880 



TIT.\NOTHERES OP ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



the same time became extinct in India, Java, and 

 Madagascar, while many of the large European mam- 

 mals survived the glacial epoch. Some very large 

 animals, such as the elephant, for instance, have been 

 shown to be veiy adaptable. At the present time the 

 elephant is found in the damp jungle and parklike 

 districts, in tree and bush steppes, in low-tying plains, 

 on plateaus and mountains. Salensky (1905.1) has 

 lately shown that the mammoth was fully adapted to 

 life on grassy plains of high latitudes. The mastodon 

 also occupied many different life habitats. 



Conclusions as to effect of hulk. — Our conclusion is 

 that bulk is not intrinsically or per se fatal. All the 

 bulky mammals which have disappeared have pos- 

 sessed some single inadaptive organ or set of organs 

 which it seems probable would have proved equally 

 fatal to animals of small size; they have lacked in 

 intelligence, resourcefulness, or brain power; they have 

 specialized to an extreme in certain directions; they 

 have reached a point where there was only a single 

 mode of living left to them, and when this was altered 

 or when a particular source of food supply was cut off 

 they perished with it. On the other hand, intelligent, 

 resourceful, and adaptively constructed large mam- 

 mals, lilce the elephant, have survived great physio- 

 graphic and bio tic changes. Presence or absence of 

 such adaptations is almost equally fatal to small ani- 

 mals; bulk in itself is not a cause of extinction; in- 

 adaptive bulky animals have disappeared side by side 

 with the inadaptive diminutive animals. 



The chief inadaptations of large mammals are the 

 following: (1) Disadvantage of the large amount of 

 food required by a large animal, which is offset by the 

 advantage that many large animals can travel long 

 distances; (2) diminished birth rate, which is a charac- 

 teristic of large animals, is a point to be noticed; as 

 a rule, the larger the animals the fewer the young and 

 the less able a species would be quickly to regain 

 numerical strength after some widespread diminution 

 in number; the diminished birth rate is, however, 

 offset by greater longevity and greater power to pro- 

 tect young from enemies. Darwin (1859.1, p. 64) 

 observes : 



The elephant is reckoned to be the slowest breeder of all 

 known animals, and I have taken some pains to estimate its 

 probable minimum rate of natural increase; it wiU be under 

 the mark to assume that it breeds when 30 years old and goes 

 on breeding till 90 years old, bringing forth three pair of young 

 in this interval; if this be so, at the end of the fifth century there 

 would be alive 15 million elephants, descended from the first 

 pair. 



VALUE OF SINGLE ORGANS IN SURVIVAL OR EXTINCTION 



Percentages oj natural increase and decrease. — Recent 

 conditions among the large African mammals as ob- 

 served by Stevenson-Hamilton (1912.1, pp. 9-95) show 

 the effects of numerical reduction and the highly varied 

 action of the same causes on different stocks and dif- 



ferent organs. As to numerical increase or decrease 

 the author estimates (p. 10) that (1) the actual net 

 annual increase of stock of the larger antelopes under 

 ordinary favorable natural conditions is not above 5 

 per cent; (2) in a region where the carnivorous ani- 

 mals have been destroyed or reduced in number the 

 net annual increase is about 10 per cent; (3) the gross 

 natural increase of the larger antelopes in ordinary 

 years is 20 per cent, which is offset by the death an- 

 nually of 5 per cent from old age and the destruction 

 of 15 per cent by the Carnivora, especially the young 

 and worn-out animals; (4) anything that checks the 

 gross natural increase and hastens the natural decrease 

 means the permanent reduction and perhaps the final 

 extinction of the stock. This balance affects the sur- 

 vival or elimination value of single organs. 



Extinction oj Artiodactyla. — Woldemar Kovalevsky, 

 a Russian paleontologist, was one of the pioneers 

 in the consideration of the survival or extinction value 

 of single organs. He observes, in his great mono- 

 graph (1876.1, p. 152), that the extinction of all 

 Artiodactyla having an inadaptive foot structure 

 and inadaptive grinding teeth occurred as follows: 

 Upper Eocene: XipJiodon, Ano-plotTierium, Biplopus; 

 Oligocene: Hyopotamus, AntJiracotTierium, Entelodon. 

 He pointed out that the inadaptation of the foot in 

 these animals consisted of a mechanical defect in the 

 manus, the third metacarpal not spreading above to 

 articulate with the trapezium as in the adaptive manus 

 of the pig and hippopotamus, and that the inadapta- ■ 

 tion in the grinders consisted of the persistent short 

 or brachyodont crowns, bunoselenodont and bunodont, 

 composed of partially rounded cones. The feet, 

 being mechanically weak in the function of the carpals 

 and metacarpals, were incapable of the elongation into 

 cannon bones, a cursorial or speed adaptation which 

 saved the lives of artiodactyls with the adaptively re- 

 duced digits. The short teeth were by his theory 

 not adapted to a supposed change of vegetation from 

 softer herbage to harder Gramineae. His paleozoologic 

 supposition that such a change of food occurred was 

 independently confirmed by the paleobotanists Saporta 

 and Marion. His conclusion as to single organs caus- 

 ing extinction (which was original) has since been 

 abundantly confirmed by subsequent observations of 

 the extinction of all forms of quadrupeds having these 

 inadaptive types of short-crowned grinders, both in 

 North America and in India. 



Inadaptation of cone and crescent teeth. — The buno- 

 selenodont or cone and crescent molar pattern is 

 typified in the titanotheres and consists of one or 

 two detached cones on the inner side of the upper 

 grinding teeth and of two crescents on the outer side. 

 It is adapted to browsing on coarse, soft food rather 

 than on hard, fine food. 



This dental type presents a cul de sac of evolution, 

 because it is incapable of transformation either into 



