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1、TriassicconodontsandtheirroleinstageboundarydefinitionMICHAELJ.ORCHARDGeologicalSurveyofCanada,625RobsonSt.,Vancouver,BritishColumbiaV6B5J3Canada(e-mail:morchard@nrcan.gc.ca)Abstract:ConodontshaveplayedanimportantroleintheconstructionofaTriassictimescale.E
2、achofthestageboundariesisreviewedinthecontextoftheirevolvingconodontfaunas.ThebaseTriassic(Induan)isdefinedbytheappearanceofHindeodusparvus,whichdevelopedfromH.praeparvus;aparallelzonationisprovidedbyNeogondolellaspecies.FortheInduan–Olenekianboundary,thea
3、ppearanceofNeospathoduswaagenisensulatowithinaplexusofsimilarspeciesisfavouredasthedefiningdatum;BorinellaandEurygnathodusalsoappearaboutthistime.ThebaseoftheMiddleTriassicAnisianstageliesclosetotheappearanceofChio-sella,withTriassospathodusandSpathicuspus
4、characterizingthelateOlenekian,andGladigondo-lellatethydisandNicoraellaconfinedtotheAnisian.ProxiesfortheAnisian–Ladinianboundary,whichisdefinedbyanammonoid,arethefirstBudurovignathusspecies.ThebasalCarnian,alsodefinedbyanammonoid,liesclosetothefirstmetapolygn
5、athids,includingM.polygnathiformisandM.tadpole.TheCarnian–NorianboundaryintervalischaracterizedbymanynewtaxainCanada,butonlyafewspeciesarecommontoTethys,notablyMetapolygnathusexgr.M.echina-tus.TheNorian–RhaetianboundaryislikelytobebasedonevolutioninMisike
6、llainTethys,withconcurrentchangesrecognizedinNorthAmericanEpigondolella.ConodontsarrivedlateonthestageofearlyBaseTriassic,Changshingian–InduanMesozoictimescaledefinition,yettheyhaveboundary(Figs2&3)becomeincreasinglyimportantinhelpingtodefinetheGlobalStrato
7、typeSectionandPoints(GGSP)TheGSSPofthePermian–TriassicBoundaryofTriassicstages.Injust40yearsofmodernstudy,(PTB)wasratifiedbytheInternationalUnionofthesemicrofossilshavebeenusedtodefineoneGeologicalSciencesin2001(Yinetal.2001).ItGSSP(baseInduan),featureintwo
8、othersthatareisdefinedattheFirstAppearanceDatum(FAD)ofdefined(Ladinian,Carnian),andarefavouredastheconodontHindeodusparvus(Kozur&Pjata-indicesforalloftheremainingboundariesunderkova)withintheH.praeparvusKozur–H.parvus
