1 1 6 Zoology of Colorado 



in the Niobrara formation, but scales are widely distributed 

 through many strata. It was formerly supposed that these 

 scales were of little or no value for scientific study, but recently 

 it has been shown that they present excellent characters.* The 

 matter assumes additional importance from the fact that in many 

 places these scales are the only available fossils which can be used 

 to determine the horizons. Owing to the presence of oil, gas and 

 coal in these Cretaceous formations, the study of fossil fish scales 

 has come to have economic as well as purely scientific significance. 

 Ignorance of the stratigraphic relations has often led to the 

 waste of large sums of money, losses which eventually have to be 

 made good by the public. 



Much later still is the fish fauna of the Florissant (Miocene) 

 shales, especially noteworthy for the presence of the interesting 

 freshwater genus Trichophanes of Cope. This fish is related to a 

 couple of genera still living in North America; isolated remnants 

 of a group which was formerly much more abundant. Another 

 vanishing type fossil at Florissant is Amia, the bowfin; it survives 

 in a common species living today in the Mississippi Valley. The 

 fishes of the Green River shales, much earlier than those of 

 Florissant, but millions of years later than the Cretaceous, are 

 abundant and beautifully preserved in one locality in Wyoming. 

 Many are sold to tourists and others, and they may be seen in 

 museums all over the country. Although we have great ex- 

 posures of the same formation in Colorado, these fishes have 

 not been found in our State, but the polished ganoid scales of the 

 gar-pike (Lepidosteus) are occasionally found. The freshwater 

 fish-family Cichlidae is well represented in the tropics of both 

 hemispheres, with very numerous genera. If, as we must assume, 

 they originated either in America or the Old World, how did they 

 get from one to the other? Some maintain that they crossed 

 in the freshwaters of a land bridge imagined to have connected 

 Africa with South America. How such a bridge could be formed, 

 and why innumerable other types of life did not cross at the 

 same time, is not sufficiently explained. But we have evidence 

 that fishes of this general type existed in the north, and it is much 

 easier to suppose that they took the northward route in the days 



*Some American Cretaceous Fish Scales, U. S. Geological Survey, Professional Paper 

 120-1. (1919). 



