The molluscs of the “Falunière” of Grignon (Middle Lutetian, Yvelines, France): quantification of lithification bias and its impact on the biodiversity assessment of the Middle Eocene of Western Europe

Geodiversitas

Loïc Villier¹  Malcolm T. Sanders¹  Didier Merle¹ 

关键词: palaeobiodiversity;    taphonomic bias;    rarefaction;    Lutetian;    Grignon;    San Giovanni Ilarione;    molluscs;    paléobiodiversité;    biais taphonomique;    raréfaction;    Lutétien;    Grignon;    San Giovanni Ilarione;    mollusques;   

DOI  :  10.5252/g2015n3a4

学科分类：生物科学（综合）

来源: Museum National d Histoire Naturelle

【 摘 要 】

Lithificationisstressedasamajorbiasforthepalaeobiodiversityevaluation.Althoughthisbiasisoftendiscussedintheliterature,ithasrarelybeenquantified.Thisworkoffersafirstestimationofdiagenesisimpactovermolluscdiversityrecordforasinglebedofthe“Falunière”ofGrignon(middleLutetian,France).Thisbedpossessestheparticularityofdisplayingtwolithologicalfacies:onelithifiedandtheotherunlithified,bothfromasametaphocoenosis.Molluscdiversitiesofthreeunlithifiedandthreelithifiedsampleshavebeencompared(1453specimensamong131species).Thecomparisonwasmadepossiblebytheconstructionofrarefactioncurvesextrapolatedfor30samplesandtheintroductionoftwoindexes:theeDG(extrapolatedDiagenesisGap)thatgivesavalueofdiversitylossbetweentwofaciesandtheSTD(sampling/diagenesisbiasthreshold)thatgivesthethreshold(innumberofsamples)afterwhicheDGcanbeestimated.Theanalysisrevealsthatnearly80%ofspeciesrichnessisnotrecordedinthelithifiedfacies,andthatlosscanreach100%forspeciessmallerthan2mm.Thebiaslinkedtospecimensizesisdiscussed,bothforlargeandsmallshells.ThedifferencesofbiodiversityrecordedamonglitholofacieshavealsobeenapproachedatregionallevelbythecomparisonoftaxonassociationsfromlithifiedandunlithifiedlithologiesfromthemiddleEoceneofParisBasin(Lutetian:Vanves,Nanterre,Damery,Fermedel'Orme,Chaussy,GrignonandVilliers-Saint-Frédéric;Bartonian:Baron),AquitaineBasin(Bartonian:BlayeandGironde)andItaly(Lutetian:SanGiovanniIlarione,Verona).ArevaluationofbiodiversityestimatesofSanGiovanniIlarionethatconsiderlithificationbiassuggeststhattheTethyanregionshousedsimilarorhigherspeciesrichnessthantheParisBasinduringtheLutetian,whichdoesnotagreewitharawdatacomparisonbutwhichwouldbetterfitwiththehypothesisofabiodiversityhotspotinthewesternTethys.Anyfuturecomparisonsofthebiodiversityfromdistinctregionsortimeintervalshavetoconsidertheconditionsofpreservationandthelithificationbias.

【 授权许可】

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