iddle Miocene vertebrates from the Amazonian Madre de Dios Subandean Zone, Perú

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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
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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.
SALMAintheLaVentaareaofColombia(Table1;Marshall,1976; Lithology of the fossil-bearing beds (i.e., channel-irondeposits,
Goin,1997;Maddenetal.,1997;Walton,1997). withFe-richpisolitegravels)providesvaluableinformationonthe
At first sight, the biochronological age for MD-67 is middle depositional environment and associated diagenetic processes:
Miocene, i.e., Colloncuran-Laventan (w15.6e11.6 Ma; Kay et al., pisolites might have formed in the ground by alteration and
1997; Madden et al.,1997), but the occurrence of a typical early concretionofhighlyferruginousgroundwatersolutionsunderwarm,
MiocenegenussuchasSipalocyonandthepotentially“plesiomor- humid,andseasonally-contrastedconditions(Tardy,1992).Accord-
phicevolutionarystage”of“Scleromys”withrespecttoitsLaventan ingly,isotopicanalysesperformedoncoevalmolluscshellsfromthe
counterparts (Walton,1997) would tend to favoura Colloncuran- Iquitosarea(w1000 kmmore tothe North) show the regionwas
earlyLaventanageforthisnewlocality(w15.6e13.0Ma;Table1). experiencingaseasonalwaterinfluxunderamonsoonal-liketropical
climatebythattime(Kaandorpetal.,2006;Wesselinghetal.,2006).
4.2. ApatitefissiontrackageofMD-67:17.1 2.4Ma Bothproxiesarethereforeingoodagreement.
OneofthestrikingfeaturesoftheMioceneofAmazoniaisthe
A fission track age was calculated on 11 apatite grains. The presenceofalargeandlong-lasting“mega-wetland”.TheAmazo-
correspondingresultsaredetailedintheSupplementaryData.The nianmega-wetlandreacheditsmaximumextentduringtheMiddle
c2test(Galbraith,1981;Green,1981)iscurrentlyusedtodiscrim- Miocene(alsocalled“Pebasphase”sensuHoornetal.,2010a,b)and
inatebetweenconcordant(P(c2)>5%)anddiscordant(P(c2)<5%) it consisted of a complex mosaic of lakes, embayments, swamps,
grain-age distributions. The MD 67 sample passes the c2 test rivers, and fluvio-tidal environments (see review in Hoorn et al.,
(P(c2)>5%)indicatingthattheapatitegrainsdisplayaconcordant 2010a,b). Our data suggest the absence of this megawetland in
populationand thattheyare derived fromhomogeneoussources the Amazonian Madre de Dios Subandean Zone of Perú (Fig. 4),
(Galbraith,1981;Green,1981). while other coeval localities such as IQ-26 and NA069 (nearby
The central age (17.1 2.4 Ma), pointing to a Burdigaliane Iquitos;Antoineetal.,2006;Pujosetal.,2009)ortheFitzcarrald
Langhian agefor the concerned grains (Table 1), is only partlyin LocalFauna(Antoineetal.,2007;Goillotetal.,2011)wereunderits
agreementwiththefaunalcontentofMD-67,interpretedasdoc- influence during the same period (Fig. 4). This environmental
umenting a Colloncuran-early Laventan age (w15.6e13.0 Ma; contrast might in turn have played some role in the faunal
Table1). discrepancies as observed in middle Miocene times between
In other words, Apatite Fission Track provides a detrital age NorthernandSouthernSouthAmerica(Maddenetal.,1997).
(17.1 2.4 Ma) for the vertebrate-yielding locality, slightly older
thanitsinferredbiochronologicalage(Colloncuran-earlyLaventan 4.4. Biogeography
SouthAmericanLandMammalAges:w15.6e13.0Ma).Beasitmay,
themiddleMioceneageoftheconcernedoutcropisfullycontra- The earliest undisputable representatives of Glyptodontinae,
dictory to its original assignment to the Paleocene-Eocene referredtoBoreostemma,originatefrommiddleMioceneLaventan
YahuarangoFormation(VargasandHipólito,1998). localitiesofLaVentaandFitzcarrald(ColombiaandPerú,respec-
tively; e.g., Antoine et al., 2007). In southern South America, the
4.3. Paleoenvironment earliest record occurs much later, with Glyptodontidium tuberifer
fromthelateMiocene-PlioceneofNWArgentina(e.g.,Olivaetal.,
Atregionalscale,theconcernedareamostlyyieldedterrestrial 2010), which is most probably tied to environmental reasons
habitats of lowelevation, with a moist forest assumed as resem- (Carlinietal.,2008).Ifconfirmed,thereferraloftheosteodermsof
bling the modern Amazonian rainforest, in terms of composition MD-67toGlyptodontinaewouldstillextendthegapbetweenthe
and biodiversity (Hoorn,1993; Antoine et al., 2006; Pons and De firstlocaloccurrencesofthegroupinlowandhighlatitudes.
