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A new Daonella from the Ladinian platform of the Esino limestone (Southern alps, Italy)

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A new Daonella from the Ladinian platform of the Esino limestone (Southern alps, Italy)
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  SHORTNOTE-NOTABREVE  ANEW  DAONELLA  FROMTHELADINIANPLATFORMOFTHEESINO LIMESTONE(SOUTHERNALPS,ITALY)  CRISTIANOLARGHI  1,2  ,MARCOBALINI  1  &VALENTINATORTI  1  Received:February7,2006;accepted:February21,2006 Keywords  : Daonella  ,EsinoLimestone,Carbonateplatform, MiddleTriassic,Ladinian,SouthernAlps.  Abstract  .Thebivalve  Daonella  Mojsisovics,1874isverycom- monintheMiddleTriassicpelagicfacies,whereastherecordofthis genusfromshallowwaterlimestonesisrare.Inthepresentpapera newspeciesof  Daonella  ,named  D.pseudograbensis  ,isdescribedfrom theEsinoLimestone,aLadinian(MiddleTriassic)carbonateplatform inthecentralSouthernAlps.ThespeciesisdescribedfromBrembana Valley,wheretheEsinoLimestoneisratherrichinbioclasticlenses yieldingfaunaswithbivalves,cephalopods,gastropods,brachiopods, coralsandcalcareousalgae. Daonellapseudograbensis  n.sp.isbasedonverywellpreserved specimens,whichareoftenarticulatedandclosed,allcomingfromthe samelocality.Thenewspeciesshowsanarrowrangeofintraspecific andontogeneticmorphologicvariations.Itiseasydistinguishablefrom theotherspeciesofthegenusfortheoutlineandornamentation;it thereforediffersfrom  D.grabensis  Kittl,1912,themostsimilarspecies, forthelongeranteriordorsalmargin. Riassunto  .Ilbivalve  Daonella  Mojsisovics,1874eÁmoltocomu- nenellefaciespelagichemediotriassiche,mentrelesegnalazionidique- stogenereinfaciescalcareediacquebasserisultanorare.Inquestanota vienedescrittaunanuovaspeciedi  Daonella  ,denominata  D.pseudo- grabensis  ,provenientedallapiattaformaladinicadelCalcarediEsino (settorecentraledelleAlpimeridionali).LaspecieeÁriconosciutasoloin ValBrembana,doveilCalcarediEsinoeÁriccoinlentibioclastichemolto fossilifereconbivalvi,cefalopodi,gasteropodi,brachiopodi,corallied alghecalcaree. Daonellapseudograbensis  n.sp.eÁdescrittasuesemplarimolto benconservati,chesonospessoarticolatieconvalvechiuse,provenien- tituttidallastessalocalitaÁ.LanuovaspeciemostraunavariabilitaÁin- traspecificaedontogeneticamoltostretta,edeÁfacilmentedistinguibile dallealtrespeciedelgenereperilcontornoel'ornamentazione;la speciepiuÁsimileeÁ  D.grabensis  Kittl,1912,dacuisidistingueperil marginedorsaleanteriorepiuÁlungo. Introduction  TheEsinoLimestoneisaLadiniancarbonate platforminLombardylocallyextremelyrichinmega- fossils.TheclassicareaofGrigne(EastofLakeComo) isknownsincetheStoppani'smonograph(1858-1860) forthefaunasrichinbivalves,gastropods,cephalopods, brachiopods,butintherecentyearsseveralextremely richlocalitiesintheBrembanaValleyarea,andinpar- ticulartheParinaValley,werediscoveredduetothe enthusiasticworkofG.Gervasutti,anamateurpaleon- tologistwhodonatedahugecollectionofmorethan 20,000specimensfromthisareatotheMuseoCivico diScienzeNaturali``EnricoCaffi''inBergamo(Paga- noni1985).Thespecimenswereverycarefullycol- lected,thereforetheGervasutticollectionprovidedthe