Anatomy of the Melanonidae (Teleostei: Gadiformes), with comments on its phylogenetic relationships

21 Pages·1993·9.1 MB·

by  Gordon J Howes

Bull. nat. Hist. Mus. (Zool.)59(1): 11-31 Issued24June 1993
Anatomy of the Melanonidae (Teleostei:
Gadiformes), with comments on
its
phylogenetic relationships
GORDON HOWES
J.
DepartmentofZoology, The NaturalHistory Museum, CromwellRd, London SW75BD
CONTENTS
Introduction 11
Materialsand methods 12
Abbreviationsusedin the figures 12
Anatomy 13
Neuromastpattern 13
Infraorbitals 14
Cranium 16
Jaws 19
Palatopterygoquadrate 20
Hyoidarch 21
Opercularbones 22
Branchialarches 22
Pectoralgirdle 23
Pelviegirdle 24
Vertebralcolumn and median fins 25
Brain 27
Swimbladder, viscera and body musculature 28
Discussion 28
Acknowledgments 30
References 30
Synopsis. The osteology and part of the soft anatomy of the gadiform family Melanonidae, represented by the
genusMelanonusGiinther, 1878, isdescribed. Melanonushasseveralderived(autapomorphic)sensoryfeaturesbut
only three osteological ones. Although contained within the Gadiformes the family is excluded from both the
Macrouroidei and Gadoidei in lacking a modified palatine and enlarged intercalar and thus represents their
sister-group designated as the Melanonoidei. The Suborder Gadoidei now comprises two families of uncertain
phylogeneticaffinity (Bathygadidae and Steindachneriidae) andtwoSuperfamilies, Moridoidea andGadoidea.
INTRODUCTION the posteriorposition (at the forebrain) ofthe olfactorybulbs
and a relatively unmodified caudal fin skeleton. The features
Marshall & Cohen (1973) used to diagnose the Melanonidae
The gadoid genus Melanonus Giinther 1878 contains two restedon softanatomicalfeatures,viz. anelaboratesystemof
species, M. zugmayeriGiinther, 1878(Fig. 1), and M. gracilis free ending neuromasts on the head and the corpus cerebelli
Norman, 1930, which together give a broad latitudinal, extending (forward) to the optic tectum.
circumglobaldistribution (Cohenetal., 1990;Howes, 1991a). Apart from a few observations on the caudal fin skeleton
Melanonus are relatively small fishes, the largest seen being and gill-arches and a description of its cranial muscles (see
230mm total length and, oddly for gadoids, are meso- below) the anatomy of Melanonus has never properly been
bathypelagic (100-3000m). Outwardly, Melanonus resembles described. Gosline (1971) complained that "No account of
astomiatoidratherthanagadoidfishwithitsdarkcoloration, theosteologyisavailable. Bycontrastthefamily Gadidae has
large, strongly-toothed jaws and tapering body (Fig. 1). received more attention from anatomists than almost any
Until Marshall (1965) recognised (without diagnosis) a other family of fishes". Despite these shortcomings several
separate family for the genus, Melanonus had been consid- assertions as to the phylogenetic position ofthe Melanonidae
ered to belong to the Moridae. Marshall (1965) and Marshall have been made.
& Cohen (1973) contended that Melanonus was the most Rosen & Patterson (1969) cited Marshall (1965; 1966) to
primitive gadiform (anacanthine) fish, a contention based on the effect that Melanonus represents a primitive gadoid.
HOWES
12 G.J.
JR &i
••'.' ' ^ ^B *
B 5*g. ^? ^fl ^^^^5
^^gMM
^^HbLv\ II ^aJJ* wm. •/
- V.'/ _^^^b
fig%£
--iaitt*^
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pupil
r^^^K H^^H^^I IPJUli II r K^^HrjlHti-HE^lB^^
Fig. 1. Melanonuszugmayerispecimen BMNH 1991.7.9:729-30, 200mm SL, lateralview.
