Ini$alStudiesofFishOtolithsAidinUnderstandingtheJonesBranchSite(LateOligocene)inSoutheastern

Mississippi

Dr.GaryL.StringerMuseumofNaturalHistory

UniversityofLouisiana-Monroe

IMPORTANCEOFOTOLITHSATTHEJONESBRANCHSITE

Teleosteanearstonesorotoliths,partofthefish’sacous4co-lateralissystem,supplyimportanttaxonomicinforma4onthatcanaugmentskeletalremains.Atmanysites,especiallyinGulfCoastandCaribbeandeposits,otolithsactuallyprovidegreaterinsightintothebonyfishesthanskeletalfossils.

Otolithscanfurnishsalientandsignificantpaleogeographyandpaleoecologydata.

Finally,otolithscanprovidegeneralbiostra4graphicparameters.

JonesBranchotolithassemblagecancontributeinalltheseareas.

Aplodinotus gemma Koken, 1888

Bestshellhashlayerwasbelowwaterlevel(whitearrow).However,about75kg(164.6lbs)ofshellhashfromCatahoulaForma4onwas

collected.JamesStarnes(MSOfficeofGeology)forscale.

Difficultyofcollec4ngdemonstratedbyMSMuseumofNaturalScience(MMNS)GeorgePhillips’awkwardanduncomfortablepostureinthecreek.

Samplefromthelowerpor4onoftheCatahoulaForma4onshowingthethinmarinelayer(shellhash).

Rareoccurrenceforme:collec4ngotolithsincloseassocia4onwithexcellentlypreserved,carbonizedfloralremains.

Asnotedearlier,75kgofbasalCatahoulaForma4onwascollected.Emphasiswasplacedonprocuringtheshellhashlayer.Allotolithsforthisstudywereobtainedbybulksampling(nootolithsrecoveredonthesurface).

Bulksampleswereairdriedcompletelybeforewaterscreening(noaddi4ves).

Bulksampleproducedanamazing14kg(31pounds)ofresidue(30meshandabove).Smallermeshwasretainedbutnotexamined.Verylargemeshwassortedbynakedeye.Allresidue5meshandsmallerwasmicroscopicallyexamined.

OtolithspecimenswerealsoobtainedonloanfromtheMMNS.

METHODOLOGY

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)

Mostoftheotolithswerepoorlypreserved,andmanyhadtobetreatedwithButvar(mostoftheMMNSspecimensweretreated).Poorpreserva4on(aragoni4cdissolu4on)couldberelatedtoexposuretofluidsatsediment-waterinterface,insitufluidsa`erburialinnearsurfacesediments,ormeteoricdiagenesis.

Inspiteofthelimita4onsofthestudyoftheotoliths(scarcityofotoliths,extremelyfriableanderodedcondi4onofmanyspecimens,andsmallsize),295iden4fiableotolithswererecoveredalongwithmanynon-descriptfragments.

Someotolithscouldonlybeassignedtofamilylevelsduetopreserva4on.S4ll,otolithsprovidedevidenceofbonyfishesrepresen4ngatleastfivefamiliesandninetaxa.

PRELIMINARYRESULTS

BonyfishesrepresentedbyotolithsfromtheCatahoulaForma4onattheJonesBranchSitewereasfollows:

Onealbulid(bonefishes),

Twotaxaofcongrids(congereels),

Onesparid(porgies),

Atleastfourtaxaofsciaenids(drums).

Itshouldbenotedthatothertaxaarepossibleinthegroupsiden4fiedasPerciformesindeterminateandSciaenidae

indeterminate.Howeverevenwiththepossibilityofseveraladdi4onalspecies,theJonesBranchotolithassemblageisquite

restrictedindiversity.

OtolithassemblagefromtheCatahoulaForma4onattheJonesBranchSitewasdominatedbysciaenidsordrums.ThefamilySciaenidaeaccountedfor84.75%ofthetotalotoliths.Foursciaenidtaxaalsorepresented55.56%ofthetotaltaxaasindicatedbyotoliths.ThreeofthesciaenidtaxaareknownonlyfromtheOligocene(Aplodinotusgemma,Aplodinotusdistortus,and“Sciaenida”radians).

