242 UPPER CRETACEOUS TELEOSTS 
Cretaceous, since there are no factors excluding the genus Enchodus from having been 
the immediate ancestor of Palaeolycus (Text-fig. 100). 
The Halecoidei are represented in the Lower Cenomanian by the most primitive 
genus Halec (d’Erasmo, 1946). Phylactocephalus occurs in the Middle Cenomanian 
and could easily have been derived directly from Halec at the end of the Lower 
Cretaceous. Hemisaurida also had its origins within the same basic stock, but would 
appear to have branched off at a slightly earlier stage than Phylactocephalus, since 
Hemisaurida is already represented in the Lower Cenomanian. The genus Halec 
remained the most generalized form and extended into the Senonian (Text-fig. 100). 
In the discussions of these fossil salmoniforms, I have attempted to show that they 
have evolved along lines represented throughout the division Protacantho- 
pterygii and to a more marked extent parallel the Myctophiformes and the 
Acanthopterygii. Each of the suborders dealt with earlier appears to express similar 
evolutionary capabilities. Within the recent Salmoniformes the Galaxioidei 
(Galaxias and Aplochiton) are often cited as being practically indistinguishable from 
the Myctophiformes especially with regard to the upper jaw (Greenwood, e¢ al., 
1966 : 366; Gosline, Marshall and Mead, 1966: 2). Thus a recent suborder 
reinforces the suggestion of the similarity in evolutionary potential between the 
fossil salmoniforms and the myctophiforms. It would seem that several of the 
salmoniform suborders have the potential, latent or expressed, to produce a more 
advanced structural complex which in most cases approaches the myctophiform 
grade. Thus the myctophiform grade (although it is proposed in this work that the 
order Myctophiformes is itself monophyletic) can be attained by other Salmoni- 
formes. 
The acanthopterygian complex of characters represents a considerable advance 
over and above the most advanced Salmoniformes and Myctophiformes. The 
major advances in feeding, locomotion and protection are exemplified by the 
protrusile upper jaw, thoracic pelvics, body shortening and deepening, and the 
development of spines in fins and on scales. These features are only encountered 
together in the single line stemming from the protacanthopterygian order Cteno- 
thrissiformes (Patterson 1964). (True protrusibility of the jaws never occurs in the 
Paracanthopterygi, although all of the other features listed above are shown.) The 
Ctenothrissiformes have been shown to be little removed from a basal salmoniform 
stock (Table I, p. 203) and also to be very similar to a basal myctophiform (e.g. 
Sardinioides). The common ancestry of these two groups (Ctenothrissiformes and 
Myctophiformes) occurs in the Lower Cretaceous. The Myctophiformes are well 
established by the Middle Cenomanian and would appear to have had their origin in 
the Albian. Nematonotus has been mentioned as being a genus which approaches 
both Myctophiformes and Ctenothrissiformes, substantiating the basal convergence 
of the two groups. Nematonotus occurs in the Cenomanian together with Acro- 
gnathus, which also approaches both groups. Sardinius, however is a probable 
derivative of the very early myctophiform lineage despite its late appearance in the 
fossil record (Upper Senonian). Sardinius closely parallels the family Myctophidae, 
particularly in the backwardly inclined suspensorium and the absence of supra- 
