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DISTRffiUnON AND ZOOGEOGRAPHY 



Considered in its entirety, the family Ageneiosidae is widely distributed 

 throughout lowland waters of South America and the Isthmus of Panama. 

 Ecological data are unavailable for nearly all species to adequately characterize 

 their habitat requirements and behavior. All species of Ageneiosus appear to be 

 ecologically confined to main river channels, oxbow lakes, lagoons, backwater 

 sloughs, and other open-water habitats associated with the large rivers of South 

 America. Tetranematichthys is apparently found in smaller lowland tributaries and 

 forested creeks (H. A. Britski, personal communication), a fact that may account in 

 part for this species' dark pigmentation pattern. The apparently generalized habitat 

 requirements and vagility of most species has probably contributed significantly to 

 their widespread ranges. 



There are scant substantive biogeographical studies of neotropical fishes, due 

 mainly to a poor state of knowledge about faunal composition of most drainages, 

 evolutionary relationships of the fishes, and inadequate geological and 

 paleontological data. The earliest serious attempts to explain distribution patterns 

 were made my Carl H. Eigenmann, who surveyed expansive areas of the continent. 

 He published numerous faunal lists (e.g., Eigenmann 1912, 1920a, 1920b, 1920c, 

 1920d, 1921), and attempted to correlate the observed distribution patterns of the 

 ichthyofauna with historical geological events known at the time. Virtually all of the 

 significant studies that addressed geographical diversification were summarized by 

 Weitzman and Weitzman (1982). In the last ten or fifteen years, a limited number 

 of phylogenetic studies have included comments about past climatological and 



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