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Records of the Western Australian Museulll 20: 187-198 (2001)_

Acanthodian microremains from the Frasnian Gneudna Formation,Western Australia

Kate Trinajstic

Department of Geology and Geophysics, The University of Western Australia,Nedlands, Western Australia 6907, Australia

Abstract - The scale variation seen in articulated acanthodian specimens(Dip/acanthus horndlls and Rhadinacanthus /ongispinus) from the NaturalHistory Museum, London IS illustrated to determine whether particular bodyregions on acanthodians dIsplay distinctive scale morphologies. This studyhas shown that, In the specimens observed, the head, shoulder girdle, lateralline, anterior flank, postenor flank, tail and fin spine insertion points are allcharacterized by different scale types. Isolated acanthodian scales found inresidues from the Gneudna Formation, Western Australia, are assigned todifferent body regions. Scales determined as coming from the same bodyregion were compared, and from these comparisons two speCIes,Acanthodidae gen. et sp indet. and Cheiracarzthus sp., have been recognized

The ratio of acanthodian scales to thelodont scales in different stratigraphlClevels in the type section was compared to determine if these ratios are areliable guide to the deposltional environment. A traditional environmentalinterpretation of the mlCrovertebrate ratios is not supported by lithologicalevidence or conodont abundance. It is concluded that the differences in thisratio do not add significant information for the interpretation on thedepositional environment of the Gneudna Formation.

INTRODUCTIONThe Acanthodii is a major group of Palaeozoic

fishes that occurs on all continents. They occur inrocks ranging from Lower Silurian to Permian age(Denison, 1979). Often acanthodians are known onlyfrom disarticulated material, with their scales and finspines commonly represented in microvertebrateassemblages (for comprehensive reviews seeDenison, 1979; Turner, 1991). Due to the rarity ofcomplete specimens, the overall morphology ofacanthodians is poorly known. The majority ofDevonian articulated material in the UnitedKingdom comes from the Welsh Borderland, theCaitlmess region, and Midland Valley of Scotland.Sites include: Turin Hill (Angus, Scotland),Achanarras County (Scotland) and Wayne HerbertQuarry, (south-west Herefordshire, England)(Watson, 1937; Miles, 1973). In Canada articulatedmaterial has been obtained from the DelormeFormation, Northwest Territories Wussel, 1951;Bernacsek and Dineley, 1 and the Escuminacl:ormation (Gagnier, 1996; Gagmer and Wilson,1996). Articulated material in Antarcbca has beenrecorded from the Aztec Siltstone, South VictoriaLand (Woodward, 1921; White, 1968; Young, 1989).In Australia enbre acanthodians have been foundnear Mt Howitt, Victoria (Long, 1983, 1986) andseveral articulated, but incomplete acanthodianshave been collected from the Bunga Beds of the

southern coast of New South Wales (Burrow, 1996).Through the study of articulated specimens,

considerable variation in the shape of scales, and inthe pattern of crown ornament, has been observedin many acanthodian species. Young (1995) carriedout one of the most comprehensive studies of scalevariation in acanthodians. In her study differencesin scale morphology were shown to be present innine taxa of Early and Middle Devonian articulatedacanthodian fishes from the British Isles. Otherarticulated acanthodians in which scale variationhas been recorded include: Machaeracal1thusbohemiws Gross (1973); Ptomacal1thus anglzcus Miles(1973) Vernicomaclll1thus waYl1ensls Miles (1973);Acal1thodes Zidek (1976, 1985); Poracan thodes l11el1l1eriValiukevicius (1992); Dip/acanthus ellsl andDip/acanthus striatus (Gagnier 1996); Kathemacanthllsrosu/el1tus and Cassidiceps vermlw/atll" Cagnier andWilson (1996). In disarticulated material intra-specific scale variation is harder to determme. Cross(1973) considered isolated scales Wells (1944) hadattributed to four species, to represent the scalevariation of one species, which he synonymized asCheiracantllOides comptus. Gross (1973) stated that itwas possible that different regions of the bodycould bear special forms of scales. He synonynuzedtwo scale types, that Wells (1944) had described astwo Acal1thoides spp., as Acal1thoides 7 dublinel1sis(Gross, 1973).

188 K. Trinajstic

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Acanthodian microremains from Frasnian Gneudna Formation 189

MATERIALS AND METHODSTo determine variation in scale morphology of

different body regions in acanthodians, fully andpartially articulated specimens at the NaturalHistory Museum, London were examined. Fouracanthodian taxa were studied. The difference inscale morphology of two acanthodians, Oiplacallt/lllshorridlls and Rhadillocallthlls IOllgispillllS, aredescribed. In addition, published descriptions of

acanthodian scale variation were used forcomparison.

