ENVIRONMENT OP THE TITANOTHEEES 



125 



similar feeding habits may be acquired in widely 

 separated habitats or greatly different environments. 

 Contrasts in structure, such as those shown below, 

 are equally notably. 



Contrast in structure between browsing and grazing types 



Grazing on the harder 

 siliceous grasses of dry 

 plains and uplands 



Gazelle 



Addax 



Grazing and browzing on 

 the tender leaves and 

 twigs of plains, thin for- 

 est and brush country 

 Sable and roan 



Grazing and browzing 

 on the tender grasses 

 of moister land and 

 swampy plains 

 "Puku 

 Cob 

 Reedbuck 



Leaf, bark, and twig 



eaters in forests 



Duiker 



Browsing on tender 



leaves and shrubs 



of partly forested 



countries 



Bushbuck 



Waterbuck 



Figure 



Browsing on succulent 



aquatic plants 



of swampy lands 



Sitatunga 



Lechwe 



). — Adaptions in the structure of the skull and teeth 

 of Herbivora to diverse habits of feeding 



Double or even multiple adaptive radiation is 

 continually in operation, first, in the structure of 

 skull and tooth, which is dependent on the nature of 

 the food, and, second, in the structure of foot and 

 body, which is dependent on the nature of the soil. 

 Thus may arise cursorial (long-limbed) grazers (long- 

 toothed), graviportal (heavy-limbed) grazers (long- 

 toothed), or cursorial (long-limbed) browsers. There 

 is no fixed law of correlation of structure of skull and 

 tooth such as was supposed by Cuvier. The law of 

 correlation as restated by Osborn (1902.214) is as 

 follows : 



Structure of feet (correlated chiefly with structure 

 of limb and body) and structure of teeth (correlated 

 chiefly with structure of skull and neck) diverge inde- 

 pendently in adaptation respectively to obtaining 



food (by feet) and eating food (by teeth) in different 

 environments. Each structural feature is evolved 

 directly to perform its own mechanical functions or 

 purposes, yet in such a manner that each is consonant 

 with the other. 



CONTINENTAL ADAPTIVE RADIATION OF THE AFRICAN 

 ANTELOPES 



The African antelopes are divided into seven sub- 

 families, all mediportal to cursorial in limb structure 

 but widely different in tooth and skull structure, as 

 shown in the table on page 124. 



The 133 or more species (Sclater, 1894.1) embraced 

 in these seven subfamilies seek food and protection 

 from enemies on the varied surface of the African 

 continent in habitats including no less than 17 differ- 

 ent kinds of country. 



Each type of habitat has food peculiarly favorable 

 to certain feeding habits to which the structure of the 

 teeth and skull is speciflcally adapted. Each type of 



CURSORIAL 

 Distance carrying 

 Gazelle 



Gemsbuck (Oryx) 

 Addax 



SALTATORIAL 

 Leaping and springing 

 Springbuck 

 MEDIPORTAL ^ Klipspringer 



Medium-weight bearing 

 Hartebeest 

 Gnu 



Sable and 

 antelopes 



SEMI-ARBOREAL 

 Progressively on 

 branches of trees 

 Impala 



GRAVIPORTAL 

 Heavy-weight bearing 

 Greater kudu 

 E'and \ \ FOSSORIAL 



Digging and uprooting 



AMPHIBIOUS 

 Swamp and river-living 

 Waterbuck 

 Puku 

 Cob 

 AQUATIC Reedbuck 



Partly fluviatile, largely 

 feeding and seeking 

 safety in the water 

 Lechwe 

 Sitatunga 



Figure 81. — Convergent adaptations in the structure of the 

 limbs and feet of ungulates 



Certain gazelles are independent of watercourses. The adaptive radiations 

 indicated above occur independently within different subfamilies. 



habitat demands modiflcations of limb, foot, and hoof 

 structure for movement in the search for food and 

 escape from enemies. 



The theory of the evolution of the antelope is that 

 in mid-Tertiary time a divergent primary radiation 