Schwarzhans (1980; 1984) combined the Melanonidae and SL, dryskullpreparedfrom 190mmSL,49°21.9'N, 11°51'W,
Moridae (produced as a cladogram in Patterson & Rosen, 1090-llOOm; 1987.1.21:597, 168mm SL, S.W. Bantry,
1989) and Cohen (1984) and Fahay & Markle (1984) also 960-920m; 1981.3.16:377, 173mm SL, West Great Sole
suggestedarelationshipwiththeMoridae, againbasedonthe Banks; 1987.1.21:598-601, 175, 187, 193mm SL, one speci-
primitive arrangement of the caudal fin skeleton. Markle men, 165mm SL (cleared and stained), 50°02'N, 11°22'W,
(1989) revised his earlier views and placed the Melanonidae 910-980m; 1930.1.12:943 (Holotype) 13°58'S, 11°43'E. Mel-
near the base ofhis cladogram making it (with the exception anonus gracilis 1887.12.7:22 (Holotype) 147mm SL, Antarc-
of the Ranicipitidae) the sister group of all other gadiforms. tic; 1930.1.12:934-936, 97, 140, 150mm SL, 46°56'S,
Nolf & Steurbaut (1989) placed Melanonidae as an unre- 46°03'W; 1988.11.4:13-20, 45, 49mm SL (cleared and
solved polychotomy with the Euclichthyidae, Macrouridae, stained), 35°13'-34°57'S, 17°50'-17° 48'E; 1988.11.4:2,
Moridae and other gadoids. Okamura (1989) omitted the 145mm SL, 50°17.7'S, 18°40.9'E, 300-150m; Percopsis omis-
family from his gadoid classification but implied (p.137) on comayus 1973.3.20:46-8, 52mm (cleared and stained), 62mm
the basis of similar anterior rib structure that Melanonus is SL, Lac Henry, Quebec, Canada; Bregmaceros sp.
closelyrelated toMerluccius. Howes (1989; 1990) also placed 1957.12.2:5-12, 54mm SL (cleared and stained) Senegal;
Melanonidae in an unresolved polychotymy, with Stein- Gaidropsarusmediterraneus Uncat. 122, 145mm (cleared and
dachneriidae, Bathygadidae and othergadoids. According to stained), Seaton Point, England.
Howes (1990, 1991a & b) the majority of gadoid families In addition, material listed in Howes (1988, 1992) and
form a monophyletic assemblage termed 'supragadoids', Howes & Crimmen (1990) was re-examined.
characterizedbycomplete fusion ofthe upperhypuralsinto a
single plate. The Macruronidae represent the plesiomorphic
Abbreviations used in the figures
lineageofthis assemblagewiththe Gadidae and Merlucciidae
being the most derived families. The Melanonidae was
aa anguloarticular
assigned with the Bathygadidae, Steindachneriidae, Moridae aap premaxillaryarticularprocess
and Euclichthyidae to the 'infragadoids' and in one scheme ac actinost
(Howes, 1991b) in alternative positions, one as the sister afc anteriorfrontalcrest
group to all gadoids excluding the Bathygadidae and Stein- ap premaxillaryascendingprocess
dachneriidae, the other as also excluding the Moridae. The ar anterior('chopstick-like') ribs
characters on which these phylogenetic positions were based ard analfin radial
are, however, ambiguous (see Discussion) and like all previ- asp autosphenotic
ousstudieshavesufferedfrom lackofanatomicalinformation bb basibranchial (numbered)
bh basihyal
about Melanonus. The following is an account ofthe osteol-
bl Baudelot'sligament
ogy and other soft anatomical features ofMelanonus.
