Memoirs of Museum Victoria 74: 63–71 (2016) Published 2016

ISSN 1447-2546 (Print) 1447-2554 (On-line)http://museumvictoria.com.au/about/books-and-journals/journals/memoirs-of-museum-victoria/

A close look at Victoria's first known dinosaur tracks

Anthony J. MArtin

Department of Environmental Sciences, Emory University, Atlanta, Georgia 30322 USA (geoam@emory.edu)

Abstract Martin,A.J.2016.AcloselookatVictoria'sfirstknowndinosaurtracks.Memoirs of Museum Victoria 74: 63–71. LowerCretaceous(Aptian-Albian)rocksofVictoria,Australiaarewellknownfortheirdinosaurbodyfossils,but

notsomuchfortheirtracefossils.Forexample,thefirstknowndinosaurtrackfromtheEumerallaFormation(Albian)ofKnowledgeCreek,Victoria,wasnotdiscovereduntil1980.Thisspecimen,alongwithtwomoreEumerallatracksfoundatSkenesCreekin1989,constitutedallofthedinosaurtracksrecognisedinLowerCretaceousstrataofsouthernAustraliauntilthelate2000s.Unfortunately,noneofthesefirst-knowndinosaurtracksofVictoriawereproperlydescribedanddiagnosed.Hence,themainpurposeofthisstudyistodocumentthesetracefossilsmorethoroughly.Remarkably,theKnowledgeCreekandoneoftheSkenesCreektracksarenearlyidenticalinsizeandform;bothtracksareattributedtosmallornithopods.Althoughpoorlyexpressed,thesecondprobabletrackfromSkenesCreekprovidesasearchimageforlessobviousdinosaurtracksinLowerCretaceousstrataofVictoria.TheSkenesCreektrackswerealsolikelyfromthesametrackway,andthusmayrepresentthefirstdiscovereddinosaurtrackwayfromVictoria.Thesetracksarethefirstconfirmed ornithopod tracks for Victoria, augmenting abundant body fossil evidence of small ornithopods(‘hypsilophodontids’)informerlypolarenvironmentsduringtheEarlyCretaceous.

Keywords Cretaceous,dinosaur,footprint,ichnology,ornithopod,tracefossil,track.

Introduction

Victoriaisworldfamousforitsdinosaurbodyfossils,whichreflectthebest-documentedpolar-dinosaurassemblageintheSouthernHemisphere (Rich et al., 2002;Rich andVickers-Rich,2003;KearandBruce,2011;Bensonetal.,2012).ThefirstknowndinosaurbodyfossilinVictoria,atheropodungualfrom the Wonthaggi Formation (Aptian) found by WilliamFergusonin1903,wasalsothefirstAustraliandinosaurfossilknown to science (Rich and Vickers-Rich, 2000; Rich andVickers-Rich,2003).However,dinosaurtracefossils,suchastracks,nests,burrows,andotherdirectevidenceofdinosaurbehavior in the Cretaceous rocks of Victoria remainedunnoticed by palaeontologists until 1980, 77 years after thefirstrecognisedbodyfossil.ThisichnologicaldroughtendedwhenThomasH.RichandPatriciaVickers-RichdiscoveredandcollectedadinosaurtrackfromtheEumerallaFormation(Albian) at Knowledge Creek, Victoria (Rich and Vickers-Rich,2000)(fig.1).

Another eight years passed before two more dinosaurtracks were noticed in a Eumeralla Formation stratum atSkenesCreekinearly1989.In2006,IrecognizedtwolargetheropodtracksintheWonthaggiFormationattheFlatRocks(“Dinosaur Dreaming”) dinosaur dig site, near Inverloch,Victoria;TylerLamb then foundanotherat the samesite in2007 (Martin et al., 2007). Three years later, the largestassemblage of polar-dinosaur tracks in the SouthernHemisphere–madebysmall-tomoderate-sizedtheropods–

was discovered in the Eumeralla Formation at MilanesiaBeach (Martin et al., 2012). Recently, closely associatedtridactylandtetradactyltracksweredescribedfromDinosaurCove,andwereinterpretedasnon-aviantheropodandavianinorigin,respectively(Martinetal.,2014).Otherwise,theonlyother trace fossilsascribed tonon-aviandinosaurs inLowerCretaceous strata of Victoria include possible burrows(Martin,2009).Nests,toothmarks,gastroliths,coprolitesandothersuchtracefossilsapparentlyhavenotyetbeendiscovered(Martin, 2014).

