February 1, 1907] 



SCIENCE 



173 



ornis may be in or near the direct line of 

 descent from Archseopteryx to some such 

 generalized dromseognathous type as is 

 represented by those curious living fossils, 

 the Crypturi, from which divergent lines of 

 evolution may have led, on the one hand, 

 to the ostriches and other flightless Dro- 

 mseognathiB, and, on the other hand, to the 

 Carinat^. Hesperornis, a degenerate and 

 in some ways highly specialized form, 

 stands certainly at the end of a side 

 branch, and has left no descendants. 



But the discoveries of most evolutionary 

 significance, as already intimated, have 

 been among the Tertiary mammals. A 

 number of series have been traced, leading 

 from generalized types in the Eocene, 

 through forms of gradually increasing spe- 

 cialization, to genera which still survive. 

 The first of these genetic series to be 

 brought to notice was the genealogy of the 

 horse, as traced by Marsh in 1874. 

 Marsh's views Avere adopted by Huxley in 

 his brilliant 'American Lectures,' and 

 thereby gained a larger share of public 

 attention than they would otherwise have 

 received. Probably no single fact or group 

 of facts brought to light since the appear- 

 ance of the 'Origin of Species' has been 

 so influential in bringing the theory of 

 evolution into general acceptance. The 

 genealogy of the horse has been corrected 

 in detail and completed by later investiga- 

 tions. The line of descent may now be 

 traced through Hyracotherium and Eohip- 

 pus of lower Eocene, Protorohippus and 

 Orohippus of middle Eocene, Epihippus 

 of upper Eocene, Mesohippus of Oligocene, 

 Anchitherium of lower Miocene, Parahip- 

 pus, Protohippus, and Pliohippus of middle 

 and upper Miocene, to Equus of Pliocene 

 and Quaternary; while side branches lead 

 to Hipparion, Hippidium, and other forms 

 which have died without issue. 



A similar series, though with not quite 

 so fine gradations, reveals the genealogy 



of the camel. From the Eocene Protylopus 

 this line is traced, through Oligocene 

 Poebrotherium, to Pliocene Procamelus, 

 whence one branch leads to Camelus, and 

 the other to the South American Auchenia. 

 It is indeed remarkable that the character- 

 istically old-world types, Equus and Came- 

 lus, should have been evolved in North 

 America and have become extinct in this 

 their original home. Another series, be- 

 ginning in the lower Eocene Systemodon, 

 ends in the modern tapirs. 



In like manner, among the very primi- 

 tive carnivores which have been classified 

 as the order Creodonta, the ancestors re- 

 spectively of the dog and the cat have been 

 recognized in the Eocene genera Vulpavus 

 and Palseonictis. 



Of extraordinary interest in an evolu- 

 tionary point of view is the most primi- 

 tive Tertiary fauna from the Puerco beds 

 discovered by Cope in 1880. In that fauna 

 is found the culmination of the Multi- 

 tuberculata, which made their first appear- 

 ance in Triassic time, and whose teeth 

 reveal their close relation to the Monotre- 

 mata. But, with those survivals from 

 Mesozoic time, appear generalized and 

 primitive forms of placental mammals, 

 wherein may be traced the ancestry of 

 mammalian groups of later Tertiary and 

 recent time. Hemiganus and Psittaco- 

 therium may be recognized as the ancestors 

 of the Edentata. And, among the most 

 primitive and generalized ungulates, the 

 Phenacodontidee, Protogonodon has been 

 recognized as possibly the ancestor of the 

 Artiodactyla, and Euprotogonia with more 

 probability as the ancestor of the Peris- 

 sodactyla. 



In the American Museum, where some 

 of our sessions are to be held, the evidence 

 of these genetic series running through the 

 Tertiary is placed before our eyes with in- 

 comparable fullness. As we behold the un- 

 paralleled richness of those collections, we 



