ENVIHONMENT OF THE TITANOTHEEES 



121 



Oligocene. Ischyromyids are abundant and include 

 terrestrial (?) and arboreal (?) forms; whether fos- 

 sorial forms existed or not is not proved. Eutypomys, 

 though referred to the Castoridae, is not at all analo- 

 gous to the modern beaver but rather to a large 

 squirrel or spermophile. 



6. Insedivora. — The leptictids have rather sharp- 

 cusped teeth and are intermediate in type between 

 opossums and tree-living erinaceids. The moderate 

 wear of the teeth is evidence against the theory that 

 their food was worms or other terrigenous forms. 

 There are no obvious arboreal adaptations in the 

 limbs and feet; perhaps they may have been semi- 

 arboreal. Their survival, unaltered as to cheek 

 teeth, from the basal Eocene is suggestive of some 

 special protection, such as spines. As for the zalamb- 

 dodonts, they may have been fossorial, Xenotherium 

 being molelike, but the evidence is insufficient. 



7. Marsupialia. — Rare. Precisely like small opos- 

 sums in the structure of the teeth. 



8. Aves. — No birds have been recorded in this 

 fauna, although they probably existed and may have 

 been even numerous and varied. 



9. Reptilia. — Crocodiles and trionychids occur in 

 the sandstone lenses; probably they were aquatic 

 forms analogous to modern crocodiles and soft-shell 

 turtles. In the clays Testudo occurs; also Xenochelys, 

 probably similar in habits to modern land tortoises 

 and marsh turtles. The lizards are apparently analo- 

 gous to the Gila monster and to some of the swift- 

 footed anguid lizards. Burrowing amphisbaenids 

 occur in the Oreodon zone but have not yet been dis- 

 covered in the lower Oligocene; no doubt they formed 

 part of the fauna; also other lizards and many snakes. 



10. Batrachia. — No batrachians have been recorded, 

 but there is no reason to suppose that they were 

 absent or rare. 



11. Pisces. — A few fragments of fresh-water fishes, 

 similar to those characteristic of muddy rivers of 

 to-day, are recorded from the Swift Current beds in 

 Canada. They will doubtless be found in the sand- 

 stones and other stream deposits of the Titanotherium- 

 bearing beds of the United States. 



SECTION 3. ADAPTIVE RADIATION, PRIMARY AND 

 SECONDARY, THROUGH CHANGE OF ENVIRONMENT 

 A CAUSE OF THE DIVERSIFICATION OF THE TITANO- 

 THERES 



HABITAT OF THE UNGULATES 



The present geographic features of modern equato- 

 rial Africa, consisting of a high central plateau, river 

 borders, savannas, and forests, exhibit a close parallel 

 to what we believe were those of the known titanothere 

 region of North America in Eocene and lower Oligocene 

 time. These conditions may also be compared with 

 those found in the existing flood plains at the head- 

 waters of the great rivers of South America east of 

 the Andes in the warm temperate and subtropical 

 but not in the tropical belt. 



101959— 29— VOL 1 10 



Adaptive radiation: Favorite habitats of existing 

 perissodactyls and elephants 



[See fig. 78] 

 RHINOCEROSES 



Rhinoceros sondaicus. Java. Typically a forest dweller, 

 occasionally found in alluvial swamps. A browser. 



Rhinoceros (Dicerorhinus) sumatrensis. Hilly forest districts 

 of Sumatra. A browser. 



Rhinoceros {Opsiceros) bicornis. Bush-covered country and 

 open plains; forested foothills in the dry season. Fairly abun- 

 dant on the top of the Aberdare, British East Africa (elevation 

 9,000 feet). A browser, feeding on shrubs, roots, leaves, etc. 



Rhinoceros unicornis. Grassy jungles of India. A grazer. 



Rhinoceros (Ceratotherium) simus. Savannas and grassy 

 plains, with swamps or water holes for wallowing. A grazer. 



TAPIRS AND ELEPHANTS 



Tapirus roulini. Pinchaque tapir of the high region of the 

 Andes and Cordilleras. A browser. 



Elasmognalhus bairdi. A hill dweller, seeking lowlands 

 during rainy seasons. A browser. 



Tapirus terrestris. A forest dweller. Lowlands of Brazil 

 and Paraguay. A browser, feeding on palm leaves, fruits, 

 water plants. 



Tapirus indicus. Lowlands and forests of India. A browser. 



Elephas (Loxodonta) africanus. Less typically a forest 

 animal than E. indicus. Savannas, dry country, and forests. 

 Ranges from the seacoast to points beyond the alpine heath 

 zone of Mount Kenia and the bamboo belt of other African 

 mountains. Ascends and descends steep places with wonderful 

 facility. A browser and grazer. 



HORSES AND ZEBRAS 



Equus burchelli. Essentially a plains dweller; often found 

 in sparse savannas. 



E. grevyi. Grevy's zebra. Low plateaus, thorn bush and 

 feather grass country that has gravelly soil. Essentially a 

 dweller in open plains and savannas. 



E. quagga (extinct). The quagga. A karoo dweller. Fre- 

 quents open, arid plains. 



E. zebra. Mountain zebra. Hilly and mountainous country. 



E. przewalskii. Przewalski horse. Gobi Desert. A steppe 

 dweller. 



ASSES 



Equus asinus. Abyssinian ass. Wiry hedge and upland 

 country. 



E. hemionus kiang. The kiang. Desolate plains in the 

 vicinity of lakes and rivers. High table-lands of Tibet (15,000 

 feet) . Coarse wiry pasture and rough hard yellow grass. 



E. asinus somalicus. Striped African ass. Borders of the 

 Nubian Desert. 



E. hemionus onager. Persian wild ass. Migrates from the 

 plains to the hills in summer. The onager of Persia. 



POLYPHYLY AMONG HOOFED MAMMALS 

 THE TITANOTHEEES AND OTHER EXTINCT FORMS 



It is astonishing to find within relatively small 

 geographic areas both Eocene and Oligocene remains 

 of many kinds of titanotheres, which lived close 

 together under very similar climatic conditions, the 

 more so because the known geographic distribution of 

 the titanotheres in Eocene time is confined to the cen- 

 tral Rocky Mountain region and extends only from the 

 Wind River Basin of Wyoming on the north to the 

 White River Basin of Utah on the south, a distance of 