'TI1e study is based on isolated scales from theCneudna FomBtion, Williambury Station, WesternAustralia. Scales described in this paper come fromthe residues of limestone digested in 10''\,acetic acid. The scanning electron micrographs weremade on a Philips 505 at the Centre for Microscopyand Microanalysis, The University of Western

• Homestead (HSD)

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Figure 2 Map of Western Australia showing the locality of the Gneudna Formation and the distrIbution of itsoutcrops.

190

Australia. Sections of scales were ground by handand examined under confocal and lightmicroscopes. Specimens from the GneudnaFormation have been deposited in the collections ofthe Western Australian Museum (WAM).

Comparative MaterialP61716 Rhadinacanthus longispinus Agassiz, 1844complete articulated specimen.P6188 Rhadinacanthus longispinus Agassiz, 1844complete articulated specimen.P6757 Diplacanthus horridus Woodward, 1892complete articulated specimen.P61859 a, b Cheiracanthus murchisoni Agassiz, 1835incomplete articulated specimen missing the head.In part and counterpart.

DESCRIPTION OF SCALE VARIATION INACANTHODIANS

Various trends in scale variation have beenreported in acanthodians (Miles, 1973; Young, 1995;Gagnier, 1996). With the exception of Watson (1937)who noted considerable variation of the scale sizeover the body of acanthodians and Gagnier andWilson (1996), who noted that scale size decreasedposteriorly in fin web scales, most studies (e.g.Miles, 1973; Valiukevicius, 1992) have concentratedon determining scale variation within species. Here,four articulated specimens from three differentgenera were examined to determine if somevariation is consistent at a higher taxonomic level.The scale variation present in two of the speciesexamined, R. longispinus and C. murchisoni, wasillustrated in Young (1995, figures 6, 9) and thevariation in the squamation of P. menneri wasdescribed by Valiukevicius (1992). The scalevariation present in D. horridus and additionalvariation noted in R. longispinus is described below.By comparing the variation in the squamation ofthese four genera, morphological scale features thatcharacterise different parts of the fish body havebeen established. Therefore, description of theunchanging scale features gives an indication of thebody position from which an individual scaleoriginated. By comparing scales from the samebody region, an indication of the variation within aspecies, and of the variation between species, canbe determined. As a result, more reliable estimatesof the numbers of acanthodian species present inmicrovertebrate assemblages can be realized.

Scale Variation in Diplacanthus horridusSeven distinct scale morphologies are identified

from different body regions of D. horridus, UpperDevonian, Scaumenec Bay, Canada. In additionthere are large dermal tesserae on the cranial roofand part of the narrow ring around the orbit. Thesize of the flank scales is, on the whole very similar,

K. Trinajstic

but they do decrease in size a little towards thedorsal and ventral surfaces and toward the tail. Thescales on the fin webs are extremely small, andbecome smaller as they are traced down toward themargin of the fin. The scales bordering the lateralline are enlarged but have the same shape as thoseabove and below them. The scales located belowthe lateral line and anterior to the pectoral fin spine(pfs) are high with a tumid base and well-definedneck (Figure 3). The crown is rounded anteriorlyand overhangs the base posteriorly. There is anornament of posteriorly converging ridges on thecrown surface. Scales above the lateral line and infront of the anterior dorsal fin (dfa) have anidentical crown shape and surface ornament; thebase, however is not as high as in scales below thelateral line (Figure 3A). Mid-flank scales at the levelof the anterior dorsal fin have a tumid base with awell-defined neck, and the crown overhangs thebase posteriorly. The ridges on the crown surface,however, extend only to the middle of the scale(Figure 3B). Scales anterior to the pelvic fin spine(pIs) are very high with the crown separated fromthe base by a well defined, constricted neck. At thejunction of the base with the neck, the base flareslaterally, extending beyond the width of the crown(Figure 3C). Scales anterior and posterior to theposterior dorsal fin spine (dfp) are also high with awell defined, constricted neck and lateral flaring atthe neck-base junction (Figure 3D-E). These scaleshowever, are not as high and the lateral basalflaring is not as extensive as in scales anterior to thepelvic fin spine. Ventral scales from around the analfin spine (af) (Figure 3E) are higher than dorsalscales from around the dorsal fin spine (Figure 3D).In contrast to anterior body scales the caudal bodyscales are relatively flat with a poorly defined neck.They are rounded anteriorly and posteriorly andthe crown does not overhang the base. The regionalvariation present on the caudal fin can be comparedto that of Acanthodes, in which four zones have beendescribed (Miles 1973).