TheKnowledgeCreektrackhasbeenfiguredinnumerouspublications, and was much reproduced for educationalpurposes (Rich andVickers-Rich, 2000, 2003). However, itand the Skenes Creek tracks have not been described norinterpretedindetail.Thusthemainpurposesofthisstudyareto: (1) thoroughly document these tracks; (2) interpret theirdinosaur makers and preservational modes; (3) assess thepalaeontologicalimportanceofthetracks;and(4)suggesthowthis information might be used to prospect for more suchtracksinLowerCretaceousstrataofVictoria.

Methods

ThethreespecimensareintheMuseumVictoriaPalaeontologyCollection(NMVP);thustheyareavailableforfurtherstudybyqualifiedresearchers.ImeasuredthetrackswithMitutoyodigital calipers, using minimum-outlines for track widths,lengths,andotherparameters(fig.2).Digit-impressionlengths

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were measured from the midline of each digit, and digit-impressionwidthswere taken perpendicular to thismidlineandmediallyalongthelengthofeachimpression.Interdigitalanglesweremeasuredwithacircularprotractor,usingadigit-impression axis radiating from a single point on the rearmarginofthetrack,asdepictedbyThulborn(1990,fig.4.5).The anterior triangle length:width ratio (sensu fig. 2 inLockley, 2009) was derived from measuring the base of atriangle, defined by the width between the lateral digitimpressions and the length of the middle digit impressionfromthatbase.Semiquantitativeandqualitativeinformation,suchas thehost lithologyandotherdescriptive traitsof thetracks, were also noted. All data are provided here andsummarized(table1)sothatfutureinvestigatorsmayexamine,test,orotherwiseattempttocorrecttheresultsreportedhere.

Descriptions

Knowledge Creek Track. On December 18, 1980, ThomasRich and Patricia Vickers-Rich discovered the KnowledgeCreektrack,catalogedasNMVP159790(fig.3,AppendixI).The trackwas located on amarine platform just above sealevel and about 100m east of Knowledge Creek. Rich andVickers-Richusedhandchiselsandrockhammerstoextractandcollectthetrack,whichtheybroughttothemuseum.

Thetrackisinaveryfine-finelithicarenite,althoughthetrackitselfisfilledwithfine-coarse,moderatelysortedquartzandlithicsandheldtogetherwithhematiticcement.Thebedis36-47mmthickandhorizontallylaminatedincrosssection,withnoapparentdisruptionsofbeddingbybioturbation.Theareasurroundingthetrackisflat,andlacksotherphysicalorbiogenicsedimentarystructuresonthissurface.Thetrackispreservedasanearlyflatbutpositive-relief(raised)epichnion,

ratherthanadepression.Itwasweatheredsuchthatitsformisexpressedinnearlyfullrelief.

Thetrackistridactylandmesaxonic.Itisalmostequantinlength and width: 106 mm long and 118 mm wide, with alength:widthratioof0.90.Theanteriortrianglelength:widthratiois0.40,withabase(width)ofthetriangleof118mmandlengthfromthatbaseof47mm.Outermostdigitimpressionswere90mmand84mmlong(leftandright,respectively),andthecentralimpressionisalsothelengthofthetrack,106mm.Medial thicknessesof the threedigit impressions,measuredperpendicular to the longaxisofeachdigit,arefromleft toright:25mm,31mm,and30mm.Usinganaverageof29mm,digit-impression widths are about 27% of footprint length.Divaricationbetween theoutermostdigit impressions is85°,whichcombinesanangleof47°betweentheleftandmiddle,and38°betweentherightandmiddle.Allthreeimpressionsareoutlinedcompletely.Digitimpressionsnarrowdistally,butaresubroundedattheirends.Thetrackbearsthreesmall,ovalprotuberances,twoonthemiddledigitimpressionandoneontheleft.Thesestructuresonthemiddleimpressionare4x8mmwide(towardthedistalend)and4x5mmwide(at therightintersectionwiththerightimpression),whereastheoneontheleftimpressionis5x5mm(outeredge).Eachstructureislabeledas“B”(for“burrow”)onfig.3b.

Thesandfillvariesfrom4mmthickattheposterior“heel”(proximal)endof the track to8-10mmthickat theanterior(distal) ends of each digit impression (fig.3c,d). Thus alongitudinal profile of the track would show a gradualthickeningofthesandfillfromposteriortoanterior.A1-mmthick, slightly curved thread-like structure, filled with thesame reddish sand as the track, cross-cuts the grey lithicarenitebelowtherightposteriorportionofthetrack(fig.3c).

Figure 1. Locality and outcropmap for Early Cretaceous dinosaurtracks found thus far inVictoria,with the three tracksdescribed inthisstudycomingfromKnowledgeCreekandSkenesCreek.Keyandlatitude-longitudecoordinatesforeachofthetracksites,fromeasttowest:FlatRocks (FR),S38°45.3’,E145°40.9’;SkenesCreek (SC),S38°42.9’,E143°44.4’;DinosaurCove(DC),S38°46.9’,E143°24.3’;Knowledge Creek (KC), S38° 45.3’, E143° 20.9’; Milanesia Beach(MB),S38°45.3’,E143°19.3’.

