■ Odonus 

 Xanthichthys 



Melichthys 



Sufflamen 



Pseudobalistes 



Balistomorphus 

 Oligobalistes 

 (Oligocene) 



Figure 66.— Hypothesized phylogenetic 

 relationships of the genera of Balistidae. 



mechanism with its basal pterygiophore nor a complex 

 extensive musculature. The third spine functionally 

 seems rather insignificant, and great variation in such a 

 structure can be expected, the variation from genus to 

 genus or within a genus being of little value to deter- 

 mining relationships. Thus, the minute third dorsal 

 spine found in Rhinecanthus, Melichthys, and 

 Xanthichthys probably does not indicate close relation- 

 ship between these three otherwise relatively dissimilar 

 genera, nor does it necessEirily indicate that they are 

 specialized in the face of almost any other evidence to the 

 contrary. The third dorsal spine is well developed in the 

 Oligocene genera Balistomorphus and, especially, 

 Oligobalistes. 



The significance of the presence of a preocular groove 

 and of specialized flexibly articulated nonoverlapping 

 scales over the tympanal region above the pectoral fin 

 base is difficult to interpret. Neither structure is present 

 in triacanthids. They occur only in balistids and not in 

 the derived monacanthids. The fossil record of the balistids, 

 first known from the Oligocene, consists of less than a 

 dozen specimens, many of them rather imperfect. The 

 specimens assigned to the three species of Balisto- 

 morphus from the Oligocene of Switzerland, including 

 the holotypes of each, have recently been reexamined, 

 and there is no indication of a preocular groove or of 

 specialized tympanal scales, but these regions are not 

 well shown on any of the specimens. However, in de- 

 scribing the well-preserved Oligobalistes robustus from 

 the Oligocene of Russia, Danil'chenko (1960:173-174) 

 specifically says that a preocular groove is absent, while 

 his statement that there is a "small body plate with 

 radial sculpture situated directly behind gill slit, level 



Figure 67.— Dentition of representative balistids: 



A. Baliatea polylepis, 56.1 mm SL, Galapagos; 

 . Xanthichthys lineopunctatus, 181 mm SL, Hawaii 



C, Odonug niger, 173 mm SL, New Guinea: 

 3, Melichthys niger, 147 mm SL, locality unknown. 



