532 Evolution and Distribution of Fishes 



cembelidae. But regarding both we are still largely in the 

 dark. In summary it is claimed that toward mid or late 

 Cretaceous time, and over an Archenchelis region, the fami- 

 lies Siluridae, Characinidae, Cyprinodontidae and Cichlidae 

 were becoming dominant. The above region connected 

 with West Africa by a south Atlantis bridge, across which 

 continuations of American and African rivers flowed, to 

 empty into a southern and a northern Atlantis sea. Wide 

 marsh, lake, and river systems traversed the whole, and 

 gave opportunity for fish migrations. Of only moderate 

 elevation probably during Cretaceo-Eocene time, the region 

 became greatly altered in Oligo-Miocene days, and the 

 bridge then largely or wholly sank beneath the Atlantic. 

 Specific and generic variation in the now isolated American 

 and African fauna then started, and so a wealth of species 

 typical of both areas gradually appeared. This is specially 

 true of Tanganyika and some other of the lakes which 

 have undergone marked diastrophic changes. 



Chapter 17. The Geographic and Geologic Relations of 

 the more primitive Fishes. 



As passage backward is made toward older rocks in- 

 creasing difficulty is felt in tracing the extent and trend of 

 dry land and freshwaters, as compared with the sea; also 

 in determining the degree to which faunal organisms have 

 spread over these. But having essayed to trace teleostean 

 distribution as affected by geologic and geographic condi- 

 tions, the same methods may be applied to the more ancient 

 and primitive fishes. The study already made of ganoid 

 fishes reveals that in early Cretaceous and in Jurassic 

 time, more or less perfect continuity of land permitted mi- 

 gration of ganoids across a great northern continent that 

 extended from at least Britain to Siberia, China, and Aus- 

 tralia. This has been named in part the Angara or as a 

 whole the Eurasian continent. 



But connection between S. E. Asia and Australia was 

 evidently broken in mid or late Cretaceous, and these areas 

 remained apart till a short-lived reunion was made In Oligo- 

 Miocene time, when brief passage of a few fishes, of mar- 

 supials and a few other animals along with certain groups 