Figure2.Trackparametersmeasuredinthisstudy.Key:TW=totalwidth;TL=totallength;L1-L3=digitlengths;W1-3=digitwidths;IA1-IA2=interdigitalangles.Anteriortriangledefinedbytotaltrackwidth (baseof the triangle) andmiddle-digit lengthmeasured fromthatbase.

A close look at Victoria's first known dinosaur tracks 65

Skenes Creek Track 1.HelmutTracksdorf,alocalcitizenandgeologistfromtheSkenesCreekarea,discoveredtwodinosaurfootprintsthereinJanuary1989,withbothcatalogedasNMVP208232 (figs.4-5,Appendix I).TracksdorfalertedMuseumVictoriaaboutthem,andpersonnelfromtheMuseumcollectedthe tracks on March 18, 1989. Although no additionalinformationisavailableaboutwhocollectedorcatalogedthesetracks, theexactfield locationof the trackswas just recently

verified,havingcomefromthesupratidalmarineplatformofrock exposed between Skenes Creek and Browns Creek(AppendixII).

The most clearly defined of the two tracks (hereindesignatedSkenesCreekTrack1)isina16x20cmcutslabofveryfine-fine,well-sortedlithicarenite.Thebedis25-41mmthick,withsevenparallelandsymmetricalripplessharingthetop surface with the track. Assuming an arbitrary “north”

Table 1.Measurements of dinosaur tracks from:KnowledgeCreek (KC1), specimenP.159790; andSkenesCreek (SC1 andSC2), specimenP.208232. Key: L = length, W = width, L:W = length:width, IA1 = left-middle interdigital angle, IA2 = middle-right interdigital angle, D=divarication(interdigitalanglebetweenleftandright),L1=leftdigitlength,L2=middledigitlength(sameastracklength),L3=rightdigitlength,W1=leftdigitwidth,W2=middledigitwidth,W3=rightdigitwidth,at-L=anteriortrianglelength,at-W=anteriortrianglewidth,at-L: W=anteriortrianglelength:width,n/a=notapplicable.AllmeasurementsareinmillimetersexceptforIA1,IA2,andD,whichareindegrees.

Track L W L:W IA1 IA2 D L1 L2 L3 W1 W2 W2 at-L at-W at-L:W

KC1 106 118 0.90 47° 38° 85° 90 106 84 25 31 30 47 118 0.40SC1 106 115 0.92 37° 46° 83° 91 106 87 n/a 34 36 43 115 0.37SC2 127 138 0.92 44° 27° 71° 102 127 103 n/a n/a n/a 43 138 0.31

Figure3.KnowledgeCreektrack,NMVP159790.a.Overalltopviewoftrackincollectedslab,withbeddingandchiselmarksevidentalongedge;scale=5cm.b.Outlineoftrackandparametersmeasured,withanteriortriangleindicated(seeFigure2forkey),B=invertebrateburrows;scale=5cm.c.Posterior-edgeviewoftrack,showingfullreliefoftrack,thinfillofcoarsesand,andpossiblesmallburrowbelow(arrow);scale=1cm.D.Anterior-obliqueviewoftrack,showinggraduallythickersandfilltowarddistalendsofdigits;scale=1cm.

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definedbytheaxisofthemiddledigitimpression,ripple-creststrend “northeast-southwest.” Ripples have amplitudes of 4-7mmandwavelengthsof30-40mm; ripplebeddingwasalsoevidentincross-section.Thetrackispreservedasanearlyflat,1-2 mm thick positive-relief (raised) epichnion, but is filledwithsandtexturallyandcompositionallyidenticaltothemainhostlithology.Itiscircumscribedandsomewhatmimickedinoutline by a 4-8mm thick quadrilateral platformbetween itandtherippledsurface.Beddinginthetrackanditsplatformismostly planar and laminated, although slight variations insurfacetopographysynchwithunderlyingripples.

The track is tridactyl, mesaxonic, and nearly equant inlength and width, at 106 mm long and 115 mm wide; thisresults in a length:width ratio of 0.92. Outermost digitimpressions were 91 mm and 87 mm long (left and right,respectively), and thecentral impression is the lengthof the

track,106mm.Therightimpressionhasaseeminglycompleteoutline,whereastheleftisapparentlyexpressedpartially.Theanteriortrianglelength:widthratiois0.37,withabase(width)at 115mm and lengthmeasured from that base of 43mm.Medialthicknessesofthetwocompletedigitimpressionsare,frommiddle toright,34and36mm.Withanaverageof35mm, digit-impression widths are about 33% of footprintlength.Divaricationbetweentheoutermostimpressionsis83°,whichcombinesanangleof37°betweentheleftandmiddle,and46°between the right andmiddle.Both themiddleandrightdigitimpressionsnarrowdistally,butaresubroundedattheirends.Anunidentifiedmodernbarnacleisattachedtothelowerright-sideedgeofthetrack.

