Short-tailed mice with a long fossil record: the genus Leggadina (Rodentia: Muridae) from the Quaternary of Queensland, Australia


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Short-tailed mice with a long fossil record: the genus Leggadina (Rodentia: Muridae) from the Quaternary of Queensland, Australia

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Title:
Short-tailed mice with a long fossil record: the genus Leggadina (Rodentia: Muridae) from the Quaternary of Queensland, Australia
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PEER-REVIEWED Paleontology and Evolutionary Science section
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Cramb, Jonathan
Price, Gilbert J.
Hocknull, Scott A.
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PeerJ
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Climate Change ( local )
Extinction ( local )
Leggadina ( local )
Muridae ( local )
Palaeoecology ( local )
Pleistocene ( local )
Quaternary ( local )
Rodents ( local )
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serial ( sobekcm )

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The genus Leggadina (colloquially known as ‘short-tailed mice’) is a common component of Quaternary faunas of northeastern Australia. They represent a member of the Australian old endemic murid radiation that arrived on the continent sometime during the late Cenozoic. Here we describe two new species of extinct Leggadina from Quaternary cave deposits as well as additional material of the extinct Leggadina macrodonta. Leggadina irvini sp. nov. recovered from Middle-Upper (late) Pleistocene cave deposits near Chillagoe, northeastern Queensland, is the biggest member of the genus, being substantially larger than any other species so far described. Leggadina webbi sp. nov. from Middle Pleistocene cave deposits at Mount Etna, central eastern Queensland, shares features with the oldest species of the genus, the Early Pleistocene L. gregoriensis. Based on the current palaeoecological interpretation of the type locality, L. webbi, represents the only member of the genus that inhabited rainforest. The succession of Leggadina species through the late Quaternary suggests an ecological replacement of the extinct large-bodied L. irvini with the extant, small-bodied L. lakedownesis at Chillagoe. At Mt. Etna, the extinct rainforest species L. webbi is replaced with the extant xeric-adapted L. forresti during the latest Middle Pleistocene. This replacement is associated with a mid-Pleistocene shift towards progressive intensifying seasonal and arid climates. Our study adds to the growing list of small-bodied faunal extinctions during the late Quaternary of northern Australia.

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Submitted 9March2018 Accepted 27August2018 Published 21September2018 Correspondingauthors JonathanCramb, jonathan.cramb@qm.qld.gov.au GilbertJ.Price,g.price1@uq.edu.au Academiceditor LauraWilson AdditionalInformationand Declarationscanbefoundon page22 DOI 10.7717/peerj.5639 Copyright 2018Crambetal. Distributedunder CreativeCommonsCC-BY4.0 OPENACCESS Short-tailedmicewithalongfossil record:thegenus Leggadina Rodentia: MuridaefromtheQuaternaryof Queensland,Australia JonathanCramb 1 ,GilbertJ.Price 1 andScottA.Hocknull 2 1 SchoolofEarthandEnvironmentalSciences,UniversityofQueensland,Brisbane,Queensland,Australia 2 Geosciences,QueenslandMuseum,Brisbane,Queensland,Australia ABSTRACT Thegenus Leggadina colloquiallyknownas`short-tailedmice'isacommon componentofQuaternaryfaunasofnortheasternAustralia.Theyrepresentamember oftheAustralianoldendemicmuridradiationthatarrivedonthecontinentsometime duringthelateCenozoic.Herewedescribetwonewspeciesofextinct Leggadina fromQuaternarycavedepositsaswellasadditionalmaterialoftheextinct Leggadina macrodonta . Leggadinairvini sp.nov.recoveredfromMiddle-UpperlatePleistocene cavedepositsnearChillagoe,northeasternQueensland,isthebiggestmemberof thegenus,beingsubstantiallylargerthananyotherspeciessofardescribed. Leggadinawebbi sp.nov.fromMiddlePleistocenecavedepositsatMountEtna,central easternQueensland,sharesfeatureswiththeoldestspeciesofthegenus,theEarly Pleistocene L.gregoriensis .Basedonthecurrentpalaeoecologicalinterpretationof thetypelocality, L.webbi ,representstheonlymemberofthegenusthatinhabited rainforest.Thesuccessionof Leggadina speciesthroughthelateQuaternarysuggestsan ecologicalreplacementoftheextinctlarge-bodied L.irvini withtheextant,small-bodied L.lakedownesis atChillagoe.AtMt.Etna,theextinctrainforestspecies L.webbi is replacedwiththeextantxeric-adapted L.forresti duringthelatestMiddlePleistocene. Thisreplacementisassociatedwithamid-Pleistoceneshifttowardsprogressive intensifyingseasonalandaridclimates.OurstudyaddstothegrowinglistofsmallbodiedfaunalextinctionsduringthelateQuaternaryofnorthernAustralia. Subjects Paleontology,Zoology Keywords Leggadina ,Muridae,Quaternary,Pleistocene,Rodents,Palaeoecology,Extinction, Climatechange INTRODUCTION Short-tailedmice Leggadina spp.aresmall-bodiedmurinesthatformpartofthe `AustralianOldEndemicRadiation' Aplin,2006 ; Watts&Aslin,1981 ,nowreferred tothetribeHydromyini Lecompteetal.,2008 .Thegenushasacomplextaxonomic history. Thomas wasthefirsttodescribeaspeciesof Leggadina ,butplaceditin thegenus Mus .Thomaslaterproposedthename Leggadina asasubgenusof Pseudomys Thomas,1910 . Iredale&Troughton elevated Leggadina tofullgenericstatus,a movesupportedby Ellerman and Tate .Severalearlyworkers Thomas, Howtocitethisarticle Crambetal.,Short-tailedmicewithalongfossilrecord:thegenus Leggadina Rodentia:Muridaefrom theQuaternaryofQueensland,Australia. PeerJ6:e5639;DOI10.7717/peerj.5639

