262 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 135. Dorsal view of cranium in three genera of gadiform fishes; left. Rhinocephalus planiceps: center, Palaeogadus intergerinus; right, 

 Merluccius merluccius. From Fedotov ( 1 976). 



of the brain and used their advanced position, adjacent to the 

 nasal capsule, as his primary character for defining the Gadi- 

 formes. This is a derived character, which has been found also 

 in cyprinids, galaxiids, and mormyrids. Svetovidov noted that 

 the olfactory lobe is located in an intermediate position in the 

 gadid Raniceps. A posterior location of the lobe was subse- 

 quently recorded in Melanonus and several macrourids and an 

 intermediate location in merlucciids, Steindachneria, the gadid 

 Raniceps, and two macrourids (Marshall and Cohen, 1973). 

 Svetovidov ( 1 969) pointed out the size dependent nature of this 

 character, especially in Merluccius (which I have verified in M. 

 bilinearis and M. productus). Further investigation is required, 

 especially in species that mature at small sizes. 



V-shaped crest on skull.— As long ago as 1903b Regan noted 

 the shared presence in Merluccius and Macruronus of prominent 

 V-shaped ridges on the frontals, which converge on the supra- 

 occipital crest. These structures have subsequently been found 

 in the extinct genera Rhinocephalus and Palaeogadus (Fig. 135) 

 as well as in some fossil percopsiforms (Rosen and Patterson, 

 1969) and are present in varying degrees in Lyconus and Stein- 

 dachneria. 



Groups and Their Relationships 



In this section I briefly discuss those taxonomic units that I 

 think require consideration and explain as best possible the 

 reasons for their placement on Fig. 1 36. 



"Protocodus" is an unnamed species' from the Paleocene of 

 Greenland (discussed by Rosen and Patterson, 1969 and Fe- 



' The name "Protocodus" is used as a designation of convenience 

 and does not have formal, nomenclatural significance. 



dotov, 1 976; I too have examined it), which is the oldest known 

 non-otolith gadiform. It has a number of characters that may be 

 interpreted as primitive for the group, including five, slender, 

 well-separated hypurals, X-Y bones, numerous procurrent rays, 

 and a V-shaped ridge on the frontals. It has a dorsal and anal 

 fin configuration much like that of Merluccius (Rosen and Pat- 

 terson, 1969). 



Muraenolepis is a highly distinctive genus with four or more 

 species. It has such primitive characters as a single anal and 

 long-based second dorsal fin, a dermal basibranchial plate (Ro- 

 sen and Patterson, 1969), the similarity of the lower hypurals 

 to pterygiophores and to caudal fin elements, and a free first 

 neural spine. Derived characters include 12-14 pectoral radials, 

 a single epural, first dorsal fin a single-rayed anteriorly placed 

 filament, vertical fins confluent around the tail, an oblique pat- 

 tern of squamation, and modifications of the first neural spine. 

 Muraenolepis is not obviously related to any other gadiform 

 and appears to represent an ancient lineage. 



Bregmaceros is another distinctive genus with no obvious 

 close relatives. Like Muraenolepis it retains a dermal basi- 

 branchial plate, but this is a primitive character, as is possession 

 of a uroneural and a set of X-Y bones in the tail. Derived 

 characters include the conjunction of the first neural spine with 

 the occipital crest, a large consolidated hypural plate supporting 

 many branched rays, a unique lateral line system, only two 

 pectoral radials, and a long dorsal ray on top of the head. The 

 tropical pelagic habitat of these fishes is also different from that 

 of any other gadiform. If fusion of the first neural spine with 

 the occipital crest has occurred only a single time, then Breg- 

 maceros must have originated after Rhinocephalus. 



Rhinocephalus is an Eocene fossil, the skull of which has been 

 described in some detail and compared with other gadiforms 

 by Rosen and Patterson ( 1 969). They mention and illustrate a 