Franceschi,2007;Hoornetal.,2010a,b). ThecavioidrodentGuiomysPérez,2010wassofarrestrictedto
Unfortunately,MD-67yieldsnopollen,spores,orplantfossils. the middle Miocene of Patagonia and Southern Bolivia, with a ?
Available proxies (dental morphology and habitat preferences of Colloncuran(w14Ma;Patagonia)-Laventan(PatagoniaþSouthern
living and fossil mammal analogues; depositional environment) Bolivia)stratigraphicrange (Fig.4;Pérez,2010;Croftetal.,2011;
thusprovideonlyindirectinformationontheenvironmentofthe Pérez and Vucetich, 2011). Accordingly, Sipalocyon was so far
concernedareabythetimefossilmammalsaccumulated. restrictedto highSouthern latitudes, fromPatagonia toSouthern
Most rodentsfromthe current assemblage, including a meso- Chile (51.5e37.5!S; Marshall, 1981; Forasiepi et al., 2006; Flynn
dont acaremyid, a hypsodont dinomyid (“Scleromys” sp.), and etal., 2008). Theco-occurrence of this stemcaviidand of Sipalo-
ahypselodontcaviid(Guiomyssp.),canbeinterpretedasanindi- cyon(37.5e48!S)inPeruvianAmazoniaextendsthegeographical
catorofopenanddustyenvironmentsunderaquitedryandwindy range of w10! and w25! more to the North, respectively (Flynn
climate (Candela and Vucetich, 2002). Yet, the dwarf Micro- etal.,2008;Croftetal.,2011).Ontheotherhand,thesmallmar-
steiromys-like erethizontid of MD-67 was most probably fully mosine M. (Mi.) laventica and the diminutive erethizontid Micro-
arboreal,likealllivingNewWorldporcupinesandtheirfossilkin, steiromyswereonlyknownintheHuilaDepartmentofColombia
asproposedbyCandelaandPicasso(2008).Accordingly,allliving duringaveryshortLaventaninterval(Fig.4;Goin,1997;Walton,
marmosinemarsupials,suchastherepresentativesofthesubgenus 1997),i.e.,laterandw15! moretotheNorththaninMD-67.
Marmosa(Micoureus)areforestdwellers,beingeitherarborealor In other words, the MD-67 assemblage both (i) postdates the
groundforagers,inmoisthabitatsrelatedtotropicalevergreenor formerly known range of taxa of mid- and high latitude affinities
mossyforests(EmmonsandFeer,1997). (Sipalocyon;Acaremyidae)and(ii)predatesthatoftaxaoflowlatitude
The appendicular skeleton of Sipalocyon is poorly known, but affinities (Marmosa (Micoureus); Microsteiromys; Glyptodontinae).
functional anatomy suggests arboreal and potential grasping Thisphenomenonissummarisedbythespatiotemporalrangeofthe
capabilitiesforthiscarnivorousmarsupial(Argot,2003,2004).The smalldinomyidrecognisedinMD-67anditskin,ifclosephylogenetic
SantaCruzBedsofPatagonia,whichyieldmostremainsofSipalo- affinities are confirmed between the representatives of Scleromys
cyon,areinterpretedasoriginatingfromatemperatecoastalplain sensustricto(earlyMioceneofPatagoniaandSouthernChile;Flynn
(BownandFleagle,1993),withmoderaterainfallandamixtureof et al., 2008) and those of “Scleromys” sensu Walton, 1997 (late
forestedhabitats/openareas/bushlandassuggestedbymammals, middleMioceneofColombiaandPeru;Walton,1997;Antoineetal.,
pollen,andterrestrialarthropods(Vizcaínoetal.,2010). 2007). Such assertion may be an artefact tied to the scarce fossil