Scale Variation in Rhadinacanthus longispinisThe scale morphologies evident in D. horridus

are also present in R. longispinis (MiddleDevonian, Old Red Sandstone, Cruaday, Orkney).However, the head is covered by irregular scalesand there is a transitional area between the headand body, which is covered by large, irregularlyarranged scales. The scales on the flank of the fishare similar in size. There is a reduction in thescale size towards the dorsal and ventral surfacesand toward the tail. The fin web is covered with amosaic of very small rhombic scales. The lateralline is bordered by enlarged scales similar inshape to the scales above and below them. Thescales located below the lateral line and anteriorto the pectoral fin spine (pfs) are high with a


cpis

E

Figure 3 Diplacanthid acanthodian showing the variation and position of scale types found on Diplacanthlls horridlls(after Denison, 1979).

tumid base and well-defined neck. The crown isrounded anteriorly and overhangs the baseposteriorly. There is an ornament of posteriorlydiverging ridges on the crown surface. There is asmall button on the centre of the scale base. Scalesabove the lateral line and in front of the anteriordorsal fin (dfa) have an identical crown shapeand surface ornament; but the base is not as highas in scales below the lateral line, and the buttonis absent. Mid-flank scales at the level of theanterior dorsal fin have a tumid base with a well-defined neck, and the crown overhangs the baseposteriorly. Scales anterior to the pelvic fin spine(pIs) are very high with the crown separated fromthe base by a well defined, constricted neck. Atthe junction of the base with the neck, the baseflares laterally, extending beyond the width of thecrown. Scales anterior and posterior to theposterior dorsal fin spine (dfp) are also high witha well defined, constricted neck and lateral

at the neck-base junction. Theseare not high and the lateral basal

flaring is not as extensive as in scales anterior tothe pelvic fin spine. Ventral scales from aroundthe fin spine are higher than dorsal scales fromaround the fin spine. In contrast to anterior bodyscales the caudal body scales are relatively flat

with a poorly defined neck. They are roundedanteriorly and posteriorly and the crown does notoverhang the base.

DiscussionSeveral morphological body scale features were

found to remain constant between these genera,and these allow the allocation of individual scalesto a particular body region. The scale morphologychanges gradually from the anterior region to thecaudal region in acanthodians, and from thelateral line to the dorsal and ventral margins.Because the morphological changes are gradual,several trends common to different genera ofacanthodians, have been identified. The anteriorflank scales of acanthodians have a high profile,and are rhombic in shape. The shape of the scalesprogressively changes from rhombic to elongatealong the flank, but they continue to have a highprofile. Towards the caudal region the scalesrevert to being short and rhombic again, thoughthey differ from scales from the anterior region inhaving a very low profile. In addition to thechange in scale shape, there is a correspondingreduction in the crown ornament (when present)from the anterior region to the caudal region (e.g.Diplacanthus striatus Agassiz, 1844; Cheiracanthus

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latus Egerton, 1861; EuthacantJzus macnicoli,Powrie, 1864; Parexus falcatus, Powrie, 1870; R.longispinus; and D. horridus). Acanthodians alsohave a number of specialised scales, particularlyaround the lateral line (Watson, 1937), theshoulder girdle (Miles, 1973) and the tail (Miles,1970). In addition there are specialised scalesaround the bases of the fin spines, but these scalesvary between genera. In Diplacanthus,Rhadinacanthus and Ptomacanthus these scaleshave a very high profile in comparison to otherbody region scales. The scales from around thebases of the dorsal fin spines have a higher profilethan scales from around the base of the ventralfin spines. The crown ornament on the scalesfrom around the base of the dorsal fin spines doesnot differ from the flank scales around them but;these scales have anteriorly flared bases with wellconstricted necks (R. longispinus and D. horridus,Figure 3). In Culmacanthus and Mesacanthus thebase of the fin spine is surrounded by enlarged,flat scales (Watson, 1937; Long, 1983).

SYSTEMATICS OF THE GNEUDNAACANTHODIAN SCALES

Order Acanthodida Berg, 1940

Acanthodida gen. et sp. indet.

