The Mesozoic era - The Australian Museum

The Mesozoic Era (252 - 66 million years ago). The Mesozoic Era spanned 252 to 66 million years ago. Australia in the Mesozoic was nothing like it is today. It ... Thiswebsiteusescookiestoensureyougetthebestexperienceon our website. Learn more Acceptandclose Skiptomaincontent Skiptoacknowledgementofcountry Skiptofooter ImagineyourselfatthedawnoftheMesozoicabout250millionyearsago...Mostlargeanimalsarereptilesratherthanmammals;therearenodinosaurs,nobirdsounds,andnoflowerstopickorgrasstomow.YoucouldevenwalkallthewayfromthenorthtothesouthpoleacrossonegiantcontinentcalledPangaea!However,thisworld,andtheplantsandanimalslivinginit,hadchangeddramaticallybytheendoftheera.AspotlightonAustraliaAustraliaintheMesozoicwasnothinglikeitistoday.Itdidnotexistasaseparatelandmass,itspositionontheglobewasmuchfurthersouthandtheclimateandplantswereverydifferent.Infact,Australia’sMesozoicstory–andthatofitsdinosaurs–isinseparablefromthoseoftheotherlandmassesthatonceformedthesouthernsuper-continentGondwana. ToggleCaption MesozoicTimeline Image: illustration ©AustralianMuseum Gondwana:thesouthernsuper-continentAtthebeginningoftheMesozoic,GondwanaformedthesouthernpartofthesinglecontinentPangaea.WhenPangaeasplitabout200millionyearsago,Gondwanabeganitsownisolatedjourneyandgradualbreak-upintothelandmassesweknowtoday–Australia,SouthAmerica,Africa,India,Madagascar,AntarcticaandNewZealand.Thispalaeo-historyisrecordedinidenticalrocksandfossilsfoundacrossthesemodernlandmasses.Whenwereconnectthemastheywereinthepast,therocksandfossilsclearlymatchup. ToggleCaption MapofGondwana,showingbreak-upintomodernlandmassesandthedistributionofkeyfossilsacrosstheselandmasses. Image: illustration ©AustralianMuseum TheMesozoicextinctionevent TheMesozoiccametoanabruptend66millionyearsagoinadramaticextinctionevent.Death.Destruction.Devastation.Whatanending.Weknowtheoutcome,butwhatwasthecause?Canwereallyknowwhathappened66millionyearsago?Andwhydoesitmattertoday? Massextinction TheMesozoiccametoanabruptend66millionyearsagoinadramaticextinctionevent.Anestimated70percentofplantandanimalspeciesperished.Manytheorieshavebeensuggestedforitscause.Thefewthatareacceptedasscientificallyvalidareplacedintotwoopposinggroups.The‘catastrophists’believethemassextinctionhappenedsuddenlyduetoameteoriteimpact.The‘gradualists’consideritwasprolongedandcausedbyclimatechangeorvolcanicactivity,withthemeteoriteonlyprovidingthefinalblow. Meteorites Manyscientistsbelievethattheimpactofoneormoremeteoriteswasthemajorcauseoftheend-Mesozoicextinction.TheideawasfirstproposedbyAlvarezandAlvarezin1979basedontheiranalysisofaclaylayerinItaly(knownastheGubbioclaylayer).Thislayeryieldedextensiveamountsofthemineralelementiridium.IridiumisscarceonEarthandconsideredtobemeteoricinorigin.Thistheorygainedmomentumasfurtherresearchturnedupavarietyofsupportiveevidencefromrocklayersdatingtoabout66millionyearsold.Theseincludesmoresitesaroundtheworldwithiridium,possibleimpactcraters,tsunamisedimentdeposits,shockedquartzandcarbonsoots.Alargemeteorite(about10-kilometre-wide)hittingtheEarthwouldbecatastrophic.Researchshowsthattheeffectswouldincludeglobalfirestorms,highmagnitudeearthquakes,tsunamis,acidrain,heatingoftheatmosphere,anddebrisanddustthatcauseprolongedwinter.Allthesewoulddevastatethebiosphere,withmassiveinitialfatalitiesfollowedbycollapseoffoodchains. CratersitestotheendoftheMesozoic