BBS and WISNER REVISION OF THE SAURIES 



adocetus or Nanichthys sunulans, is the basic type 

 of the family, and that the dwarf forms are deriva- 

 tive. 



DEVELOPMENT OF BEAK 



In their early ontogeny, the Scomberesocidae, 

 like other synentognathous fishes, pass through 

 changes in physiognomy (Figure 2), involving 

 especially the upper and lower beaks. The degree 

 of metamorphosis varies greatly among the four 

 species. 



The most dwarfed scomberesocid, E. adocetus, 

 exhibits the least change, retaining rather heavy, 

 little-produced jaws throughout life. The upper 

 jaw remains relatively short, and rounded in top 

 view, and the lower jaw increases with growth of 

 the fish only very slightly in production and slen- 

 derizing. 



Next in degree of age changes is C. saira, in 

 which the premaxillaries become more pointed 

 forward and the dentaries become slightly pro- 

 duced and slenderized, but not to a degree fully 

 warranting the designation of either jaw as a 

 beak. In contrast with Scomberesox and Nanich- 

 thys, the snout does not further increase in rela- 

 tive length after the fish reaches the standard 

 length of about 50 mm i Figure 2 ). In contrast, the 

 snout increases in relative length throughout the 

 life span of Nanichthys and in Scomberesox until a 

 length of about 200 mm has been attained. 



Next in the series we may rate the largest, and 

 in many other respects the most extreme form, S. 

 saurus. Very small juveniles have a short muzzle, 

 with the lower jaw, as in all the species, the 

 heavier (Figure 2). Very early the jaws both be- 

 come sharper forward and begin to elongate. The 

 process is initially somewhat more accelerated in 

 the lower jaw, but at no stage do the developing 

 beaks simulate the condition found in halfbeaks, 

 for the developing upper beak is always much 

 more than half as long as the lower. Liitken's 

 ( 1880) indication to the contrary resulted from his 

 inclusion of TV. sunulans into what he treated as 

 the developmental series of S. saurus (see p. 533). 

 In fact, the relative projection of the lower jaw 

 decreases but little with age (Figure 2). 



The most extreme ontogenetic changes in 

 physiognomy are displayed by the next-to-most 

 dwarfed form, N. simulans (Figure 2). Until it 

 reaches about 30 mm SL the jaws are scarcely 

 produced. Soon, however, the premaxillaries be- 

 come pointed forward and begin to elongate, but 



slowly. The dentaries become very slender and, in 

 juxtaposition, elongated forwai-d far beyond the 

 slender conjoined tips of the premaxillaries. When 

 the standard length has reached 60 mm, the lower 

 beak ofNanichthys, in contrast with Scomberesox, 

 is more than twice the length of the upper. 

 Nanichthys thus displays the closest approach to 

 the halfbeak condition, but it can hardly be said to 

 pass through a halfbeak stage, as do the belonids 

 and two genera commonly (Oxyporhamphus) 

 and/or regularly (Fodiator) placed in the Exocoe- 

 tidae (Lutken 1880; Nichols and Breder 1928; 

 Breder 1932, 1938; Hubbs 1933; Parin 1961). The 

 projection of the lower jaw as a proportion of 

 length offish increases sharply with age, at least 

 for the usual standard lengths of about 90 mm in 

 the specimens available to us. 



PHYLOGENY 



Only two extant genera of the family Scom- 

 beresocidae, Scomberesox Lacep'ede 1803, and 

 Cololabis Gill 1895, have been recognized. They 

 have been differentiated primarily on the basis of 

 the degree of development of the jaws into beak- 

 like structures; in Scomberesox each jaw is 

 definitely prolonged, very slender, fragile, and 

 elongate, whereas in Cololabis the jaws remain 

 short, less fragile, and only moderately pointed 

 (Figures 1, 2). In each genus the lower jaw projects 

 slightly beyond the upper. Both genera comprise 

 slender, elongate fishes, bearing, as do the unre- 

 lated Scombridae, a file of separated finlets that 

 largely fill the interval between the caudal fin and 

 the main parts of the dorsal and anal fins. Scom- 

 beresox attains a standard length rarely in excess 

 of 450 mm, although there are undocumented re- 

 ports of 500 mm. Cololabis reaches about 350 mm 

 SL. 



Despite the several expressed opinions to the 

 contrary (below), we regard the merely pointed 

 muzzle, with projecting chin, as in Cololabis and 

 Elassichthys (Figure 2), as a primitive feature, 

 and as also in Arrhamphus, Chriodorus, and 

 Melapedalion of the halfbeaks. We also regard the 

 beaks of Scomberesox and Nanichthys as deriva- 

 tive therefrom. Jordan and Evermann (1896) 

 surmised that Cololabis "represents the immature 

 state of Scomberesox" — a view repeated by others 

 of that school. Schlesinger (1909) definitely 

 treated the jaws of Cololabis as secondarily 

 foreshortened. Nichols and Breder ( 1928) went so 

 far as to characterize Cololabis as "... a recogniz- 



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