Skenes Creek Track 2. This probable dinosaur track (hereincalled Skenes Creek Track 2) was also cataloged as part ofNMVP208232(fig.5,AppendixI).Basedonitssamespecimen

Figure4.SkenesCreekTrack1,NMVP208232.a.Overalltopviewoftrackincollectedslab,withrocksawcutsevidentonthreesides,aswellassymmetricalandparallelripplemarksbelowtrack;scale=5cm.b.Close-upoftrack,showingraisedreliefandthin,laminated“platform”aboveripplemarks;scale=5cm.c.Outlineoftrackandparametersmeasured,withanteriortriangleindicated(seeFigure2forkey);scale=5cm.

Figure5.SkenesCreekTrack2,NMVP208232(sharedwithTrack1).a.Overalltopviewoftrackincollectedslab,withrocksawcutsevidentonfivesidesandfracturecuttingacrossanteriorpartoftrack;scale(left)incentimetresandmillimetres.b.Close-upoftrack,showingraisedreliefandthin, laminated“platform”aboveripplemarks;scale=5cm.c.Outlineof trackandparametersmeasured,withanterior triangleindicated(seeFigure2forkey);scale=5cm.

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number and havingmany identical sedimentary traits as theSkenesCreekTrack1,IconcludethatitwasalsodiscoveredbyHelmutTracksdorfin1989,thenlatercollectedfromthesamemarine-platform bedding plane by Museum of Victoriapersonnel at the same time as Skenes Creek Track 1. Thissuppositionissupportedbytwoadjacentrock-sawcutsattheprobable discovery site, which were relocated by HelmutTracksdorfin2013andMikeCleelandin2014(AppendixII).

Thetrackisinapentagonalslab(cutbyarocksaw)withlongdimensionsof24x21cm;a fracture runs transverselyacross the track (fig. 5a). The lithology is identical to thathosting theSkenesCreekTrack1,consistingofaveryfine-fine,well-sortedlithicarenite,withabedthicknessof30-40mm.Thetopsurfaceofthebedhassixparallel,symmetrical,and low-amplitude ripples underneath the track. Using anarbitrary“north-south”definedbythemedialaxisofthetrack,ripple-crests trend “northeast-southwest.” Ripples haveamplitudesof5-7mmandwavelengthsof25-40mm;ripplebeddingwasvisibleincross-section.AlsolikeSkenesCreekTrack 1, it is preserved as an almost-flat, positive-reliefepichnion, filled with sand texturally and compositionallyidenticaltothatofitshostrock.Thetrackiscircumscribedbytwo levels, one about 5 mm above the rippled surface andanother inner and topmost level that is about 2 mm thick.Again, like Skenes Creek Track 1, bedding in both upperlevels is mostly planar and laminated, with variations insurfacetopographycorrespondingwithunderlyingripples.

SkenesCreekTrack2 is apparently tridactyl,with threerounded points opposite another rounded end, which areassumed as the anterior and posterior parts of the track,respectively. Using this configuration, track length was 127mm,whereasthewidthwas138mm,resultinginalength:widthratio of 0.92. Owing to vague outlines of presumed digitimpressions, width measurements were not attempted, butlengthscouldbemeasured,yielding102mmfortheleftdigitimpression and 103 mm for the right. Assuming thisconfiguration, the interdigital angles were 44° (left-middle)and27°(middle-right),foradivaricationof71°.Theanteriortriangle length:width ratio was also calculable, yielding avalueof0.31,with thebase (width) thesameas trackwidth(138mm)andlengthmeasuredfromthatbaseof43mm.Theposteriorpartofthetrackisslightlyindentedalongitsmargin,andthelower-leveloutlinejustbelowthemeasuredpartofthetrack is bilobed. Three unidentified modern barnacles areattachedon the lowermost bedding surface, all to the lowerrightofthetrack,butwithoneproximalandtwomoredistal.

