 antelopes and that is now in the highest stage of ra- 

 diation and adapted to a great variety of physiographic 

 and biotic conditions, as shown in the primary and 

 secondary adaptations in the seven subfamilies of the 

 African antelopes. 



The African antelopes: Subfamilies, habits, and environment 



Subfamilies and habits 



Antilopinae (browsers and grazers) 



Gazelles 



Pallahs (impalas) 



Springbucks 



Gerenuks 



Saigas 



Bubalidinae (mostly grazers) : 



Gnus 



Hartebeests 



Blesboks 



Sassabies 



Tragelaphinae (browsers and graz- 

 ers): 



Elands 



Koodoos 



Bush bucks 



Bongos 



Situtungas 



Hippotraginae (grazers) : 



Roan antelopes 



Sable antelopes 



Gemsboks 



Addaxes 



Neotraginae (browsers and graz- 

 ers): 



KUpspringers 



Oribis 



Dik-diks 



Cephalophinae (mostly browsers) ; 

 Duikers 



Environment 



Plains and deserts. 

 Thorny bush and glades. 

 High veldts. 

 Deserts and bush. 

 Steppes. 



Open plains. 



Open forests or plains. 



Open rolling country. 



Open forests and flats. 

 Stony hills. 

 Forests. 

 Dense forests. 

 Swamps and lagoons. 



Thin forests. 

 Rolling uplands. 

 Open deserts. 

 Waterless deserts. 



Hills, mountains. 

 Thin forests. 



Dense forests and bush. 



The African anteloyes: Subfamilies, habits, and environment — 

 Continued 



An incipient or attempted adaptation to a grazing 

 life is seen in the teeth of certain titanotheres. Most 

 titanotheres are browsers. Broadly speaking, her- 

 bivorous animals that live on open plains are grass 

 eaters and tend to become gregarious in habit and 

 cursorial in locomotion, whereas those that prefer the 

 shady depths of the forests are browsers, are of soli- 

 tary habit, and are mediportal in locomotion. There 

 are exceptions, such as the black rhinoceros (Rhi- 

 noceros {Opsiceros) Mcornis), which now frequents the 

 treeless plains of East Africa but which is habitually 

 a browser, although it is at times a grazer. The long- 

 necked giraffes are fond of rather dry and fairly open 

 country and are not found in strictly forested regions, 

 yet they are wholly browsers, being especially fond of 

 the leaves of certain thorny acacias, notably Acacia 

 girajfa, and the related short-necked okapi, which is 

 found only in the dense forests of the Congo, is a 

 browser. 



The principles of adaptation shown in the skull and 

 teeth of Perissodactyla to browsing and grazing habits 

 are described in Chapters V and VI of this monograph. 

 The adaptation of the limbs of the Perissodactyla to 

 speed and weight are described in Chapter VII. 



In general, the competition and range for food 

 among hoofed animals is accompanied by lengthen- 

 ing of the limbs from medium-paced (mediportal) 

 types to either swift-moving (cursorial) types or heavy- 

 bodied (graviportal) types. Similarly, adaptation of 

 the grinding teeth to browsing habits is seen in the 

 short-crowned (brachyodont) types, and transition to 

 the grazing habit is accompanied by lengthening 

 (hypsodontism) of the crowns of the grinding teeth. 

 Such changes are accompanied by changes in the pro- 

 portions of the head to adapt the action of the teeth 

 to browsing or to grazing. We observe a passage 

 from short-headed (brachycephalic) to long-headed 

 (dolichocephalic) forms of skull. In adaptive radia- 

 tion every possible combination of lengthening and of 

 shortening of skull, tooth, limb, and foot may arise, 

 as well as notable coincidences of structure in different 

 forms, for similar kinds of food may be found and 