Material ExaminedWAM 98.4.1; WAM 98.4.2 and 500 other complete

scales (WAM 99.8.69-74)

HorizonsKT Beds 4,12,20, 21A, 22, OFB (Figure 1)

Description of Morphotype 1 (Figure 4A-C)This scale is pale orange in colour with a thin

translucent crown. The outline of the scale isrhombic. The anterior edge does not overhang thebase (Figure 4A-B), but the posterior edgeoverhangs the base slightly. The tumid andrelatively high base is separated from the crown bya well defined neck There are concentric growthrings visible on the base.

Description of Morphotype 2 (Figure 4D-E)The outline of the scale is rhombic (Figure 40). It

is longer than scales of morphotype 1 (Figure 4A-B). The posterior edge of the unornamented crownoverhangs the base. The constricted neck is welldefined. Sharpey's fibre bundles are visible on themoderately high tumid base (Figure 4E).

Description of Morphotype 3 (Figure 4F-G)The scale shape is rhomboid; the crown is thin

and flat; the anterior edge is rounded and does not

K. Trinajstic

overhang the base (Figure 4F). There is no ornamenton the crown surface. The neck is well defined andseparates the crown from a low base. The base isshaped like a cross and there are visible Sharpey'sfibre bundles (Figure 4G).

Description of Morphotype 4 (Figure 4H-J)These scales are typically elongated in shape, the

crowns being longer than wide (Figure 41). Thecrown is thin with a shallow, mid scale depression.There are numerous pores opening onto the crownsurface. Anteriorly, the crown is rounded and levelwith the base (Figure 4H). The posterior edge of thecrown forms an acute angle and overhangs the base(Figure 41). There is a narrow, well-formed neckseparating the crown from the convex base (Figure4H-J). The neck is deeper posterioriy thananteriorly, and there is no ornamentation visible. Atthe contact between the base and neck, the baseflares to form a narrow ridge (Figure 4H-I). Thebase is higher than wide with clear Sharpey's fibrebundles visible (Figure 4H).

HistologyThere appear to be microscopic dentine tubercles

on the crown surface, similar to those described byDerycke and Chancogne-Weber (1995) (Figure 4C).There is a thick dentine layer on the crown (Figure4K) with straight dentine tubules directedcentripetally on the crown growth zones (Figure4L). In longitudinal section, long tubules of dentinecan be seen extending up the neck towards thecentre of each growth zone (Figure 4K). Theascending canals are narrow, not much wider thanthe dentine tubules. The base is of acellular bonepenetrated by numerous fine canals. Sharpey'sFibres are arranged in pyramidal layers in the base.

Allocation of Scales to Body RegionAlthough some acanthodians have scales with no

crown ornament, considerable variation in scalemorphology from different body regions is stillapparent. The shapes of scales from Ischnacanthusgracilis Egerton, 1861 were described by Young(1995) as rhombic, sub-rhombic or polygonal, beingrelatively flat to gently convex and smooth. Thissame variation in shape and height is seen in thescales referred here to Acanthodidae gen. et sp.indet. above. Comparisons with articulatedacanthodians (Young, 1995) suggest that the short,deep scales (morphotype 1) collected from theGneudna Formation are from the anterior regionsof the fish; the elongated, deep scales are from theflank regions (morphotype 2); the rhombic lowscales with the cross-shaped base are from caudalregions (morphotype 3); and the scales with thelateral extensions to the base are from around theinsertion points of fin spines (morphotype 4). As


Figure 4 Scales identified as Acanthodidae gen. et sp. indet. A-B, morphotype 1 - anterior body scales; C,microomament on crown surface; D-E, morphotype 2 - flank scales; F-G, morphotype 3 - caudal scales; H-J, morphotype 4 scales from around the base of the fin spine insertion points; K, saggital section of amorphotype 1 scale; L crown section of a morphotype 1 scale. Scale bars = 1.0 mm.

the different smooth-crowned morphotypes in theGneudna Formation samples correspond to variantsfound on an individual fish, they are assigned hereto a single species. However, this will remainconjecture until a complete articulated specimen isfound.

Taxonomic AssignmentThe scales are referred to the Family

Acanthodidae but are not assigned to any knowngenus or species. The assignment of isolatedunornamented scales to a genus or species isdifficult, due to a lack of diagnostic features. TheAcanthodidae gen. et sp. indel. scales describedhere, evoke the description of Acanthodes

guizhouensis Wang and Turner, 1985, in having anelongated posterior crown ending in an acute point,a slightly curved anterior margin and a depressionnear the centre of the crown. This species isrecorded from the upper Famennian of Morocco(Derycke-Khatir, 1994) and China (c. Deryckepersonal communication 1998) and the LowerCarboniferous of China (Wang and Turner, 1985).