Albulidsorbonefisheswerethesecondmostabundantgroupbutcomprisedonly2.71%ofthetotalotoliths.Thedominanceofsciaenidtaxaisquiteevidentandpronounced.

SeveraloftheJonesBranchtaxawererepresentedbyonlyoneortwootoliths(congrids,sparids,flounders).

Byfar,themostabundantspeciesintheotolithassemblageoftheCatahoulaForma4onattheJonesBranchLocalitywerethe

followingsciaenidtaxa:

Sciaenapseudoradians(Dante&Frizzell,1965)

AplodinotusgemmaKoken,1888

AplodinotusdistortusNolf,2003

Scale=1mm

CloselyrelatedRecentfishesrepresentedbyotolithsintheCatahoulaForma4on.

Onealbulid(bonefishes)

Twotaxaofcongrids(congereels)

Onesparid(porgies)

Oneparalichthyid(large-toothflounders)

CloselyrelatedRecentfishesrepresentedbyotolithsintheCatahoulaForma4onattheJonesBranchLocality

Atleastfourdifferentspeciesofsciaenidsordrums

Althoughsciaenidsdominatedtheotolithassemblagenumericallyandtaxonomically,specimenswereunusuallysmall.

Completeornearlycompletesciaenidsotolithsrangedfromapproximately1.65mmto10.27mm.

However,98.47%ofthecompletesciaenidotolithsiden4fiedtospecies(131specimens)were5.99mmorless.

Smallsizeisfurtheremphasizedinthat91.6%ofthesciaenidotolithswere3.99mmorless.

Thereisalinearrela4onshipofthesizeoftheotolithsandtheageofthefish.

IMPLICATIONSOFSCIAENIDOTOLITHSIZE

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).

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.

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.

ModifiedfromAtlasofMesozoicandCenozoicCoastlines

PALEOGEOGRAPHICIMPLICATIONS

NorthAmerica

Atlan&cOcean

SouthAmerica

PaleogeographyfortheEocene-Oligocene(35Ma)

Mapfrom“PaleogeographicandTectonicHistoryofNorthAmerica–KeyTimeSlices”(dataandmapcourtesyofRonBlakey,ColoradoPlateauGeosystems,2013).

Analysis:Mapindicatesshallowmarinecondi4onsandpossibleestuarineenvironmentsfortheJonesBranchLocality.Thisinterpreta4onisalsosupportedbytheotolithassemblage.

UnitedStates

MS

GulfofMexicoMexico

OligocenepaleogeographyforsoutheastU.S.basedonmappedOligocenestate-scalesurfacegeology(Dr.S.Ebersole,2016,GeologicalSurveyofAlabama).

Otolithsappeartosupportthisscenarioanddatasetextremelywell.

MS

GulfofMexico

Atlan:cOcean

Oligoceneshorelineshowninblue

Jones ★

BranchSite

PRELIMINARYCONCLUSIONS

• Microscopicexamina4onofresiduefromashellhashlayerinthebasalCatahoulaForma4on(upperOligocene,Chapan)attheJonesBranchLocalitynearWaynesboro,Alabama,hasproduced295otolithsthatrepresentatleast5familiesand9taxaofbonyfishes.

• Bonyfishesindicatedbyotolithswerequiterestrictedindiversity.

• Otolithassemblagewasdominatedbyrepresenta4vesofthefamilySciaenidae,whichaccountedfor84.75%ofthetotalotoliths.Threedrumtaxa,Sciaenapseudoradians,Aplodinotusgemma,andAplodinotusdistortus,werebyfarthemostabundant.

• Severalofthesciaenidspecies(Aplodinotusgemma,Aplodinotusdistortus,and“Sciaenida”radians)areknownonlyfromtheGulfCoastOligocene.

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.

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:

QUESTIONSORCOMMENTS?

GLS