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Middle Miocene vertebrates from the Amazonian Madre de Dios PDF

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Middle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú Pierre-Olivier Antoine, Martin Roddaz, Stéphanie Brichau, Julia Tejada-Lara, Rodolfo Salas-Gismondi, Ali Altamirano, Mélanie Louterbach, Luc Lambs, Thierry Otto, Stéphane Brusset To cite this version: Pierre-Olivier Antoine, Martin Roddaz, Stéphanie Brichau, Julia Tejada-Lara, Rodolfo Salas- Gismondi, et al.. Middle Miocene vertebrates from the Amazonian Madre de Dios Suban- dean Zone, Perú. Journal of South American Earth Sciences, 2013, vol. 42, pp. 91-102. ￿10.1016/j.jsames.2012.07.008￿. ￿hal-00956894￿ HAL Id: hal-00956894 https://hal.science/hal-00956894 Submitted on 7 Mar 2014 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Open Archive TOULOUSE Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 11085 To link to this article : doi:10.1016/j.jsames.2012.07.008 URL : http://dx.doi.org/10.1016/j.jsames.2012.07.008 To cite this version : Antoine, Pierre-Olivier and Roddaz, Martin and Brichau, Stéphanie and Tejada-Lara, Julia and Salas-Gismondi, Rodolfo and Altamirano, Ali and Louterbach, Mélanie and Lambs, Luc and Otto, Thierry and Brusset, Stéphane Middle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú. (2013) Journal of South American Earth Sciences, vol. 42 . pp. 91-102. ISSN 08959811 Any correspondance concerning this service should be sent to the repository administrator: [email protected] Middle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú Pierre-Olivier Antoinea,*, Martin Roddazb, Stéphanie Brichaub, Julia Tejada-Larac,d, Rodolfo Salas-Gismondic, Ali Altamiranoc, Mélanie Louterbachb,e, Luc Lambsf, Thierry Ottof, Stéphane Brussetb aInstitutdesSciencesdel’Évolution,UMR-CNRS5554,CC064,UniversitéMontpellier2,PlaceEugèneBataillon,F-34095Montpellier,France bGéosciences-EnvironnementToulouse,UniversitédeToulouse,UPS(SVT-OMP),LMTG,CNRS,IRD,14AvenueÉdouardBelin,F-31400Toulouse,France cMuseodeHistoriaNatural-UniversidadNacionalMayorSanMarcos,DepartamentodePaleontologíadeVertebrados,AvenidaArenales1256,Lima11,Perú dInstitutFrançaisd’EtudesAndines,AvenidaArequipa4500,Lima18,Perú eInstitutPolytechniqueLasalleBeauvais,DépartementGéosciences,19ruePierreWaguet,F-60026BeauvaisCedex,France fEcoLab,UMR5245CNRS-UPS-INPT,UniversitédeToulouse,118RoutedeNarbonne,F-31062ToulouseCedex9,France a b s t r a c t AnewmiddleMiocenevertebratefaunafromPeruvianAmazoniaisdescribed.Ityieldsthemarsupials Sipalocyon sp. (Hathliacynidae) and Marmosa (Micoureus) cf. laventica (Didelphidae), as well as an unidentified glyptodontine xenarthran and the rodents Guiomys sp. (Caviidae), “Scleromys” sp., cf. quadrangulatus-schurmanni-colombianus (Dinomyidae), an unidentified acaremyid, and cf. Micro- Keywords: steiromyssp.(Erethizontidae).ApatiteFissionTrackprovidesadetritalage(17.1 2.4Ma)forthelocality, Colloncuran-earlyLaventan slightlyolderthanitsinferredbiochronologicalage(Colloncuran-earlyLaventanSouthAmericanLand Marsupialia Mammal Ages: w15.6e13.0 Ma). Put together, both the mammalian assemblage and lithology of the Rodentia fossil-bearinglevelpointtoamixtureoftropicalrainforestenvironmentandmoreopenhabitatsunder Biochronology Fissiontrackage a monsoonal-like tropical climate. The fully fluvial origin of the concerned sedimentary sequence Biogeography suggeststhattheAmazonianMadredeDiosSubandeanZonewasnotpartofthePebasmega-wetland System by middle Miocene times. This newassemblage seems to reveal a previously undocumented “spatiotemporaltransition”betweenthelateearlyMioceneassemblagesfromhighlatitudes(Patagonia andSouthernChile)andthelatemiddleMiocenefaunasoflowlatitudes(Colombia,Perú,Venezuela,and ?Brazil). 1. Introduction exceptionsofLaVenta(latemiddleMiocene,Colombia;Kayetal., 1997) and Fitzcarrald local fauna (eastern Perú; Antoine et al., ThemiddleMioceneperiodischaracterisedbythelastclimatic 2007; Goillot et al., 2011; Pujos et al., in press), middle Miocene optimum (MMCO, for Middle Miocene Climatic Optimum) before mammals are virtually unknown in tropical-equatorial South asustainabledeteriorationculminatingwithPlioceneePleistocene America(e.g.,Negrietal.,2010). iceages(Zachosetal.,2001,2008).InNorthernSouthAmerica,this Thepresentworkaimstoreportanewvertebratelocalityfrom MMCOcoincideswiththeemergenceofthe“Pebassystem”,alarge the Subandean Zone of Southwestern Peru, designated MD-67 wetland with marine influence partly engulfing what is lowland (S12!38.6830; W71!19.2840; w428 m Above Sea Level) and doc- Amazoniatoday(forreview,seeHoornetal.,2010a,b). umentingtheconcernedinterval.MD-67wasdiscoveredbyoneof This environment was particularly favourable to biodiversity us (MR) nearby Pilcopata (Cusco) in 2007 (Fig. 1). The corre- and it allowed a wide array of organisms, such as molluscs, sponding results are exposed hereunder in systematic, bio- arthropods,andplantstobefossilised(e.g.,Hoorn,1993;Antoine stratigraphical,andbiogeographicalperspectives. etal., 2006;PonsandDeFranceschi,2007;Jaramilloetal., 2010; Wesselingh and Ramos, 2010). By contrast, and with the notable 1.1. Geologicalcontext The western Amazon drainage basin extends today from * Correspondingauthor.Tel.:þ33467143251;fax:þ33467143640. southernColombiatonorthernBolivia(Hoornetal.,2010a).Since E-mailaddress:[email protected](P.