AnumberofcratersitesaroundtheworlddatetotheendoftheMesozoic.TheChicxulubCraterinMexicoisthemostlikelysiteoftheimpact.This200-kilometrewidecraterwasaccidentallydiscoveredin1991bygeologistsdrillingforoil.TheShivaCraterhasalsobeenproposed.ThiscraterisfoundattheIndia-Seychellesrift.Itwouldhavebeenabout600kilometreslongand450kilometreswidewhenfirstformed,buthasseparatedduetosea-floorspreading.Iftheoriginalmeteoritebrokeintofragments,onecouldhaveformedtheShivaCraterwhiletheotherimpactedatChicxulub.Itisestimatedthatameteoritewithadiameterofatleast10kilometreswouldhavebeenneededtocreatea200-kilometre-widecrater,liketheoneatChicxulub.TheenergyreleasedfromameteoritethissizewouldbeaboutamilliontimesthepoweroftheatomicbombdroppedonHiroshimain1945. ToggleCaption Impactsitesofmeteoritesworldwide. Image: illustration ©AustralianMuseum Themapshowssixmajorend-Mesozoiccratersites:Chicxulub,MexicoSilverpit,NorthSeaBoltysh,UkraineShiva,IndianOceanEagleButte,CanadaVistaAlegre,Brazil ToggleCaption CloseupmapofMexico,showingmeteoriteimpactsite. Image: illustration ©AustralianMuseum Shockedquartz Shockedquartzhasacrystalstructurealteredbysuddenextremepressurefromeitherviolentvolcaniceruptionsormeteoriteimpacts.Samplesfromtheend-Mesozoicextinctionlayeraremostlikelycausedbyameteoriteimpact. ToggleCaption Shockedquartz Image: AlanHildebrand ©AlanHildebrand Impactlayer ThisrocksamplefromNewZealandshowsthelayerformedduringtheend-Mesozoicextinctionevent.Over200extinctionlayersitesaroundtheworldhaveproducedelevatedlevelsofthemetaliridium.IridiumisrareintheEarth’scrustbutrelativelycommoninmeteorites. ToggleCaption ThisrocksamplefromNewZealandshowsthelayerformedduringtheend-Mesozoicextinctionevent. Image: illustration ©AustralianMuseum Samplelabels(fromtopofsampletobottom):Recoveryzone-Palaeogenerock:containsfossilsofmarinelife,butnotasmanyasbeforetheend-Mesozoicevent.Deadzone-Palaeogenerock:containsnofossilsofmarinelifeexceptforasmallamountofplankton.Boundaryzone-end-Mesozoicrock:containshighlevelsofiridium.Normalzone-Cretaceousrock:containslotsoffossilsoflotsofdifferenttypesofmarinelife. Volcanoes Notallscientistsagreethatameteoriteimpactcausedtheend-Mesozoicextinction.Somesuggestthattheextinctionoccurredoveranextendedperiodoftimeduetomassivevolcanism.Theyarguethatmuchoftheevidenceputforwardtosupportthemeteoriteimpacttheorycouldhavebeenduetovolcanicactivityinstead.TheendoftheCretaceouswasoneofthemostintenseperiodsofvolcanicactivityinEarth'shistorywithanumberofsitesshowingevidenceoflargescaleeruptions.Inparticular,theDeccanTrapsinIndiacoveranareaof800,000squarekilometres.TheywereformedoverafewmillionyearsneartheendoftheCretaceouswhenhugevolumesoflavawerereleasedinaseriesoferuptions.OthersitesofpossiblemassivevolcaniceruptionshavebeenfoundinCameroonandtheCoralSea.Largescaleeruptionswouldhaveresultedinseveraltrilliontonnesofashandtoxicgases,suchassulphurdioxideandcarbondioxide,beingpumpedintotheair.Thesecouldcausecatastrophicchangestotheclimateincludingprolongedwinters,seasonalchanges,globalwarmingandaridity,alongwithotherimpactssuchasacidrain,andchemicalchangestotheoceansurfaces.TheDeccaneruptionscertainlyaffectedlocalfloraandfauna,butevidencesuggeststhatitmayhavehadlittledirectaffectonglobalextinctions.FossilsfoundaroundtheTrapsshowthatlifewasresilientinthisenvironment,includingdinosaurlife. ToggleCaption