There are several other genera erected forarticulated fish within the family Acanthodidae,including Mesacanthus Traquair, 1888, Protogon-acanthus Miles, 1966 and Traquairichthys Whitley,1933, which have unornamented scales and cannotbe distinguished from each other, based on onlyscale morphology. In addition to these is the genus

194

Acanthodes Agassiz, 1833 to which many isolatedunornamented scales have been referred in the past.Zidek (1976) considered Acanthodes as a nomendubium and Denison (1979) considered that manyDevonian scales attributed to Acanthodes are notfrom that genus. Gross (1973) stated that scalescharacteristized by unornamented crowns arefound repeatedly among members of theacanthodian radiation. Wang (1984) also consideredthat true Acanthodes only occur in lowerCarboniferous - Perrnian strata.

To date, the only articulated acanthodian knownfrom the Lower Frasnian of Australia isHowittacanthus kentoni Long, 1986, recently placedin its own family Howittacanthidae by Zajic (1995).This family is considered to be closely related to theAcanthodidae because of comparable features in thejaw (Zajic, 1995). Like members of the FamilyAcanthodidae the Howittacanthidae andMesacanthidae possess unornamented scales. ThisHowittacanthidae is represented by a single species,H. kentoni, and is only recorded from easternAustralia.

Family Cheiracanthidae Berg, 1940

Genus Cheiracanthus Agasssiz, 1835

Cheiracanthus sp_ indet.

Material Examined46 complete scales (WAM 99.8.75-80)

HorizonsKT Beds 4, 9, 14, 21, 22 and OFB (Figure 1)

Description of Morphotype 5 (Figure SA-B)The crown is elongate, being longer than wide.

An ornament of between 10-12 raised parallel ribsextends from the anterior edge to the posterior thirdof the scale (Figure SA-B). There is a narrowunornamented rim around the margin of the scale(Figure SA). The anterior edge of each rib bifurcates(Figure SA). The anterior edge of the scale isrounded and slightly overhangs the base. There is ashallow mid-scale depression which is characteristicfor Cheiracanthus. The posterior edge of the crown ispointed and overhangs the base. A well definedneck separates the crown and deep, tumid base.There are four openings visible in the neck (FigureSB). Sharpey's fibre bundles are visible on the base.

Description of Morphotype 6 (Figure SC-D)This scale type is rhomboid. The anterior margin

is rounded and the posterior margin is broken(Figure 50). The anterior and posterior edges of thecrown overhang the base. The crown surfaceornament consists of 6-8 parallel ribs, which

K. Trinajstic

bifurcate anteriorly (Figure SC-D). The ribs extendto the middle of the scale, disappearing towards theback. There is a constricted neck and a deep tumidbase.

Description of Morphotype 7 (Figure SE-F)Morphotype 7 (Figure SE-F) is very similar to

morphotype 6. The anterior and posterior crownmargins overhang the base (Figure SH). The crownornament consists of eight parallel ribs, whichbifurcate anteriorly (Figures SF--G). The ribs extendto the middle of the scale. The posterior margin ofthe scale is scalloped. There is a constricted neckand a deep tumid base.

Description of Morphotype 8 (Figure 51-])The scale type is rhomboid irl shape with a low

profile (Figure SI-J). The crown surface is veryabraded with only traces of the ribbed ornamentremaining (Figure SI). As with the other scalesdescribed, there is an unornamented rim around theanterior edge of the scale. The crown does notoverhang the base. There are four canals in theneck, which separates the crown from the flattenedbase. The base is shaped like a cross.

Description of Morphotype 9 (Figure SG-H)The specimens representing this scale type are

abraded. They have a rhombic to elongate shape(Figure SG-H). The posterior edge of the crown isscalloped and overhangs the base (Figure SG). Theornament consists of 4-8 parallel ribs that bifurcateanteriorly. There is an unornamented rim aroundthe margin of the scale. A well defined andconstricted neck separates the crown and deeptumid base. The neck contains four canals. At thejunction of the base and neck, the base flareslaterally, approaching the width of the crown(Figure SH).

HistologyThe crown is composed of orthodentine. In

sagittal section it can be seen that the main dentinetubules do not possess many side branches (Figure5K). This is characteristic of Cheiracanthus. A seriesof growth zones can be seen along the anterior edgein sagittal section and along the dorsal and lateraledges in sagittal section. In the centre of the neckthree ascending canals are present. One of theseextends to the crown; the other two extend to theneck. The base is acellular.