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1910 ; Ellerman,1941 ; Tate,1951 placedanyverysmallAustralianrodentspecieswithan accessorycusponM 1 in Leggadina ,butsomeauthors Ellerman,1941 ; Tate,1951 noted thatseveralspeciesnowsynonymisedinto L.forresti weredistinctfromallothers. Ride synonymised Leggadina backinto Pseudomys ,onlytohaveitresurrectedagainby Mahoney&Posamentier . Covacevich&Easton consideredthattheCentralShort-tailedMouse, L.forresti listedas Pseudomysforresti ,waswidespreadacrossQueensland.However,individuals fromthenortheastofQueenslandwerelatershowntobedistinctby Watts and Baverstocketal. ,andsubsequentlynamed Leggadinalakedownensis .Laterauthors consideredthatall Leggadina innorthernAustraliawereconspecificwith L.lakedownensis Moroetal.,1998 ,with L.forresti restrictedtothecontinent'sinterior.Noadditional extantspeciesof Leggadina havebeendescribedsincethattime,althoughregionalvariants havebeenrecognised Cooperetal.,2003 . Leggadina istraditionallyincludedinthe` Pseudomys division'`Conilurini',which alsoincludes Conilurus , Mesembriomys , Leporillus , Notomys , Zyzomys , Mastacomys and Pseudomys itself Musser&Carleton,2005 .However,molecularphylogeniesindicatethat Conilurus , Mesembriomys and Leporillus areactuallythesistergroupofthe` Uromys division' Uromys , Melomys ,andrelatedgenera,makingthe` Pseudomys division'paraphyletic Rowe etal.,2008 ; Steppanetal.,2005 .Regardless,thepositionof Leggadina asacloserelativeof Zyzomys anda Pseudomys / Notomys / Mastacomys cladeiswell-supported Ford,2006 ; Rowe etal.,2008 .Mostrecentlyananalysisby Smissen&Rowe found Leggadina tobe thesistercladeof Zyzomys . Leggadina hasarelativelylongfossilrecordforanAustralianmurinegenusspanning muchoftheQuaternary.TheearliestrecordscomefromtheEarlyPleistoceneRiversleigh WorldHeritageArea,northwesternQueensland Klinkhamer&Godthelp,2015 and Fisherman'sClifffossildepositsinsouthernNewSouthWales Crabb,1977 ; Breed&Ford, 2007 .MiddlePleistocenereportsinclude Hocknull 2005 ; 2009 and Hocknulletal. fromcavedepositsatMt.Etna,centralQueensland.Recentowlroostdepositsincentral Australiacommonlycontaintheskeletalanddentalremainsof L.forresti e.g. Baynes& Johnson,1996 ,whilst L.lakedownensis hasbeenrecordedfromcavedepositsinnorthern WesternAustralia Startetal.,2012 . Inlightofnewmaterialnowavailableforanalysis,weherereviewthefossilrecordof Leggadina innortheasternAustralia,erecttwonewspeciesfromfossilsofPleistoceneage, anddescribeadditionalmaterialreferrabletotheextinct L.macrodonta .Theevolutionand palaeoecologyofspeciesof Leggadina arediscussed,withimplicationsforourunderstanding ofthewiderAustralianmurinefauna. MATERIALANDMETHODS SpecimenswereobtainedaspartofongoingpalaeontologicalinvestigationsofPleistocene depositsinQueensland.Theseincludethefossil-richcavedepositsoftheMountEtna centraleasternQueenslandandChillagoenortheasternQueenslandareas,andopen fluvialdepositsatFloravillenorthwesternQueenslandFig.1.Thefossilmaterial Crambetal., PeerJ ,DOI10.7717/peerj.5639 2/27

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Figure1MapofQueensland,Australia,showingthestudylocalities. Full-size DOI:10.7717/peerj.5639/fig-1 comprisesmaxillae,dentariesandisolatedteeth.Allfossilsdescribedinthispaperare accessionedintothecollectionsoftheQueenslandMuseum,Brisbane,Australia. ImageswereobtainedusingaVisionaryDigital`passportstorm'camerasystemand aHitachiTM-1000environmentalscanningelectronmicroscopeattheQueensland Museum.MeasurementsweretakenusingMitutoyodigitalcallipers.Dentalterminology followsFig.2. TheelectronicversionofthisarticleinPortableDocumentFormatPDFwillrepresent apublishedworkaccordingtotheInternationalCommissiononZoologicalNomenclature ICZN,andhencethenewnamescontainedintheelectronicversionareeffectively publishedunderthatCodefromtheelectroniceditionalone.Thispublishedwork andthenomenclaturalactsitcontainshavebeenregisteredinZooBank,theonline registrationsystemfortheICZN.TheZooBankLSIDsLifeScienceIdentifierscanbe Crambetal., PeerJ ,DOI10.7717/peerj.5639 3/27

