A partly endemic euryhaline fish fauna (otoliths, teeth) from the Early ...
Ini&al Studies of Fish Otoliths Aid in Understanding the Jones ...
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Ini$alStudiesofFishOtolithsAidinUnderstandingtheJonesBranchSite(LateOligocene)inSoutheastern
Mississippi
Dr.GaryL.StringerMuseumofNaturalHistory
UniversityofLouisiana-Monroe
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IMPORTANCEOFOTOLITHSATTHEJONESBRANCHSITE
Teleosteanearstonesorotoliths,partofthefish’sacous4co-lateralissystem,supplyimportanttaxonomicinforma4onthatcanaugmentskeletalremains.Atmanysites,especiallyinGulfCoastandCaribbeandeposits,otolithsactuallyprovidegreaterinsightintothebonyfishesthanskeletalfossils.
Otolithscanfurnishsalientandsignificantpaleogeographyandpaleoecologydata.
Finally,otolithscanprovidegeneralbiostra4graphicparameters.
JonesBranchotolithassemblagecancontributeinalltheseareas.
Aplodinotus gemma Koken, 1888
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Bestshellhashlayerwasbelowwaterlevel(whitearrow).However,about75kg(164.6lbs)ofshellhashfromCatahoulaForma4onwas
collected.JamesStarnes(MSOfficeofGeology)forscale.
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Difficultyofcollec4ngdemonstratedbyMSMuseumofNaturalScience(MMNS)GeorgePhillips’awkwardanduncomfortablepostureinthecreek.
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Samplefromthelowerpor4onoftheCatahoulaForma4onshowingthethinmarinelayer(shellhash).
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Rareoccurrenceforme:collec4ngotolithsincloseassocia4onwithexcellentlypreserved,carbonizedfloralremains.
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Asnotedearlier,75kgofbasalCatahoulaForma4onwascollected.Emphasiswasplacedonprocuringtheshellhashlayer.Allotolithsforthisstudywereobtainedbybulksampling(nootolithsrecoveredonthesurface).
Bulksampleswereairdriedcompletelybeforewaterscreening(noaddi4ves).
Bulksampleproducedanamazing14kg(31pounds)ofresidue(30meshandabove).Smallermeshwasretainedbutnotexamined.Verylargemeshwassortedbynakedeye.Allresidue5meshandsmallerwasmicroscopicallyexamined.
OtolithspecimenswerealsoobtainedonloanfromtheMMNS.
METHODOLOGY
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Approximately9.6kg(21.2lbs)ofresidueexaminedwithanOlympusbinocularstereo-zoommicroscope(0.67to4.0x).
Standardmicropaleontologytray(5x9cm)u4lized.Basedonweightofonetrayofresidue,es4matedthat2,345trayswereexaminedtoobtainotolithspecimens.
Examiningresiduewasquitedifficult:amountofresidue,rarityofotoliths,presenceofhardenedclayclasts(evena`errepeatedwaterscreening),veryabundantquartzsandgrains,andeffectsofreworking,erosion,etc.Manyofclayclastsandmolluskshellswereroundedandresembledtheshapeofotoliths.
METHODOLOGY(con$nued)
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Mostoftheotolithswerepoorlypreserved,andmanyhadtobetreatedwithButvar(mostoftheMMNSspecimensweretreated).Poorpreserva4on(aragoni4cdissolu4on)couldberelatedtoexposuretofluidsatsediment-waterinterface,insitufluidsa`erburialinnearsurfacesediments,ormeteoricdiagenesis.
Inspiteofthelimita4onsofthestudyoftheotoliths(scarcityofotoliths,extremelyfriableanderodedcondi4onofmanyspecimens,andsmallsize),295iden4fiableotolithswererecoveredalongwithmanynon-descriptfragments.
Someotolithscouldonlybeassignedtofamilylevelsduetopreserva4on.S4ll,otolithsprovidedevidenceofbonyfishesrepresen4ngatleastfivefamiliesandninetaxa.
PRELIMINARYRESULTS
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BonyfishesrepresentedbyotolithsfromtheCatahoulaForma4onattheJonesBranchSitewereasfollows:
Onealbulid(bonefishes),
Twotaxaofcongrids(congereels),
Onesparid(porgies),
Atleastfourtaxaofsciaenids(drums).
Itshouldbenotedthatothertaxaarepossibleinthegroupsiden4fiedasPerciformesindeterminateandSciaenidae
indeterminate.Howeverevenwiththepossibilityofseveraladdi4onalspecies,theJonesBranchotolithassemblageisquite
restrictedindiversity.
