332 DISCOVERY REPORTS 



Group 2. Alepisauridae, Anotopteridae, Omosudidae and Paralepididae 



Intermuscular bones present; parietals not fused with frontals (no information on Anotopterus) ; 

 anus much nearer to insertion of pelvic fins than to origin of anal fin ; eyes normally formed ; definite 

 trend towards development of elongate to very elongate body forms. 



It will be noticed that there are certain morphological trends within these two groups. In addition 

 to those listed under the group headings, mention has been made already (pp. 322-31) to others, which 

 can be briefly summarized here. There are tendencies to the development of a lightly ossified skeleton, 

 to the loss of scales, and to the acquisition of means for dealing with very large prey (certain of the 

 mandibular and palatine teeth have become large stabbing canines, and the tissues of the stomach and 

 body wall are distensible). As in the more generalized Isospondyli, the pectoral fins are also set low 

 down on the shoulders and make an angle of less than 45 ° with the horizontal axis of the body. 



These trends lead to more specialized forms, but within each of the two groups there is one family 

 with a more generalized character complex. For example, in Group 1 the Scopelarchidae are fully 

 scaled and have lingual teeth, whereas both these features are absent in the Evermannellidae. In 

 Group 2, some of the Paralepididae are also fully scaled, in contrast to the other three families, the Alepi- 

 sauridae, Anotopteridae and Omosudidae. In discussing the relationships of the Paralepididae, Harry 

 (1953 a) pointed out that Magnisudis has many generalized features in common with the Aulopidae and 

 with another myctophoid family, the Chlorophthalmidae. He also considered that the ' Paralepididae 

 are most closely related to the Anotopteridae. They both have the same general proportions, essen- 

 tially similar osteology, the same peculiar cartilaginous development of the jaws, which is found in 

 these two families alone in the order, and a good number of other similarities.' These two families 

 also show striking resemblances in the development of scale-like ossifications along the lateral line 

 (Text-figs. 5 c and 7) and in certain skull features already mentioned on p. 322. 



The remaining two families in Group 2, the Alepisauridae and Omosudidae, are perhaps the most 

 nearly related of all. Regan (191 1) observed that Omosudis has a head, mouth and teeth very much like 

 Alepisaurns, and both genera have completely lost the scaling, even along the lateral line. 



The alepisauroid fishes are difficult to define, lacking diagnostic characters and it might be 

 argued that they are not a monophyletic group. But Simpson (1953), after expressing his belief that 

 the fissipede carnivores are monophyletic, remarked that he was unable to find a single character 

 that occurred in all fissipedes and in no other mammals. Again, Berg (1940), after defining the 

 Clupeiformes ( = Isospondyli), concluded by remarking that 'this order, from which a series of higher 

 orders has arisen, represents an artificial assemblage, its separate members, as may be seen from the 

 diagnosis, greatly differing from one another. In time, the Clupeiformes will doubtless be divided 

 in many orders.' 



If the Isospondyli are considered to be merely a convenient grouping of fishes of a 'certain level of 

 organization ', then the same may be true of the Iniomi. It has been pointed out on p. 305, that the 

 Iniomi have evolved beyond the ' isospondylous level ' mainly in that the premaxillaries exclude the 

 maxillaries from the gape, and it is possible that more than one group of isospondylous — or more 

 likely pre-isospondylous — fishes may ' have tried this experiment ' with these jaw-bones. There may 

 well be some parallel with the early evolutionary history of mammals. 'Palaeontologists use an arbi- 

 trary criterion that a reptile became a mammal when the dentary-squamosal joint developed and the 

 functional jaw-movement ceased to be on the articular-quadrate joint. This line was probably crossed 

 separately by at least five different lineages. . .' (Simpson, 1953). 



It has also been stressed by Simpson that the development of a higher group of animals seems 

 always to be bound up with definitive adaptive features correlated with a spread into some major living 