-O.Antoine). Pliocenetimes(Espurtetal.,2007,2010),theAmazonianforeland http://dx.doi.org/10.1016/j.jsames.2012.07.008 2. Materialandmethods 2.1. Paleontology Allthevertebratefossilremainsdescribedherewererecovered eitherbyhand-pickingontheferruginouscrusttoppingtheMD-67 localityduringtheexploratory2007fieldtrip,orbyexcavatingand byscreen-washingofthecorrespondingsedimentduringthe2009 field season. In 2009, ca. 200 kgof rough sediment were screen- washed,usinga1mmmesh.Anewsurveyin2011unfortunately showedthefossil-yieldingoutcrophadbeenwashedawaybythe MadredeDiosRiverinthemeantime(Fig.2C). Fragmentsofturtleplatesandcrocodileteethwerealsorecov- eredinMD-67.Astheydonotdisplaydiagnosticfeatures,theywill notbedescribedhere.Bycontrast,neitherfishnorplantremains wereunearthedinMD-67. Amongmammalianremains,amesio-labialfragmentofahyp- selodont upper toothreferable toa toxodontid notoungulatewas recognisedinMD-67.Thisspecimen,ofpoorbiochronologicaland environmentaluse,istheonlyremainunambiguouslyassignableto nativeungulatesintheconcernedlocality. Thenomenclatureusedformarsupialdentitionisadaptedfrom that of Goin and Candela (2004). Morphological features of the cavioid rodent are described and diagnosed following the termi- nologyandphylogeneticcharactersproposedbyPérez(2010).For dental features of the dinomyid, octodontoid, and erethizontid rodents,wefollowthenomenclatureofWoodandWilson(1936), asmodifiedbyAntoineetal.(2012). Exceptwhenmentioned,dimensionsaregiveninmm. 2.2. Apatitefissiontrackanalysis(AFTA) Apatitegrainsweremountedandpolishedforetchingtoseveral thenaturalspontaneousfissiontracks.Apatiteswereetchedusing 5NHNO3at20!Cfor20s.Etchedgrainmountswerepackedwith mica external detectors and corning glass (CN5) dosimeters and irradiatedintheFRM11thermalneutronfacilityattheUniversity ofMunichinGermany.Followingirradiationtheexternaldetectors Fig.1. Locationandgeologicalmapofthestudiedarea,intheAmazonianMadrede were etched using 48% HF at 20 !C for 25 min. Analyses were DiosSubandeanZone,Perú;modifiedafterVargasandHipólito(1998). carried out on a Zeiss Axioplan microscope at a magnification of $1250, using a dry ($100) objective. Confined track length basin has been divided into two foreland basin systems (sensu measurements were made using a drawing tube and digitising DeCelles and Giles, 1996): the North Amazonian foreland basin tablet,calibratedagainstastagemicrometre.Single-grainAFTages systemandtheSouthAmazonianforelandbasin,separatedbythe werecalculated using the externaldetector method and the zeta FitzcarraldArch(Roddazetal.,2005).TheSouthAmazonianfore- calibration approach, as recommended by the I.U.G.S. Subcom- landbasinsystemcomprisestheSouthernPeruvianandNorthern mission on Geochronology (Hurford, 1990). Track length Bolivianforelandbasins.TheSubandeanZoneispartoftheMadre measurementswererestrictedtoconfinedtracksparalleltothec- deDiosforelandbasin(Fig.1).ThesouthernmostpartoftheSub- crystallographicaxis. andean Zone is structured bya syncline (Salvación Syncline) fol- lowedbyathrust-relatedanticline(PantiacollaAnticline)andthe MadredeDiosblindthrustfront(Fig.1). 2.3. Institutionalabbreviations Thefossiliferousoutcropdips35!SWwithaN130strike(Fig.2). Itcropsoutinthesouthernflankof thePantiacollaanticlineand AMNH,AmericanMuseumofNaturalHistory,NewYork,USA; was originally mapped as part of the PaleoceneeEocene Yahuar- IGM, Ingeominas (Instituto Nacional de Investigaciones en Geo- ango Formation, based on sedimentary facies, but without any ciencias, Minería y Química, Museo Geológico, Bogotá, Colombia; biostratigraphic constraint (Vargas and Hipólito, 1998). The ISE-M, Institut des Sciences de l’Évolution, Montpellier, France; Yahuarango Formation (northern Perú) is poorly dated and it MACN, Museo Argentino de Ciencias Naturales Bernardino Riva- consists mainly of red siltstones and mudstones forming distal davia,BuenosAires,Argentina;MLP,MuseodeCienciasNaturales fluvialdeposits(seeRoddazetal.,2010forareview). deLaPlata,LaPlata,Argentina;MNHN,MuséumNationald’Histoire The fossiliferous level corresponds to a 1 m-thick sand-and- Naturelle, Paris; MUSM, Museo de Historia Natural de la Uni- gravel channel of fluvial origin, with iron-rich pisolites and top- versidadNacionalMayorSanMarcos,Lima,Perú;UCMP,University ped by a ferruginous duricrust (Fig. 2A). These features coincide ofCaliforniaMuseumofPaleontology,Berkeley,USA;UFAC,Labo- withalateriticprofile(e.g.,Tardy,1992).Thefossiliferouschannel ratóriodePesquisasPaleontológicas,UniversidadeFederaldoAcre, developedoverpaleosolmudstones(Fig.2AandB). RioBranco,Brazil. Fig.2. MiddleMiocenevertebratelocalityMD-67,intheAmazonianMadredeDiosSubandeanZone,Perú.A.Detailofthefossil-yieldingredsand-and-gravelchannel,developing overredclays(paleosol),asdiscoveredinOctober2007.Notethedippingofthetoppingsurface(ferruginousduricrust).PicturebyPatriceBaby.B.Detailofthetransitionbetween theunderlyingredclays(top)andthegravelchannel,withiron-richpisolites(blackballs,atthebottom).PicturebyPatriceBaby(samedayasinFig.2A).C.ThesameareainAugust 2011.Thefossil-yieldingchannel(denotedbythewhitedottedline)hadbeenwashedawaybytheMadredeDiosRiverinthemeantime.PicturebyLaurentMarivaux.