242 Evolution and Distribution of Fishes 



If we think only however of the recorded telecst fishes 

 of the Eocene period about 52 are freshwater genera in 

 whole or in part, while 47 are purely marine. It follows 

 from what has been said that there is clear evidence of 

 two successive teleostean developments and progressions 

 from a primitive freshwater to a marine environment. 

 First, from freshwater ganoid ancestors belonging to the 

 groups Pachycormidae, Aspidorhynchidae, Pholidophori- 

 dae and Leptolepidae originated the late Jurassic or Cre- 

 taceous families Saurodontidae, Holosauridae, Enchodon- 

 tidae, and others already cited. These were suddenly and 

 very extensively obliterated by the close of the Cretaceous, 

 largely owing, as we would consider, to the world-wide 

 effects of a tremendous volcanic activity in most of the conti- 

 nental centres. Second, in part from evolving genera of the 

 above groups that escaped destruction, in large part how- 

 ever by a later and new migration from freshwaters by 

 members of the Clupeidae, Aphredoderidae, Berycidae, 

 Percidae and others during Eocene days, the progenitors 

 of our existing and abundant marine teleost fauna were 

 established. Details of all of the above are elaborated 

 later on (p.p. 357, 373). 



II. Oligocene-Miocene Formation. As already ac- 

 cepted by Saporta, Cope, Lesquereux and more recent 

 authors, complete conformability of strata, and continuity 

 of organismal types can be traced from the Upper Eocene 

 to the lower Oligocene and up into Miocene strata in some 

 areas alike of the Old and New World. But a distinct 

 break and unconformability is observed in other regions. 

 Further, frequent elevations and depressions of land-levels 

 took place, so that freshwater, marine, and even eolian 

 land deposits were laid down. Steady evolution of new 

 genera and families of plants and animals, as well as elimi- 

 nation of older types proceeded rapidly. All of the im- 

 portant groups of animals had now appeared except the 

 genus Homo, so far as we know. 



Separation of the land-masses into such as now exist had 

 almost completely been effected by end of the period. Ex- 

 plain it as we may also, the flora in wide regions of the 

 Northern Hemisphere took on a semi-tropical aspect, and 