Allocation of scales to body regionA greater degree of variation is present in

acanthodian scales with crown surface ornamentthan in acanthodian scales that are unornamented.This is because the type of crown ornament mayvary in addition to the shape of scales, depending


Figure 5 Scales identified as Cheiracanthus sp. A-B morphotype 5 - anterior body scales; C-D, morphotype 6 - flankscale; E-F, morphotype 7 - flank scales; I-J, morphotype 8 - caudal scales; G -H, morphotype 9 - scales fromaround the base of the fin spine insertion points; K, sagittal section of morphotype 1 scale. Scale bars = 0.1mm.

on the region of the body that the scales are located.The crown ornament in Euthacanthus macnicolishows considerable variation in the number ofridges and the distance each ridge extendsposteriorly along the crown surface (Young, 1995).A reduction in the length of the ridges on the crownsurface from the anterior region to the caudal regionof the fish is also observed in Diplacanthus horridus(Figure 3). There is also variation in the base ofornamented acanthodian scales. Gross (1973)observed that the height of the base increases

towards the anterior of the fish in Machaeracanthusbohemicus. Relatively high scales with tumid basesoccur in the anterior region of the fish, and scaleswith low bases occur in the caudal region of the fish(pers. observation). A greater variation in the shapeand height of scale bases is apparent in D. horridus(Figure 3).

In Cheiracanthus sp., variation in the crownsurface ornament and in the height and shape ofthe base can also be observed. Scales with a highprofile and deep tumid base also have the most

196

numerous and longest ridges on the crownsurface, suggesting that these scales came fromthe anterior region of the fish's body(morphotype 5). Scales in which the ridge numberand length are less, but which still retain a highprofile and tumid base (morphotypes 6 and 7),are considered to have come from the flankregion of the fish. Scales that are relatively flatand have ridges only in the anterior third of thescale (morphotype 8), are interpreted as havingcome from the caudal region of the fish. Scaleswith a lateral extension above the tumid base(morphotype 9) are considered to have come fromaround the fin spine insertion points. These scaleshave correspondingly shorter and fewer ridges onthe crown surface.

There are two characters that remain consistentin the crown surface ornament of Cheiracanthussp. that suggest that all scales are from the samespecies. These characters are: the bifurcation atthe anterior end of each ridge and the presence ofa narrow, raised lip around the anterior edge ofeach scale. As with the Acanthodidae gen. et sp.indet. scales described above, all scale types fromthe different body regions present onacanthodians are represented in the samples fromthe Gneudna Formation. Accordingly, it isconcluded that all Cheiracanthus sp. scales arefrom a single species.

STRATIGRAPHIC DISTRIBUTION ANDDEPOSITIONAL ENVIRONMENTS

Thelodont scales have been used to indicatebathymetry in Early Devonian sediments. A higherproportion of thelodont scales compared toacanthodian scales is considered to representnearshore, or shallow water conditions (Marss andEinasto, 1978; Turner, 1984, 1999; Burrow, 1997).The microvertebrate assemblages from the typesection of the Gneudna Formation do not supportthese findings.

Thelodont scales are proportionally mostabundant in the beds KTl-5, KT6-9 and KTlO-18(Figure 1). These beds, which consist of crinoidal/brachiopodal packstone, have been interpreted asrepresenting a shallow nearshore environment. Inthe beds KT6-9 ptyctodont remains (Long andTrinajstic in press) are well preserved and insome cases partially articulated, indicating lowerenergy, offshore depositional conditions. Herethelodont scales are more abundant thanacanthodian scales. In the upper part of the typesection, from KTl9 to 22 and OFB, thelodontscales are rare and acanthodian scales are mostabundant (Figure 1). According to Marss andEinasto (1978) these proportions should indicatean offshore environment. However, these bedsare interpreted as having been laid down in

K. Trinajstic

extremely shallow water, with sediments mainlyconsisting of a well-sorted shell hash having ahigh quartz content.

There are three possible reasons why thelodonts/acanthodian scale number ratios do not providehere a reliable environmental indicator in theGneudna Formation. During the Givetian andFrasnian, the thelodonts declined in number anddiversity, with no thelodonts known after theFrasnian. Thus the ratios of acanthodian tothelodont remains may only be an effectiveenvironmental indicator for the Early and MiddleDevonian, when thelodonts were diverse andabundant, and not hold for the Frasnian. Evidenceto support this comes from the study of conodontratios, in particular the ratios of Icriodus toPolygnathus, in the section. Like thelodonts, theratios of certain conodonts have been successfullyused as environmental indicators. In the GneudnaFormation the conodont ratios (R. Nicholl personalcommunication 1997) are consistent with thelithological interpretations of the depositionalenvironments for each interval.

