145 



tuberculation occurs in other North American Phoxinus species. If P. oreas was conside- 

 red as a separate genus from Phoxinus, the other species of Phoxinus would form a pa- 

 raphyletic group. 



Biogeography of Phoxinus 



Among North American freshwater fishes, the two largest families, Cyprinidae and Per- 

 cidae, comprise the major part of the primary and secondary Recent freshwater fish com- 

 munity (Patterson 1981, May den 1991). These two families are considered by some to 

 have originated in Europe and/or Asia (Banarescu 1972, 1989). Three hypotheses have 

 been proposed to interpret the relationship between the freshwater fish faunae of Eurasia 

 and North America, i.e., "Amphi-Atlantic" hypothesis, "Old Pacific connection" vicariant 

 hypothesis, and "Bering land connection" dispersal hypothesis. These hypotheses can be 

 summarized as following. 



1) The Amphi- Atlantic hypothesis implies that the freshwater fish fauna in Europe and in 

 North America bears a closer relationship than either does to the fauna in Asia (see Ba- 

 narescu & Coad 1991). The trans- Atlantic connection between Europe and North Ame- 

 rica was present until Early Eocene (Brown & Gibson 1983; Briggs 1986). Patterson 

 (1981) claimed that relationships of Amia species indicated North America more closely 

 related to Europe than to Asia. Wiley (1992) proposed that the ancestor of Percidae pro- 

 bably originated in Early Tertiary before the final opening of the North Atlantic, without 

 indicating the place of the ancestral origin. Banarescu (1989) stated that the ancestor of 

 the Percini of Percidae, prevailing in Europe, and the Etheostomatini, endemic to North 

 America, was split by the breaking down of the Atlantic connection between North Ame- 

 rica and Europe. The above hypotheses might be considered to support an "Amphi-At- 

 lantic" hypothesis. No evidence from Cyprinidae was found supporting this hypothesis 

 because no cyprinid was known from Europe before the Oligocene (Kimmel 1975. Ca- 

 vender 1986, 1991, Bogutskaya 1991), and no cyprinid fossils have been found in North 

 America until the Oligocene (Cavender 1986, 1991). The Atlantic connection seems too 

 early for the migration (if there was a migration) of the ancestor of cyprinids into North 

 America from Europe, or vice versa. 



2) The Old Pacific Connection hypothesis claims that east Asia and North America share 

 a close relationship (see Howes 1984), and the splitting of the ancestor of (at least some) 

 cyprinids in North America and Asia was due to the separation between Asia and North 

 America. A series of collisions among several plates between Siberia and North America 

 happened during the Cretaceous (Fujita 1978). This hypothesis might be supported by the 

 distribution of Polydontidae (Patterson 1981, Grande & Bemis 1991), and the relations- 

 hips of some insect groups (e.g., caddisflies; see Ross 1974). It may explain the distribu- 

 tion of the monotypic genus Notemigonus of eastern North America and its relationship 

 to the genus Alburnoides of southwest Asia (Banarescu & Coad 1991). It may also be 

 relevant to the relationship within the aspinine of cyprinids (Howes 1984). However, the 

 earliest cyprinid was found in the Oligocene in North America (Cavender 1986. 1991) 

 which is much younger than the Cretaceous. 



