282 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



CFR 



A Muraenolepis 



Fig. 144. Hypothesized acquisition of gadoid caudal structure from 

 condition in Muraenolepis (see text). X and Y bones shaded. Abbre- 

 viations: CFR: caudal fin rays; EP: epurals; HS: haemal spines; IH: 

 inferior hypural; NS; neural spine; PH: parhypural; PU,: first preural 

 centrum; R; radials; SH; superior hypural; U,: first ural centrum; U,; 

 second ural centrum. 



Dunn and Vinter, 1984, MS). Primary and total caudal fin ray 

 counts also exhibit some difference in symmetry and patterns 

 of evolutionary change. Morids are the only group of tailed 

 gadiforms that show noticeable asymmetry in superior versus 

 inferior secondary caudal rays (Table 76). Morids and some 

 phycines have relatively low total caudal fin ray counts (20-38) 

 and numerous groups have some genera with six primary caudal 



fin rays. Markle (1982) interpreted both of these as primitive 

 states. 



The caudal oi Muraenolepis differs from most other gadiforms' 

 in its complete continuity with both dorsal and anal fin rays 

 (Fig. 144A). It is virtually identical to that of the ophidiiform, 

 Brotula (Monod, 1968), differing only in number of rays sup- 

 ported by the parhypural (one vs. two). The typical gadoid 

 caudal fin skeleton is easily derived from the condition in Mu- 

 raenolepis, which we identify as the primitive state. The primary 

 requirement is the acquisition of X and Y bones and modified 

 spines of the first preural centrum, both sets of which must have 

 cartilaginous articulating surfaces entering into support of cau- 

 dal rays. X and Y bones are present in Muraenolepis as the 

 penultimate radials of the dorsal and anal fins. If the last radials 

 fuse with the spines of the first preural centrum, both sets of 

 preural caudal bones (with cartilaginous articulating surfaces) 

 are acquired. 



A second requirement is an interspace (lacking rays and ra- 

 dials) between the caudal fin and the dorsal and anal fins. This 

 condition could have been satisfied in one of two ways. Rays 

 (and their supporting radials) anterior to the X and Y bones 

 might have been lost, and subsequent changes in caudal ray 

 numbers would then involve the addition of secondary rays 

 lacking radials. A less parsimonious scenario involves the loss 

 of radials (only) anterior to the X and Y bones which leaves a 

 continuous dorsal-caudal-anal fin including some anterior un- 

 supported rays. In this case, further variation in numbers of 

 secondary caudal rays would involve both increases and de- 

 creases. The hypothesized ancestral gadoid condition is shown 

 in Fig. 144B. Presumably, this ancestor would have had 16 

 caudal fin rays (one each on X and Y bones, first preural neural 

 and haemal spines, each epural and parhypural, six on the 

 superior hypural and three on the inferior hypural). This total 

 is close to the lowest known (and presumably most primitive) 

 counts in certain morids (Table 76) and corroborates the sug- 

 gestion that higher counts in Melanonidae, Gadidae and Mer- 

 luccius are derived states brought about through the acquisition 

 of additional rays lacking radial support (Fig. 144C). In Brosme 

 this acquisition has resulted in a secondary elimination of the 

 caudal peduncle and an almost continuous dorsal-caudal-anal 

 fin (Markle, 1 982: fig. 7C). The acquisition of rays has apparently 

 occurred asymmetrically in some morids, where ventral sec- 

 ondary rays outnumber dorsal. 



Olfactory lobes.— J\\e position of olfactory lobes relative to na- 

 sal organs and the forebrain has been used as a systematic char- 

 acter in gadiforms by Svetovidov (1948, 1969) and Marshall 

 ( 1 965). This character develops during ontogeny since the bulbs 

 are close to the forebrain in young of all gadiforms (Rass in 

 Svetovidov, 1948; Marshall, 1965). It reaches the most derived 

 state adjacent to olfactory capsules in "nearly all of the Gadi- 

 dae," "most species of Macrouridae," Muraenolepis (Marshall. 

 1966b) and Merluccius (Inada, 1981b). Olfactory lobes are be- 

 tween the forebrain and olfactory capsules in Bregmaceros and 

 next to the forebrain in other merlucciids and Steindachneria 

 (Marshall, 1966b). 



We are not certain how to interpret the available information 



' The caudal fin of Macruromis novaezelandiae. though much reduced 

 in over-all size, is similar to that of Muraenolepis \n its confluence with 

 dorsal and anal fins. 