TheDeccanTrapsinIndiacoveranareaof800,000squarekilometres.TheywereformedoverafewmillionyearsneartheendoftheCretaceouswhenhugevolumesoflavawerereleasedinaseriesoferuptions. Image: - ©AustralianMuseum ToggleCaption Basalticlavaspecimen,DR16555.FromtheDeccanTraps,India.LateCretaceous65millionyearsago. Image: Robertjones ©AustralianMuseum Amixingpotofcauses Anotherpossibilitysuggestedbysomescientistsisthatavarietyoffactors,noneofwhichwereindividuallydecisive,causedthemassextinctionsattheendoftheMesozoic.Theextinction'event'tookmillionsofyearswiththefinalextinctioncoincidingwiththemeteoriteimpact.FossilandgeologicalevidenceindicatesgradualchangesonaglobalscaleweretakingplacebeforetheendoftheCretaceous.Thesechangesincludedvolcanicactivity,shiftingcontinentalplatesthatalteredtheclimateandenvironment,fallingsealevelsandmountainbuilding.Significantplantextinctionswereoccurringatthistimeandthefossilrecordinsomeareassuggeststhatdinosaurpopulationswerealsoindecline. Whythedifferenceofopinion? Scientistsagreeinanumberofareas.Forinstance,theyagreethatattheendoftheCretaceoustheglobalclimatewaschanging,thattherewasmajorcontinentalplatemovementandoceanregression,thatincreasedvolcanicactivitywasoccurring,thatdinosaurdiversitywasdecliningandthatameteoriteimpacted.However,theydifferintheirassessmentoftheevidenceandthedegreetowhicheachfactorcontributedtothemassextinctionevent.PartofthereasontheyinterprettheevidencedifferentlyisduetothelackoffossilsandsamplesitesfromtheendoftheMesozoic(onlythenorthwestUSAhasbeenextensivelystudied).Inaddition,alackofknowledgeaboutdinosaurphysiologyanditsroleintheirextinction,alongwithwhysomeanimalgroupsdiedwhileotherssurvived,makesdefinitiveanswersalmostimpossible. WhoSurvived? Findingoutwhatcausedthemassextinctionisonething.Howandwhysomegroupsofanimalssurvivedwhenothersdidnotisanother.Unfortunately,gapsinthefossilrecordandourknowledgeabouttheextinctioneventmeanwemayneverhavealltheanswers.Afewpatternsdoemerge.Lifeintheseaswashardesthit.Manygroupsoflandanimalsthatwereeitherlargeorwarm-blooded,suchasnon-aviandinosaurs,pterosaursandprimitivebirds,alsosufferedseverelosses.Thosethatsurvivedtendedtoliveinfreshwaterriversorlakes,weresmall,hadwidespreaddistributionsorwerecold-blooded. ToggleCaption Diagramofmodernextinctionsurvivors. Image: illustration ©AustralianMuseum Listofsurvivinggroups(fromtoptobottomofgraphic):insectsmolluscsmammalsturtleslizardsandsnakescrocodilesfishbirds(theropoddinosaurs)Listofgroupsthatdidnotsurvive:mosasaursicthyosaursplesiosaurspterosaurstheropods(otherthanbirds)sauropodsornithopodsstegosaursankylosaursceratopsians Crocodilesurvivors