bo basioccipital
boc basioccipitalcondyle
br branchiostegalray
MATERIALS AND METHODS cb ceratobranchial(numbered)
cc cerebellarcorpus
ccr cerebellarcrest
Specimens used for anatomical descriptions (all from BMNH cfc centralfrontalcrest
cl cleithrum
collections): Melanonus zugmayeri Uncat. 230mm, 'Discov- cm coronomeckelianbone
ery' Stn 11550, 10.VII.1987, 20°25.5'N, 19°39.5'W, CO coracoid
775-825m; 1991.7.9:729-730, 220mm, 95mm SL, de dentary
20°25.8'N-31.4'N, 19° 39.8'W-38.0'W, 800-875m; dex dorsalsectionofepaxialismuscle
1991.7.9:731-733, cleared & stained, 66, 100, 130mm SL, dhy dorsohyal
17°1.2'N, 19°57.8'W, 400-495m; 1987.1.21:595-596, 215mm dr dorsalfinray
ANATOMY OFTHE MELANONIDAE 13
dorsalfin radial pc postcleithrum
epibranchial (numbered) pfc posterior(diagonal) frontalcrest
epibranchial toothplate phy posterohyal
ectopterygoid pmp postmaxillaryprocessofpremaxilla
erectoranddepressordorsalismuscles pop preopercle
entopterygoid PP parapophysis
epural prn prooticnotch
epineural ps parasphenoid
extrascapular psl parasphenoidascendinglaminae
epioccipital pte pterotic
exoccipitalcondyle pts pterosphenoid
exoccipitalcartilage ptt posttemporal
exoccipitalflange pu preuralvertebra (numbered)
exoccipital pyc pyloriccaeca
foramen forglossopharyngeal nerve qu quadrate
foramen forvagus nerve ra retroarticular
facial lobe Rcl ramuscanalislateralisnerve
foramenmagnum rd retractordorsalis muscle
foramen foroccipital nerves re rostrodermosupraethmoid
frontal sb swimbladder
flexorverttrailsmuscle sbp swimbladderpocket
flexorventralisinferiorismuscle sc scapular
granulareminence sea supracarinalisanteriormuscle
gas-gland scl supracleithrum
gonad so supraoccipital
gut sop subopercle
haemal arch spt intercalarsocket forposttemporal limb
hypobranchial (numbered) St stomach
hyomandibularfossa sy symplectic
hypophysis ul uralcentrum
hypural (numbered) V vertebra (numbered)
interarcualcartilage vex ventralsectionofepaxialismuscle
intercalar vhy ventrohyal
interhyal vo vomer
infraorbitals (numbered)
interopercle
interradialis muscle
ANATOMY
kidney
lateralethmoid
liver
lateralethmoid-palatine ligament Neuromast pattern (Fig. 2).
mandibular-interopercularligament
trigeminal lobe Melanonus has a unique pattern of free-ending neuromasts
Meckel'scartilage coveringthe head in addition to those more usual neuromasts
mesonephricduct contained in the sensory canals. There are two morphotypes
mesethmoidcartilage of the former: 1) the most numerous, are long, flange-like
metapterygoid
structures which occur on the skin covering the upper rim of
myoseptalstrandssupportingribs
the infraorbitals, the snout, cheek muscles, preoperculum
medullaoblongata
cranial nerves and top of the head; 2) button-like structures confined to
nasal specific areas on the lowercheek, snout and frontal.
firstneural arch The flange-like neuromasts are usually arranged longitudi-
nervebranchservingadductorarcuspalatinimuscle nallyand more orlessin rows. In thesnout region, individual
acoustic nerve neuromasts may be slightly curved or angled to the general
buccalisbranchoftrigeminal trunk directionoftheothers(Fig. 2B). Ontopofthehead, rowsare
infraorbital branch oftrigeminal trunk more definite and those on the snout tend to converge
lateralline nerve anteriorly where the organs close to the midline are larger
nneeruvreomoafstsusprtayoprebsit1aalndbr2anch innervating posterior canal than the others (exceptional is the star-shaped arrangement
enclosed neuromast posterior to the medial extrascapular sensory pore in M.
nasal rosette zugmayeri); the neuromasts close to the midline on the
supraorbital branchoftrigeminal central part ofthe frontal are also nearly twice the length of
olfactorybulb the others (Fig. 2A). In M. zugmayeri the neuromasts along
opercle the anterior part ofthe supraoccipital have a regular arrange-
olfactorytract ment (Fig.2A) but in M. gracilis they form a pocket or
parietal enclosed area. Distribution on the preoperculum is irregular
parhypural and sometimes sparse (the skin is often missing from this
ppeallvaitcinbeone region and it is not possible to make precise counts).
pharyngobranchial (numbered) The pitlines ofbutton-like organs are in a double row near
the border of the snout, in a patch above the nares, as an
#
HOWES
14 G.J.
nml
'V'/.V
' iflll
/' n \i'
i.
