ENVIRONMENT OF THE TITAN OTHEEES 



123 



480 kilometers (298 miles). The continental extent 

 of the distribution of the titanotheres, which is still 

 unknown, was undoubtedly far greater, including, 

 perhaps, the larger part of the North American 

 continent and certainly extending into Asia. In 

 Oligocene time the known geographic distribution 

 was somewhat larger, including an area extending from 

 Colorado to southern Alberta and measui'ing from 

 north to south about 1,200 kilometers (746 miles). 

 Titanotheres lived also in eastern Europe, both in 

 Transylvania' and Rumelia, also in Mongolia. 



Our present Icnowledge of the geologic horizons of 

 the titanotheres is still extremely meager regarding 

 certain strata. The extent of our knowledge is sum- 

 marized below. 



Geologic horizons of the known genera and subgenera of the 



titanotheres 

 Lower Oligocene; upper, middle, and lower levels: Brontops, 



Diplocloniis, Alloys, Menodus, Brontotherium, Megacerops. 

 Upper Eocene; Uinta C (true Uinta) : Telmatherium, Man- 



teoceras, Diplacodon, Prolitanoiherium, Eotilanolherium. 

 Upper Eocene; Washakie B and Uinta B: Metarhinus, Rhadi- 



norhinus, Mesatirhinus, DoUchorhinus, Manteoceras, Tel- 

 matherium, Diploceras. 

 Middle Eocene; upper part of Bridger formation : Mesatirhinus, 



Manteoceras, Palaeosyops, Telmatherium. 

 Middle Eocene; lower part of Bridger formation: Limno- 



hyops, Palaeosyops, Eometarhinus. 

 Lower Eocene; Wind River formation: Lamhdotherium, Eoti- 



tanops. 



As compared with what we observe among the hoofed 

 animals living to-day these titanotheres certainly 

 dwelt near one another under very similar conditions 

 of climate but in different feeding ranges and local 

 habitats; they sought the same watercourses, and 

 their remains were entombed in similar deposits. As 

 the whole tendency of discovery up to the present 

 time has been to multiply the phyla, to separate and 

 diversify the titanotheres, the probability is that many 

 other kinds of titanotheres lived in other parts of 

 North America and Asia. 



The evolutionary principle underlying these diversi- 

 ties Osborn (1902. 214, p. 353) has called adaptive 

 radiation, which is the application to paleontology of 

 the idea of divergence as conceived and developed 

 successively by the studies of Lamarck, Darwin, 

 Huxley, and Cope." Radiation is a broader principle 

 than divergence, because it implies evolution in every 

 direction possible to the organism. The idea of 

 radiating branches from central forms assists the 

 imagination, because the known radiations of extinct 

 animals must be supplemented by the unknown radia- 

 tions, and it is most remarkable how these missing 

 radii have been discovered in group after group of 

 animals. Such adaptive "radiation" is either "con- 

 tinental" — that is, it occurs where diversities in food, 



" See also Osborn, H. F., 1902.214; 1905.267; 1910. 345; 1910. 346; Stevenson- 

 Hamilton, J., 1912. 1; Sclater, P. L., 1894. 1; Lydekker, K., 1893. 1; Gregory, J. W.^ 

 1896.1; Blanford, W. T., 1888.1; Kobelt, W., 1902.1; Schimper, A. F. W., 1903.1; 

 Lonnberg, E,, 1912. 1; Roosevelt and Heller, 1914. 1. 



soil, or climate prevail over large areas — or "local" — 

 that is, it occurs where marked diversities prevail in 

 relatively small areas. The radiation among the 

 titanotheres in southern Wyoming and northern Utah 

 seems to have been largely "local," indicating that the 

 physiography of the mountain basin was highly 

 diversified. 



One of the results of adaptive radiation is poly- 

 phyletic evolution, the existence within families of a 

 large number of independent minor branches that 

 may pursue more or less divergent evolution in local 

 or continental regions but that may come together in 

 river and flood-plain basins, so that their fossil re- 



LIMBS AND FEET 



Short-limbed, plantigrade,] AMBULATORY 

 pentadactyl, ung:uicu-> or 



late stem ^ ^^JTORRESTRIAL 



CURSORIAL 

 Digitigrade 



OMNIVOROUS 



(Grass 

 Herb 

 Shrub 

 Fruit 

 ^. „.„„o|..„.. ™<" 



"~-^^[Carr' 



MYRMECOPHAGOUS 

 Dentition reduced 



Stem INSECTIVOROUS 



Figure 79. — Original radiation of the unguligrade 

 Herbivora, Carnivora, and Inseotivora, showing 

 the adaptations of teeth, limbs, and feet to various 

 habits and environments 



mains are found in the same localities and deposits. 

 Polyphyletic evolution has been discovered so fre- 

 quently, among both the mammals and the lower forms 

 of life, that it may be considered the rule and mono- 

 phyletic evolution along single lines the exception. 

 Some of the examples of polyphyletic evolution among 

 extinct mammals that ha^'e been determined in com- 

 paratively recent years are the following: 



Contemporaneous 

 branches, or phyla 

 Oreodonts (Cope, Wortman, Peterson, Matthew, Doug- 

 lass) 7-9 



Lophiodonts (Osborn, Deperet) 5-7 



Anthracotheres (Stehlin, Deperet, Andrews) 6-8 



Rhinoceroses (Osborn) 8-9 



Horses (Osborn, Gidley, Matthew) 8-9 



Titanotheres (Osborn) 10-12 



Elephants and mastodons (Osborn) 7-10 