Interpretations and Discussion

The twomost completelypreserved tracks fromKnowledgeCreek and Skenes Creek (Track 1) were very likely pesimpressions made by small ‘hypsilophodontid’ ornithopodsakin to Atlascopcosaurus, Fulgurotherium, or Leaellynasaura, all of which are in the Eumeralla Formation (Rich andVickers-Rich,1999;Richetal.,2010). ThesetracefossilsthusconstitutethefirstornithopodfootprintsdiscoveredinLowerCretaceousrocksofVictoria;allothersfoundsincethe1980shavebeenattributedtotheropods(Martinetal.,2007,2012,

2014). The interpretation of tracks as ornithopod tracks isbased on track forms, sizes, and their preservation in stratachronologicallyclosetothosecontainingtheskeletalremainsof these ornithopods in theEumerallaFormation (Rich andVickers-Rich, 2003; Kear and Bruce-Hamilton, 2011). ThesecondprobabledinosaurtrackfromSkenesCreek(Track2),although less definite in outline, is also likely from a smallornithopodandcomesfromthesamebedastheothertrack.Furthermore,itmayhavebeenpartofthesametrackwayasthemorecompletelydefinedtrack.

The two comparable tracks fromKnowledge Creek andSkenesCreekTrack1areremarkablysimilarinsizeandform(Figure 6). Both tracks are tridactyl, presumably reflectingdigitsII-IV,withdigitII-IVdivaricationsof85°(KnowledgeCreek) and 83° (Skenes Creek Track 1). Their lengths andwidthsarenearlyidentical,theirdigit-impressionwidthsvarybyonlyafewmillimeters,andmiddledigit-impressionwidths(digit III) are27%and33%of footprint length (KnowledgeCreek and Skenes Creek Track 1, respectively). Moreover,theiranteriortrianglelength:widthratiosarenearlyconvergent,at 0.40 for theKnowledgeCreek track and 0.37 for SkenesCreek Track 1. Their expression as positive-relief epichnia,alongwiththeotherlesscompletelypreservedSkenesCreekichnite, is also noteworthy, implying their preservationalconditionsmayhavebeensimilaraswell.However,becausethe tracks are nearly symmetrical and do not show anypressure-releasestructuresrelatedtomovement(sensu Martin et al., 2012), I cannot identify digit impressions II or IV ineithertracks,norstatewithcertaintywhethereitherrepresentsarightorleftfootprint.

Both quantitative and qualitative traits indicate theKnowledgeCreekandSkenesCreekTrack1 tracefossilsareornithopodtracks.Length:widthratiosofabout0.9,digitII-IVdivaricationsof83-85°,anterior-trianglelength-widthratiosofabout0.4, relatively thickdigits, and rounded (blunt)endsondigit impressions are all consistent with ornithopod tracks(Moratalloetal.,1988;Lockley,2009;MateusandMilàn,2010;Martinetal.,2012;Farlowetal.,2012).RelativelysmallsizesofthetracksalsoagreewithassessmentsofEumerallaFormationdinosaur assemblages, which are dominated by small‘hysilophodontids’ (Rich andVickers-Rich, 1999;Rich et al.,2002).Apossiblycomparableichnogenusinsizeandformtothese tracks isDinehichnus isp. (sensuGierlińskietal,2009,fig. 7), reported from the Late Jurassic of Poland andNorthAmerica,andinterpretedasthatofasmallornithopod(LockleyandFoster,2006;Foster,2007;Gierlińskietal.,2009;Lockleyet al., 2009). Furthermore, the Victoria tracks resembleIguanodontipus,whichhasbeenattributedtoEarlyCretaceousiguanodontids(Sarjeantetal.,1998;CobosandGascó,2012),althoughtheseareoftenmuchlarger(Castaneraetal.,2013).InAustralia, Wintonopus of the Lower Cretaceous WintonFormation (Queensland) is another small ornithopod trackcomparable to the Victoria specimens (Thulborn andWade,1984;Romilioet al., 2013). In short, similaritiesbetween theVictoria tracks and these ichnogenera affirm that their likelytracemakersweresmallornithopods.Thetrackscanbefurtherusedtoestimatetracemakersizeviaafootprintformulaof4.0xfootprint length = hip height (Alexander, 1976; Henderson,

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2003).Using this formula, theKnowledgeCreek andSkenesCreek (Track 1) ornithopod tracemakers had hip heights ofabout42cm(basedon10.6x4.0=42.4cm).Owingtoitspoordefinition, thehipheightof the trackmaker forSkenesCreekTrack2wasnotcalculated,butifitdoesindeedbelongtothesametrackway,itcanbeassumedassimilartothatofTrack1.

