512 Evolution and Distribution of Fishes 



Aspidorhynchidae, Semlonotldae, and Leptolepidae." But 

 in freshwaters "abundant representatives of the Semion- 

 otidae Pholidophoridae, and Leptolepidae," became pro- 

 genitors of our existing freshwater teleost groups. The 

 transition types shown between some of these are discussed 

 in their structural details. 



It thus results that great marine deposits like the Ben- 

 ton-Niobrara enclose a rich and characteristic fauna, chief 

 amongst which are elasmobranch and teleostean fish re- 

 mains Great freshwater deposits also like the Laramie 

 proclaim equally clearly their formation over continental 

 areas, while the fish remains in these are well known. On 

 the land also a striking mammalian fauna existed. From 

 the oil shales therefore of Central Europe, and from the 

 Lower Benton or Mowry shales of N. America come great 

 supplies of petroleum derived from marine Cretaceous 

 fishes. And from the great masses of Laramie shale come 

 the Cretaceous freshwater supplies of the Central western 

 States. The fish-bearing strata of Westphalia, the Sussex 

 beds of England, and the Sahel-Hakel beds of Lebanon are 

 also reviewed. 



Chapter 8. The physical and biological environment of 

 fishes from Eocene to recent time. 



The pronounced volcanic and sedimentation changes 

 that proceeded during the last period were largely continued 

 at intervals now, and seem to have reached a climax during 

 late Miocene time. Solidification, thickening, and faulting 

 of the earth's crust also, aided by volcanic action, gave 

 rise to the great ridges that, after denudation and earth 

 sculpture, now form our main mountain chains. By dam- 

 ming up of water courses, by elevation of coastal mud 

 areas, and related changes meanwhile, those large lakes 

 and wide flood-plains arose, the deposits of which can readi- 

 ly be traced. 



During the oldest or Eocene epoch thick freshwater 

 as well as marine beds can be traced over wide areas of ex- 

 isting continents. Alike in Europe and America flowering 

 plants and not least dictoyledons have left their remains 

 often alongside lake mussels, insects, ganoid and teleostean 