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OtolithassemblagefromtheCatahoulaForma4onattheJonesBranchSitewasdominatedbysciaenidsordrums.ThefamilySciaenidaeaccountedfor84.75%ofthetotalotoliths.Foursciaenidtaxaalsorepresented55.56%ofthetotaltaxaasindicatedbyotoliths.ThreeofthesciaenidtaxaareknownonlyfromtheOligocene(Aplodinotusgemma,Aplodinotusdistortus,and“Sciaenida”radians).
Albulidsorbonefisheswerethesecondmostabundantgroupbutcomprisedonly2.71%ofthetotalotoliths.Thedominanceofsciaenidtaxaisquiteevidentandpronounced.
SeveraloftheJonesBranchtaxawererepresentedbyonlyoneortwootoliths(congrids,sparids,flounders).
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Byfar,themostabundantspeciesintheotolithassemblageoftheCatahoulaForma4onattheJonesBranchLocalitywerethe
followingsciaenidtaxa:
Sciaenapseudoradians(Dante&Frizzell,1965)
AplodinotusgemmaKoken,1888
AplodinotusdistortusNolf,2003
Scale=1mm
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CloselyrelatedRecentfishesrepresentedbyotolithsintheCatahoulaForma4on.
Onealbulid(bonefishes)
Twotaxaofcongrids(congereels)
Onesparid(porgies)
Oneparalichthyid(large-toothflounders)
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CloselyrelatedRecentfishesrepresentedbyotolithsintheCatahoulaForma4onattheJonesBranchLocality
Atleastfourdifferentspeciesofsciaenidsordrums
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Althoughsciaenidsdominatedtheotolithassemblagenumericallyandtaxonomically,specimenswereunusuallysmall.
Completeornearlycompletesciaenidsotolithsrangedfromapproximately1.65mmto10.27mm.
However,98.47%ofthecompletesciaenidotolithsiden4fiedtospecies(131specimens)were5.99mmorless.
Smallsizeisfurtheremphasizedinthat91.6%ofthesciaenidotolithswere3.99mmorless.
Thereisalinearrela4onshipofthesizeoftheotolithsandtheageofthefish.
IMPLICATIONSOFSCIAENIDOTOLITHSIZE
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TounderstandthesignificanceofthesizeofJonesBranchsciaenidotoliths,twoRecentGulfofMexicodrumswereu4lizedasanalogs.Otolithsweremeasuredforthereddrumandblackdrumfromone-year-oldtofour-years-old.
SizedatawerealsoobtainedforAplodinotusgrunnienssincetwoofJonesBranchsciaenidswereclassifiedinthisgenus.
LengthsforotolithsofSciaenopsocellatus(reddrum)rangedfrom14.65to19.24mm(one-year-oldtofour-years-old),Pogoniascromis(blackdrum)ranged10.37to16.88mm(one-year-oldtofour),andAplodinotusgrunniens(freshwaterdrum)rangedfrom5.90to9.80mm(one-year-oldtofour).
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Applyinganyofone-yearsizerangesforthethreedifferentspecies(14.65mm,10.37mm,and5.90mm),alloftheJonesBranchsciaenidotoliths,exceptforafewspecimens,wouldrepresentdrumsthatarelessthanone-year-old(seegraph).
Recentecologicaldataindicatethatjuvenileblackdrumsprefershallow,nutrient-rich,turbidwaterssuchas4dalcreeksandchannelsandevenfreshwaterhabitats(i.e.,reducedsalini4es).
Otherdrums,suchastheAtlan4ccroaker,remaininestuariesun4ltheyarethree-years-old.ManyotherGulfofMexicodrumsdisplaysimilardistribu4onpalerns.
Therefore,size(i.e.,ageoffish)oftheJonesBranchsciaenidotolithsappearstoindicateanestuarinetypeenvironment.
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PALEOECOLOGICALSIGNIFICANCE
Predominanceofthesciaenidotolithsandtheirsize(i.e.,ageoffish)arestrongindicatorsofestuaries,4dalchannels,andpasses(reducedsalini4es).Over98%ofthesciaenidspecimensaresmallerthan5.99mmandrepresentfishthataremostlikelylessthanone-year-old(larvalandjuveniles).Thehighlyrestrictedagecomposi4onindicatesaspecificenvironment.