Secondly, many beds within the GneudnaFormation have been extensively affected bypost-depositional dolomitization. Thin sectionsof these beds show many fossil ghosts and themicro-remains recovered from residue arepoorly preserved. The actual fossil ratios of thedolomitized beds may be skewed due to preser-vation bias as a result of diagenic changes.

Thirdly, it is considered that the microvertebrateremains in the area where the type section of theGneudna Formation was deposited, with theexception of those in bed KT7, have beentransported before deposition. Microvertebrateremains are disarticulated and predominantly occurin packstone, due to post-depositionalconcentration. The Gneudna Formation is alsounusual in that there is a complete absence ofacanthodian fin spines in the section. The fish-bearing units in the Gneudna Formation aregenerally well sorted and the absence ofacanthodian fin spines could be explained throughwinnowing.

The difference in the proportion of acanthodianscales to thelodont scales does not provide anybathymetirc information that would indicate thedepositional environment of the GneudnaFormation.

ACKNOWLEDGEMENTS

My thanks to Dr Per Ahlberg, for allowing me towork on the collections of the Natural HistoryMuseum. To Dr Kim Dennis-Bryan for herhospitality while in Britain and help in finding myway through the collections of the Natural HistoryMuseum. To Carole Burrow for her valiant attempts


to try to teach me scale histology and acanthodianphylogeny, and to my supervisors Drs David Haig,Sue Turner, Mark Wilson, Carole Burrow and JohnLong for reviewing the manuscript and theirhelpful comments.

REFERENCES

Agassiz, L. (1833-1844). Recherches sur les poissons fossiles:2. contenant l'histoire des Ganoides. Neuchatel,Imprimerie du Petit-Pierre, 1833-44: 85-200.

Agassiz, L. (1844-1845). Monographie des Poissons fossilesdu Vieux, Gres Rouge ou systeme Devonien (Old RedSandstone) des Iles Britammiques et de Russie. xxxvi +171 pp, Neuchatel & Soleure.

Berg, L.S. (1940). Classification of fishes, both recent andfossil. Travaux de l'Institut de Zoologie de I'Academie desSciences de I'URSS, Leningrad 5: 87-517.

Bernacsek, G.M. and Dineley D.L. (1977). Newacanthodians from the Delorme Formation (LowerDevonian) of Northwest Territories, Canada.Palaeontographica 158A: 1-25.

Burrow, C. (1996). Taphonomy of acanthodians from theDevonian Bunga Beds (Late Givetian/Early Frasnian)of New South Wales. Boucot Festschrift. HistoricalBiology 11: 213-228.

Denison, RH. (1979). Acanthodii. In H.-P. Schultze (ed.)Handbook of Paleoichthyology, Pt 5: 62 pp., GustavFischer Verlag, Stuttgatt, New York.

Derycke-Khatir, C. (1994). Microrestes de Vertebres duPaIe020ique superieur de la Manche au Rhin: BiodiversiU-Biostratigraphie-Biogeographie. These de Doctorat,Universite de Lille, 2 volumes: 1-248.

Derycke, C. and Chancogne-Weber, C. (1995).Histological discovery on acanthodian scales from theFamennian of Belgium. In H. Lelievre, S. Wenz, A.Blieck and R. Cloutier (eds), Premiers vertebres etvertebres inferieurs, Geobios Memoire special 19: 31-34

Egerton, P. (1861). British fossils. (Descriptions ofTristichopterus, Acanthodes, Climatius, Diplacanthus,Cheiracanthus). Memoirs of the Geological Survey UnitedKingdom 10: 51-75.

Gagnier, P.-Y. (1996). Acanthodii. In H.-P Schultze and RCloutier (eds), Devonian fishes and plants of Miguasha,Quebec, Canada: 149-164, Verlag Dr Friedrich Pfeil,Munich.

Gagnier, P.-Y and Wilson, M.V.H. (1996). Early Devonianacanthodians from northern Canada. Palaeontology 39:241-258.

Gross, W. (1973). Kleinschuppen, Flossenstacheln undZahne aus europischen und nordamerikanischenBonebeds des Devons. Palaeontographica 142A: 51-155.

Huxley, T.H. (1861). Preliminary essay upon thesystematic arrangement of the fishes of the Devonianepoch. Memoirs of the Geological Survey of the UnitedKingdom 10: 1-40

Long, J.A. (1983). A new diplacanthoid acanthodian fromthe Late Devonian of Victoria. Memoirs of theAssociation of Australasian Palaeontologists 1: 51- 65.