, ;
M ''Hi M/
• 1 1 -|
// ///// I ,'
1
I I J ' I 1, •» /' ' \
-\
X
*-. /
' ' ' 'i/l / \
w
i \ /
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-3
l
Fig. 2. Distributionofneuromaststypes 1 and2in A, Melanonuszugmayeriondorsalsurfaceofheadand B, M. gracilisonlateralsurface
ofhead. C, innervationpatternoftype 1 neuromastsinsubnasalregion (rightside) ofM. zugmayeri(dashed linesindicate nerves, arrow
headsindicateterminationofnervebranch; large arrowpointsanteriorly). In thisandsubsequent figures, scale barsin millimetre divisions.
oblique row across the lower part ofthe cheek and a double pterotic, one in the parietal, one in each extrascapular, three
row across the epioccipital region (Figs 2A,B). The neuro- in the first infraorbital, one in the second, third and fourth,
masts do not extend backwardson tothe body. two in the fifth and one in the sixth, and five in the
There are about 500 flange-like neuromasts covering the preoperculum.
entire head. Innervationisbythe ramuscanalislateralis (Rcl
sensu Freihofer, 1970) which exits from the posterior frontal Infraorbitals (Fig. 3).
foramen to anastomose through a loose fascia of connective
tissue. The neuromasts are innervated by subranches stem- There are six infraorbital bones, the first long and relatively
mingfrom acomplex nerve network (Fig. 2C). deep with a broadly fretted ventral border, the outer flange
The Rcl nerve branchesfrom the supraorbital trunk ofthe which forms the roof to the sensory canal extends as a shelf
trigeminal complex, (Fig. 17), a condition similar to that in along the anterior halfofthe bone, but curves laterally along
Merluccius (Freihofer, 1970). The branch innervating the the posterior half. The ascending process which contacts the
large posterior neuromasts enclosed in the frontal sensory posteriorwallofthelateralethmoidistallandspine-like. The
canal detaches separately from the supraorbital trunk, second infraorbital is confluent with the first and is as deep
whereas in Merluccius the nerves separate offtogether. butonly asixthofitslength. The medial laminaofthe thirdis
The large, plate-like neuromasts, housed in the sensory widely separated from that of the second although the
canalsnumbertwointhenasalbone, threeinthefrontal(one dorsolateral flange is nearly in contact. The third together
beneath the anterior medial ridge, one beneath the lateral with the fourth form the posteroventral corner of the orbit
arch and one posteriorly), one in the anterior part of the and the fourth has only a short orbital margin and flange
ANATOMY OFTHE MELANONIDAE 15
Fig. 3. Infraorbital bonesofM. zugmayeriinspecimensof: A, 66mmSL; B, 100mm SLandC, 130mm SL.
posteriorly, the body of the bone is expanded. The fifth Unlike other gadiforms where the posterior (fifth and
infraorbital has a longorbital margin, the lowerpartofwhich sixth) infraorbitals are shallow, those of Melanonus are as
projects anteroventrally in front ofboth the third and fourth deep as the anterior ones. The anterior curvature of the
to which it is connected by strong connective tissue; it has a upper infraorbital (dermosphenotic) is more reminiscent of
narrow flange along its upper orbital border. The sixth some macrouroids (see below) than gadoids. The central
(dermosphenotic)isas largeasthefifthandhasapronounced position of the ascending process of the first infraorbital is
orbital curvature which brings its anterior tip to the same probably a plesiomorphic gadiform feature (on the basis of
vertical plane as the ascending process of the first infraor- commonality) as is the reduced size of the second infraor-
bital. bital. The extension ofthe lower part ofthe fifth infraorbital
In the two smaller specimens of M. zugmayeri examined, and the enlargement of the dermosphenotic are, because of
thedorsolateralflangeremainsundevelopedonthefirst, fifth their restricted distributions, taken to be derived features.
and sixth infraorbitals of the 66mm specimens and the According to Iwamoto (1989) among macrouroids, exclusion
ascendingprocessofthefirstinfraorbitalisinclinedanteriorly ofthethirdandfourthinfraorbitalsfromtheorbitisaderived
in both (Fig. 3A). The anteroventral border of the fifth condition. In Melanonus similar exclusion has resulted from
infraorbital is less pronounced and in the 100mm SL speci- ventral extension of the fifth infraorbital whereas in the
menitstipliesmedialtotherimofthefourthinfraorbital;the macrouroids illustrated by Iwamoto (1989, fig. 5G) it is due
sixth lacks the anterior elongation of the larger (130mm SL) to re-alignment of the fourth infraorbital which covers the
specimen (Figs 3B, C). orbital borders ofthe second and third.
