18 



G.J. HOWES 



Fig. 6. Melanonus zugmayeri: A, vomer in ventral view; B, nasal 

 of left side in dorsal view (broken outline indicates anterior nasal 

 opening; C, extrascapulars of left side in lateral view; 

 D, intercalar (left, lateral view). All from a specimen of 173mm 

 SL. 



flange rising from the base of the basioccipital (Fig. 7B). The 

 basioccipital is a trowel-shaped bone the blade of which forms 

 the posterior basicranium and the handle, the occipital 

 condyle (Figs 4,5,7). The supraoccipital (Figs 4A, 5A,B, 7) is 

 well-ossified and lies flush with the frontals, its crest confined 

 to its posterior margin; laterally, the bone is bevelled where it 

 meets the parietal. Posteriorly its ventral margin is bordered 

 by the exoccipital. 



The otoliths have been described and figured by Nolf & 

 Steurbaut (1983; 1989). 



Comments on cranial features 



Melanonus has a plesiomorphic ethmo-vomerine region, 

 namely a broadly rounded ethmoid lacking any dorsal eleva- 

 tion as in macrouroids and with a single, narrow point of 

 contact with the lateral ethmoid (Howes & Crimmen, 1990; a 

 more extensive area of contact appears to be a feature of 

 some supragadoids, Howes, 1990); a laterally expanded lat- 

 eral ethmoid which contacts the ascending process of the first 

 infraorbital ligamentously on its posterior face (Howes, 

 1987); vomer with a relatively short shaft and well-formed 

 teeth (absence of vomerine teeth in Macrouroidei and some 

 gadoids is considered independently derived; see Okamura, 

 1989; Inada, 1989; Howes, 1990). Ophidiiforms have as 

 broad a variability of the ethmovomerine region as gadiforms 

 but the lateral ethmoid is characterised by the presence of 

 basal twin facets which firmly unite with the large palatine 

 head. Furthermore, the lateral wing of the lateral ethmoid is 

 usually reduced and feebly developed, but always has a 

 lateral facet which articulates with the first infraorbital 

 (Howes, 1992). 



The frontals of Melanonus have a plesiomorphic gadiform 

 morphology; both gadoid and macrouroid taxa bear frontal 

 crests of varying development as do ophidiiforms and this 



may be a 'paracanthopterygian' feature. Howes (1990:79) 

 noted the lack of ventral frontal laminae in Melanonus and 

 considered this a derived condition associated with the ante- 

 rior displacement of the frontal area of the brain (see p. 27). 

 Ventral frontal laminae are widely distributed amongst ophi- 

 diiforms. There is no prominent V-shaped ridge pattern on 

 the frontals in Melanonus and no 'mucosal' cavity, a feature 

 of supragadoids. 



Nasal bones are plesiomorphically separated in the midline 

 but in macrouroids are joined for most of their lengths, a 

 feature regarded as synapomorphic for the group (Iwamoto, 

 1989; Howes & Crimmen, 1990). Among gadiforms the size 

 of the nasals is variable but they are nearly always large, 

 trough-like bones containing two neuromasts. Among plesio- 

 morphic gadoids (e.g. Bathygadidae) the size of the nasals 

 approaches that of macrouroids but the bones remain sepa- 

 rated along the midline. The melanonid condition is thus 

 considered plesiomorphic although the nasal bones have a 

 distinct apomorphic shape which more closely approaches 

 that of some macrouroids than gadoids. 



The pterotic of Melanonus has a plesiomorphic gadiform 

 morphology and resembles that of Bathygadidae in being 

 broad with a rounded posterior margin and short hyomandib- 

 ular fossa (Howes & Crimmen, 1990, fig. 6). 



The pterosphenoid is unusually large for a gadiform; the 

 widespread condition (and among ophidiiforms) being small, 

 occupying the dorsoposterior region of the orbit and widely 

 separated from the lateral ethmoid. The enlarged anteriorly 

 extended bone is therefore considered autapomorphic for 

 Melanonus. The parasphenoid displays no particular derived 

 feature and corresponds with the situation in the majority of 

 gadiforms, namely a broad flat keel with parallel laminae 

 (Howes, 1990:81). 



The deeply incised trigeminal notch of the prootic resem- 

 bles most closely that of some Phycidae and the Muraenolepi- 

 didae, but unlike those taxa the anterior wall of the prootic is 

 directed medially as in most infragadoids and macrouroids 

 (Howes, 1990:82). The intercalar is small in comparison with 

 that in other gadiforms where in gadoids it is exceptionally 

 large covering the entire posterolateral cranial wall. A large 

 intercalar is one of the characters diagnostic of paracan- 

 thopterygians but is secondarily absent in lophiiforms and 

 batrachoidiiforms. Among ophidiiforms and percopsiforms 

 the intercalar is generally not as large as that of gadiforms, 

 and in those two former groups is confined to the upper half 

 of the posterior cranial wall and does not extend ventral to 

 the basioccipital anteriorly but is interrupted by the prootic. 



The relationship between the epioccipital and supraoccipi- 

 tal is an unusual one amongst gadiforms in that the posterior 

 walls of the exoccipitals meet across the midline and so 

 exclude the supraoccipital from contributing to the upper 

 margin of the foramen magnum. Elsewhere in paracan- 

 thopterygians this condition occurs among ophidiiforms 

 (Howes, 1992) where the exoccipital has enlarged backward 

 and upward to cover the posterior margin of the supraoccipi- 

 tal. Even in the largest cleared and stained specimen of M. 

 zugmayeri examined for this feature the ventral tip of the 

 supraoccipital does not reach the margin of the foramen 

 magnum (Fig. 7B). The supraoccipital lacks a dorsal crest, 

 there being a posterior lamina (Fig. 7). Howes (1990:82) 

 discussed the variability of the supraoccipital crest amongst 

 gadoids. An elevated cranial crest is possibly the plesiomor- 

 phic condition for paracanthopterygians but a low, reduced 

 crest is widely distributed amongst all groups and in lophii- 