basisforscientificcontributionsonammonoids(Fantini Sestini1994,1996)andbrachiopods(Torti&Angiolini 1997).Thisshortnotedealswiththebivalves,whichare oneofthemostcommongroupsrecordedintheEsino LimestoneofBrembanaValleyarea. TheEsinoLimestoneincentralBrembanaValley  ThecentralBrembanaValleyisaninterestingarea forthestudyoftheEsinoLimestone(Fig.1),notonly  RivistaItalianadiPaleontologiaeStratigrafiavolume112no.11pl.pp.167-174April2006  1DipartimentodiScienzedellaTerra,Universita Á degliStudidiMilano,ViaMangiagalli34,20133Milano,Italy.E-mail:cristiano.larghi@agip.it,marco.balini@unimi.it 2Presentaddress:EniE&PDivision,ViaEmilia1,20097S.DonatoMilanese(MI),Italy.  becausetheunitiswellexposed,butespeciallybecause itisrelativelywellaccessible.ThedeeplyincisedParina ValleyprovidesanaturalcrosssectionEast-Westor- ientedwhichcutstheplatformoftheEsinoLimestone fromthetop(BrenoFormationatMonteOrtighera),to thebase(BuchensteinFormationonthevalleyfloor).MoreovertheParinaValleycrosssectionislocatedina verycomplexsettingofthecarbonateplatform,very closetoabasinthatwasdevelopedimmediatelySouth tothesouthernslopeoftheParinaValley(Jadouletal.1992).TheGervasutticollectionwascollectedfromvar- ioussiteslocatedalongtheParinaValley,from2km westofOltreilColletothevalleymouth.Themost richanddiversifiedfossil-bearinglocalitiesareactually concentratedinthemiddlepartoftheParinaValley (dottedframeinFig.1). TheoccurrenceofDaonellids  Daonellidsarenotthemostcommonbivalves withintheEsinoLimestoneofcentralBrembanaValley, buttheycanbefoundwithinthecollectionsfromthe sitesS747,S944E-F,S1011E-F-P,S1046,S1062,S1170, S1171,S1188,S1191,S1490,S1491andS1603A(Torti 1999).Inparticular,thethanatocoenosisfromsite S1188,isofgreatinterestbecauseoftheextraordinary preservationofthedaonellids:thespecimensinfactare notflattened,andoftenthevalvesarearticulatedand closed.Thebiometricanalysisonthefaunashowsa monotypicpopulationofmediumtolargesizedspeci- mens(Fig.2).Moreoverthesystematicanalysisdemon- stratesthatthispopulationcannotbeincludedinanyof thespeciesof  Daonella  ,thenweseparateitasthenew species  Daonellapseudograbensis  . Stratigraphicpositionandageof  Daonella pseudograbensis  n.sp.  ThesiteS1188consistsofslopedebris,andis locatedonthelefthandsideoftheBrembanaValley, 1kmNorthofthejunctionoftheParinaRiverwiththe BremboRiver(Fig.1).Thedebrisisfromoutcrops locatedalittlehigher,i.e.,probablybetween650and 850a.s.l.Theuncertainpositionof  Daonellapseudogra- bensis  n.sp.withintheEsinoLimestone,isonlyinpart duetothecollectionexsitu,butmostlyreliesonthe lackofbio-chronostratigraphicdatafortheEsino LimestoneatthemouthoftheParinaValley.Ammo- noidcalibrationoftheEsinoLimestoneisavailableonly forthemostfossiliferouspartoftheunitinthemid ParinaValley(seedottedframeinFig.1;FantiniSestini 1994,1996).There,thefossiliferoussuccessioncovers theintervalfromtheCurioniitotheArchelausZones (LowerLadiniantolowerUpperLadinian:FantiniSes- tini1996).Thentheageof  Daonellapseudograbensis  n.sp.couldbecomprisedwithinthisinterval.Amore accuratedatingisnotpossibleatthepresent,because thepositionoftheammonoidzoneswithintheEsino Limestoneshowssignificantlateralchanges(Fantini Sestini1996,tab.2).Theboundariesoftheammonoid  LarghiC.,BaliniM.