■ . ''. 177 



western populations, but I have not found morphological evidence to support this 

 idea (see comments under species account of y4./?arda/K). Vari (1988) noted 

 variation between the Lake Maracaibo populations of Cyphocharax magdalena and ...^ 

 Roestes alatus and conspecific populations to the west of the Lake Maracaibo basin, 

 and attributed the differences to reduced gene flow (due to partial isolation 

 resulting from the intervening central cordillera of the Andes between the Rio 

 Magdalena basin and the Lake Maracaibo basin). Nevertheless, the presumed 

 nonconspecificity of populations of several other taxa between these two areas has 

 not been critically studied. 



The distribution of A. pardalis is phylogenetically informative, although 

 somewhat problematic. The faunal region that it occupies has been discussed 

 extensively, and is the best known of the continent (the western region of Vari 

 1988). There is considerable endemism in the Rio Magdalena, and various degrees 

 of faunal distinction among the other river drainages to the west and south (Vari 

 1988, 1989c). Prior to the uplift of the Andes, the circum-Magdalena region was in 

 contact with the Orinoco- Amazon basin. Following vulcanism in the region, there 

 were widespread local extinctions, accounting for the present-day lower faunal 

 diversity of the Magdalena basin, in comparison to the Orinoco and Amazon basins 

 (Lundberg et al. 1986). The separation of the Magdalena fauna from the Orinoco 

 and Amazon basins subsequently allowed for allopatric speciation to occur. In spite 

 of the speciation in this region, however, Lundberg and his colleagues (1986, 1988) 

 found evidence of remarkable evolutionary stasis in two species, based on Miocene 

 fossils of the characid Colossoma macropomum and the pimelodid Phractocephalus 

 hemiliopterus from the coastal areas of the northwest Andes. Both of the above 

 extant species are presently widely distributed throughout the Amazon and Orinoco 

 basins, but neither species occurs today in the Rio Magdalena. Lundberg used the 

 fossil evidence and the current distributions of these fishes to demonstrate that 