Otherdinosaurtracemakersthatcouldhavemadetridactyltracksincludesmalltheropods,suchasthoseinterpretedfromthe Eumeralla Formation dinosaur tracksite at MilanesiaBeach (Martin et al., 2012) or a single non-avian theropodtrackfromDinosaurCove(Martinetal.,2014).However,theMilanesia and Dinosaur Cove theropod tracks were “thin-toed,” with middle digit widths of only 5-16% of footprintlengths.Incontrast,digitsoftheKnowledgeCreekandSkenesCreektracksweremorethantwiceasthick,at27and33%offootprint lengths (respectively). Furthermore, most of theMilanesiaBeachtrackshadthin(sharp)clawmarks,whicharealso characteristic of theropods (Martin et al., 2012, and references therein). Avian theropods (birds) were alsodiscountedaspossibletracemakersfortheKnowledgeCreekandSkenesCreektracksforthesamereasons,aswellasforhaving digital divarications of 83-85°; bird tracks moretypicallyhavedivaricationsof95-120°(Lockleyetal.,1992;Falk et al., 2011;Martin et al., 2014).Both tracks also lackevidenceofadigitIimpression,atraitnotedintwosimilarlysizedaviantracksfromtheEumerallaFormationatDinosaurCove(Martinetal.,2014).

Thepositive-relief(raised)expressionofall threetracks,yetonbedtopsasepichnia,isunusualformostfossiltracks.Fossil tracks are normally preserved either as depressions(negative-relief epichnia)or asnatural castsonbedbottoms(positive-reliefhypichnia)(Lockley,1991;Farlowetal.,2012).Because all three specimens were recovered from marineplatforms eroded by tides and waves, their positive-relief

preservationimpliesthatsedimentfillingthetrackswasbettercemented – and hence more resistant to weathering – thantheirhostrocks.Thisdifferentialcementationandweatheringthatresultedinconvexdinosaurtracksonbedtopswasalsonoted for large theropod tracks in theWonthaggiFormation(Aptian) at the Flat Rocks (“Dinosaur Dreaming”) dig site(Martinetal.,2007).AnunevenfillandcementationprobablycontributedtothevaguedefinitionofSkenesCreekTrack2,inwhichthe“truetrack”isburiedbelowtheoutwardlyexpressedpositiveepichnion.

Track surfaces are mainly uniform, but the KnowledgeCreek track contained three oval-outlined protuberances,which I interpret as cross-sections of invertebrate burrows(figs.3a,b).Theburrowswouldhavebeenmadeinanoriginallythickerbedcomposedof thesamemedium-coarsesand thatfilledthetrack.Athinverticalstructurewiththesamesandfillunderneathandtowardtherearofthetrackisalsolikelyaburrow,butoneintheunderlyinghostlithologyandpassivelyfilled by sand from above. Owing to insufficient details,ichnotaxawerenotassignedtotheseburrows.

SkenesCreekTrack2,despiteitslargerdimensionsandlessdefiniteoutline,issimilarenoughtoitscompaniontrackfromthesamesitethatitisalsointerpretedasadinosaurtrack,andprobablythatofasmallornithopod.Thissuppositionisbasedonitstridactylform,roundedendstotheprobabledigitimpressions,alength:widthratioof0.92,andananterior-trianglelength:widthratio of 0.31, which again are consistent with ornithopodtracemakers(Lockley,2009).Oneofthe“interdigital”anglesonSkenesCreekTrack2roughlycorrespondedwiththatofTrack1(44°versus46°,respectively);however,divaricationwasnotablydifferent(71°versus83°,respectively).Asmentionedbefore,theoriginaldepressions(“truetrack”)forbothTracks1and2arelikelyunderneaththecurrentlyexpressedpositive-reliefoutline,filled with sand that later cemented differently from the

Figure6.SkenesCreekTrack1(left)andKnowledgeCreektrack(right)together,allowingforaside-by-sidecomparison.TheslabholdingtheKnowledgeCreektrackisslightlythicker(~10mm)thantheSkenesCreekslab,hencetheyarenotbeingviewedonexactlythesamehorizon;scale=10cm.

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surrounding substrate.Thesedepressionsmayevencut acrossthe ripples underneath the track or deformed surroundingsedimentssothatthesubsequentfillandcementationofthatfillaffectedtheoutwardappearanceandweatheringofthetracksonthesamemarineplatform.

