Raup - Periodicity of Extinctions

Raup - Periodicity of Extinctions - Proc.Nati.Acad. Sci. USA

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Unformatted text preview: Proc.Nati.Acad. Sci. USA Vol.81,pp.801-805, February 1984 Evolution Periodicityofextinctionsinthegeologicpast (evolution/timeseries/paleontology) DAVID M. RAUP AND J.JOHN SEPKOSKI, JR. DepartmentofGeophysicalSciences, UniversityofChicago,Chicago,IL60637 ContributedbyDavidM. Raup, October 11,1983 ABSTRACT The temporal distribution ofthemajor ex- tinctionsoverthepast250millionyearshasbeeninvestigated statisticallyusing various forms oftime seriesanalysis. The analyzedrecordisbasedonvariationinextinctionintensityfor fossilfamiliesofmarinevertebrates,invertebrates,andproto- zoansandcontains12extinctionevents.The 12eventsshowa statisticallysignificantperiodicity(P< 0.01)withamean in- tervalbetween eventsof26 millionyears. Two oftheevents coincidewithextinctionsthathave been previouslylinkedto meteoriteimpacts(terminalCretaceousandLateEocene).Al- thoughthecausesoftheperiodicityareunknown, itispossible thattheyarerelatedtoextraterrestrialforces(solar,solarsys- tem, orgalactic). Virtually allspecies ofanimals and plantsthat have ever lived are now extinct, and the known fossilrecord docu- ments some 200,000such extinctions.Ithasbeen generally assumedthatextinctionisacontinuousprocessinthesense thatspeciesarealwaysatriskandthatmassextinctionssim- plyreflectrelatively short-term increases inthatrisk.Fol- lowingthisview,the extinctionprocess isoftendescribed mathematicallyasatime homogeneous processusingstan- dardbirth-deathmodels (1-3).Thereisincreasingevidence, however, that many extinctions are actually short-lived eventsofspecialstress,separatedbyperiodsofmuchlower, or even negligible, risk. Fischer and Arthur (4)departed fromconventionbyarguingthatthemajorextinctionevents ofthepast 250 millionyears (ma)occurred periodicallyat nearlyconstant intervals of32 ma (seealso ref. 5).Their studyusedalimiteddatabase,andnostatisticaltestingwas done. The purpose ofthis paper, therefore, isto test the propositionofperiodicityintherecordofmarineextinctions overthepast250ma (LatePermianto Recent) byusing as rigorousamethodologyaspresentdatapermit. DATA BASE ThedataforthisstudycomefromSepkoski'scompilation(6) ofthetemporalrangesof -3,500familiesofmarineanimals (vertebrate,invertebrate, and protozoan), butthe subsetof data and method of expressing extinction intensity differ fromourpreviousanalysesofthesedata(7,8).Forthepres- entstudy,aculledsubsetofthetotalsample was used: all familieswithlow-resolutionranges, notknown tothelevel ofthestratigraphicstage,were eliminated,as were families notedbySepkoski(6)ashavingquestionabletaxonomic or stratigraphicdesignations.Inaddition,familiesstilllivingto- daywereignoredinordertoavoidthedampingeffectofthe "Pull ofthe Recent" (9). This cullingprocess reduced the sample substantially(567forthe Late Permian toRecent) butinsodoingremovedmuch ofthenoisethatcharacterizes datasetsofthiskind....
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Raup - Periodicity of Extinctions - Proc.Nati.Acad. Sci. USA

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