(For interpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.) 2.4. Otherabbreviations B).Theprotoconeisbulbous,muchlowerthanthelattercusps,and widely remote from them, which further determines a wide dist., distal; est., estimated; FAD, First Appearance Datum; H, triangular basin which is bordered by a faint preprotocrista and height;HI,HypsodontyIndex(¼H/MDL);L,length;max,maximal; alowpostprotocrista.Thepostmetacristaisstronglydevelopedand LLO,LastLocalOccurrence;MDL,mesio-distallength;mes,mesial; distallyconvex,withaflatandhighverticalwearfacetbutwithout SALMA,SouthAmericanLandMammalAge;W,width. carnassialnotch(Fig.3B).Thestylarshelfissmoothandreduced, with faint or absent cusps. Yet, a rounded crest surrounds the 3. SystematicPaleontology mesiolabialcornerofthetooth,whichwaseitherinterpretedasan ectocingulumora“CuspB”(Marshall,1978;Forasiepietal.,2006). ClassMAMMALIALinnaeus,1758 The main morphological features of this tooth (tribospheny, CohortMARSUPIALIAIlliger,1811 reducedprotocone,paraconeandmetaconecloselyappressed,and OrderDIDELPHIMORPHIAGill,1872 reducedstylarshelfandcusps)pointtoacarnivorousmarsupial,as SuborderSPARASSODONTAAmeghino,1894 defined by Muizon (1999: 502). The presence of a thick and low SuperfamilyBORHYAENOIDEAAmeghino,1894 protocone, and of equally developed paraconule and metaconule SubfamilyHATHLIACYNIDAEAmeghino,1894 allow referring it as to a medium-sized hathliacynid borhyaenoid SipalocyonAmeghino,1887 (Forasiepi et al., 2006). Accordingly, comparison was made with Sipalocyonsp. CladosictisAmeghino,1887(earlyMioceneof ArgentinaandChile; Flynnetal.,2002)SipalocyonAmeghino,1887(Colhuehuapian-San- MUSM 1967 is a much worn and eroded tooth, with a tribos- tacrucian of Patagonia; Marshall, 1981), Acyon Ameghino, 1887 phenicbunodontpatternandthreebrokenroots(onelingualand (middle Miocene of Southern Bolivia; Forasiepi et al., 2006), and twolabialones).FollowingtheworkofForasiepietal.(2006),this NotogaleLoomis,1914(DeseadanofBoliviaandArgentina;Muizon, toothisinterpretedasarightM3ofacarnivorousmarsupial.Itis 1999).Asimilarlarge-sizedlingualbasinisonlyobservedinNoto- roughlytriangularinocclusalview,withastraightmesialside(mes galemitis(Ameghino,1897),asillustratedbyMarshall(1981:Figs.54 W¼5.10),alongandbilobeddistolingualborder(maxL¼6.69), and55).Basedoncompatibleproportions/sizeandonthepresenceof and a concave labial side (MDL ¼ 4.67). Crown height equals anectocingulum,MUSM1967showstheclosestaffinitieswiththe 3.24mm.Theparaconeandthemetaconehavetheirbasestwin- M3ofSipalocyongracilis Ameghino,1887 (AMNH107401-001;FM ned,thusdeterminingaveryshortpremetacrista.Evenifitstipis 9254-001; Santacrucian) and Sipalocyon externa (Ameghino,1902) brokenawayanderoded,theparaconewaslow,withafaintpre- (Colhuehuapian;Marshall,1981).ItdiffersfromS.externainhaving paracrista; the most prominent cusp is the metacone, which alowerandsmootherprotocone,averywidelingualbasin,labially- occupies a central position in occlusal view (Fig. 3A and B). The displacedparaconeandmetacone,andinshowingamoredeveloped paraconuleandthemetaconuleareequallydeveloped,andclosely paraconuleandmetaconule(Marshall,1981),butcloselyresembles appressedtotheparaconeandmetacone,respectively(Fig.3Aand the M3 of S. gracilis from “Río Coyle” (maxilla MNHN SCZ 122, Fig.3. FossilmammalremainsfromtheMD-67locality,middleMioceneoftheAmazonianMadredeDiosSubandeanZone,Perú.AeB.Sipalocyonsp.,rightM3(MUSM1967)in labial(A)andocclusalviews(B).C.Marmosa(Micoureus)cf.laventica,leftM3lackingtheprotocone(MUSM1968).Reconstructedareasappearingrey(reconstructionbasedon Marshall,1976:text-Fig.2).DeE.Glyptodontinaeindet.,isolatedosteodermsinexternalview.D,MUSM1720;E,MUSM1585.FeH,Guiomyssp.,leftM1/2(MUSM1970)inocclusal (F),labial(G),andmesialviews(H).IeK,“Scleromys”sp.,gr.quadrangulatus-schurmanni-colombianus.Leftd4(MUSM1971)inocclusalview(I).Leftm1(MUSM1972)inocclusal(J) andlabialviews(K).L,Acaremyidaeindet.,leftm1/2(MUSM1973)inocclusalview.MeN,cf.Microsteiromyssp.LeftP4(MUSM1974)inocclusalview(M).Right?M3(MUSM1975) inocclusalview(N).Scalebar¼2mm(AeB,FeK),5mm(DeE),or1mm(C,LeN). TournouërCollection;SantaCruzFormation,Patagonia)inallthese SuperfamilyDIDELPHOIDEAGray,1821 aspects. Sipalocyon has a ColhuehuapianeFriasian range, so far FamilyDIDELPHIDAEGray,1821 restrictedtomiddleandhighlatitudes(37.5e48!S;Marshall,1981; SubfamilyDIDELPHINAEGray,1821 Flynn et al., 2008). Recognition of a hathliacynid closely allied to TribeMARMOSINIReig,KirschandMarshallinReig,1981 Sipalocyon,herereferredastoSipalocyonsp.,widelyextendsnorth- GenusMarmosaGray,1821 wardthegeographicalrangeofthegenus. SubgenusMicoureusLesson,1842sensuVoss,andJansa,2009: lateral,andposteriorfiguresarereducedinsize.Theprincipalfigure 101 is slightly convexon MUSM 1720, while it is flat on MUSM 1585. Marmosa(Micoureus)cf.laventicaMarshall,1976 Osteodermsarethin(MUSM1720:3.5mm;MUSM1585:4.8mm), with a punctuated surface, and serrated edges. The principal and MUSM1968isaleftuppermolariformtooth,theprotoconeof radialsulciarewideandshallow.Piliferouspitsarelargeandlocated which was broken away. This tooth has a dilambdodont tribos- in some intersections of the principal sulcus and the radial sulci