Long, J.A. (1986). A new Late Devonian acanthodian fishfrom Mt Howitt, Victoria, Australia, with remarks on

acanthodian biogeography. Proceedings of the RoyalSociety of Victoria 98: 1-17.

Long, J.A. and Trinajstic, K.M. (in press). An overview ofthe Devonian microvertebrate faunas of WesternAustralia. Courier ForscJllIngsinstitut Senckenberg.

Marss, T. and Einasto, R. (1978). [Distribution of thevertebrates in deposits of various facies in the northBaltic Silurian Esti NSV teaduste Akadeemia Toimetisedgeoloogia, 27: 16-22. (In Russian with Englishsummary).

Miles, R.S. (1966). The acanthodian fishes of theDevonian Plattenkalk of the Paffrath trough inRhineland.

Miles, R.s. (1973). Articulated acanthodian fishes fromthe Old Red Sandstone of England, with a review ofthe structure and evolution of the acanthodianshoulder girdle. Bulletin of the British Museum ofNatural History (Geology) 24: 113-213.

Mory, A. (1996). GSWA Gneudna 1 Well completionreport Merlinleigh Sub-basin, Carnarvon Basin,Western Australia. Geological Survey of WesternAustralia Record 1996/6.

Powrie, J. (1864). On the fossiliferous rocks of Forfarshireand their contents. Quarterly Journal of the GeologicalSociety of London XX: 413-429.

Powrie, J. (1870). On the earliest known vestiges ofvertebrate life; being a description of the fish remainsof the Old Red Sandstone of Forfarshire. Transactionsof the Geological Society Edinburough 1:284-301.

Russel, L.S. (1951). Acanthodians of the Upper Devonian,Escuminac Formation, Miguasha, Quebec. Annals andMagazine of Natural History 4: 401-407.

Turner, S. (1991). Palaeozoic vertebrate microfossils inAustralasia. In P. Vickers-Rich, J.N. Monaghan, RF.Baird and T.H. Rich (eds), Vertebrate palaeontology inAustralasia: 429-464. Pioneer Design Studios withMonash University Publications Committee,Melbourne.

Valiukevicius, J.J. (1992). First articulated Poracanthodesfrom the Lower Devonian of Severnaya Zemlya. In E.Mark-Kurik (ed.), Fossil fishes as living animals: 193-214, Academia 1, Academy of Sciences of Estonia.

Wang J. (1984). Geological and paleogeographicdistribution of Devonian fishes in China. VertebrataPalasiatica 22: 219-229.

Wang, J. and Turner, S. (1985). Vertebrate microfossils ofthe Devonian Carboniferous boundary, Muhuasection, Guizou Province. Vertebrata Palasiatica 23:223-224.

Watson, D.M.S. (1937). The acanthodian fishes.Philosophical Transactions of the Royal Society of LondonB, 228: 49-146.

Wells, J.W. (1944). Fish remains from the MiddleDevonian Bone Beds of the Cincinnati Arch region.Palaeontographica Americana 3: 99-160.

White, E.!. (1968). Devonian fishes from the Mawson-Mulock area, Victoria Land, Antarctica. Trans-Antarctic Expedition 1955-1958. Scientific Reports,Geology 16: 1-26.

Woodward, A.s. (1892). Further contributions toknowledge of the Devonian fish-fauna of Canada.Geological Magazine 9: 481-485.

198

Woodward, A. S. (1921). Fish-remains from the UpperOld Red Sandstone of Granite Harbour, Antarctica,British Antarctica ('Terra Nova') Expedition, 1910.Natural History Report (Geology) 1: 51-il2.

Young, G.c. (1989). New occurrences of culmacanthidacanthodians (Pisces, Devonian) from Antarctica andsoutheastern Australia. Proceedings of the LinneanSociety of New South Wales 111: 12-25.

Young, V.T. (1995). Micro-remains from Early andMiddle Devonian acanthodian fishes from the u.K.

K. Trinajstic

and their biostratigraphic possibilities. lchthyolithIssues Special Publication 1: 65-il8.

Zidek, J. (1976). Kansas Hamilton Quarry (UpperPennsylvanian) Acanthodes, with remarks on thepreviously reported North American occurrences ofthe genus. The University of Kansas, PalaeontologicalContributions Paper No. 83, 1-41.

Manuscript received 18 November 1999; accepted 7 April2000.

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