HOWES
16 G.J.
me
esc
so
Fig.4. NeurocraniumofM. zugmayeriinA, dorsal andB,ventralviews. In A, the rightparietal, rightnasal and leftposttemporal have
beenremoved. InB, dashedoutlinecircleson the prooticandintercalarindicate the positionsoftheotoliths.
Cranium (Figs 4-8). medial wall extends backward to directly contact the
pterosphenoid.
Initsoverall shape the cranialroofis almostsquare, the most The nasals (Fig. 4A) are large, almostentirelycoveringthe
noticeable feature being the deep indentation of the lateral lateral ethmoid and are narrowlyseparated from one another
frontal border anterior to the sphenotic, and the prominent in the midline by the rostrodermosupraethmoid. Each bone
anterolateral projections of the lateral ethmoid wings has prominent anterior and posterolateral processes, two
(Fig. 4A). dorsal processes, lateral and medial, are folded inward to
The ethmoiddorsal surface (rostrodermosupraethmoid) is, form curved flanges which support the skin roofing the
in keeping with that of other gadoids (Howes & Crimmen, sensory canal. In large specimens the nasals tend to become
1990: 166), being narrow and cruciform with a steep anterior narrow with attrition ofthe anterior process (Fig. 6B).
slope (Fig. 5B). The ossified anterior wall of the ethmoid Thefrontalsare nearlysquareexceptthattheposteriorhalf
forms most of the nasal cavity and a thin, vertical septum of of the lateral border is deeply indented. Anteriorly, close to
A
ethmoid cartilage separates the cavities medially. shallow the midline is a high, arch-shaped crest (afc, Fig. 4A), a
bed of cartilage separates the base of the ethmoid and the similar but longer arch is situated in the centre of the bone
vomer. The vomerhasathick, broadly roundedhead bearing and is sometimes divided into two separate crests (cfc.
on either side 6 or 7 teeth in smaller specimens and 10-12 in Figs 4A, 5B), posteriorly is a low, diagonal crest (pfc,
larger(Figs 4B,6A). Insmallerspecimensofbothspeciesthe Fig. 4A). All these crests shelter a neuromast foramen and
teeth are more or less arranged in a single row but in larger serve to support the skin covering the frontal canal system.
specimens the posterior teeth tend to be in a patch with one Posteriorly, the frontal margin meets the pterotic, is over-
or two stout and caniniform being almost twice the length of lapped by the parietal and partially overlaps the anterior
their neighbouring teeth and three times that ofthe symphy- border of the supraoccipital. There are no ventral frontal
seal teeth (Fig. 6A). The vomerine shaft is relatively short, laminae. The parietals (Figs 4A, 5B) are thin, near-diamond
extending to just beyond the posterior level of the lateral shaped bones each with a single neuromast foramen and
ethmoid. The base of the lateral ethmoid is long and broad posterolaterally covered by the median extrascapular. There
and where it meets the vomer bears a deep cavity into which is no parietal crest.
inserts the palatine ligament. The wall ofthe lateral ethmoid The autosphenotic (Figs 4A,B, 5B) has a prominent,
is thin and projects forward at an angle of45°. The postero- bluntly rounded lateral process and is overlapped by the
ANATOMY OFTHE MELANONIDAE 17
SO
esc
exo
pro f/X bo v1
Fig. 5. NeurocraniumofM. zugmayeriin A, posteriorand B, lateralviews. In B, theintercalarisunshaded, the marginsofthe bones
underlyingit indicated bydashed lines. C, parasphenoidof66mm SLspecimen indorsalview.