phenicpattern,alargestylarshelf,andfourstylarcusps(termedAe (Fig.3DeE). D). It bears one lingual and two labial roots. The tooth is almost Theconcernedosteodermscannotbeconfidently identifiedat unworn and its dimensions are very small (MDL ¼ 1.75; est genus or species level because their characteristics are widely W¼1.8).Themetaconeismuchlargerandhigherthanthepara- distributedinseveralclades.However,theyarelikelytodocument cone. There was neither paraconule nor metaconule. All these a single small and unknown taxon within the Glyptodontinae features point to a marmosine didelphid rather than to a micro- (smaller than the oldest glyptodontine genus known so far, Bor- biothere(Marshall,1976).MUSM1968wascomparedtotheM1e eostemma from Laventan SALMA), because of the combination of M3seriesUCMP108563of“M.laventicaMarshall,1976”fromthe the following characters: (i) osteoderms flat or smoothly convex, middleMioceneofLaVenta,Colombia,describedandillustratedby (ii)surfacepunctuated,(iii)principalfigurecompletelysurrounded Marshall (1976: text-Fig. 2), as well as to the isolated M1 IGM by peripheral figures, and (iv) quadrangular “U”-shaped cross 251011 and M3 IGM 250278 of the same species and area, as section of the sulci. The latter feature has been suggested as described and figured under the name “M. laventicus” by Goin a noncranial character that differentiates Glyptodontinae from (1997:Fig.11.2).Itsisometricproportions,moderatedissymmetry PropalaehoplophorinaewithinGlyptodontidae(Carlinietal.,2008). (withalingualpartslightlymesiallydisplaced),andconcavelabial Asaconsequence,areducedsizeealmosttwicesmallerthanthe borderinocclusalviewallowidentifyingitasanM3.Themissing correspondingosteodermsinBoreostemmaeandthepresenceof part of the tooth was virtually reconstructed, based on available thinosteodermsmightrepresentaplesiomorphicconditionforthe illustrationsofM.(Mi.)laventica(Fig.3C).Therewasneitherjunc- Glyptodontinae. On the other hand, the posteriorly displaced tionbetweenthepreprotocristaandtheparaconenorbetweenthe positionoftheprincipalfigure,aswellasthereductioninsizeof postprotocristaandthemetacone.ThestylarcuspAisdisconnected posterior,medial, andlateral peripheral figures,appearastiedto from the paracone and from the preparacrista. The stylar cusp B thelocationoftheosteodermsinthecarapace(i.e.,submarginal), appears as the strongest cusp, as it does in fresh teeth of most insteadofrepresentingaplesiomorphictrait(i.e.,principalfigure marmosines (Rossi et al., 2010: 22). There is a deep mesiolabial closetotheposteriormargin),asseenonglyptatelinesandPara- notch for the metastyle of M2, but neither labial, nor distal propalaehoplophorus(seeCroftetal.,2007). cingulum, as in M. (Mi.) laventica (Marshall,1976) and the living species M. (Mi.) demerarae Thomas,1905 (ISE-M V-1590). Athick OrderRODENTIABowdich,1821 cingulum, running along the labial half of the mesial side, was InfraorderHYSTRICOGNATHITullberg,1899 connecting thestylarcusp A and theprotoconethrough the pre- ParvorderCAVIOMORPHAWood,1955 protocrista,asintheisolatedM3IGM250278ofM.(Mi.)laventica SuperfamilyCAVIOIDEAFischerdeWaldheim,1817 (Goin,1997).Thiscingulumismuchstrongerandthetoothca.30% FamilyCAVIIDAEFischerdeWaldheim,1817 smaller than in M. (Mi.) demerarae. Even if their overall size is Guiomyssp. comparable,thestylarcuspsaremuchstrongerandthenotchfor themetastyleofM2ismuchdeeperinMUSM1968thanintheM3s MUSM 1970 is a very small tooth (L ¼ 2.93; W ¼ 2.61), hyp- ofthelivingMarmosa(Marmosa)murinaLinnaeus,1758(Linnaeus’s selodont(i.e.,“euhypsodont”followingPérez,2010),preservingthe MouseOpossum;ISE-MV-1109). occlusalsurface,butthebasalmostpartofwhichcrownisbroken Basically, the size, proportions, and morphological features of away(Fig.3GeH).ThistoothisinterpretedasaleftM1orM2.Itis MUSM1968closelymatchthoseoftheM3ofM.(Mi.)laventicafrom bilobed, with lozenge-shaped lobes connected by a thick labial LaVentaarea,Colombia,i.e.,theonlyfossilspeciesdescribedand bridge; the mesial lobe is slightly smaller than the distal one namedforthisgenussofar(Goin,1997).Thestratigraphicalrange (Fig.3F).Theocclusalsurfaceofbothlobeslacksanyfossetteand ofM.(Mi.)laventicaspanstheLaVictoriaFm.andthebaseofthe theapexofeachlobeisnotconstrictedatthecurrentwearstage. Baraya Mb. of the overlying Villavieja Fm. in La Venta region, The hypoflexus is transversely developed (reaching c. 80% of the Colombia (w13.5e13.0 Ma; Goin,1997; Madden et al.,1997: 511; transversewidthofthecrown)andfunnel-shaped;cementisfilling Gradstein et al., 2005). If the close affinities of MUSM 1968 with thebottomofthehypoflexus,whichispointingdistallyandlabially. Marmosa(Micoureus)areconfirmed,thiswouldbethesecondfossil A shallow furrow faces the tip of the hypoflexus. There is no occurrenceofthisliving(sub-)genus(Goin,1997). transverse dentine crest crossing each lobe (Fig. 3F). Enamel is present all around the crown but interrupted on the labial most InfraclassEUTHERIAGill,1872 partofeachlobe. OrderXENARTHRACope,1889 The bilobed pattern of this molar is characteristic of cavioid SuborderCINGULATAIlliger,1911 caviomorph rodents (Pérez, 2010; Croft et al., 2011). Among Cav- SuperfamilyGLYPTODONTOIDEAGray,1869 ioidea,thehypselodontpatternofthistoothimpedesitsreferralto FamilyGLYPTODONTIDAEGray,1869 