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Figure2Molarcuspterminologyforspeciesof Leggadina . AUppermolars.BLowersmolars.Terminologyismodifiedfrom Musser and Aplin&Helgen .Abbreviations:acc,accessorycusp; T1acc,T1accessorycusp;T1sup,T1supplementarycusp;a-lin,antero-lingualcuspid;a-buc,anterobuccalcuspid;amr,anteriormedialridge;md,metaconid;pd,protoconid;ed,entoconid;hd,hypoconid; bc,buccalcingulid;pc,posteriorcingulid;pcc,posteriorcingulidcuspid;pl,posteriorloph.Theterm `complex'isusedwhereindividualcuspscannotbedistinguished. Full-size DOI:10.7717/peerj.5639/fig-2 resolvedandtheassociatedinformationviewedthroughanystandardwebbrowserby appendingtheLSIDtotheprefixhttp://zoobank.org/.TheLSIDforthispublicationis: urn:lsid:zoobank.org:pub:3C34C73B-4800-4256-BC9E-0E7B50689024.Theonlineversion ofthisworkisarchivedandavailablefromthefollowingdigitalrepositories:PeerJ,PubMed CentralandCLOCKSS. Geographicandgeologicalsettings Floraville Numerousvertebrate-bearingfossildepositsoccurinthevicinityofFloravilleDowns Stationinnorth-westernQueenslandFig.1.Thedepositsarepredominantlyfluviatile, occurringadjacenttothewesternbanksoftheLeichhardtRiverandassociatedtributaries. Thefossil-bearingsedimentsconsistofsilts,clays,sands,andgravels,includingsomewith extensive insitu carbonates. Fossilcollectingonthestationhasbeensporadicsincethe1970s,withnosingle depositsubjectedtoextensiveanddetailedexcavation.Themajorityoffindshavebeen ofsurfacespecimensandincludemostlymegafaunaltaxai.e.,large-bodiedextinct Quaternaryvertebratesincludinggiantmarsupialsandcrocodiles.Wherefossilcollecting hasadoptedtechniquesconducivetotherecoveryofsmall-bodiedspeciese.g.,sievingof sedimentsandfossilsusingfine-meshsievesfromselecteddeposits,significantand Crambetal., PeerJ ,DOI10.7717/peerj.5639 4/27

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diversevertebrate-richassemblageshavebeenrecovered Rich,1991 .Thedeposits havepreviouslybeenconsideredtobePlio-Pleistocene Godthelp,1999 ; Tyler,Archer& Godthelp,1994 ,however,recentradiometricdatingstronglysuggeststhatthedepositsare MiddlePleistocene Price,2013 .Moreover,thefossilassemblageslacktypicalPliocenetaxa suchasthelarge-bodiedwombat-likemarsupial Euryzygoma ,buthaveyieldednumerous specimensofthecloselyrelated Diprotodon ,aspeciesfoundexclusivelyinPleistocene deposits Priceetal.,2009 . Chillagoe FossilassemblagesfromtheChillagoearea,north-easternQueenslandFig.1havebeen recoveredfromcavernousandfissure-filldepositswithinoutcropsofDevoniankarst limestone Price,2013 ; Priceetal.,2013 .Thenewrecordsof Leggadina fromChillagoeare derivedfromtwocavesystems,MacropedesWaterholeCaveandFernCave. TheMacropedesWaterholeCavedepositiscurrentlyundated,butcontainsbothextant speciesandmultipleextincttaxa,includinghithertoundescribedmurinerodents Cramb, 2012 .Thefossilassemblagealsocontainsspecimensassignableto Rattus Cramb,2012 , agenusthatispurportedtohavearrivedinAustraliaaround0.85.28Ma Roweetal., 2011 ,thuspotentiallyconstraininganupperagelimitforthedepositasEarlyPleistocene. Thebrecciateddepositisdominatedbyclayswithoccasionalboneclasts.Thesediments withinthedepositclearlyhavealonggeologicalhistoryhavingaccumulatedwithinthe cave,lithified,andthensubsequentlyeroded.We,therefore,hypothesisethatthedeposit isMiddletoLatePleistoceneinage. In2009duringanexploratorysearchofthecaveforfossils,asmall 125gsamplewas collectedfromahollowinthebreccia,whereerodedfossilshadaccumulated.Afterthe significanceofthesamplewasascertaineditwashopedthatadditionalfieldworkwould recoveradditionalsamples.Unfortunatelythecavewasfloodedatthetimeofasubsequent fieldtrip,makingthedepositinaccessible. PreviousinvestigationsatFernCavehavetargetedexcavationofanarchaeological depositwithinite.g., Goodalletal.,2009 .However, Leggadina specimensexaminedinthis paperwerederivedfromanactiveowl-roostpositionedonaledgehighabovethedeposit. Thespecimenswerecollectedatthetimeoftheoriginalarchaeologicalinvestigationsca. 1985AD,buthaveremainedunpublisheduntilnow.Thesedimentsareunconsolidated, andwereexcavatedinfivecmspits.Theowlroosthasnotbeendated,butatleastsomeof theskeletalmaterialwithinitisclearlyRecent.Basedonthesizeofthedepositwesuspect thefaunaareHolocenetorecentinage. Mt.Etnaregion Fossilspecimensof Leggadina collectedfromtheMt.Etnaregionhavecomefromnumerous limestonecavedeposits,locatedonMt.Etna,theadjacentLimestoneRidgeandnearby Olsen'sCave Hocknull,2005 ; Hocknulletal.,2007 ; Hocknull,2009 ; Price&Piper,2009 ; Cramb,Hocknull&Webb,2009 ; Cramb&Hocknull,2010a ; Priceetal.,2015 .Themajority ofthefossil-richdepositsatMt.Etnawereinitiallyexposedasaresultoflimestonemining activitiesonthewesternsideofMt.Etna,whilefossildepositsatLimestoneRidgeand Olsen'sCavearederivedfromnaturallyexposeddepositsordepositsexposedthrough Crambetal., PeerJ ,DOI10.7717/peerj.5639 5/27