Althoughno informationwas recorded about the spatialrelationshipoftheSkenesCreektracksonthemarineplatformwhen andwhere theywere recovered in 1989, the rock-sawcuts corresponding to their locationswere foundbyHelmutTracksdorf in June 2014, which was confirmed byMichaelCleeland in February 2015 (Appendix II). Interestingly, therectangularoutlinesoftherock-sawcutsaredirectlyalignedandinasandstonebedwithlow-amplituderipples,withripplecrestsorientedobliquelyrelativetotheoutlines.Furthermore,both trackshavesimilar formsandareatopripplesorientedthesamewithrespecttofootprintdirections,i.e.,“northeast-southwest”withtrackspointingtowardanarbitrary“north.”Consequently,thesetrackslikelybelongtothesametrackwayandweremadebythesameindividualornithopod.Ifso,thesewould constitute the first discovered dinosaur trackway inVictoria, usurping a small-theropod trackway discovered atMilanesia Beach in 2010 (Martin et al., 2012). To test thispreliminary interpretation, the exact distance betweenincisions will need to be measured, and rock-saw outlinesshouldbecomparedtotheshapesandorientationsofthetworecoveredslabs.Conversely,ifthetracksarenotaligned(e.g.,point in opposite directions) and the collected slabs do notcorrespondtotheoutlines,theycanbereasonablyattributedtoseparatetrackwaysmadebysimilartracemakers.

Unfortunately,allthreetracksareisolatedspecimenstakenout of context from their original field exposures in 1980(KnowledgeCreek)and1989(SkenesCreek).Thusverylittleadditionalinformationcanbesaidaboutthepalaeoenvironmentstrodden by their ornithopod tracemakers. The EumerallaFormation is interpreted as a series of fluvial channel-fill,overbank, and floodplain facies deposited in circumpolar riftvalleys,withlesscommonalluvialorlacustrinefacies(Bryanetal.,1997;Tosolinietal.,1999;Vickers-Richetal.,1999).Giventhisbroad framework, themostprobablepalaeoenvironmentsfordinosaursmakingpreservabletrackswouldhavebeenpointbarsorfloodplains,whicharecommonsitesfordinosaurtrackpreservation (Martin, 2014). If the Skenes Creek trackmakerwaswalking on afloodplain, ripples underneath these tracksmight have been current ripples, exposed after water flowedoverthatsurface.Similarmodernoccurrencesofcurrentrippleslater cross-cut by vertebrate tracks, providing a possibleanalogue for theSkenesCreek tracks,weredescribed fromaArctic point bar in Alaska (Martin, 2009b). The largestassemblageofdinosaurtracksfromtheEumerallaFormation–foundatMilanesiaBeachanddescribedfromtwoseparateslabsof the same sandstone bed – was also in what were likelyfloodplain sandstones (Martin et al., 2012). Indeed, thecircumpolar setting of these river valleys during the EarlyCretaceousmeant thatdinosaurtracksmighthavebeenmadeandpreservedonlyseasonally,fromspringthroughfall(Martinet al., 2012). If so, this limiting factor may account for therelativerarityofdinosaurtracksandothertracefossilsinLowerCretaceousstrataofVictoria(Martinetal.,2012).

Conclusions

Thefirstknowndinosaur tracks fromVictoriamaybesmallandfew,butnonethelesscarryusefulinformationaboutEarlyCretaceous dinosaurs in Victoria. For one, the KnowledgeCreek andSkenesCreek tracks are from localitieswherenodinosaur bones are yet known, therefore confirming adinosaurian presence at each of these places. Secondly, thetracks demonstrate that dinosaurs – specifically smallornithopods – actually lived in the palaeoenvironments oftheseplaces.Incontrast,mostdinosaurbodyfossilsinVictoria,suchasthosefromtheFlatRocks(“DinosaurDreaming”)siteat InverlochandDinosaurCove,were likely transportedanddeposited in fluvial channels (Rich andVickers-Rich, 2000;Richetal.,2003).Lastly,thesetracksarethefirstdiscoveredEarly Cretaceous ornithopod tracks from Victoria, and theSkenesCreektracksmayrepresentthefirstdiscovereddinosaurtrackwayinVictoria.Thesefindsthussupplementcomparativelyabundantbodyfossilsof‘hypsilophodontids’intheWonthaggiandEumerallaFormations.

The preservation of these small ornithopod tracks aspositive-relief epichnia, as well as those of large theropodtracksintheWonthaggiFormation(Martinetal.,2007),alsomaybe typicalmodesofpreservation fordinosaur tracks inLowerCretaceousstrataofVictoria.Hencefutureresearchersscanning bedding planes of the Wonthaggi and EumerallaFormationsmightadjusttheirsearchimagesforraisedtrackson bed tops, rather than just depressions. Furthermore, lessdefiniteformsofdinosaur,suchasthatofSkenesCreekTrack2, shouldnotbe soeasily ignoredordismissedonce found.Givenalloftheseinsights,Ihaveeveryconfidencethatmoredinosaurtrackswillbediscovered,whetherfromornithopods,theropods, or other tetrapod taxawhose trace fossil recordsare not yet known from this otherwise palaeontologicallywell-studiedareaofAustralia.