Asteromys,Luantus,Chubutomys,andPhanomys(Pérez,2010).The SubfamilyGLYPTODONTINAEGray,1869 funnel-shaped hypoflexus points to the clade including Eocardia Genusandspeciesindet. robusta, Guiomys unica, and crown cavioids (Pérez, 2010). The absenceoftransversedentinecrestoneachlobediscardsreferring Two isolated carapace osteoderms were found. They are small this tooth as to Prodolichotis pridiana or Orthomyctera chapadma- (MUSM1720:W¼16,preservedL¼22;MUSM1585:W¼13,L¼17), lense, while the funnel-shaped hypoflexus further distinguishes quadrangular to pentagonal in shape, with large round principal MUSM 1970 from P. pridiana (Walton, 1997; Pérez, 2010). The figures near the posterior edge. In both osteoderms, the principal presence of a single labial furrow makes it distinct from upper figureiscompletelysurroundedbyperipheraloneseeightinMUSM molarsofE.robusta.Tosumup,themorphologyofthisspecimen 1720(Fig.3D)andsixinMUSM1585(Fig.3E)e,althoughmedial, pointstoastemcavioidand,togetherwithitssmallsize,itisonly consistent with Guiomys Pérez, 2010, the smallest and earliest lophids, and a posterolophid isolated before wear). By their caviidknownsofar,fromthemiddleMioceneofPatagonia(?Col- dimensionsandpattern,theyareprovisionallythoughttodocument loncuranandLaventanSALMAs;Pérez,2010;PérezandVucetich, asingletaxon.ScleromysAmeghino,1887istheearliestrepresen- 2011) and the Laventan of Quebrada Honda, Bolivia (Croft et al., tative of Dinomyidae (Horovitz et al., 2006). The high crown, 2011). This left molar is provisionally referred to as Guiomys sp., mesiodistalelongation,quadrangularcontour,largeandpersistent asitis15e20%smallerthantheteethofthetypeandonlyspeciesof fossettids,andstraightaspectofthemesialborderofMUSM1972 thelattergenus(Pérez,2010;Croftetal.,2011). discardanyreferraltothetypicalSantacrucianspeciesofScleromys, i.e.,thetypespeciesScleromysangustusAmeghino,1887andScle- SuperfamilyCHINCHILLOIDEAKraglievich,1940 romys osbornianus Ameghino 1894 (Argentinian Patagonia). The FamilyDINOMYIDAEPeters,1873 presentspecimenseemstobesomewhatclosertoS.quadrangulatus SubfamilyPOTAMARCHINAEKraglievich,1926 (pre-Santacrucian “Pinturan” age, Patagonia, Argentina; Kramarz, “Scleromys”sp.,gr.quadrangulatus-schurmanni-colombianus 2006) and to Scleromys sp. (Mariño Formation, ?early Santa- crucian, Mendoza, Argentina; Cerdeño and Vucetich, 2007) in MUSM1971isaleftd4.Itislow-crownedandelongatemesio- sharingbothasmallsizeandaquadrangularcontour.MUSM1972 distally, with a trapezoid occlusal outline, widening distally further resembles S. quadrangulatus in having a straight mesial (MDL¼5.04;W¼2.81;H¼3.10;HI¼0.62).Ithasan“F-G-I-I”lophid border, and a mesiodistal elongation. However, the lower molars pattern,withdistinctivefeaturessuchastaeniodonty(seeAntoine referredtoS.quadrangulatusarelower-crownedthanMUSM1972 etal.,2012),elongatecristidsconnecteddistolinguallytotheante- andtheylackpersistentfossettids.Thelatterfeatureissofaronly rolophid and the metalophid, a circular supernumerary cuspid observedinS.sp.fromtheMariñoFormation(CerdeñoandVucetich, mediodistal tothe anterolophid, and a short transverse supernu- 2007), “S.” schurmanni Stehlin,1940 and “S.” colombianus Fields, merarylinguallophiddistaltothemetalophid(Fig.3I).Thehypo- 1957, from the Laventan of Colombia and Peru (Fields, 1957; lophid and the posterolophid are straight, oblique, distinct, and Walton,1997; Antoine et al., 2007). Similarly, in the Patagonian parallelonetoanother.Thehypolophiddisplaysasmallmesiolabial speciesofScleromys,themetalophulidIIistypicallyreduced,being spur. The enamel band is crenulated on the mesial side of the shorterthanthemetalophulidI.Inthataspect,MUSM1972seemsto posterolophid.Suchcrenulationsoccurfrequentlyinpotamarchine beclosertotheLaventanspeciesfromColombiainhavingalarger teeth (especially in Potamarchus murinus; Sant’Anna Filho,1994). metalophulid II. Nevertheless, in the latter taxa (the generic Thistoothistwicesmallerthand4sof“Olenopsis”/Drytomomysfrom assignmentofwhichischallengedbymostauthors;e.g.,Patterson theMiddleMioceneofLaVenta(Colombia;Fields,1957:330,Fig.18; and Wood, 1982; Walton, 1997), teeth are noticeably larger, Candela and Nasif, 2006) and of Fitzcarrald (Perú; Antoine et al., higher-crownedandwiderlabiolinguallythaninMD-67.Regardless 2007). Inaddition,MUSM1971isquitedistinct fromthed4of P. ofthelingualhypolophideposterolophidjunction(notyetoccurring murinusfromthemiddletolateMioceneoftheUpperJuruá,Brazil inMUSM1972),theMD-67specimenmatchesanm3referredto (AMNH58535;Sant’AnnaFilho,1994),inhavingatrapezoidocclusal “Scleromys cf. S. schurmanni” from the Laventan Fitzcarrald local outlineandinbeingtetralophodont,insteadofbeingquadrangular fauna of Peruvian Amazonia (MUSM 1566; Antoine et al., 2007; and pentalophodont, respectively. MUSM 1971 is tetralophodont, Negri et al., 2010), beingonly narrowerlabiolinguallyand lower- half the size of, and much less hypsodont (HI ¼ 0.62) than the crowned.Inaddition,thislowermolarhassimilarproportionsand pentalophodontp4sreferredtoSimplimusindivisus(MLP15-244a: lophid pattern as an m2 from the middle to late Miocene of the HI w 2.92; Laguna Blanca/Río Fénix, Friasian SALMA, Patagonia; Upper Juruá, Brazil (UFAC DGM 582M; Sant’Anna Filho, 1994) Vucetich,1984)andtoSimplimussp.