478 Evolution and Distribution of Fishes 



Congo proves that connection between lake and all three 

 rivers was once possible. 



The recording by Moore of Protopterus not only from 

 Tanganyika, but also from Albert Edward and Victoria 

 Nyanza, similarly proves the fundamental identity of 

 certain species over a wide area. 



Passing to the bony fishes, it can be definitely asserted 

 that, unless all past palaeontological data are defective, the 

 early teleosts branched off from freshwater ganoids during 

 late Jurassic and early Cretaceous time. But only in the 

 late Cretaceous and early Eocene periods did they become 

 abundant and spread abroad into many and varied regions. 

 We have already claimed and accepted it that the four 

 leading families reached Western and later Central Africa 

 from eastern S. America at one or the other time. Tan- 

 ganyika, as well as other of the central lakes, must then 

 have become stocked with one or a few parent forms of 

 each of the four families, since we would consider that these 

 lakes were then of rather low elevation, and were more or 

 less connected with each other during flood times. These 

 parent forms multiplied, and becoming geographically re- 

 stricted to definite centres or lines of migration, owing to 

 geologic changes proceeding, started varietal aind later 

 specific peculiarities. Then toward close of the Oligocene 

 or in early Miocene time, marked earth shrinkage, faulting, 

 and volcanic activity combined to deepen Tanganyika — that 

 included then Kivu — and to shut it off wholly from other 

 lakes as a long rift valley. 



For reasons that we seem to be wholly ignorant of as 

 yet, environal surroundings favored multiplication of the 

 Cichlidae beyond all others. But that about 75 species of 

 this family should have evolved in a single lake, and also 

 that most of them are specifically peculiar to It are equally 

 arresting facts. 



Elevation of the entire deep narrow rift lake to about 

 2700 feet, caused isolation of It, and made It different from 

 the lower Nyasa, and the more elevated Nyanzas. This 

 also seems in part to account for a progressive evolutionary 

 separateness, from late Oligocene to recent time. 