Acknowledgements

I amextremelygrateful toThomas (Tom)RichandPatricia(Pat) Vickers-Rich for their guidance, mentorship, andfriendshipovertheyears,startingwithasabbaticalIenjoyedatMonash University in 2006 and visits to Australia sincethen. I thankErichFitzgerald (MuseumVictoria) foraskingme to write this manuscript, as well as Lisa Buckley andAnthony Romilio for their insightful and helpful reviews.Appreciation is extended to David Pickering, Lesley andGerryKool,MichaelandNaomiHall,andMichaelCleelandfor their time in thefieldwithme,aswellaseducating thisinexperiencedYankwhenever he dropped in for a too-briefglance at their lovely Lower Cretaceous rocks. HelmutTracksdorf and Michael Cleeland also were invaluable inhelpingtodocumenttheoriginaldiscoverysiteoftheSkenesCreektracks.TheEmoryUniversityFacultyTravelFundandthe Center for International ProgramsAbroad assistedwithsomeofmytravelexpensesduringvariousvisits.Lastbutnotleast,Iamindebtedtomywife,Ruth,nicknamed“Lefty”byher fellow southpaw Tom, for her sinistral support duringmuchoftheresearch.

A.J. Martin70

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AppendicesAppendix I. Specimen Label Information

Specimen label information for Knowledge Creek track:P.159790;Dinosaur track,OtwayGroup,KnowledgeCreek,Victoria on wave platform about 100 m east of mouth of

A close look at Victoria's first known dinosaur tracks 71

Knowledge Creek. T. Rich Exp., 18-12-1980 [December 18,1980]

Specimen Label Information for Skenes Creek tracks:P.208232;T.H.RichExp.,18-3-1989[March18,1989]SkenesCreek(Catalog149).Locality:Shoreplatform,SkenesCreek.

Appendix II. Discovery of the Skenes Creek Tracks

ThespecimenlabelforthetwoSkenesCreektracksdoesnotcredittheiroriginaldiscoverer,andrepeatedinquiriesposedtopersonnelatMuseumVictoriaandlong-timevolunteersdidnotresult in anyone taking credit for finding them. So I wasgratifiedtolearnin2013thatcreditfortheirdiscoveryshouldgotoHelmutTracksdorf,ageologistwholivedinVictorianearSkenesCreekatthetimeoftheirdiscovery.

InOctober2013,Mr.Tracksdorfreadablogpostwrittenbyme referring to the track.Mr. Tracksdorf sentme an e-mailmessage,receivedonOctober20,2013,revealingthathewasthepersonwhofoundthetracks.Accordingtohismessage,hethen reported these tracks and their location to MuseumVictoriapersonnel.Severalmonthsafterreportingthem,hedidnotreceiveaconfirmationfromMuseumVictoriaonwhetherornotthetrackswererecovered.However,helatervisitedthesiteandsawwheretheyhadbeencutoutofthemarineplatform.The e-mail message was sent by Helmut Tracksdorf andreceivedbyme(AnthonyJ.Martin)at5:43p.m.onOctober20,2013. The full, verbatim text of the e-mail is available forreadingwithpermissionofbothMr.Tracksdorfandmyself.

Later,onJuly9,2014,Trackdorfcontactedmeagainviae-mail with more information about the probable originallocation of the tracks; he copied Thomas Rich, DavidPickering, Lesley Kool, and Michael Cleeland onto thismessage.Inthismessage,hedescribedtherock-sawcutsonthemarineplatformas50-100mwestofBrownsCreek(eastof both SkenesCreek and PetticoatCreek) and about 50msouthoftheGreatOceanRoad.Alongwiththisdescription,TracksdorfprovidedaGoogleEarthimageofthelocality,aswellasphotographsofthesiteandrock-sawcutsinthemarineplatform,withthephotostakeninJune,2014byTrackdorf’sbrother (name not given). These descriptions aided me infiguringtheapproximatelatitude-longitudecoordinatesofthetracks. On February 17, 2015, Cleeland and his wife (Pip)stoppedby the location to look for the rock-sawcutson themarineplatform,relocatedthem,andphotographedtherock-sawcuts;thesewerealignedwithoneanotherandinarippledsandstone very similar to those of the Skenes Creek tracks(NMVP208232).OnMarch2,2015,hesentthesephotographsto Rich, Pickering, Kool, Trackdorf, and me. Given thisconfirmation,weweresatisfiedthatthisisindeedthediscoverysiteofthetracks.

In deference to their long-established nickname as the“Skenes Creek tracks,” I recommend retaining this locationdesignation, rather than adopting the more geographicallyappropriate“BrownsCreek tracks.” I also suggest that futureresearcherssearchingformoresuchdinosaurtracksinthisareamight concentrate their efforts on rippled sandstones in themarineplatformbetweenPetticoatCreekandBrownsCreek.