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guanomining.Thefossildepositsarevariableintheirlithology,rangingfromphreaticallyderivedbrecciated,redclay-dominatedsedimentsthroughvadose-derived,speleothemrichyellowclay-richsedimentstoguano-derived,chocolate-brownorganic-richsediments Hocknull,2009 .Alldepositsarevariablycementedwithcarbonate;well-cementedsamples werecollectedasblocksanddigestedinaceticacidbaths.Lessconsolidateddepositswere excavatedinfivecmspitswherepossible.OneimportantsiteQML1312Elephanthole Cavewasdestroyedin1988,beforesystematicsamplingcouldbeundertaken.Itis neverthelesswellrepresentedbyasamplecollectedbycaverspriortothecaves'destruction Hocknull,2005 . Uranium-thoriumdatingplacesthemajorityofdepositsintheareawithinthelast 500ka,withsomee.g.,Olsen'sCaveasrecentasthelateHolocene Hocknulletal.,2007 ; Priceetal.,2015 .Theolderdepositsinthearea>500kaBPcontainnumerous speciesinterpretedasindicativeofaclosedrainforestpalaeoenvironment,whiledeposits datedto<250kaBPmostlycontaintaxathataremoreindicativeofopen,xerichabitats Hocknull,2005 ; Hocknulletal.,2007 . RESULTS Systematicpalaeontology ClassMammaliaLinnaeus,1758 SubclassTheriaParkerandHaswell,1897 SupercohortPlacentaliaBonaparte,1838 OrderRodentiaBowdich,1821 FamilyMuridae Illiger,1811 LeggadinaThomas,1910 Typespecies: MusforrestiThomas,1906 Otherspecies: L.lakedownensisWatts,1976 L.gregoriensisKlinkhamer&Godthelp,2015 L.macrodontaKlinkhamer&Godthelp,2015 Genericdiagnosis.Speciesof Leggadina aredistinguishedfromallothermuridsbyaunique combinationofcharactersincludingthepossessionof:largeaccessorycusponM 1 ;large, lingualcuspsonM 1 )]TJ/F75 7.9701 Tf 6.217 0 Td [(2 postero-lingualofassociatedlophs;commonlydiamond-shapedT1 onM 1 ;T1supplementarycuspcommonlypresentonM 1 ,althoughvariablyexpressed; uppermolarcuspsslopedposteriorly;M 1 / 1 enlarged;M 3 / 3 reduced,suchthatM 1 / 1 is longerthanM 2 )]TJ/F75 7.9701 Tf 6.217 0 Td [(3 = 2 )]TJ/F75 7.9701 Tf 6.216 0 Td [(3 combined;largeposteriorpalatalforamen;broadposteriorcingulid cuspidonM 1 ;lowermolarcuspsslopedanteriorly;apexofeachlowermolarcuspdrawn infrommarginsofbase. Genericremarks. Leggadina canbeseparatedfromallotherAustralo-Papuanmurinesbythelargeaccessory cusponM 1 ,largeposteriorpalatalforamen,enlargementofM 1 / 1 withassociatedreduction ofM 3 / 3 sothatM 1 / 1 ismorethanhalfthelengthofthemolarrow.Smallspeciesof Pseudomys e.g., P.delicatulus sharesomesimilaritieswith Leggadina ,butdifferbyhaving Crambetal., PeerJ ,DOI10.7717/peerj.5639 6/27

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Figure3Fossilsof L.lakedownensis and L.forresti fromcavedepositsatChillagoeandMountEtna. ADUpperdentions:AQMF55619 L.lakedownensis rightmaxilla;B L.lakedownensis QMF55618 leftmaxilla;CQMF58982 L.forresti rightmaxilla;DQMF58983 L.forresti leftmaxilla.EGLower dentitions:EQMF55621 L.lakedownensis rightmandible;FQMF55620 L.lakedownensis right mandible;GQMF58981 L.forresti leftmandible.Scalebar D 1mm.APF,anteriorpalatalforamen.The buccaledgeoftheAPFiscurvedin L.lakedownensis ,butstraighterin L.forresti . Full-size DOI:10.7717/peerj.5639/fig-3 asmalleraccessorycusponM 1 ,lessdevelopmentoftheT1supplementarycusponM 1 , smallerposteriorpalatalforamen,proportionallysmallerM 1 / 1 andlargerM 3 / 3 M 1 / 1 commonlyhalfthelengthofthemolarrow,andasmallerposteriorcingulidcusponM 1 . Morphologicaldifferencesbetweenthetwoextantspeciesof Leggadina see Watts,1976 ; Cooperetal.,2003 ; VanDyck,Gynther&Baker,2013 arepartiallybasedonintactskulls. However,mostfossilsarerepresentedbyfragmentaryremains,suchthatonlyasubsetof featurescanbeusedtodiagnosefossilspecieswithin Leggadina .Thosecharactersinclude: thelengthandwidthofM 1 ;lengthofaccessorycusponM 1 ;relativelengthofM 2 compared toM 1 ;relativereductionofM 3 ;lengthofM 1 ;andtheshapeoftheposteriorendofthe anteriorpalatalforamen. Leggadinaforresti Thomas,1906 Fig.3 Crambetal., PeerJ ,DOI10.7717/peerj.5639 7/27

