there has been virtually no morphological divergence in these two species for at 

 least the last 6-15 million years. ^ 



Vari (1989a) found that there was significant speciation among curimatids 

 prior to the uplift of the Andes. The evidence for this was an area cladogram based 

 on a well-corroborated phylogeny, in which the Rio Magdalena basin fell at a 

 relatively high node on his tree, thus suggesting that more basal clades had 

 differentiated prior to the Miocene. In this study, unfortunately, the closest sister 

 relationship oiA.pardalis was not determined; thus, the significance of its trans- 

 Andean distribution is obscure. Phenetically, this species is most similar to the fork- 

 tailed species with encapsulated swimbladders, which includes species distributed 

 throughout the entire extent of the range of the family. This would suggest that 

 speciation of taxa involving the ancestor of the latter clade occurred prior to the 

 uplift of the Andes. 



Ageneiosus valenciennesi is found only in the lower reaches of the Rio 

 Parand-Rio Paraguay system, which is a region of high ichthyofaunal endemism 

 (Vari 1988). The only congeners that also occur in this system aieA. brevifilis and 

 A. ucaycdemis, which are very broadly distributed throughout the continent. The 

 relationship oiA. valenciennesi with the large fork-tailed species of the Amazon is 

 not surprising, considering that there are a number of characiforms that occur in 

 both basins (Vari 1988), suggesting a more extensive historical connection between 

 the Amazon and Paraguay basins than is commonly cited. Nevertheless, isolation of 

 the Paraguay apparently allowed for allopatric speciation of ^4. valenciennesi. UA. 

 ucayalensis and A. valenciennesi are sister species, their present distributions is 

 indicative that^. ucayalensis redispersed into the Rio Parand basin following 

 speciation. 



The distribution oiA.piperatus, as currently known, is restricted to the area 

 around the Guiana Shield, in the Rio Essequibo and in the Rio Branco. This region 







i f 



