FRESHWATER FISH FAUNA 193 



America (Cyprinidae, Catostomidae, Ictaluridae, Aphredoderidae, 

 Centrarchidae, Salmonidae, Cyprinodontidae, Cottidae, and Gas- 

 terosteidae) . The first five are primary division freshwater fishes; 

 the remainder are of diverse origin (boreal, secondary tropical, 

 marine types or derivatives). Certain Miocene fossils from the Great 

 Basin, e.g., from the Humboldt Formation, Nevada, indicate that 

 at this time there were kinds of fishes (a sucker, Amyzoji, and a pirate 

 perch, Trichophanes) quite unlike those that now inhabit the West; 

 Miocene and Pliocene sunfishes (Centrarchidae) of extinct genera 

 from Oregon, Nevada, and Utah demonstrate that this family, now 

 largely restricted to eastern North America, was then more wide- 

 spread. A minnow from British Columbia, Leiiciscus rosei (Hussakof, 

 1916), thought to be of Miocene age, probably represents the living 

 genus Richardsonius , and a Miocene minnow from Nevada is of 

 essentially modern facies (Hubbs and Miller, 1948, p. 26), From 

 these sketchy data it may be inferred that during the long Miocene 

 epoch and extending into the Pliocene, one family (Aphredoderidae) 

 and a number of genera {Amyzon, sunfishes, Trichophanes) became 

 extinct in the West, though relatives have persisted in eastern North 

 America, and that, although the Miocene fauna as a whole is quite 

 different from the existing fishes, at least one modern freshwater 

 type {Richardsonius) probably became established during this 

 epoch. 



Two early Pliocene fossils from beds within the Lahontan system 

 of Nevada, a killifish {Fiindulus nevadensis) and a stickleback 

 (Gasterosteus doryssus), belong to genera of coastal and lowland dis- 

 tribution living today in western North America only along the 

 Pacific slope. Their entrance into Nevada, perhaps in late Miocene 

 or early Pliocene times, may have been from the southwest by way of 

 what is now the Death Valley region, since fossil killifishes of the 

 same genus occur there (Miller, 1945b) and sticklebacks are found 

 as far south today as northern Baja California. 



Middle Pliocene fossils from the Bidahochi formation in the 

 Colorado system of northern Arizona represent species of Gila and 

 Ptychocheilus similar to the living forms that are adapted to a swift- 

 water habitat. This suggests that the Colorado was then a swift 

 river, and such an ecological picture is supported by recent studies 

 of geologists on the evolution of the Colorado (Repenning et al., 

 manuscript), A Pliocene minnow from the Esmeralda formation of 



