SOUTH AMERICAN CHARACID FISHES — WEITZMAN 153 



striking their prey harder. The jaws of the Nannostomina are far 

 more speciahzed than those of the Pyrrhulinina, The large post- 

 temporal fossa in the Pyrrhulinina is an interesting specialization. 

 The large amount of muscle tissue found in this area undoubtedly 

 is associated functionally with feeding and swimming behavior, but 

 this needs further study. 



In addition to the differences between the Pyrrhulinina and 

 Nannostomina noted in the classification above, these two groups 

 have a consistent difference in body shape. The body form in the 

 Nannostomina usually is smoothly fusiform, whereas that in the 

 Pyrrhulinina is not, the profile showing a slight notch behind the 

 dorsal fin, the belly being more or less flat, and the back being less 

 arched. Of all the species in the Nannostomina, Nannostomus espei 

 has a body shape closest to that of the Pyrrhulinina. 



Despite the differences between the Pyrrhuhnina and the 

 Nannostomina, I believe they may be united justifiably in the tribe 

 Pyrrhulinini, based on the morphological characters listed above. 



The relationships of the Pyrrhulinini are, without doubt, with 

 the Lebiasinini, and these two tribes form the subfamily Lebiasininae, 

 The characters Usted in the classification for this subfamily (p. 148) 

 are held in combination by no other characids. A full discussion of 

 the relationships between the Lebiasinini and the Pyrrhulinini should 

 await fuller treatment of the genera in these two tribes. 



From the information at hand it seems safe to conclude that the 

 Pyrrhulinini were derived from characids somewhat similar perhaps 

 to the existing members of the Lebiasinini and that the Pyrrhulinina 

 and the Nannostomina had a common ancestor. Neither of these 

 two subtribes can be derived from the other, but their common 

 ancestor must have differed from the recent members of the Lebiasinini 

 in the structure of the jaws and reduction of the laterosensory system 

 of the head. 



Relationships of the Lebiasininae and Erythrininae 



What are the relationships of the Lebiasininae and Erythrininae 

 that can be determined from the present osteological study? Con- 

 sidering the absolute lack of fossil evidence in this case, inferences 

 about phylogenetic relationships based on recent material are bound 

 to bear only a vague resemblance to the actual course of evolution; 

 nevertheless, an attempt should be made to indicate relationships 

 even if this involves nothing more than noting that certain groups 

 appear associated because they have a certain number of characters 

 in common. 



