April 13, 1900.] 



SCIENCE. 



567 



evolution. The Monotremes also may have 

 entered NoTOGiEA by either of these routes. 

 ISTorth America is the only part of the 

 globe where Cretaceous mammals are known 

 at present. In the late Cretaceous we ap- 

 pear to discover evidence of the existence 



lieved to be related to the Hyracoidea, 

 upon the affinities of these forms turns the 

 problem whether South America derived 

 the sources of its great radiation from 

 Africa ' or from South America. (See 

 Chart IV.) 



Chart IV. — Order of Mammals placed in their hypothetical chief centers of adaptive radiation during the 

 Tertiary Period. 



of the following orders : Inseetivora, Creo- 

 donta or ancestral Carnivores, hoofed ani- 

 mals or Amblypoda and perhaps the earli- 

 est Monkeys or Mesodonta. In the basal 

 Eocene we certainly find primitive Mon- 

 keys or Mesodonta ; Eodentia and Taeni- 

 odonta or ancestral Edentata. A land con- 

 nection with South America in the early 

 Eocene would therefore have supplied Ne- 

 ogcea with the Edentates as well as the stem 

 forms from which might have been derived 

 its wonderful radiation of hoofed animals — 

 the Litopterna,Typotheria and Toxodontia ; 

 together with the remarkable radiation of 

 the Hj'stricomorph or porcupine-like ro- 

 dents and of two families of Monkeys. 



The exact zoological affinities of the 

 oldest mammalian or Pyroth&rium fauna of 

 South America remain to be determined. 

 Pyrotheriiim itself is considered by Ame- 

 ghino (1895) as the source of the order 

 Probosoidia while other ungulates are be- 



Four streams of migration to and from 

 ISTeog^a appear to have occurred ; the 

 first established its autochthonous fauna 

 or distinctive radiation of peculiar ungu- 

 lates and edentates. The second related 

 this region with Africa, via Antarctica ; this 

 contact, ill addition to the problematical 

 Proboscidia and Hyracoidea above alluded 

 to, apparently introduced stem forms of 

 Edentates into the Ethiopian region from 

 which were derived the Pangolins and Aard 

 Varks ; these peculiar edentates together 

 with Armadillos all occur in southern 

 France in the lower Oligocene (Fihol, 1893); 

 this land bridge also distributed the Cape 

 Golden moles, Chrysochloridce ; these facts 

 and others too numerous to mention serve 

 to show the vast importance of the ex- 

 plorations in Patagonia and make us im- 

 patient for the exact conclusions which are 

 forthcoming from the materials brought 

 together by Ameghino and Hatcher. 



