4IO Evolution and Distribution of Fishes 



bridge — extended over into Europe, but owing to a sea 

 barrier that cut in between eastern Europe, North Atlantis, 

 and the Angara continent, they failed as a group in reaching 

 Siberia. Only since union of these land masses has slight 

 further migration eastward been effected. 



In review then it may be said that given the above 

 Cretaceous-Eocene land bridges, and their relation to 

 present continental land masses; given also the inclination 

 in former Cretaceous-Tertiary times, for some of the fresh- 

 water species to become brakish and later coastal marine 

 dwellers, as is abundantly and strikingly indicated by Bou- 

 lenger for west African teleostean fishes, we may exactly 

 and minutely explain the origin, migrations and present 

 distribution of all the Acanthopterygii. For starting in 

 lakes of northern central North America, as types akin to 

 but somewhat simpler than Percopsis or Columbia, evolu- 

 tion and distribution went hand in hand for production 

 there of Aphredoderidae, Centrarchidae and Percidae. 

 From one or other of the two last started the primitive 

 freshwater Serranidae, that later branched off almost whol- 

 ly into marine life. From most if not all of these "primary" 

 groups, derivative forms had eventually invaded the brakish 

 waters, still later the shores, of all of the geographic areas 

 above indicated. While, as in the case of the Cichlidae, 

 Pomacentridae, Labridae and Scaridae, it is possible readi- 

 ly to trace continuous modification and specializing evolution 

 proceeding during such migrations; in other cases outlined 

 in last chapter, more minute comparisons will require to 

 be instituted before complete assurance is obtained as to 

 derivative origins, in relation to geographic and geologic 

 conditions. 



To appreciate the possible origin of the Berycidae in 

 connection with geologic conditions, one has to trace the 

 changes proceeding over the North American continent 

 during Lower or Comanchean and Upper or later Cretace- 

 ous times. For while such genera as Acrogaster, Dinop- 

 teryx, Homonotus, Hoplopteryx, Pycnosterinx and Spheno- 

 cephalus have been described from upper Cretaceous rocks 

 of Europe or W. Asia, we would regard these all as mi- 

 grants from the active centre of evolution, viz. the North 



