Generalized conditions in ostraciids can be considered 

 those which deviate the least from the structure of the 

 ancestral aracanids. Only two anterior vertebrae are fus- 

 ed in aracanids, so the involvement of only four vertebrae 

 in the fusion complex of all but one species of ostraciins is 

 less specialized than the involvement of five in the lacto- 

 phrysins. Aracanids have single unbranched neural 

 spines, as do lactophrysins, and the trifid neural spines of 

 some of the vertebrae in ostraciins can be considered as 

 specialization. Aracanids have no lateral or other expan- 

 sions toward the distal ends of the last dorsal and anal fin 

 basal pterygiophores for support of the carapace, nor do 

 the lactophrysins, and the expansions of these pterygio- 

 phores in ostraciins can be considered a specialization. 

 The higher numbers of dorsal, anal, and pectoral fin 

 rays, and of the dorsal and anal fin basal pterygio- 

 phores, in lactophrysins is more similar to that of 

 aracanids than are the lower numbers found in ostra- 

 ciins, the latter again more specialized. In aracanids the 

 haemal spine of the penultimate vertebra is autogenous, 

 while only among the lactophrysin ostraciids are there 

 species with the penultimate haemal spine autogenous, 

 the ostraciins again having the more specialized condi- 

 tion. Moreover, it is only among the species of ostraciins 

 that the penultimate and the preceding one or two 

 haemal spines are reduced in size, solid and without a 

 foramen for the haemal canal, the ostraciins again at 

 least tending to have a more specialized caudal fin sup- 

 porting apparatus than in the lactophrysins. The 

 moderate degree of lateral flange development across the 

 surface of the centra in aracanids is about intermediate 

 between that of the moderate to well-developed flanges 

 found in ostraciins and that of the moderate to poorly 

 developed flanges of lactophrysins. 



In only two ways can ostraciins be considered more 

 generalized than lactophrysins. In aracanids and os- 

 traciins a small myodome is present, but this has been 

 essentially lost by lactophrysins. Aracanids and ostra- 



Ostracion 



Rhynchostracion 



Acanthostracion 



Eolactoria 

 (Eocene) 



Figure 178.— Hypothesized phylogenetic relation- 

 ships of the genera of Ostraciidae. 



ciins both have an Indo-Pacific distribution, while that 

 of lactophrysins is Atlantic. 



In short, in most of the anatomical characters discuss- 

 ed above, with the notable exception of the anterior 

 vertebral fusion and mydome development, the lacto- 

 phrysins are seen as the more generalized of the two sub- 

 families. It seems best to assume that the lactophrysins 

 have remained more generalized than the ostraciins in 

 nearly all respects, except that the myodome became 

 reduced and the fifth vertebra became involved in the 

 anterior fusion complex in all species, while the generally 

 more specialized ostraciins retained from the same 

 generalized stock that gave rise to both subfamilies a 

 slightly better developed myodome and a less extensive 

 anterior vertebral fusion complex. In this view it is likely 

 that the Ostraciidae diverged into two lines in the Indo- 

 Pacific, with the more specialized ostraciins eventually 

 becoming dominant there to the exclusion of the lacto- 

 phrysins, which remained anatomically closer to the 

 ancestral stock, and were only permanently successful in 

 the Atlantic, in what is perhaps at least a partially relict 

 distribution. 



Within the Lactophrysinae three genera were recogniz- 

 ed by Fraser-Brunner (1935b:317, 1941c:307), exclu- 

 sively on the basis of carapace characters, Acantho- 

 stracion for the species (quadricornis, polygonius, 

 guineensis, and notacanthus) with the carapace closed 

 behind the dorsal fin and with preorbital as well as 

 postanal carapace spines, Rhinesomus for the two species 

 (bicaudalis and triqueter) with the carapace closed 

 behind the dorsal fin, no preorbital carapace spines but 

 with the postanal spines present or absent, and Lacto- 

 phrys for trigonus, with the carapace open behind the 

 dorsal fin, no preorbital carapace spines but with 

 postanal spines. Since the presence of preorbital spines 

 seems to have no more magical phylogenetic quality than 

 the presence of postanal spines, one could with equal 

 simplicity group together those species with postanal 

 spines (Acanthostracion, Lactophrys, and Rhinesomus 

 bicaudalis) as distinct from R. triqueter, and within the 

 former group split off R. bicaudalis and L. trigonus from 

 Acanthostracion on the basis of the presence or absence 

 of preorbital spines, and further separate R. bicaudalis 

 and L. trigonus on the basis of whether the carapace is 

 closed behind the dorsal fin. A great many such com- 

 binations are as logically valid on the basis of carapace 

 characteristics alone. With this in mind, most workers 

 have not recognized all three genera as valid, variously 

 lumping them all together in one genus (Lactophrys) or 

 recognizing Lactophrys for the three species without 

 preorbital spines and Acanthostracion for the four 

 species with preorbital spines. 



Several skeletal characters indicate the advisability of 

 recognizing two genera rather than one or three for the 

 Lactophrysinae. In Lactophrys and Rhinesomus the 

 penultimate haemal spine is autogenous while in 

 Acanthostracion it is fused to the centrum. In Lacto- 

 phrys and Rhinesomus there are three postanal (pos- 

 terior to the last vertebra supporting the anal fin) 

 vertebrae while in Acanthostracion there are four in three 