&TortiV. 168  Fig.1-Geologicalsketchmapofthe ParinaValleyarea(redrawn fromJadouletal.1992,fig.1).Thestarshowstheposi- tionofsiteS1188.1)Angolo Limestone;2)PrezzoLime- stone;3)BuchensteinForma- tion;4)Perledo-Varenna Limestone;5)EsinoLime- stone;6)BrenoFormation; 7)ValSabbiaSandstoneand GornoFormation;8)S.Gio- vanniBiancoFormation;9).Quaternarydeposits.Dotted frameemphasizesthemost fossiliferouspartoftheEsino LimestoneinParinaValley (seeFantiniSestini1994, 1996;Torti&Angiolini 1997).  zonescannotthereforebelaterallytracedfromthemid ParinaValleytotheBrembanaValley. SystematicPalaeontology  Supragenerictaxonomy,shellmorphologyand dimensionalterminologyistakenfromMcRoberts (2000)and/orfromSchatz(2004),withtheexception ofthetermplicawhichishereusedfortheelementsof radialsculpture.Allfiguredanddescribedspecimensarehousedat theMuseoCivicodiScienzeNaturali,PiazzaCittadella 10,24100Bergamo,Italy.Numberingofspecimens:specimensareidentifiedbyinventorynumber(acronym MSNBG)andsamplenumberinbrackets.Thelatter reportsthelocalityofcollectionandthenumberof   Anew  Daonella   fromtheladinianplatformoftheEsinoLimestone  169  Fig.2-Comparisonbetweentype specimensof  Daonellapseu- dograbensis  n.sp.andthe holotypeof  D.grabensis  Kittl,1912.A)Height  vs  Lenght.B)B  vs  A;C)On- togenyofspecimens MSNBG11314a(S1188/1) andMSNBG11313a (S1188/2).Measurements arelistedintheAppendix.  thespecimen.Theholotypeof  Daonellagrabensis  Kittl, 1912ishousedatNaturhistorischesMuseumWien (NHMW),Austria. Acronyms  .A:lengthoftheanteriorhingeline;B:lengthoftheposteriorhingeline;  á  :angularvaluebe- tweentheposteriorhingelineandthelineconnecting thebeakwiththeposterior-mostshellpoint(fordetails abouttheseparameters:Schatz2001a).Class  Bivalvia  Linnaeus,1758 Subclass  Pteriomorphia  Beurlen,1944,emend.Waller,1978 Order  Pterioida  Newell,1965,emend.Waller,1978 SuperfamilyHalobioideaCampbell,1994 FamilyHalobidaeKittl,1912 Genus  Daonella  Mojsisovics,1874  Typespecies: Halobialommeli  Wissman,1841  Daonellapseudograbensis  n.sp. Pl.1,figs1-23;Fig.3.1-4.?2005  Daonella  sp.-Schatz,p.191,fig.1E. Etymology  .Thenamepointsoutthemorphologicalsimilarities with  D.grabensis  Kittl,1912. Typeseries  .Holotype:MSNBG11313a(S1188/2)(Pl.1,Fig.11;Fig.3.1-4).22paratypes(PL.1,Fig.1-10,12-23):MSNBG11314a (S1188/1),11313b(S1188/3),11313f(S1188/7),11315a(S1188/9), 11315b(S1188/10),11316a(S1188/12),11316b(S1188/13),11317 (S1188/15),11318a(S1188/17),11318b(S1188/18),11319(S1188/20), 11320(S1188/22),11321(S1188/24),11322a(S1188/25),11323a (S1188/29),11323b(S1188/31),11323c(S1188/32),11323d(S1188/ 33),11323e(S1188/34),11323f(S1188/35),11324(S1188/36),11314b (S1188/37). Otherspecimensnotincludedinthetypeseries  .23speci- mens:MSNBG11313c-e(3specimens),11313g(1specimen),11323g (1specimen),11325(2specimens),11326(1specimen),11327(3speci- mens),11328(1specimen),11329(1specimen),11330(1specimen), 11331(1specimen),11332(2specimens),11333(6specimens). Typelocality  .Site1188,BrembanaValley(BG,Lombardy, NorthernItaly). Stratumtypicum  .EsinoLimestone,midBrembanaValley. Diagnosis.  