FRESH-WATER FISHES— MYERS 353 



to say nothing of the vastly more primitive bichirs; I cannot but 

 believe that these were probably present in Africa before the cichlids, 

 carps, or characins. If there has been a wide Tertiary or even late 

 Cretaceous bridge across the South Atlantic, why do we find not a 

 single, solitary representative of any of them (save again the osteo- 

 glossids) in South America? I refuse to believe that competition in 

 South America could have killed them off; they have survived just 

 as acute competition in Africa. 



If we are to have a South Atlantic bridge in the late Cretaceous 

 or earliest Tertiary, the only kind I can conceive as fitting the re- 

 quirements of the fishes is one like WiUis's (1932) Brazil-Guinea 

 isthmus in the Atlantic, and from Schuchert's data, it may have 

 still been partly in existence up to the very end of the Mesozoic. 

 If our fishes were present in the earliest Eocene, they may have been 

 there at the end of the Cretaceous. Such a narrow isthmian con- 

 nection, with its short, swift rivers, would not provide a broad high- 

 way for all the fresh-water fishes, but it would allow to pass the 

 very same aggressive types that are now held in common by Africa 

 and South America. The lowland, slow-water mormyrids, panto- 

 donts, kneriids, and bichirs might very well be kept out of South 

 America while more active, swift-water fishes passed. Again, the 

 isthmus may not have been connected at both ends at the time the 

 teleostean fishes came on the scene, and the transfer may have been 

 alternate, or only one-way, but this seems unlikely. Any way one 

 looks at it, the weak little lowland nandids, present in both conti- 

 nents, are problematic if one supposes a bridge that excluded 

 mormyrids. 



In any event, the fish evidence indicates there has been no South 

 Atlantic connection since the Eocene. I have carefully compared the 

 entire external anatomy and osteology of the African and South 

 American characins that are supposed to show the closest intercon- 

 tinental relationship (the African Brycinus and Alestes and the 

 American Brycon). My conclusion is that both the African and 

 American fishes are closely similar only because each is a generalized, 

 dominant, and aggressive animal of a type that has probably changed 

 little since the more modern types of characins originated. Moreover, 

 in my studies of the cyprinodonts (Myers, 1931) I have compared the 

 difficult-to-separate South American Rivulus and African Aphyosemion, 

 They both belong to a rather specialized group of genera (the tribe 

 Rivulini), and are imdoubtedly closely related, but it should not be 

 overlooked that they belong to the secondary division of fresh-water 

 fishes, and that a fortuitous marine dispersal of one or more species 

 at some time in the Tertiary is not impossible, particularly if a Brazil- 

 Guinea ridge remained for a time as an island chain. 



