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The extremely diverse freshwater fish fauna of South America has received a 

 moderate amount of taxonomic study, beginning in particular with the pioneering 

 work of many notable 19th and early 20th century naturalists and ichthyologists, 

 during an intense period of descriptive ichthyology (Bohlke et al. 1978). However, 

 not until relatively recently have there been detailed studies of selected neotropical 

 fish taxa using more modem and objective systematic methods and theory, 

 particularly quantitative and phylogenetic systematics. Because the task of revising 

 many of these groups is a formidable one, many recent studies have focused on 

 relatively small taxa, well-defined subgroups of larger, more diverse groups, or have 

 tended to neglect detailed species-level taxonomy in favor of attempts to establish a 

 better knowledge of higher-level relationships. There have been relatively few 

 studies of phylogenetic relationships among catfishes, or siluroids, and few recent 

 taxonomic revisions of larger groups. This is particularly true of the neotropical 

 fauna, which constitutes about 59% of the catfishes in the world, as estimated by 

 Nelson (1984). Consequently, although our understanding of neotropical freshwater 

 fish systematics has improved considerably in recent years, the taxonomy of many 

 groups remains in an extremely fragmented state, and the ichthyofauna as a whole is 

 still among the most poorly known worldwide. Emphasizing problems in catfish 

 evolution, Lundberg and Baskin (1969) and Gosline (1975) argued that studies of 

 single structural complexes might reveal a better understanding of phylogenetic 

 relationships, at least among higher groups. However, this assumption is reliable 

 only if one assumes that the comparisons being made are across sufficiently broad 

 taxonomic categories to formulate accurate generalizations, and that the currently 

 accepted taxonomy of groups included under study reflect natural taxa. 

 Furthermore, as Howes (1983) noted, a strong reliance on one or few characters can 

 produce a misleading hypothesis of phylogenetic relationships. Conversely, Bohlke 

 et al. (1978) and the National Research Council (1980) suggested that, in light of 