(UFACDGM533M:HIw2.88; referred to “S.” colombianus, by reference to specimens from La UpperJuruá,middle-lateMiocene,Brazil;Sant’AnnaFilho,1994).On Venta, Colombia. However, the tooth from MD-67 is distinctly theotherhand,itssizeandproportionsrecallthoseofd4sof“S.” smaller,lower-crowned,andlessprismatic. schurmannifromLaVenta,Colombia,asillustratedbyFields(1957: Tosumup,thedentalpatternandtheocclusalcontourofMUSM 285, Fig. 5). The pattern is quite similar, especially for the distal 1972matchthoseofseveralspeciesreferredtoScleromyssensulato, lophids. Yet, the occlusal pattern of mesial lophids and cuspids eitherofpre-Santacrucian(S.quadrangulatus)orofLaventanages observed in MUSM 1971 prevents from referring it to “S.” schur- (“S.”colombianusand“S.”schurmanni;Fields,1957).Thesetaxaare manni. Teeth of “S.” colombianus (La Venta; Fields,1957; Walton, likelytoforma“lineage”distinctivefromthetypicalSantacrucian 1997)areca.20%largerthanboth“S.”schurmanniandMUSM1971. Scleromyscluster,ashypothesisedbyKramarz(2006:59).Following MUSM 1972 is a left lower molariform and hypsodont tooth, thatscheme,thecrownheight,proportions,andfossettiddevelop- with a quadrangulate occlusal contour and a straight anterior mentofMUSM1972shallcoincidewitha“transitionalevolutionary border (Fig. 3J). It is high, elongate mesiodistally and at an early stage” between S. quadrangulatus from the early Miocene of stage of wear (MDL ¼ 4.14; W ¼ 3.72; H ¼ 8.4; HI ¼ 2.03). The Argentina and the representatives of “Scleromys” from the late mesiodistal and labiolingual lengths of the tooth diminish and middleMioceneofNorthernSouthAmerica(Fields,1957;Sant’Anna increasestronglywithwear,respectively,whichallowsinterpret- Filho, 1994; Walton, 1997; Kramarz, 2006; Antoine et al., 2007; ingitasanm1at“stageofwearn!2”,bycomparisonwithserial CerdeñoandVucetich,2007).Assuch,thesespecimens,provision- sections of molariform teeth of “S.” colombianus as proposed by ally referred to as “Scleromys” sp., may document a “Friasian” to Fields (1957: 318e319, Fig.14). Roots are still developed and the Colloncuranmorphologicalgradeforpotamarchinedinomyids. neck is well-marked (Fig. 3K). This tooth is tetralophodont and taeniodont,withobliqueandlargelophids.Theshortmetalophulid SuperfamilyOCTODONTOIDEAWaterhouse,1839 IandthelongermetalophulidIIareconnectedatbothlingualand FamilyACAREMYIDAEAmeghino,1902 labialends.Thehypolophidandtheposterolophid(damagedinits Genusandspeciesindet. distolingualpart)arenotconnectedlinguallyatthecurrentstageof wear,buttheywouldjoininlaterstages.Contrarytootherlophids, MUSM1973isadiminutivelowermolar(MDL¼1.72;W¼2.10), theposterolophidiscurvedandconcavemesiolinguallyinocclusal roughly square in occlusal view, and with a rather high crown view,joiningathickandmesially-displacedhypoconid. (“mesodont”sensuVucetichandKramarz,2003).Itisinterpretedas Thesetwolowerteethhaveatypicaldinomyidocclusalpattern aleftm1orm2.Thistoothhasatetralophodontpattern,withbulky (i.e., high-crowned, tetralophodont, taeniodont, with oblique lophidsandnocuspidwellindividualised(Fig.3L).Enamelisthick, especiallyonthelabialhalfofthemolar.Inocclusalview,themesial MUSM 1974 is a left P4 with a circular occlusal outline marginisstraightandthedistaloneconvex.Thelophidsarethick, (L¼2.14;W¼2.20).Itispreservedataveryearlystageofwear transverselyoriented,andseparatebydeepandwideflexids.The (just erupted). Accordingly, there is no wear facet due to the hypoflexidisdeep(italmostreachesthelingualhalfofthetooth), contact with a mesial or a distal tooth (Fig. 3M). The crown is nearlytransverse,and“U-shaped”inocclusalview.Thetalonidis much higher lingually than labially. The tooth was biradiculate, narrowerthanthe“trigonid”,duetotheweaklingualdevelopment withlingualandlabialrootsmesiodistallyelongate.Theocclusal of the posterolophid, thus providing a trapezoid shape to the pattern is restricted to the apical-most part of the crown, with occlusalcontourofthetooth.ThemetalophulidIiscompleteand distinct cusps. The tooth is tetralophodont, with a thin but straight,withathickmesiolabialprojection,pointinglinguodistally complete anteroloph, curved distolingually, with a prominent andjoiningthemetalophulidII.ThemetalophulidIIislong,andit protocone.Theparaflexusistriangularinocclusalview,andopen also joins the metalophulid I at the lingual margin of the tooth, bothlinguallyand labiallyat thecurrentstageofwear.Thepro- determining a mesial fossettid, oval and elongate transversely tolophisoblique,shortlingually,andindependentfromadjacent (closedanteroflexid).Thejunctionbetweenbothmetalophulidsis lophsatbothends;thelingualprotolophisalowandconstricted somewhat constricted lingually, mesial to the mesostylid. The crest.Theparaconeisdistinctandbulky.Thehypoflexusisdeep ectolophid is distinct and oblique. The hypolophid is transverse, and wide (i.e., there is no endoloph). The lingual cusps, still and it connects lingually a smoothly constricted entoconid. The distinct at the current stage of wear, would be coalescent after mesoflexidisopenlingually untilalatestageofwear.Themeta- a smooth wear. The mesoflexus is open lingually and medially; flexidisalsoopenlingually,anditwouldnotgetclosedevenwith themureislowandconstricted,interruptedatthecurrentstage