frontal, parietal and pterotic. The underside of the bone Theprootics (Figs 4B, 5B) are large with a deeptrigeminal
bears a deep, almost transverse fossa into which articulates notch. The posterior border of the bone is rounded and
the hyomandibular. The pterotic (Figs 4A,B, 5A,B) accom- partially overlapped by a relatively small, ovoid intercalar to
modates the posterior portion of the hyomandibular fossa which is attached the inferior limb of the
along a third ofits lateral border. The wall of the pterotic is posttemporal(Figs 4B, 5A,B, 6D). The small, pinnacle-like
somewhat bullate and its cranial surface forms a prominent epioccipitals contact the posterolateral margins of the
lateral shelf. supraoccipital and posteriorly the dorsal borders of their
Thepterosphenoid (Figs 4B, 5B) is long and deep forming respective exoccipitals; laterally each epioccipital is overlain
most of the dorsomedial wall of the orbit, anteriorly it by the second extrascapular (Fig. 4A).
contacts the frontal and posteriorly the autosphenotic and The exoccipitals are deeply depressed posteriorly and con-
prootic. The parasphenoid (Figs 4B, 5B,C) has a broad keel tainalarge, backwardlyfacingvagusforamen (Figs 5A,B, 7).
with, extendingfromitscentre, along, lowascendingprocess Medially, the bones meet across the midline by flange-like
which extends laterally at a low angle to the horizontal plane projections. Posteriorly there is an ovate, cartilage-filled
to meet the prootic; paired, parallel laminae rise from the process the base ofwhich meets its antimere in the midline.
central region of the keel to meet the bases of the lateral Inside each exoccipital a long, ventrally directed process
ethmoid wing (Fig. 6). extends from the medial surface to contact a shallow dorsal
HOWES
18 G.J.
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
ofsupragadoids.
Nasal bones are plesiomorphically separated inthe 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 containingtwo neuromasts. Amongplesio-
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 ofsome macrouroids than gadoids.
The pterotic of Melanonus has a plesiomorphic gadiform
morphology and resembles that of Bathygadidae in being
broadwith aroundedposteriormargin andshorthyomandib-
Fig. 6. Melanonuszugmayeri: A,vomerinventralview; B, nasal ularfossa (Howes & Crimmen, 1990, fig. 6).
ofleftside in dorsalview(brokenoutline indicatesanteriornasal The pterosphenoid is unusually large for a gadiform; the
opening; C, extrascapularsofleftsidein lateralview; widespread condition (and among ophidiiforms) being small,
D, intercalar(left, lateralview). Allfrom aspecimenof 173mm occupying the dorsoposterior region of the orbit and widely
SL. separated from the lateral ethmoid. The enlarged anteriorly
extended bone is therefore considered autapomorphic for
flange risingfrom the base ofthe basioccipital (Fig. 7B). The Melanonus. The parasphenoid displays no particular derived
basioccipitalisatrowel-shapedbone the bladeofwhichforms feature and corresponds with the situation in the majority of
the posterior basicranium and the handle, the occipital gadiforms, namely a broad flat keel with parallel laminae
condyle (Figs4,5,7). Thesupraoccipital (Figs 4A, 5A,B, 7) is (Howes, 1990:81).
well-ossifiedand liesflush with the frontals, itscrestconfined The deeply incised trigeminal notch of the prootic resem-
toitsposteriormargin; laterally, theboneisbevelledwhereit blesmostcloselythatofsome Phycidaeandthe Muraenolepi-
meets the parietal. Posteriorly its ventral margin is bordered didae, but unlike those taxathe anteriorwall ofthe prootic is
by the exoccipital. directed medially as in most infragadoids and macrouroids
The otoliths have been described and figured by Nolf & (Howes, 1990:82). The intercalar is small in comparison with
Steurbaut (1983; 1989). that in other gadiforms where in gadoids it is exceptionally
A
large covering the entire posterolateral cranial wall. large
Comments on cranialfeatures intercalar is one of the characters diagnostic of paracan-
thopterygians but is secondarily absent in lophiiforms and
Melanonus has a plesiomorphic ethmo-vomerine region, batrachoidiiforms. Among ophidiiforms and percopsiforms
namely a broadly rounded ethmoid lacking any dorsal eleva- the intercalar is generally not as large as that of gadiforms,
tion as in macrouroids and with a single, narrow point of and in those two former groups is confined to the upper half
contactwith the lateral ethmoid (Howes & Crimmen, 1990; a of the posterior cranial wall and does not extend ventral to
more extensive area of contact appears to be a feature of the basioccipital anteriorly but is interrupted bythe prootic.