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Diagnosis:See Thomas ,towhichwecanaddthefollowingfeaturesthathaveproved usefulwhenidentifyingfossilspecimens: Leggadinaforresti isasmallspecieswithinthe genusandpossessesthefollowinguniquecombinationofcharacters:enlargedM 1 / 1 ,heavily reducedM 3 / 3 ,stronglydevelopedaccessorycusponM 1 variablydivided,moderatelyto well-developedT1supplementarycusponM 1 ,andananteriorpalatalforamenthathasa straightbuccaledgeonthemaxillaandtaperstoapointposteriorly. Material.QML1312;ElephantHoleCaveSystem,MountEtna:QMF55341leftmaxilla, QMF55646leftmaxilla,QMF55647rightmandible,QMF55648leftM 1 ;QML1313A; SpeakingTubeCaveSystemsubsampleA,MountEtna:QMF55649leftmaxillafragment withM 1 ,QMF55649leftmaxillafragmentwithM 1 ;QML1456;ColosseumChamber, CapricornCaves:QMF55148leftmaxilla,QMF55149rightmaxilla,QMF55150right maxilla,QMF55151rightmaxilla,QMF55152leftmandible,QMF55153rightmandible, QMF55767rightmaxilla,QMF58981leftmandible;QML1466HoneymoonSuite, CapricornCaves:QMF58982rightmaxilla,QMF58983leftmaxilla. Remarks. L.forresti isidentifiedherebyitslargeaccessorycusplargerthanthoseof L.gregoriensis and L.webbi ,relativelysmallsizedentitionsmallerthan L.macrodonta and L.irvini sp.nov.,andrelativelystraightbuccalmarginoftheanteriorpalatalforamena,which alsotaperstoapointposteriorlyunlikethecurvedbuccaledgeandcommonlyrounded posteriorterminationoftheanteriorpalatalforamenain L.lakedownensis . L.forresti occursinseveralMiddlePleistocenetoHolocenecavedepositsintheMountEtnaregion, withtheoldestrecordfromasubsampleofSpeakingTubeCavedesignatedQML1313A withaminimumageof280ka.Interestingly,whilethemainQML1313assemblageis dominatedbyhydric-adaptedfaunainterpretedasarainforestpalaeoecologyatthetimeof deposition Hocknull,2005 ; Hocknull,2009 ; Hocknulletal.,2007 ,theQML1313Asample containsapeculiarmixtureofhydricandxeric-adaptedtaxa.Thisisinstarkcontrasttothe knownhabitatofextant L.forresti ,aspeciesfoundingrasslands,shrublandsandsparsely vegetatedplainsofinlandAustralia Reid,2008 . Leggadinalakedownensis Watts,1976 Fig.3 Diagnosis:See Watts . Material:QML1466;FernCave-owlroostdeposit:QMF55269partialskull,QMF55353 rightmaxilla,QMF55354leftmaxilla,QMF55355rightmaxilla,QMF55356leftM 1 , QMF55618leftmaxilla,QMF55619rightmaxilla,QMF55620rightmandible,QMF55621 rightmandible. Remarks. Theabovespecimensarereferredto L.lakedownensis becausetheypossessanenlargedM 1 / 1 , heavilyreducedM 3 / 3 ,stronglydevelopedaccessorycusponM 1 commonlydivided, prominentT1supplementarycusp,andananteriorpalatalforamenthatiscommonly roundedposteriorly.Ofthesecharacters,theshapeoftheanteriorpalatalforaminaseems tobethemostusefulcharacterfordistinguishingspecimensof L.lakedownensis from L. forresti inQueensland,although Cooperetal. foundittobevariableandtherefore Crambetal., PeerJ ,DOI10.7717/peerj.5639 8/27

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Figure4 Leggadina.irvini sp.nov. QMF55326rightmaxillafragmentwithM 1 fromQML1507MacropediesWaterholebreccia.Scalebar D 1mm. Full-size DOI:10.7717/peerj.5639/fig-4 lessusefulinspecimensfromWesternAustralia. Watts statedthattheposteriorend oftheanteriorpalatalforamenisroundedin L.lakedownensis .Thisiscertainlythecase intheholotypeandtwooftheparatypes,butoneparatypeQMJM1293hasitpointed instead.Wesuggestthatamoreusefulcharacterisationofthisfeatureisthatthebuccal marginoftheanteriorpalatalforamenof L.lakedownensis iscurved,whilethatof L.forresti isrelativelystraight. Specimensof L.lakedownensis havethusfarbeenrecordedonlywithintheRecent owlroostofFernCaveintheChillagoearea,butdonotoccurwithintheolderfossil breccias. Leggadinairvini sp.nov. Figs.45 Holotype.QMF55326rightmaxillafragmentwithM 1 . Typelocality.QML1507;MacropediesWaterholeCavebreccia,Chillagoe,north-eastern Queensland.Amassivebrecciathatoncefilledmuchofthechamber,sinceerodedto relativelysmallblocksthatarestill insitu .Theageofthebrecciaisuncertain,butislikely MiddleorLatePleistocene. Etymology:ThisspeciesisnamedforMr.DouglasIrvininhonourofhiscontributionsto, andsupportof,palaeontologicalworkincavesofeasternAustralia. Crambetal., PeerJ ,DOI10.7717/peerj.5639 9/27

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Figure5ComparisonofrightM 1 of L.irvini with L.macrodonta . AQMF55326 L.irvini .B QMF55624 L.macrodonta rightM 1 .Scalebar D 1mm. Full-size DOI:10.7717/peerj.5639/fig-5 Diagnosis.Aspeciesof Leggadina thatdiffersfromallothermembersofthegenusbybeing substantiallylargerthananyothercurrentlyknownspeciesFig.6.Additionally,theM 1 possessesawell-developedaccessorycuspdividedinholotypeandonlyknownspecimen, andlargediamond-shapedT1inocclusaloutline. Description. Maxilla.QMF55326preservestheportionofthemaxillasurroundingM 1 andpartofthe zygomaticarch;brokenedgesofmaxillaslightlyroundedandpolishedduetoerosion frombreccia;shapeandpositionoftheanteriorpalatalforamencannotbediscernedwith certainty;portionofanteriormarginofposteriorpalatalforamenmaybepreserved,but damageandroundingofspecimenmakesthisuncertain. M 1 .Crownelongate,oval-shapedinocclusaloutlinewithamarkedantero-lingualindent; Cuspsmoderatelyworn,butappeartoberelativelylow-crowned;accessorycuspvery large,dividedintotwosmaller,oval-shapedanteriorcusplet;largercrescent-shaped lingualcusplet;T1shapedlikeadiamondinocclusaloutline;T1large,robust,slightly smallerthanT2-3complex;T1postero-lingualofT2;T3in-linewithT2;T2posterior edgeformsa116degreeanglewithT1;T3heavilyreducedtoasmall,buccalprojectionof T2;T4-6lophmorewornthanT1-3;T4similarinsizetoT1butsemicircular-shapedin occlusaloutline;T5antero-buccalofT4andantero-lingualofT6;T6muchlargerthanT3, possiblymoredistinctwhenunworn;T4joinedtoT8-9complexbyashort,narrowridge; T8directlyposteriorofT5;T9aroundedbuccalprojectionofT8,distinguishedbyashallow Crambetal., PeerJ ,DOI10.7717/peerj.5639 10/27

