NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 155 



of undivided Carboniferous are found in Nicaragua and Honduras,^ and rocks 

 of Pennsylvanian ^ and Mississipian age occur in Chiapas, Guatemala. 



Koken,'' in his map of the Permian, shows the sea extending across the 

 Central American area, apparently on the evidence of Fusilina found in 

 ■British Honduras and Chiapas. 



No Permian deposits have been found in Central America, but the 

 Guadalupian fauna of Girty shows that there was a body of water over 

 trans-Pecos Texas and a portion of southeastern New Mexico, in Permian 

 time, which was connected with the European Permian seas. If the animals 

 of this sea were derived, as is possible, from a Mediterranean Tethys, the 

 isolation of North America from South America is certain and demonstrated. 

 If, as Koken has suggested, the fauna reached the site of the Guadalupian 

 Mountains through the Pacific rather than through a Mediterranean sea, 

 there still remains the evidence of a sea across Central America in the Fusi- 

 linas of British Hondtiras and Chiapas. 



It seems to me far more likely that the North American fauna originated 

 in the northern land-mass, developing from some such forms as Sauravus 

 costei Thevenin, from the Stephanien of France, and Eosauravus copei 

 Williston, from the Linton coal-beds of Ohio, and spread freely in late Car- 

 boniferous time after a considerable evolution, such as is suggested by the 

 fauna of the Pittsburgh shale. Of this fauna we have representatives in the 

 specialized Proterosauria of Eiu"ope and the Poliosauridce of North America, 

 probably in many of the amphibia of both continents, and even in Edapho- 

 saurus of Saxony and Bohemia, Pennsylvania (?), and New Mexico. It is 

 not probable that free communication across the North Atlantic continent 

 was interrupted at the time the Pittsburgh shale was laid down, and the 

 genus Edaphosaurus, or its immediate ancestor, was probably already in 

 existence and had spread east and west. 



Shortly after this stage the free passage across the North Atlantic conti- 

 nent was interrupted either by an arm of the sea (the southern extension of 

 the Davis Strait) or by the elevation of the Hercynian chain on the North 

 Atlantic continent. This isolated a fauna in North America which, devel- 

 oping by itself, resulted in the assemblages found in the Texas, Oklahoma, 

 Kansas, Illinois, and Prince Edward Island beds. 



For the third possible connection we have no evidence from vertebrate 

 fossils. It is suggested by White "^ that the fern Gigantopteris may have 

 reached North America by this route. 



THE FATE OF THE AMERICAN FAUNA. 



The North American fauna developed per se, and apparently disappeared 

 before the beginning of the Triassic. It is very evident why some forms 

 should have so disappeared, for they had reached a degree of specialization 



° Willis, U. S. Geological Survey, Professional Paper 71, p. 345. 

 >> Willis, ibid., p. 425. (Report of Sapper's work.) 

 " Koken, Festband d. Neues Jahrb. ftir G. M. u P., 1907, Tafel xix. 

 "i White, David, Proc. U. S. Nat'l Mus., vol. 41, p. 511 et seq., 1912. 

 II 



