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343 Zitteliana 344 GEOLOGICAL AND PA L EONTO L O G CA L 1. I BACKGROUND Soft Senonian - Paleocene Sediments are widespread over (BiozoneM).Thesebiozonesandtheirstratigraphicpositions Israel. The Late Coniacian - Campanian succession consists werecorrelatedwithzonesandmarkersofotherfossilgroups mainlyofhomogenouschalks,overlainbymassivebrecciated (Reissetal.1985;Honigsteinetal.1987). cherts ofLateCampanianage. Argillaceous chalks dominate TheSenonianostracodeassemblagesconsistofmorethan60 Maastrichtian strata. Paleocene Sediments consist mainly of different species. Species of the subfamilvTrachvleberidinae marls and marly chalks (Flexer 1968). Most ofthese strata (e.g. group Cythereis) and ofthe genera Brachycythere and containratherriehmacrofossilandmicrofossilassemblages. Protobuntonia are dominant as well as smooth forms (e.g. TheConiacian-Campanianchalkscorrespondtoshallow- Cytherella).Allostracodespeciesaremarinetypesandpointto water environments in an inner to mid-shelf region. The Sedimentationinamoderateshelfenvironment. paleodepthcurveforthesedepositsshowsagradualsea-level Aftertheprominentdefaunationofostracodes(innumberof rtihsees(eFal-leexveerledturali.ng19t86h)e,LfaotlelCoawemdpabnyiaans.igAnifriecannetwelodwseerai-nlgevoelf srpicehctiieasnasinwelIlsraaesl,inPaplopeuolcaetnieonstdreantsaitcyo)ntdauirningagtahienMariacshte-r rise oecurred during the Maastrichtian. The strata were de- assemblagesofabout20differentspecies.ThemarinePaleo- posited inaseries ofbasins in anouter-shelftoupper-slope cenefaunasaredominatedbythegeneraOrdoniya,Mauritsina environment,withdysaerobicconditionsonthebottomofthe andsmoothforms(e.g.KritheandCytherella).Cristaeleberis sea.TheenvironmentofthePaleoceneSedimentsissimilarto retimlataBasSIOUNI,1971andMegommatocytheredenticulata that of the Maastrichtian, though somewhat shallower and (Eskir,1968)(describedbyHonigstein1984asOertliella}cf. withmorenormalmarineconditions. rasbaalbekensis)arereportedfromSenonianstrataandproeeed TheSenonianostracodefaunasofIsraelwerefirstdescribed intothePaleoceneofIsrael,asinneighbouringcountries(e.g. byHonigstein(1984). Ostracodes are relativelycommon in BasSIOUNI 1971; Bassiouniand Luger 1990).Two LateSan- Late Coniacian - Campanian Sediments and allow a bio- tonian - CampaniansubspeciesofCythereismesa reoceurin zonation into five ostracode assemblage zones (S-l to S-5). EarlyPaleoceneSedimentsaltertheirdisappearencelastingthe During Maastrichtian times, only few ostracodes oeeur wholeMaastrichtian. CYTHEREIS MESA: OCCURRENCES AND 2. EVOLUTIONARY STRATEGIES 2.1 THE OCCURRENCE OF CYTHEREIS MESA Cythereis or to any other known genus of the Trachy- Cythereismesaanditsfoursubspeciesweredescribedfrom leberidinae. However, becauseofits typical external features SenonianSedimentsbyHonigstein(1984,seealsoHonigstein for the Cytheracea, as well as its partly preserved internal 1985).These forms are known hitherto only from Israel. C. elements,itisattributedheretoCythereis. mesa is a relatively large form, (0.8-1 mm length), which is ThesubspeciesofC.mesadifferbytheirornamentationof characterized by astrongsubcentral node, adistinet median the carapace and the position ofthe posterior end. C. mesa ridge and a prominent posteroventral node. Its ventral view centroleviata with a smooth carapace and C. mesa centro- (PI.1, Fig. 5)issubtriangularandpiain,becauseofthesharp reticulata with a reticulated carapace, both with a centrally edgeoftheelevatedventralridgetowardsthecontactmargin. pointedposteriorend,oeeurinLateConiacian-LateSantonian C. mesa probably does not belong definetely to the genus strata(OstracodezonesS-ltoS-3).Thetwosubspecieswitha Plate1 mesamesaHONIGSTEIN.-Femalecarapace,leftvalve,HarTuv-1,No.T-7364,Campanian. mesamesaHonigstlin.-Malecarapace,rightvalve,Shefaram-1,No.T-7361,EarlyCampanian. mesaventroreticulataHonigstein.-Female(?)carapace,leftvalve,Shefaram-1,No.T-7074,LateSantonian. mesaventroreticulataHonigstein.-Malecarapace,rightvalve,BeerShevaSH9,T-7177,EarlyCampanian. mesaventroreticulataHonigstein.-Malecarapace,ventralview,HarTuv-1,No.T-7364,Campanian. mesamesaHonigstein.-Femalecarapace,dorsalview,NahalHavarim,SB320,EarlyPaleocene. mesamesaHonigstein.-Malecarapace,leftvalve,HörHaHar,HH24,EarlyPaleocene. mesamesaHonigstein.-Femalecarapace,rightvalve,HörHaHar,HH22,EarlyPaleocene. mesaventroreticulataHonigstein.-Malecarapace,leftvalve,NahalHavarim,SB304,EarlyPaleocene. mesaventroreticulataHonigstein.-Femalerightvalve,SdeBoqer,AR539,EarlyPaleocene. Zitteliana,20,1993 Honigstein,A.,Hirsch,F., Rosenfeld,A.