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Figure6PlotofM 1 dimensionsforspeciesof Leggadina fromQuaternaryfossildepositsin Queensland. Blueopensquare= Leggadinagregoriensis Rackham'sRoost;greenX= Leggadina webbi QML1311H,1311J,1313;darkblueasterisk, Leggadinaforresti QML1312,1456,1457;purple filledsquare, Leggadinalakedownensis QML1466;red C , Leggadinamacrodonta Floraville5C;black dot, Leggadinairvini QML1507.Measurementsinmillimetres. Full-size DOI:10.7717/peerj.5639/fig-6 cleftontheanteriorslopeoftheloph;anteriorcingulumweaklypresentonT1,continuing topoorlydefinedlingualcingulumbetweenbasesofT1andT4;buccalcingulumweakly expressedandappearstobepresentbetweenthebasesofT3andT6;posteriorcingulum appearsabsent,butmayhavebeenobliteratedbyinterstitialmasticatorywear;M 1 has threerootslargeanterior,elongatelingual,andpostero-buccal. Remarks. Theholotypeisreferredto Leggadina basedontheextremedevelopmentoftheaccessory cusp,diamond-shapedT1withsupplementarycusp,andposteriorly-displacedT1and T4.ThesizeofthisspeciesM 1 dimensions:3.52 1.86mmisenoughtoeasily distinguishitfromallotherspeciesof Leggadina Fig.6.Incomparison, L.macrodonta hasalargest-recordedM 1 lengthof3.22mmandM 1 widthof1.75mmQMF57276 andQMF57267,respectively.Measurementsfrom Klinkhamer&Godthelp .The holotypeandonlyspecimenof L.irvini isworn,sothefulllengthoftheM 1 islikelygreater thanmeasuredinFig.6.Relianceonsizedifferencesalonetoinformtaxonomicdecisionsis sometimesproblematice.g. Price,2008b ,butherewenoteadditionalmorphologiesthat allowseparationof L.irvini fromthelargestpreviouslyknownspecieswithinthegenus, L.macrodonta .Inadditiontooverallsize,theholotypeof L.irvini isfurtherdistinguished fromallknownspecimensof L.macrodonta byhavingamorerobustaccessorycuspand T1onM 1 .Somespeciesof Leggadina displayminorvariationinthesecusps,however,the Crambetal., PeerJ ,DOI10.7717/peerj.5639 11/27

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degreeofexpressionofthesefeaturesin L.irvini canonlybeassessedfurtherfollowing recoveryofadditionalspecimens. L.irvini isfurtherdistinguishedfrom Leggadinawebbi sp.novseebelowand L. gregoriensis byitslargeraccessorycusp. Leggadinawebbi sp.nov.Fig.7,AppendixS1 Holotype.QMF55628leftmaxillawithM 1 )]TJ/F75 7.9701 Tf 6.216 0 Td [(3 . Typelocality.QML1313;SpeakingTubeCaveSystem,MountEtna,easterncentral Queensland. Othermaterial.QML1313;SpeakingTubeCaveSystem,MountEtna:QMF55629left maxilla,QMF55630leftM 1 ,QMF55631rightmandiblefragmentwithM 1 ,QMF55632 rightmandible,QMF55633leftmandible,QMF55634leftmandible.QML1311H;Speaking TubeCaveSystem,MountEtna,QMF55642leftM 1 ,QMF55634leftM 1 ,QMF55644left M 1 ,QMF55645rightmandible;QML1311J;SpeakingTubeCaveSystem,MountEtna: QMF55635leftmaxillafragmentwithM 1 ,QMF55636leftM 2 ,QMF55637leftmandible, QMF55638leftmandible,QMF55639leftM 2 ,QMF55640rightmandiblefragmentwith I 1 andM 1 ,QMF55641rightmandible; Etymology.ThisspeciesisnamedforGregoryWebbinrecognitionofhissupportforstudies ofcavefossilsinQueensland,andhisbroadercontributionstoAustralianpalaeontology. Diagnosis.Aspeciesof Leggadina thatcontainsthefollowinguniquecombinationof characters:M 1 / 1 slightlylongerthanhalfofmolarrowAppendixS1;M 3 / 3 moderately reducedinsizeproportionallysmallerthanthatof Pseudomys spp.,butless-reducedthan L.forresti and L.lakedownensis ;accessorycusponM 1 relativelysmallsmallerthanthatof L. forresti and L.lakedownensis ;T1onM 1 notgreatlyenlarged;uppermolarsmoderately overlapping;anteriorpalatalforaminaposteriorlynarrow. Description. Maxilla.Nocompletemaxillaeareknown.Theanteriorpalatalforaminaareposteriorly narrow. M 1 .Crownelongateandoval-shapedinocclusaloutline,withmarkedindentonanterolingualedge;mostspecimenshavearelativelysmallforaspeciesof Leggadina accessory cusp;accessorycuspcommonlyconfinedtolingualmarginonbaseofT2onespecimen, QMF55635,hasitwrappingaroundtheanteriorofT2;T1accessorycuspabsent;T1oval ordiamond-shapedinocclusaloutline;T1postero-lingualofT2,joiningaftermasticationrelatedweartoT1bis;T1bisvariablydeveloped,positionedimmediatelylingualofT2;T2 similarinsizetoT1;T3reducedinsize;T4directlyposteriorofT1;T5directlyposterior ofT2andantero-buccalofT4;T4crescent-shapedinocclusaloutline,joinedtoT5bya narrowridge;T4joinedtoT8byalowridge,moreevidentaftermoderatetoheavywear; T5triangularinocclusaloutline,slightlylargerthanT4;T6ovaltosub-circularinshape, directlybuccalofT5whenunworn,reducedbutlesssothanT3;T7absent;T8rounded, slopingposteriorly;T9reducedandfusedtoT8,stilldistinctwhenunworn;M 1 hasthree rootslargeanterior,elongatelingual,andsmallpostero-buccal. Crambetal., PeerJ ,DOI10.7717/peerj.5639 12/27

