Ranzania 



Figure 326.— Hypothesized phylogenelic 

 relationships of the genera of Molidae. 



than the other two genera, these specializations often 

 associated with the streamlining of the body for what is 

 probably more rapid and sustained swimming. 



The specialized features of Ranzania (i.e., the features 

 further removed in comparison to Mola-Masturus from 

 those of the hypothetical pre-Triodon ancestral group, 

 discussed under Triodon) are: 1) the funnellike lips, 

 closing to a vertical groove; 2) the falcate pectoral fins, 

 resting in an indented region on the carapace; 3) the 

 thickened, angular scale plates of the carapace; 4) the 

 pseudocaudal fin distinctly set off from the dorsal and 

 anal fins in adults; 5) the great posterior prolongation of 

 the epiotics and of the supraoccipital crest; 6) the un- 

 ossified vomer; 7) the anterior displacement of the basi- 

 sphenoid; 8) the greater anterodorsal prolongations of 

 the basioccipital, meeting in the midline over the neural 

 canal; 9) the strong interdigitation of the neural arches 

 and spines of the abdominal and more anterior caudal 

 vertebrae leading to greater rigidity of the vertebral 

 column within a slightly less flexible carapace; 10) the 

 loss of the sixth branchiostegal and great enlargement of 

 the fifth; 11) the loss of the posterior portion of the sub- 

 operculum; 12) the elongate, rodlike operculum; 13) the 

 interdigitation of the actinosts to one another; 14) the 

 great platelike expansion of the postcleithrum beneath 

 the carapace in the region of the pectoral fin; 15) the 

 decreased width of the anterior end of the parasphenoid; 

 16) the articulation of the posterior region of the palatine 

 with the dorsal surface of the parasphenoid; 17) the 

 elongation of the basal pterygiophores, and the greater 

 obliqueness of them and their neural and haemal spine 

 supports; 18) the grouping in pairs of most of the 

 successive sets of two haemal spines of the caudal 

 vertebrae; 19) the complexity of the first basal pterygio- 

 phore of the dorsal fin; and 20) the anterior expansion of 

 the bases of the first dorsal and anal fin rays. 



Conversely, a lesser number of features of Romania 

 can be considered more generalized than in Mola- 

 Masturus, these being: 1) the lesser reduction in the 

 number of caudal vertebrae, the centrum of the 10th be- 

 ing retained; 2) the branching of the rays of the pseudo- 

 caudal fin not much less than that of the dorsal and anal 

 fins; 3) the better development of the interoperculum 

 and mesopterygoid; 4) the lack of a secondary larval 



stage; 5) the lack of a deep collagenous layer under the 

 scales, probably associated with the better ossification of 

 the skeleton; 6) the gill rakers perhaps less concealed in 

 adults; 7) ceratobranchials not as deep bodied; and 

 8) the second abdominal vertebra without prominent 

 anterior and posterior extensions of its neural arch and 

 spine. 



On the whole, Ranzania has far more specializations 

 than do Mola and Masturus, and Ranzania must be con- 

 sidered to be the more specialized of the two lines of 

 molid diversification. The fewer specializations of MoUx 

 and Masturus (the opposite of the generalized condi- 

 tions of Ranzania discussed above) can be assumed to 

 have arisen after the divergence of the early molids into 

 the two lines leading on the one hand to Mola and the 

 slightly more specialized Masturus and, on the other 

 hand, through even greater specialization, to Ranzania. 



Raven (1939b), on the basis of the musculature and 

 skeleton, also concluded that Ranzania was more 

 specialized than Mola and Masturus, while Fraser- 

 Brunner (1951), on more superficial and fewer char- 

 acters, believed Ranzania, in spite of certain specializa- 

 tions, to be the most generalized of the molids, and 

 Masturus to be slightly more generalized than Mola, 

 primarily because of the reputed retention of true caudal 

 fin rays in the medial lobe of the pseudocaudal fin. 



Relationships to the other Tetraodontoidei.— As dis- 

 cussed under the Triodontidae, molids have their closest 

 anatomical affinity among the gymnodonts with the trio- 

 dontids, retaining a number of generalized features (e.g., 

 fourth gill and gill slit; basisphenoid; unmodified first 

 branchiostegal ray; uninflatable gut; general configura- 

 tion of the bones of the snout) from their triodontid 

 ancestry while at the same time becoming remarkably 

 specialized with the abortion of the rear end of the body 

 and the encasement of the relatively slow swimming 

 body in a firm or thickened skin. While molids are most 

 closely related to triodontids, they undoubtedly evolved 

 from them at a level of organization somewhat less 

 specialized than that of the Recent Triodon, as discussed 

 more fully under the latter. 



Molids have sometimes been thought to be closely 

 related to diodontids, since both the premaxillaries and 

 dentaries are fully fused to their opposite members only 

 in these two families of gymnodonts. However, as dis- 

 cussed under Triodon, the fusion of the premaxillaries 

 and dentaries is not that complex an event and the 

 phylogenetic usefulness of it is meager within the gymno- 

 donts. While it is true that the generalized biting edge 

 dentition of diodontids (with numerous small units) 

 could have given rise to that of molids (discrete units es- 

 sentially absent), the structure of the rest of the head and 

 body of diodontids is extremely unlike that of molids, 

 there being no similarities such as are found between 

 molids and triodontids. In one other superficial respect 

 there is a minor similarity between molids and diodon- 

 tids. Diodontids have a short caudal peduncle and a 

 reduced number of caudal vertebrae, especially of those 

 posterior to the dorsal and anal fin bases, while in molids 



392 