& Flexer,A.:Cythereismesa Platt ventrallypointedposteriorend,C.mesamesa(smoothform; Iteration PL1,Figs.1-2)andC.mesaventroreticulata(reticulatedform; Thefadingawayofataxondoesnotautomaticallymeanits PI.1,Figs.3-5),weredescribedhithertofromLateSantonian- extinetion.Often,whenconditions,similartothosebeforethe Campanian Sediments (Zones S-3 to S-5; Honigstein et al. disappearenceofthespeciesreoccur,restorationofthattaxon 1987). In Maastrichtian strata these ostracodes were not takes place. This phenomen, called by Jablonski Lazarus- observed, even though they are relatively large and very effect,mayberelatedwithheterochrony. distinctive. InthetypesectionofPaleocenestratainsouthernIsraeland Migration intwoothernearbysections,sampledfortheinvestigationof EarlyCenozoicostracodes,C.mesamesa(PI.1,Figs.6-8)and Migration offossil species in space and time oecurs often. C.mesaventroreticulata(PI.1,Figs.9-10)reoccurinthelower Nerineids, common in Europe during the Bathonian, were partoftheprofiles, appearing several meters above the K/T drivenawaybytheborealspreadduringtheCalloviantothe boundary level and common in layers of the NP-3-NP-4 gondwanean shores of the Tethys. There, they found an nannoplankton biozones (Moshkovitz, GSI; pers. comm.). ecologicshelter,evolvedfurtherandrecolonizedthenorthern The Paleocene specimens ofboth subspecies of C. mesa are epicontinentalseasoftheTethysduringthemiddleOxfordian shown to be taxonomically identical with their Senonian (Hirsch1979).Ostracodes,e.g.SimeonellabrotzenorumSohn, counterparts(PI. 1). whichisreportedfromtheLadinianoftheSephardicprovince, ThepossibilityofredepositionofLateCretaceousfossilsin migratedduringtheCarnianintotheAlpinerealm(Gerryetal. PaleoceneSedimentswastakeninaccount,butcanbeexcluded 1990). duetothegoodpreservationoftheostracodesandtheabsence of coexisting Late Cretaceous foraminifera and calcareous Exccptionalsurvival nannoplanktoninthesesamples(Siman-TovandMoshkovitz, GSI, pers. comm.). Therefore, the reappearence of the two eveErxytrfoesmseillygrsoluopwfrevoomltuhteiobnrarcahteisopcoadnLbiengoublsaetrovethdeicnonmemarolny subspecies of C. mesa after a 10 million years gap must be cockroach. This long-range phenomen braves evolution like relatedtootherfactors. biblicaloldMethusalem.ThismavapplyalsotoCristaeleberis reüadataandMegommatocytheredenticulata,whichoeeurin 2.2 DISCUSSIONONEVOLUTIVESTRATEGIES IsraelcontinuouslyfromtheEarlySenoniantilithePaleocene, Thegeneticmechanism,intendcdtoWarrantthesurvivalof crossingeventheK/Tboundary,whichrepresentsabarrierfor theoriginalmodelthroughoutgenerationsisonlyvalidaslong manyfossilgroups. as viable living conditions remain relatively the same. Some species have a high adaptive tolerance, and thus a better 2.3 THECASEOFCYTHEREISMESA possibility for long survival than very specialized taxa. The latter are more vulnerable to changing conditions, and their ThetwoLateSantonian-CampaniansubspeciesofC.mesa reactionis„perishorchange". reappearinsimilarquantitiesinEarlvPaleocenestrataofIsrael, after a gap of 10 million years. No redeposited fossils were foundinthesesamples.Therefore,whatevolutionaleffectcan Heterochrony beinvokedforthere-oecurrenceofidenticalformsaftersucha TheconeeptofpaedomorphosiswasdevelopedbyGould longtimespan? (1977), usingHaeckel'soldconeept forevolutivestrategies, ThedisappearenceofC.mesaduringtheMaastrichtianmay amongwhichprogenesisand neoteny,mimicbackwardevo- beduetooxygendeficiencyneartheseabottom.Afterthere- lution.Theretardationorontheotherhand,theaccelerationof establishmcntofbetterecologicalconditionsduringthePaleo- reproduetive maturation can be caused by environmental cene,arepetitionofthespeciesseemspossible.But,generally changes.Thestrategyofprogenesis,thespeedingupofsexual Cytheracean species evolved fast and both subspecies sur- maturity, is usedwhen conditions improvedramatically and prisingly reoccurinourmaterial(Lazarus-effect). But,where cthoendoitrigoannsi,stmofreeelprtohdeucuergtehetmosetalkveesadasvafnasttagasepoofsssiubcleh.oOptnimtahle Mwaaassttrhiechtshiealnt?erC.fomrestaheresppreecsieenststoarmeilgartiavteelyilnatrogeduarnidngorntah-e contrary, once all niches are fully packed and among other mented ostracode species that can be hardly overlooked. fisactnoerost,ennuyt,ritehnetssbleocwianmgesdcoarwcne,athnedrseasvpionngseoofftthheeoorngtaongiesnmics fAlrtohmouagdjha,ceinttwaarseahsitwhietrhtosirmeiploarrteMdaasotnrliychftrioamn aIsnrdaelPaalnedocennoet process by retardation. These strategies can be observed in rock formations, asJordan and Egypt (e.g. Bassiouni 1971, Tlraitaisonsicchcaonngoedsonmtast,chpreeueseteadtiicngseeax-tlienveetliofnl,uewthuaetrieonsthe(Hpiorpsuch- Bfuatsusrieo,uCn.imaensdaLwuigllerbe1f99o0u)n,ditincaMnidndoltebeEaesxtcelrundMeadasttharticihntitahne 1992). 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