Mediumtolargeshell,subtriangularinoutline, highlyinequilateral,slightlyprosocline,longerthanhigh.Beaksmall, orthogyrous,anterior(A/Bnear0.52),slightlyraisedabovethestraight rectilinearhingemargin.Radialornamentationmainlygivenbypri- maryandsecondary(bifurcated)plicae,tertiaryplicaeveryrare;plicae veryweakontheanteriortriangularfield.Wellevidentcommarginal rugae. Description.  Theshelliselongated,withthemax- imumlengthofnearly7cm.Thevalvethicknessisthin.Thehingemarginisrectilinearandlong,theposterior- mostshellpointisclosetotheposteriorendofthe hingeline(  á  isnearly10ë);theAtoBratioisquite constantduringtheontogenesisinthedifferentexam- inedspecimens(nearly0.51-0.53).Theonlyremarkable allometricvariationisalittlenegativegrowth(valve lengthtovalveheightratiochangesfromnearly2.7at juvenilestageto2.3atamorematurestage,e.g.MSNBG11313a(S1188/2)andMSNBG11314a (S1188/1)).Thebeakissmallandanterior,slightlyraised abovethestraighthingemargin.Theconvexityofthe shellissomewhatemphasizedneartheumbonalarea.Theradialornamentationisgivenbyplicaesepa- ratedbynarrowfurrows.Theplicaeareabout100-110 alongtheventralmargininmaturespecimens(e.g.MSNBG11314A[S1188/1],MSNBG111313A [S1188/2],MSNBG11316A[1188/12];Fig.3a;Pl.1, figs.6,11).Thesecondaryplicaeareoriginatedbybi- furcationatvariableheightonflank.Thebifurcation  LarghiC.,BaliniM.&TortiV. 170  Fig.3-1)Holotypeof  D.pseudograbensis  n.sp.MSNBG11313a(S1188/2).2)detailofthebeak.3)detailoftheanteriortriangularfield.4) detailoftheposteriorsector,a)firstbifurcation.b)secondbifurcation.Scalebars:10mm.  generallyisnotsymmetricalandthelargersecondary plica,inamoredistalpartoftheflankcanbefurther divided,thusoriginatingtertiaryplicae.Thisasynchro- noustrifurcationpattern,whenpresent,isgenerally limitedtotheposteriorsectoroftheshell,wherethe plicaearelonger.Insectiontheplicaeareweakly rounded,butthewideronesbecomeratherflat.The plicaeonthecentralsector,wheretheshellisalittle inflated,slightlybentwithanteriorconcavity.Theradialornamentationisweaklydefinedon theanteriortriangularfield(angularvalueofitnearly 20ë),thisfieldalsoincludesanarrowercompletelypli- cae-freetriangularsector(angularvaluenearly2ë-3ë) visiblebelowthehingemargin.Asimilarnarrowpli- cae-freetriangularsector(angularvaluesnearly3ë-4ë)is alsoposteriorlyvisible.Thepatternofplicaeisnotperfectlysymmetric onthetwovalves(MSNBG11319[S1188/20],MSNBG 11320[S1188/22]:Pl.1,figs1a-b,5a-c).Thecommarginalsculptureismadebywellevi- dentrugaeandgrowthlines.Theornamentationontheinternalcastisweaker thantheornamentationofoutersurfaceoftheshell (specimensMSNBG11313b[S1188/3]and11317 [S1188/15]). Discussion.  Onlyveryfewspeciesamongthe verywidevarietiesofdaonellidscanbecomparedwith  D.pseudograbensis  n.sp.Themostsimilaroneis  Dao- nellagrabensis  Kittl,1912,thatwaserectedonthebasis ofasingleflattenedspecimenfromtheMuschelkalkof Grab,nearGrahovo(Bosnia)(Kittl1912,pl.2,fig.17). D.grabensis  Kittlshowsasimilaroutlineandornamen- tation,butexhibitsamoreanteriorbeak(A/B=0.41) andalongerposteriordorsalmarginwhichallowsan easyseparationfrom  D.pseudograbensis  n.sp.