Crocodilesandalligatorsareoftenviewedasthegreatsurvivorsfromthedinosaurage,andalsomistakenlyaslivingdinosaurs.Thequestionisoftenaskedastowhyandhowtheysurvivedthismassextinctionwhennon-aviandinosaursdidnot.Firstly,notallcrocodilefamiliesdidsurvive-infact,quiteanumberdidbecomeextinct,particularlythelarge-bodiedones.Anumberofreasonshavebeensuggestedtoexplainwhytheothergroupsofcrocodilesdidsurvive.Theseinclude:acold-bloodedabilitytocontinuetofunctionatlowbodytemperatureandsorequirelessfoodasmoderncrocodileshaveimmunesystemsthatcansustainterribleinjuries,ancientcrocodilesmayalsohavehadthisabilitylivingcrocodilescantoleratelongperiodsofdarknessandpoorconditionsmanyspeciesappearedtoliveinfreshwaterenvironmentswhichwerelessimpactedbytheextinctioneventmostanimalseitherproducelotsofoffspringthatarelefttorearthemselvesorasmallnumberofoffspringthattheyexpendenormousenergyraising.Crocodilesareamongthefewanimalsthatdoboth,asfemaleslayupto60eggsandoftenprotectthenestandyoung.Insomespecies,bothmalesandfemalesprotecttheyoung. Afinalthought… Canweuseourfascinationwithdinosaursandtheir‘extinction’andbeinspiredbythosethatsurvivetoday?Birdsareahighlysuccessfulgroupwithabout10,000livingspeciesbuttheircontinuedsurvival,alongwiththatofmanyotheranimals,dependslargelyonus.Wearecurrentlycontributingtoanothermassextinctionevent. Youmayalsobeinterestedin... DrArthurBacheWalkom,Director,1941-1954 DrArthurBacheWalkom,Director,1941-1954 Discovermore Steropodongalmani Steropodongalmani,aplatypus-likemonotremefromtheEarlyCretaceousofAustralia,wasthefirstMesozoicmammaldiscoveredfromAustralia.ItisknownfromanopalisedlowerjawwithmolarteethfoundattheminingtownofLightningRidgeinnorthcentralNewSouthWales. Steropodongalmani Discovermore AustralianMuseumMagazineVolume07Issue10 AMPublication Readmore Dinosaursandtheirrelatives DiscovertheMesozoiceraofthedinosaurs!Dinosaursareclassifiedasagroupofreptiles,althoughsomeoftheirfeaturesarefoundinmammalsandbirdslivingtoday. TheMesozoiceraDinosaurfactsheetsAustraliandinosaurs Findoutmore Whatisthegeologicaltimescale? Historicalrecordsonlygobackafewthousandyears,andareinadequatetotreatmostgeologicalprocesses. Readmore RecentandMesozoicserpulidsinpentagonaltubes:testingtheaffinitybythetubeultrastructures AMPublication Readmore Mesozoic-CainozoicVolcanismofAustralia AMPublication Readmore Dinosaurfactsheets LearnmoreaboutthedinosaursdiscoveredhereinAustraliaandacrosstheglobe. TyrannosaursspeciesChinesedinosaurs Learnmore TheRockhamptonplumeanditsLateMesozoictrace?MesozoicGeologyoftheEasternAustralianPlate AMPublication Readmore TheextentofUpperMesozoicIgneousActivityinrelationtolamprophyricintrusionsinTasmania AMPublication Readmore TheMesozoicEra(252-66millionyearsago) TheMesozoicEraspanned252to66millionyearsago.AustraliaintheMesozoicwasnothinglikeitistoday.Itdidnotexistasaseparatelandmass,itspositionontheglobewasmuchfurthersouthandtheclimateandplantswereverydifferent. Discovermore Re-evaluationoftheMesozoicmantisshrimpUrsquillayehoachibasedonnewmaterialandthevirtualpeeltechnique. AMPublication Readmore Youhavereachedtheendofthemaincontent. Gobacktostartofmaincontent Gobacktotopofpage Backtotop Youhavereachedtheendofthepage.Thankyouforreading. TheAustralianMuseumrespectsandacknowledgestheGadigal peopleastheFirst PeoplesandTraditionalCustodiansofthelandand waterwaysonwhichthe Museum stands. Imagecredit:gadigalyilimung(shield)made byUncle Charles Chicka Madden Closemodaldialog   Searchwebsite SubmitSearch CloseModalDialog CloseModalDialog CloseModalDialog CloseModalDialog CloseModalDialog CloseModalDialog CloseModalDialog