some supragadoids, Howes, 1990); a laterally expanded lat- The relationship between the epioccipital and supraoccipi-
eral ethmoid whichcontacts the ascendingprocessofthe first tal is an unusual one amongst gadiforms in that the posterior
infraorbital ligamentously on its posterior face (Howes, walls of the exoccipitals meet across the midline and so
1987); vomer with a relatively short shaft and well-formed exclude the supraoccipital from contributing to the upper
teeth (absence of vomerine teeth in Macrouroidei and some margin of the foramen magnum. Elsewhere in paracan-
gadoids is considered independently derived; see Okamura, thopterygians this condition occurs among ophidiiforms
1989; Inada, 1989; Howes, 1990). Ophidiiforms have as (Howes, 1992) where the exoccipital has enlarged backward
broadavariabilityofthe ethmovomerine region asgadiforms and upward to coverthe posterior margin ofthe supraoccipi-
but the lateral ethmoid is characterised by the presence of tal. Even in the largest cleared and stained specimen of M.
basal twin facets which firmly unite with the large palatine zugmayeri examined for this feature the ventral tip of the
head. Furthermore, the lateral wing of the lateral ethmoid is supraoccipital does not reach the margin of the foramen
usually reduced and feebly developed, but always has a magnum (Fig. 7B). The supraoccipital lacks a dorsal crest,
lateral facet which articulates with the first infraorbital there being a posterior lamina (Fig. 7). Howes (1990:82)
(Howes, 1992). discussed the variability of the supraoccipital crest amongst
The frontals of Melanonus have a plesiomorphic gadiform gadoids. An elevated cranial crest is possibly the plesiomor-
morphology; both gadoid and macrouroid taxa bear frontal phic condition for paracanthopterygians but a low, reduced
crests of varying development as do ophidiiforms and this crest is widely distributed amongst all groups and in lophii-
ANATOMY OFTHE MELANONIDAE 19
so rial
exca
boc
Fig. 7. Melanonuszugmayeriposteriorpartofcranium in lateraloblique viewof 130mmSLspecimenshowingin A, first neural archand
vertebraattached and in B, removedtoexpose the posteriorfeaturesofthe basi- andexoccipitals. Note thesupraoccipitaldoesnot
contributeto the borderofthe foramen magnum.
formsandophidiiformsappearsto be the common condition. irregular single row, numbering 22 in 88mm and 100mm SL
Itis assumed that thisfeature hasbeen repetitivelyevolvedin specimensofM. zugmayeri,2%in a 130mmand34in a 175mm
these groups. SLspecimen. Theanteriorteeth aresmallfollowedbyfouror
five successively larger ones, then four orfive relatively large
Jaws (Fig. 8) teeth separated by three orfoursmallerones. Posteriorly the
teeth diminish in size. The anguloarticular (Fig. 8G) is tall
The premaxilla (Fig. 8C) has tall, thin and widely separated with a steep posterior slope and short, vertical anterior
ascending and articular processes, and a tall, spine-like margin; the articular condyle is long and narrow. The coro-
postmaxillaryprocess. The toothedsurface isnarrow, bearing nomeckelian bone (Fig. 8G) is a well-developed, cylindrical
for most of its length two rows of sharp pointed teeth. The element with slight dorsal and ventral posterior flanges. The
outer row teeth are straight or extend slightly laterad, the retroarticular (Fig. 8G) is boot-shaped, the leg being curved
inner row teeth which are about twice the length ofthe outer forward and the foot long and shallow. A strong labial
areinwardlycurved;posteriorlythere arethreerowsofteeth, ligament is anchored to the rim ofthe dentary (Howes, 1988,
the ones ofthe centre row being the same size as those ofthe fig- 12).