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Figure7 Leggadinawebbi sp.nov. AQMF55629leftmaxilla;BQMF55628leftmaxilla; CQMF55635leftmaxillafragmentwithM 1 ;DQMF55636leftM 2 ;EQMF55631rightmandible fragmentwithM 1 ;FQMF55640rightmandiblefragmentwithI 1 andM 1 ;GQMF55641right mandiblewithM 1 )]TJ/F75 5.9776 Tf 4.663 0 Td [(2 ;HQMF55638leftmandible;IQMF55645rightM 3 ,removedfrommandible; JQMF55639leftM 2 .Scalebar D 1mm. Full-size DOI:10.7717/peerj.5639/fig-7 Crambetal., PeerJ ,DOI10.7717/peerj.5639 13/27

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M 2 .T1well-developed,ovaltosemicircular-shapedinocclusaloutline;T2absent;T3 variablyexpressed,smallifpresente.g.,QMF55628,55635;T1incontactwithposterolingualmarginofT8ofM 1 ;T1directlyanteriortoT4;T4tear-shaped,semicircularin occlusaloutlineafterwear;T4postero-lingualofT5,joinedbynarrowridge;T5triangular inocclusaloutline,pointinganteriorly;T6notheavilyreduced,fusedtobuccalcorner ofT5;T4joinedatbasetoT8bylowridge;T8triangularinocclusaloutline;T9heavily reduced,notdiscernibleonsomespecimens;M 2 hasthreerootsantero-buccal,lingual, andpostero-buccal. M 3 .Reduced,butnohyper-reducedspecimensknown;crowntapersposteriorlyto approximatelyhalftotalwidthinocclusaloutline;T1incontactwithpostero-lingual marginofT8ofM 2 ;T1sub-circulartosemicircularinocclusaloutline;T1directlyanterior ofT4andantero-lingualofT5-6complex;T4small,tear-shaped,joinedtoT5-6complex bynarrowridge;T5-6complexrounded,taperingtojunctionwithT4;T6indistinguishable fromT5,possiblyabsent;T8-9complexreduced,narrowerthanT4-6loph;M 3 hasone majorrootthatisbifurcated. M 1 .Crownelongatewithrelativelylargegapsbetweenlophs;anteriorlophcommonly relativelynarrowincomparisontootherspeciesof Leggadina ,boomerangorsemicircularshapedinocclusaloutlinedependingondegreeofwear;antero-lingualandantero-buccal cuspsfused;antero-lingualcuspslopestobaseofmetaconid;antero-lingualcusphas second,smallerridgeslopingtobuccalmarginofbaseofmetaconid;antero-buccalcusp slopestobaseofprotoconid;protoconiddirectlyposteriorofantero-buccalcuspand immediatelybuccalofmetaconid;protoconidandmetaconidsubequalinsize,both tear-shaped,pointedtowardsjunctionatmidpointofanteriormarginofsecondloph; protoconidandmetaconidmergeafterheavywear,butstilldistinguishablebyindents atmidpointofanteriorandposteriormarginsofloph;hypoconiddirectlyposteriorof protoconidandimmediatelybuccalofentoconid;hypoconidjoinedtoprotoconidbya lowridgeonthebuccalmarginofthecrown,almostformingabuccalcingulid;entoconid slightlylargerthanhypoconid;hypoconidandentoconidtear-shapedinocclusaloutline, taperingtopointslightlyanteriorofanteriormarginsofbothcusps;shortandbroad posteriorcingulidcusponwell-developedposteriorcingulid;posteriorcingulidcommonly wrapsaroundbaseofhypoconid,continuingtobaseofprotoconid;M 1 hastworoots anteriorandposterior. M 2 .Roughlysquare-shapedinocclusaloutline;twolophscomprisingtheprotoconidmetaconidandhypoconid-entoconid;protoconid-metaconidlophbroaderthan hypoconid-entoconidloph,andmorerobustatbase;allmajorcuspstear-shapedin occlusaloutline;protoconidtapersantero-linguallytomeettaperingpointofmetaconid atmidpointofanteriormarginofanteriorloph;hypoconidjoinsentoconidinlikewise fashion;lowshelforvariablysmallposteriorcingulidcusponposteriormarginofcrown betweenbasesofhypoconidandentoconid;M 2 hastworootsanteriorandposterior. M 3 .Verysmall;allknownspecimenshavetwolophs;protoconidandmetaconidelliptical inocclusaloutline,alignedwithlophsofothermolars;posteriorlophapproximatelysame sizeandshapeasprotoconid;M 3 hasoneroot,bifurcatedintoanteriorandposterior. Crambetal., PeerJ ,DOI10.7717/peerj.5639 14/27

