412 Evolution and Distribution of Fishes 



spread withdrawal of the waters. The mediterranean sea 

 disappeared, and the borders of the land were extended 

 seaward on the east, the south, and the west, and the con- 

 tinent became nearly or quite as large as now." 



How enormous were the lacustrine and marsh land 

 deposits of the Lower Cretaceous is shown by their attain- 

 ing in places a thickness of from 4000 to at least 15,000 

 feet, while the coal beds, the often abundant plant remains 

 of warm temperate or subtropical character, the bitumin- 

 ous zones and the remains of fishes as well as of reptiles, all 

 proclaim an environment suited to an abundant freshwater 

 life. Similarly in the Upper Cretaceous the heavy deposits 

 of Dakotan, of Montana, and of Laramie age, all prove 

 that opportunities for evolution of freshwater species were 

 ample. But the distinct evidences of extensive oscillations 

 and local marine invasions on both land and lake regions, 

 afforded the opportunities for gradual migration of fresh- 

 water fishes seaward. 



Bearing in mind then that the four genera of Aphre- 

 doderidae — Amphiplaga, Asineops, Erismatopterus and 

 Trichophanes — have all been reported from Lower Terti- 

 ary beds; that the even more primitive acanthopterygian 

 genera Percopsis and Columbia, which connect with Salmon- 

 idae, are both living North American types, it seems highly 

 probable that primitive representatives of the Berycidae 

 branched off into marine life during Lower Cretaceous 

 times, and into some of the marine areas that seem often 

 then to have taken the place of the land. As evidenced by 

 fossil remains, and by distribution at the present day, the 

 group probably spread abroad both eastward by seaways 

 that covered New Jersey and interior parts, to west central 

 America, either temporarily or for a prolonged period. 

 Thence along the edge of the North Atlantis bridge, the 

 evolving genera could readily extend their passage till 

 they reached the European shore expanses and northward 

 connections of Upper Cretaceous date. Thus could be ex- 

 plained the presence of the six genera already named that 

 have been laid bare, from rocks in England on the west 

 to those of Mt. Lebanon on the east. 