Bonefishes(albulids),althoughverylimited,suggestaveryshallowmarineenvironment(probablyinnershelfor<20m).Othertaxa(congereels,porgies,andflounders),representedbyonlyfivespecimens,alsoindicateextremelyshallow,marinewaters.
Paleogeographyindicatedbyotolithsappearstoconfirmseveralpaleogeograpicmapsforthearea.
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ModifiedfromAtlasofMesozoicandCenozoicCoastlines
PALEOGEOGRAPHICIMPLICATIONS
NorthAmerica
Atlan&cOcean
SouthAmerica
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PaleogeographyfortheEocene-Oligocene(35Ma)
Mapfrom“PaleogeographicandTectonicHistoryofNorthAmerica–KeyTimeSlices”(dataandmapcourtesyofRonBlakey,ColoradoPlateauGeosystems,2013).
Analysis:Mapindicatesshallowmarinecondi4onsandpossibleestuarineenvironmentsfortheJonesBranchLocality.Thisinterpreta4onisalsosupportedbytheotolithassemblage.
UnitedStates
MS
GulfofMexicoMexico
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OligocenepaleogeographyforsoutheastU.S.basedonmappedOligocenestate-scalesurfacegeology(Dr.S.Ebersole,2016,GeologicalSurveyofAlabama).
Otolithsappeartosupportthisscenarioanddatasetextremelywell.
MS
GulfofMexico
Atlan:cOcean
Oligoceneshorelineshowninblue
Jones ★
BranchSite
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PRELIMINARYCONCLUSIONS
• Microscopicexamina4onofresiduefromashellhashlayerinthebasalCatahoulaForma4on(upperOligocene,Chapan)attheJonesBranchLocalitynearWaynesboro,Alabama,hasproduced295otolithsthatrepresentatleast5familiesand9taxaofbonyfishes.
• Bonyfishesindicatedbyotolithswerequiterestrictedindiversity.
• Otolithassemblagewasdominatedbyrepresenta4vesofthefamilySciaenidae,whichaccountedfor84.75%ofthetotalotoliths.Threedrumtaxa,Sciaenapseudoradians,Aplodinotusgemma,andAplodinotusdistortus,werebyfarthemostabundant.
• Severalofthesciaenidspecies(Aplodinotusgemma,Aplodinotusdistortus,and“Sciaenida”radians)areknownonlyfromtheGulfCoastOligocene.
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PRELIMINARYCONCLUSIONS(con$nued)
• Oneofthemostuniquefindingswasthesizeofthesciaenidotoliths,whichhasalinearrela4onshiptofishage.Over98%ofthesciaenidotolithspecimensweresmallerthan5.99mm.
• Sciaenidotolithsofthissizemostassuredlyrepresentfishthatarelessthanone-year-old(larvalandjuveniles).Theagecomposi4onofthesciaenidsisastrongindicatorofaspecificenvironment.
• Predominanceofthesciaenidotoliths,preferredhabitatsofsciaenidsbasedonRecentanalogs,andsizeofthedrumotoliths(i.e.,ageoffish)arestrongindicatorsofestuaries,4dalchannels,andpasses(reducedsalini4es)incloseproximitytoshallowmarinecondi4ons.
• Whethertheotolithswerereworkedorsyndeposi4onalwiththebasalCatahoulaForma4onrequiresfurtherinves4ga4on.
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ACKNOWLEDGEMENTS
• GeorgePhillips(PaleontologyCurator,MississippiMuseumofNaturalScience)andJamesStarnes(Geologist,MississippiOfficeofGeology)wholoanedotoliths,accompaniedauthortosite,andassistedincollec4ng,• AndyWellerfromWaynesboro,MS,obtainedpermissiontocollect,• Dr.S.Ebersole(AlabamaGeologicalSurvey)andDr.R.Blakey(ColoradoPlateauGeosystems)forpaleogeographicmaps,• Dr.R.Patzner,Dr.J.E.Randall,Dr.F.Costa,Dr.D.Flescher,Dr.D.Smith(withO.OzenandE.Irmack),Mr.BarrelChris4e,andMs.KarenHoneyculgraciouslyallowedtheuseofpicturesofRecentfishesfromFishBase,• Dr.DirkNolf,RoyalBelgianIns4tuteofNaturalSciencesforhissupport,• Dr.MelissaCook,Na4onalMarineFisheriesService,MississippiLaboratoryprovidednumerousfishforotolithandgrowthstudies.
Sincereapprecia4onisextendedtothefollowing:
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QUESTIONSORCOMMENTS?
GLS