MATTHEW. CLIMATE AXD EVOLUTION 



235 



gioiis we know too little of the early Tertiary faunae to say when the 

 perissoflactyls first appeared, but they are absent from the Oligocene 

 fauna of Egypt, from the Pleistocene and modern faunae of Australia 

 and of all oceanic islands. This accords with the natural inference from 

 their size, proportions and habits that they would be strictly limited by 

 land connection in their geographic distribution. 



Besides the surviving groups, the early perissodactyls gave rise to sev- 

 eral extinct families, the lophiodonts, palaiotheres, titanotheres and chali- 



Liarif ancestors 

 o/' Horses, 



n 'a.fe Tertiarij 



until Ph/s to ce-ne^ 



Fig. 17. — Distrthution of Equidce, living (solid Mack) and Pleistocene (shaded) 



Early Tertiary ancestors are found In Nearctic and Palsearctic regions. The American 

 series is more direct than that of Europe until the late Tertiary. This and other con- 

 siderations indicate the center of dispersal as in northeastern Asia or northwestern 

 Xorth America. 



cotheres, none of which are known to have invaded the southern conti- 

 nents. 



Equida'. — The Ijest known phylum of the order, that of the horses, is 

 certainly not a direct genetic succession, as regards known species, but 

 approximately so as regards the known genera. The successive genera 

 are progressively more specialized in accordance with their geological 



