VI CONTENTS 



Chapter XI — Continued. 

 Section 2 — Continued. 



Environmental causes of extinction — Continued. Page 



The living environment 867 



Plants 867 



Insects and Protozoa 869 



Epidemics 871 



Birds 874 



Mammals 874 



Contrasts between external (environmental) and internal causes of extinction 877 



Internal causes of preservation and extinction 877 



Immunitj- and adaptation 877 



Bulk not inherently inadaptive 878 



Value of single organs in survival or extinction 880 



Inadaptation of extreme specialization 883 



Survival of the unspecialized 883 



Irreversible evolution 883 



Inadaptation of dominant organs 883 



Selection of sexually dominant organs 884 



Causes of overdevelopment 884 



Rates of breeding and extinction 884 



Self-extinction through arrested variation 886 



Special features of the extinction of the titanotheres 886 



Conclusions regarding the theory of natural selection of Darwin and Wallace 887 



Summary of conclusions 888 



Bibhography of literature relating to the extinction of faunas cited in section 2 889 



Appendix. Eocene and Oligocene titanotheres of Mongolia 895 



Index 947 



ILLUSTRATIONS 



Plate Page 



XLIII. Probable arrangement of muscles of occiput and neck in Brontops rohustus 726 



XLIV. Musculature of the fore and hind limbs of Palaeosyops leidyi 726 



XLV. Ontogenesis of the torns of domestic cattle 894 



XLVI. Models of heads of Eocene titanotheres, showing brachycephaly, mesaticephaly, and dolichocephaly 894 



XLVII. Disharmonic differential evolution of characters in skulls and teeth of titanotheres 894 



XLVIII. Extinction or survival of 23 families of artiodactyl ungulates 894 



XLIX. Brain of Eocene mammals compared with that of modern and other mammals 894 



L. Type skulls of Palaeosyops leidyi and Mesaiirhinus petersoni 894 



LI. SkuUs of Telmatherium idlimum and Manteoceras manteoceras 894 



LII. Skulls of Dolichorhinus hyognathus and Metarhinus fluviatilis 894 



LIII. Skull form in Eocene titanotheres (brachycephalic, mesaticephalic, and dolichocephalic) 894 



LIV. Upper and lower grinding teeth of Lamhdotherium and Eotitanops 894 



LV. Comparison of incisors and canines in Eocene titanotheres 894 



LVI. Lower grinding teeth of Limnohyops and Palaeosyops 894 



LVII. Upper dentition of Limnohyops 894 



LVIII. Upper dentition in four species of Palaeosyops 894 



LIX. Upper dentition in three species of Palaeosyops 894 



LX. Upper dentition of Limnohyops and Palaeosyops 894 



LXI. Type skull of Palaeosyops leidyi, palatal view 894 



LXII. Upper and lower premolars of Limnohyops and Palaeosyops 894 



LXIII. Grinding teeth of Telmatherium and Manteoceras 894 



LXIV. Upper dentition of Telmatherium validum 894 



LXV. Dentition of Telmatherium and Sthenodectes 894 



LXVI. Skull and jaw referred to Sthenodectes incisivus 894 



LXVII. Upper dentition of Manteoceras 894 



LXVIII. Incisors and canines of Protitanotherium emarginatum 894 



LXIX. Upper and lower teeth of Protitanotherium, progressive stages 894 



LXX. Lower dentition of Brachydiastematherium transilvanicum 894 



LXXI. Lower dentition of Mesatirhinus, Metarhinus, and Dolichorhinus 894 



LXXII. Upper dentition of Mesatirhinus amd Dolichorhinus 894 



LXXIII. Upper dentition of Dolichorhinus 894 



LXXI V. Upper dentition of Dolichorhinus, Metarhinus, and Bhadinorhinus 894 



LXXV. Skulls and jaw of Dolichorhinus 894 



LXXVI. Skulls of Dolichorhinus, side view 894 



LXXVII. Skulls of Dolichorhinus, palatal view 894 