(Fig.2).Theevanescentcommarginalornamentationof  D.gra- bensis  ,withrugaewellvisibleonlyonumbonalarea, mightbeduetothepoorpreservationoftheonlyspeci- men,thusitssculptureisnoteasilycomparablewith thatof  D.pseudograbensis  n.sp. Daonellaobtusa  Rieber,1968exhibitsabeakante- riorlyplaced,butitislesselongated(lowervalueof length/heightratio)andlesssubtriangularthan  D.pseu- dograbensis  n.sp. Daonellaelongata  Mojsisovics,1874 and  Daonellacaudata  Frauenfelder,1916displayasub- centralbeakonthehingeline.Somesimilaritiescanbe foundalsowith  Daonellapichleri  Mojsisovics,1874, recentlyrevisedbySchatz(2001b).Neverthless  D.pi- chleri  islesselongatedandnotsubtriangular.Moreover itexhibitsaprosogirousbeakandwellvisibleplicaeon theanteriormargin.ThespecimensfiguredbySchatz(2005,p.191, fig.1E)as  Daonella  sp.,couldbeprobablyincludedinto  D.pseudograbensis  n.sp. Age.  Theageof  Daonellapseudograbensis  n.sp.is probablycomprisedbetweentheEarlyLadinianand earlyLateLadinian,i.e.,betweentheCurioniiandthe ArchelausZone.  Aknowledgments  .Thiscontributionwouldnothavebeenpos- siblewithoutthetremendousworkdonebyGiustoGervasuttiinthe fieldandforthepreparationofthespecimens.Wearegreatlyindebted withA.Paganoni(MuseoCivico``E.Caffi'',Bergamo)forthevery kindhelpduringseveralvisitstotheGervasutticollectionhousedat theMuseoCivico``E.Caffi'',aswellasfortheloanofthedaonellids.F.TatzreiterandH.Summesberger(Wien)providedkindsupporttoVT andMBfortheexaminationofKittl'scollectionhousedintheNat- urhistorischesMuseumWien.SpecialthankstoM.Gaetaniforthecriticalrevisionofthe manuscript.  Anew  Daonella   fromtheladinianplatformoftheEsinoLimestone  171  PLATE1 Figs1-23-  Daonellapseudograbensis  n.sp.,typeseries,allthe specimensatnormalsize,exceptforfigs.9a,-b (MSNBG11322a(S1188/25))whicharex1.5.Figs1a,-b-ParatypeMSNBG11320(S1188/22),articulatedspe- cimen,a:rightvalve,b:leftvalve.Fig.2-ParatypeMSNBG11313b(S1188/3),rightvalve.Fig.3-ParatypeMSNBG11316b(S1188/13),leftvalve.Fig.4-ParatypeMSNBG11323a(S1188/29),rightvalve.Figs5a,-b,-c-ParatypeMSNBG11319(S1188/20),articulatedspe- cimen,a:leftvalve,b:dorsalview,c:rightvalve.Fig.6-ParatypeMSNBG11314a(S1188/1),leftvalve.Fig.7-ParatypeMSNBG11314b(S1188/37),rightvalve.Fig.8-ParatypeMSNBG11324(S1188/36)rightvalve.Figs9a,-b-ParatypeMSNBG11322a(S1188/25),articulatedspe- cimen,a:dorsalview,b:rightvalve.Fig.10-ParatypeMSNBG11323c(S1188/32),leftvalve.Fig.11-HolotypeMSNBG11313a(S1188/2),leftvalve.Fig.12-ParatypeMSNBG11321(S1188/24),rightvalve.Fig.13-ParatypeMSNBG11317(S1188/15),rightvalve.Fig.14-ParatypeMSNBG11316a(S1188/12),rightvalve.Fig.15-ParatypeMSNBG11313f(S1188/7),leftvalve.Fig.16-ParatypeMSNBG11315b(S1188/10),rightvalve.Fig.17-ParatypeMSNBG11315a(S1188/9),leftvalve.Fig.18-ParatypeMSNBG11323d(S1188/33),leftvalve.Fig.19-ParatypeMSNBG11323e(S1188/34),leftvalve.Fig.20-ParatypeMSNBG11323f(S1188/35),leftvalve.Fig.21-ParatypeMSNBG11323b(S1188/31),leftvalve.Fig.22-ParatypeMSNBG11318a(S1188/17),leftvalve.Fig.23-ParatypeMSNBG11318b(S1188/18),rightvalve.
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