inner(Figs 8D,E). In a 100mm SLspecimenofM. zugmayeri TheoveralljawmorphologyofMelanonusisplesiomorphic
the posterior teeth are so arranged as to form distinct for gadiforms, the upper jaw bones, apart from having a
transverse rows (Fig. 8F) but this is not evident in the 66mm smaller postmaxillary process of the premaxilla, are little
or 130mm SLspecimens. Themaxilla has atall articularhead different from those in bathygadids (Howes & Crimmen,
and a short medial articular process forming a rather acute 1990). Macrouroids are characterised by having a large
angle with the head (Figs 8A,B). The shaft of the bone is postmaxillary process of the premaxilla situated posteriorly
slender and posteriorly bears shallow dorsal and ventral (Okamura, 1970; Howes & Crimmen, 1990). There is no
processes. 'gadoid notch' at the base of the postmaxillary process. The
The dentary (Fig. 8G) isshortand deepwith acorrespond- lower jaw more closely resembles that ofgadoids or ophidii-
ing shallow mentomeckelian cavity; it has a high steep forms than macrouroids in having a relatively shallow angu-
coronoid process. The sharp pointed teeth are set in an loarticular and boot-shaped or J-shaped retroarticular.
20 G.J. HOWES
i^riWM^,^iHim'twr'iTrT«T*
cm
mc
Fig.8. Melanonuszugmayeri, jawbones. Aand B right maxillafroma 130mm SLspecimen in: (A) dorsal and (B) medialandslightly
ventralviews; C, premaxillain lateralview; D-Fpremaxilla, anterior(D) andposterior(E) regions from 130mm SLspecimen and (F)
100mmSLspecimen,ventralviews; G, lowerjawof130mmSLspecimenin medialview.
Macrouroids tend toward a deeper anguloarticular and The melanonidpalatine isunique amongstgadiforms, in its
greater variability in the shape of the retroarticular (Oka- length, nature ofcontact with the pterygoids, and in bearing
mura, 1970; Howes & Crimmen, 1990). A boot-shaped teeth. The common condition, and one which is considered
retroarticular is lacking in both percopsiforms and lophii- synapomorphic for gadiforms (p.29) is for the palatine to be
forms. reduced in length with a vertical or slightly angled posterior
border meeting a similar blunt margin of the ectopterygoid
Palatopterygoquadrate (Fig. 9) a19n8d9;foHromiwnegs,ah1i9n9g0e,-t1y9p9e1bj;oinHto(wseeesf&iguCrresiminmeOnk,am1u9r9a0),.1T9h7i0,s
Thepalatine(Fig. 9A,B) islong, itsposteriortipextendingto union differs from that commonly encountered in other
nearly halfway along the ectopterygoid, its rostral process is paracanthopterygians where the posterior limb of the pala-
long and slender and overlies the maxilla, its base bears a tine is attenuated and articulates firmly with the leadingedge
broad facet which articulates with the ethmoid cavity and the of the entopterygoid and lateral face of the ectopterygoid.
bodyofthebonerisestoahighposteriorcrest. There aretwo Percopsids resemble gadiforms in having a near vertical
rowsofsharply pointed teeth. abutment of the palatine with the ento- and ectopterygoids
The anterior part ofthe ectopterygoid (Fig. 9A) lies along (Fig. 9D). However, there is aposteriorstem which overlaps
the medial face of the palatine and its ventral stem reaches the upper lateral margin of the ectopterygoid. Macrouroids
the quadrate joint; laterally it is slightly overlapped by the are characterised by the lack of direct contact between the
entopterygoid (Fig. 9A). The latter is a relatively large bone palatine and ethmovomerine bloc (Howes & Crimmen,
with a rounded dorsal profile and is sloped mesad, its 1990).
posteriorborderiswellseparatedfromthe hyomandibularby Norman (1930) noted there were 'teeth on the pterygoid1,
the metapterygoid. The metapterygoid (Fig. 9A) is axe- an error perpetuated by Howes (1991b, caption to fig. 35).
shaped its posterior margin rising high up the leading edge of The pterygoid bones of Melanonus display plesiomorphic
the hyomandibular shaft. morphologies; the large entopterygoid and high posterior