heavywear.Theposterolophidiscurved,withastronghypoconid of wear. The third loph is very short, restricted to the centro- andashortlingualarm(gettinglongerwithwear). distal part of the crown, and interpreted as a mesolophule; it is Boththe tetralophodontpattern and small sizeofMUSM 1973 connected lingually to the anterior arm of the hypocone and allowattributingittoanearlydivergingoctodontoid.Theabsenceof labially, to the mesoloph. The posteroloph is thin, with a hypo- aneight-shaped-patternduetothelingualopeningofthemetaflexid coneandametaconedistinctandbulky.Itextendsmesiolabially discards referring this tooth to the Octodontidae (Vucetich and tothemetaconeuntilafaintcusp,interpretedasamesostyleand Kramarz, 2003). Among Echimyidae, the transverse orientation of facing the paracone. The posteroflexus, still open mesiolabially, thelophidsimpedesanyreferraltoAdelphomyinae,whiletetralo- wouldbequadrateatlaterstagesofwear. phodonty distinguishes it from Echimyinae (Vucetich et al.,1993; A right pentalophodont molar (MUSM 1975; L ¼ 2.44 mm; Kramarz, 2001). MUSM 1973 resembles Protacaremys (Colhuehua- W ¼ 2.11 mm) has three broken roots, with two labial roots pian-ColloncuranSALMAsofPatagoniaandChile;Flynnetal.,2008) (circular cross section) and a mesiodistally elongate lingual one, inhavingdeep,transverselyelongateandpersistentfossettids/flex- whichpointtoanuppermolar(Fig.3N).Acontactfacetisvisible ids (notably the antero-fossettid/-flexid), but differs from it inthe onthemesialsideofthecrown,butnotonthedistalside.Given absenceofpinchedandcuspidatelophids,intheU-shaped,trans- the stage of occlusal wear, it allows identifying this tooth as verselyorientedandsmoothhypoflexid,inthecompleteandearly aprobableM3,evenifthetoothisonlyslightlytaperingdistally(as lingual junction between the metalophulidsI and II(anterolophid in M2s) and if the hypocone is also located as in an M2, i.e., andmesolophidsensuVucetichandKramarz,2003),andinlacking lingually displaced with respect to what is generally observed in afigure-eightocclusalpattern(Kramarz,2001). M3s.Theocclusalpatternislongerthanwide,witha“EUJ”-shaped Ontheotherhand,thedentalpatternofMUSM1973isstrongly occlusal design. All the lophs are moderately worn, with slight reminiscent of Acaremyidae (Acaremys, Sciamys, and Galileomys; constrictions, and a low obliquity. The anteroloph is the most VucetichandKramarz,2003).Itdiffersfromthem1sandm2sof developed loph, and it connects a labiolingually compressed and Galileomys in a marked mesodonty, the presence of transverse oblique paracone. The paraflexus is oval, elongate transversely, lophids,flexids,andfossettids,astrongertransversedevelopment openlabiallybutclosedlinguallybyalowandconstrictedlingual oftheU-shapedhypoflexid,andinthelingualconnectionbetween protoloph. The protoloph is straight, slightly oblique, and it the two mesial lophids (Vucetich and Kramarz, 2003; Kramarz, connects a strong paracone, labially. It joins the mesolophule 2004). It resembles more Sciamys and Acaremys. Nevertheless, it lingually,throughastrongbutveryshortmure,orientedsagittally. can be distinguished from Sciamys, as illustrated by Arnal and Themesostyleandtheparaconeareremoteandthemesoflexusis Vucetich(2011),bythequadrangularocclusalcontour(moreelon- wide and U-shaped in occlusal view (open labially). The meso- gatemesiodistallyinSciamys),byashorterlabialarmofthepost- lophuleistransverselyorientedandS-shaped,withalabiodistally- erolophid,andbysmallerdimensions.Itdiffersfromknownspecies oriented mesostyle. The metaflexus is wide, comma-shaped, still ofAcaremysinhavingamesolophidreachingthelingualwalland labiallyopenatthisstageofwear,andclosedlinguallybyalabio- determiningatransverselyelongateanterofossettidpersistentuntil lingually compressed hypocone and its strong anterior arm. The latestagesofwear,twofeatureswhichareonlyobservedinSciamys posteroloph is short, but it extends mesiolabially until the meta- amongacaremyids(VucetichandKramarz,2003).Itfurtherdiffers cone,thusformingadistolabialwall.Theposterolophissomewhat fromAcaremysinhavingamuchsmallermetaconid,anarrowerand constrictedlabiallytothehypoconeandlinguallytothemetaloph. transversallylongermesoflexid,alesspenetratinghypoflexid,and The latter is short, oriented mesiolabially, connected to the mid- aposterolophidnarrowermesiodistally.Asaresult,MUSM1973is posteroloph and disconnected to both the distolabial wall and likelytodocumentalaterepresentativeofAcaremyidaewithcloser themetacone,thusformingasmallposterofossettejoinedlabially affinitiestoSciamysandAcaremysthantoGalileomys,provisionally tothemetaflexus. identifiedas“Acaremyidaeindet”. Thepentalophodontpatternoftheuppermolar,thelowloph- obliquity,andthecircularocclusaloutlineoftheP4,aswellasthe SuperfamilyERETHIZONTOIDEAThomas,1897 lowcrownandthickenamelofbothteeth,pointtoerethizontids. FamilyERETHIZONTIDAEThomas,1897 Giventheircompatiblesizeandpattern,bothteethareassumedto cf.Microsteiromyssp. document a single diminutive taxon. The fossil record of Erethi- zontidae ranges from the Late Oligocene up to Recent times Two upper molariform teeth are assigned to a small (Vucetich et al., 1999; Candela and Morrone, 2003). Accordingly erethizontid. and whenever possible, these teeth were compared to those of