158 



UNGULATA 



ORDER VII 



Various hypotheses have been advanced concerning the ancestry of the 

 horse and of other genera of the Equidae. Cuvier early directed attention to 

 the relationship of Palaeotherium and Equus ; Huxley determined that Equus, 

 Hipparion, Anchitherium and Paloplotherium (Plagioloplms) were developmental 

 stages in an evolutionary series, in which Kowalevsky substituted Palaeo- 

 therium mediimi for Paloplotherium. The gradual modification of the equine 

 foot and dentition was also so thoroughly worked out by Kowalevsky, that 

 the pedigree of the horse with the stages above mentioned seems established. 

 The discoveiy of numerous genera in North America furnished still further 

 evidence of the ancestry of the Equidae. Marsh showed that the latter 

 continent contained a far more nearly complete series of evolutionary 

 stages, and that the modern horse probably originated in the New World, 

 not in Europe, 



According to the present state of knowledge, the following genealogical 

 table may most nearly represent the pedigree of the Equidae : 



Europe (and Asia). 



Equus 



1 



North America. 



Equus 



1 



South America. 

 Equus 



\ 



Pliohippus Hippidium 



Neohipparion 



Hipparion Protohippus 



Merychippus 



Parahippus 



I 

 Hypohippus— 



Anchitherium Miohippus 



I 

 Mesohippus 



I 



Epihippus 



Orohippus 



I 

 Eohippus 



Tetraclaenodon 



The European genera Paloplotherium, Palaeotherium, Propalaeotherium, 

 Anchilophus, Lophiotheriiim, and Pachynolophus are without importance for the 

 phylogen}'- of the true horses. They all appear nearly at the same time, 

 and become extinct simultaneously. Their common ancestor seems to be a 

 Hyracotherium. 



Family 4. Titanotheriidae.^ 



Nasal bones projecting freely, smooth or furnished with two obtuse conical bony 

 protuberances. Orbits open posteriorly. Dental formula : ^ ' ' ' ' ■ In later 



o-\j, J ,^~0 .o . 



' Douglass, £., Titanotheres from Uinta Deposits. Annals Carnegie Mus., vol. iv., 1911. — 

 Hade, Q , A memoir upon the genus Palaeosyops. Journ. Acad. Nat. Sci. Philad., 1892, vol. 

 ix. — Hatcher, J. B., Cranial Element.^ of Titanotherium. Annals Carnegie Mus., 1901. — Amer. 

 Naturalist, 1895, p. \QS\.— Marsh, 0. C, Amer. Journ. Sci., 1876, vol. .xi. ; 1889, vol. xxxvii. ; 

 1890, vol. xxxix.—Osborn, H. F., Bull. Amer. Mus. Nat. Hist. New York, 1902, 1908, 1913. 