Protosteiromys (Deseadan, Patagonia; Wood and Patterson,1959), 4. Discussion of Eosteiromys Ameghino, 1902, Hypsosteiromys Patterson, 1958, Parasteiromys Ameghino,1903,andBranisamyopsisCandela, 2003 4.1. Biochronologicalage (Colhuehuapian, Argentina; Patterson, 1958; Candela, 1999, 2003; Dozo et al., 2004; Kramarz, 2004; Kramarz and Bellosi, Glyptodontidxenarthransareofpoorbiochronologicalinterest, 2005;Vucetichetal., 2010),ofSteiromysAmeghino,1887(Santa- especiallywhenidentifiedabovegenuslevel.Caviomorphrodents crucian-?Laventan; Patagonia, ?Colombia; Fields, 1957; Walton, arethemostdiversegroupinMD-67,withfourtaxaencompassing 1997; Candela, 1999), of Neosteiromys Rovereto, 1914 (?Collon- foursuperfamilies(Octodontoidea,Erethizontoidea,Cavioidea,and curan-Huayquerian; Northwestern Argentina; Candela, 1999, Chinchilloidea;Vucetichetal.,1999).CaviidaehavetheirFADinthe 2004), of Microsteiromys Walton, 1997 (Laventan; Colombia; latest (or post-) Colloncuran of Patagonia, with Guiomys (Pérez, Walton, 1997), and of Erethizon Cuvier, 1823 (Recent; Candela, 2010; Pérez and Vucetich, 2011), a genus which is recognised at 1999). MD-67 (Fig. 3FeH; Table 1). Acaremyidae had a Colhuehuapian- The teeth from MD-67 are half the size of than those of all Colloncuran stratigraphical range (Vucetich and Kramarz, 2003) knownRecentandfossilErethizontidaebutMicrosteiromysjacobsi while the hathliacynid marsupial Sipalocyon had only an early Walton,1997,ofcompatiblesize(Walton,1997).NoP4isdescribed Miocene record so far (Colhuehuapian-Santacrucian; Marshall, fromanyDeseadanerethizontid.TheP4fromMD-67differsfrom 1981).Assuch,MD-67mightextendupwardtheknownrangeof all known Recent and fossil Erethizontidae but Eosteiromys bothtaxa,andthusrepresenttheirLastLocalOccurrence(Table1). homogenidens Ameghino, 1902, in having a labially-displaced Ontheotherhand,therecognitionofMarmosa(Micoureus)andof hypocone. A circular occlusal outline is only observed in a Microsteiromys-like dwarf porcupine in MD-67 predates the E.homogenidens(holotypeMACNA-52-165)and?SteiromysfromLa previous FAD of both taxa, formerly restricted to the Laventan Venta(Walton,1997).Tetralophodontyandlowlophobliquityalso characterises the P4 of Eosteiromys, ?Steiromys, and Steiromys detentusAmeghino,1887(MLP15e17).MUSM1974furtherdiffers Table1 fromthedP4ofParasteiromysuniformis(Ameghino,1903)inhaving StratigraphicrangeofthemiddleMiocenevertebratelocalityMD-67asinferredby a marked mure, and in bearing flexi labiolingually compressed mammalianbiochronologyandfissiontrackdatings(seeSupplementaryData).Data (Candela,1999). Its paraflexus, which is closed labially, makes it fromWalton(1997),Vucetichetal.(1993,2010),VucetichandKramarz(2003), distinctfromtheP4ofBranisamyopsispraesigmoidesKramarz,2004 Kramarz(2004,2006),Gradsteinetal.(2005),KramarzandBellosi(2005),Cerdeño andVucetich(2007),Croftetal.(2011),andPérezandVucetich(2011). andS.detentus(Kramarz,2004:14,Fig.7).ItalsodiffersfromtheP4 ofNeosteiromysbombifronsRovereto,1914inhavingnolingualwall (Candela,2004:61,Fig.3). The upper molar from MD-67 differs from all known erethi- zontidsinitslabially-interruptedmetalophandinitsmesiodistal elongation(e.g.,Candela,1999,2004;Vucetichetal.,2010).Itssize is also very distinctive, as it is twice smaller than in all known taxa,exceptM.jacobsi,ofsimilardimensions(Walton,1997).The pentalophodont pattern makes it distinct from Protosteiromys medianus,Hypsosteiromysaxiculus,andSteiromys(Patterson,1958; WoodandPatterson,1959;Candela,1999;Dozoetal.,2004).The presence of a mure and the late labial closure of the paraflexus discard any referral to Parasteiromys or Neosteiromys (Candela, 1999). Thepresenceofadistalconstrictionlabiallytothehypoconeand linguallytothemetalophisonlyobservedinParasteiromysfriantae Candela, 1999 (but not in P. uniformis; Candela, 1999: Fig. 2), E. homogenidens (type, MACN A-52e165) and E. cf. homogenidens (Kramarz, 2004). However, all these taxa are characterised by lower-crownedteeth,amuchlargersize,andacompletemetaloph, i.e.,reachingthelabialsideofthetooth. Tosumup,thepatternandmorphologicalfeaturesoftheP4and of the upper molar from MD-67 show certain affinities with E. homogenidens (Colhuehuapian), and Steiromys (Santacrucian-? Laventan) to a lesser extent, while size is only compatible with Microsteiromys(Walton,1997).MicrosteiromysWalton,1997isthe smallest known representative of New World porcupines, with a geographic and stratigraphic range thus far restricted to the Baraya Memberof the Villavieja Fm. of Colombia (c.13e12.5 Ma, middle Laventan; Madden et al., 1997; Candela and Morrone, 2003). This diminutive monotypic genus is only known by two mandibles,whichmakesitimpossibletocomparewiththeavail- ableteethfromMD-67(Walton,1997).However,weassumethat these teeth are likely to document a close ally of Microsteiromys Walton,1997,herereferredtoascf.Microsteiromyssp.Giventheir morphologicalaffinities withtaxa spanningtheearlyandmiddle Miocene interval, these specimens cannot be used with much confidenceinabiochronologicalperspective.

Description:
and Otto, Thierry and Brusset, Stéphane Middle Miocene vertebrates from the .. To sum up, the dental pattern and the occlusal contour of MUSM.
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