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Figure8 L.macrodonta. AQMF55622rightmaxillafragmentwithM 1 ;BQMF55623leftmaxilla fragmentwithM 1 ;CQMF55626partialrightmandible;DQMF55627leftmandible;EQMF55625 leftmandible.Scalebars D 1mm. Full-size DOI:10.7717/peerj.5639/fig-8 Remarks.Theupperdentitionof L.webbi issimilartothatofsomeoftheverysmall speciesof Pseudomys .However,weassignsuchmaterialto Leggadina onthebasisofits largeposteriorpalatalforaminaandbroadposteriorcingulidcuspidonM 1 .Additionally, L.webbi differsfrom L.forresti byhavinglessoverlapbetweentheuppermolarsand havingaproportionallysmallerT1andaccessorycusponM 1 . L.webbi differsfrom L.lakedownensis byhavinglessoverlapbetweentheuppermolars;havingaproportionally smallerM 1 / 1 andlargerM 3 / 3 ,proportionallysmallerT1andaccessorycusponM 1 ,and havingposteriorlynarrowanteriorpalatalforamina. L.webbi differsfrom L.macrodonta bybeingsmaller,lackingaT1supplementarycuspcommonlypresenton L.macrodonta , havingamoredevelopedanteriormedialridgeandmoredevelopedbuccalcingulid ontheM 1 . L.webbi sharesseveralfeatureswith L.gregoriensis includingsize,possessionofa relativelysmallaccessorycusponM 1 ,andarelativelysmallT1ontheM 1 .Itdiffersby lackingadefinedT7onM 1 . Leggadinamacrodonta Klinkhamer&Godthelp Figs.5and8 Locality:Allspecimensarefromthesite5CandadjacentWoodbineCreek,bothonthe westernbankoftheLeichardtRiver,FloravilleStation,northwestQueensland. Diagnosis:See Klinkhamer&Godthelp forsomediagnosticcharactersforthemaxilla andassociationdentition.Hereweaddthefollowingcharacters:amoderatelylarge-toothed Fig.6,Table1speciesof Leggadina withaposteriorlyroundedanteriorpalatalforamen, andarelativelynarrowanteriorlophonM 1 . Crambetal., PeerJ ,DOI10.7717/peerj.5639 15/27

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Table1Dentaldimensionsofadditionalspecimensof L.macrodonta . Allmeasurementsinmillimetres. N meansdminmax M 1 length32.920.032.862.96 M 1 width31.610.021.581.65 M 1 length32.310.032.262.34 M 1 width31.470.011.451.48 M 2 length31.390.041.321.47 M 2 width21.390.081.311.46 M 3 length10.73nanana M 3 width10.78nanana M 1 )]TJ/F75 8.3287 Tf 6.496 0 Td [(3 length14.42nanana Referredspecimens:QMF55622partialrightmaxillawithM 1 ;QMF55623partialleft maxillawithM 1 ;QMF55624rightmaxillafragmentwithM 1 ;QMF55625leftmandible withI 1 ,M 1 )]TJ/F75 7.9701 Tf 6.217 0 Td [(3 ;QMF55626partialrightmandiblewithM 1 )]TJ/F75 7.9701 Tf 6.217 0 Td [(2 ;QMF55627leftmandible withM 1 )]TJ/F75 7.9701 Tf 6.217 0 Td [(2 . Description. Additionalfeaturesofthemaxilla:Theanteriorpalatalforamenendsinlinewiththe anteriormarginofthelingualrootofM 1 ;buccalmarginofanteriorpalatalforamenat leastpartiallycurved,butallspecimensaretoodamagedtodeterminetheshapeofthe posteriorendoftheforamen. Dentary.Allknownlowermolarsexhibitmoderatetoheavywear.Onespecimen QMF55625preservestheI 1 ,butnospecimenshaveanintactcoronoidprocess,articular facetorangularprocess. M 1 .Roughlyovoidinocclusaloutline,butwithmorerectangularposteriorend;first lophnarrowerthansecondorthirdlophs;firstlophrounded,kidney-shapedinocclusal outline;antero-buccalandantero-lingualcuspidscannotbedistinguishedonanyavailable specimensduetoheavywear;weakbuccalridgeslopingfromantero-buccalcuspidtobase ofprotoconid,butlackingonantero-lingualcuspid;antero-lingualcuspwithverysmall ridgeslopingtobuccalmarginofbaseofmetaconid;protoconidposteriorandslightly buccalofantero-buccalcuspid;metaconiddirectlylingualofprotoconid;protoconidand metaconidsubequalinsize,eachtaperingtowardstheother,joinedbytallridge;hypoconid directlyposteriorofprotoconidanddirectlybuccalofentoconid;hypoconidandentoconid subequalinsize,slightlysmallerthanprotoconidandmetaconid;hypoconidandentoconid bothtear-shaped,eachtaperingtowardstheother,meetingatanteriormarginofloph; lowridgeconnectsbaseofprotoconidtobaseofhypoconid,butdoesnotcontinueinto abuccalcingulidonpostero-buccalcornerofhypoconid;posteriorcingulidcuspidwell developed,lenticularinocclusaloutline,taperingbuccallyalongbaseofposteriorfaceof hypoconid;tworootspresentanteriorandposterior. M 2 .Almostsquare-shapedinocclusaloutline;protoconid-metaconidlophformsbroadest partofcrown;protoconidlargerthanmetaconid,becominglessobviousafterheavywear; protoconidandmetaconidbothtear-shaped,althoughprotoconidislonger;protoconid Crambetal., PeerJ ,DOI10.7717/peerj.5639 16/27

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andmetaconidmeetonanteriormarginoflophandcrownatmidlineofmolarrow; hypoconid-entoconidlophslightlynarrowerthanprotoconid-metaconidloph;hypoconid posteriorandslightlylingualofprotoconid;entoconidlingualandslightlyanteriorof hypoconid;hypoconidandentoconidbothtear-shaped,eachtaperingtowardtheotherto meetatthemidpointbetweenthem;smallposteriorcingulidcuspidnestledimmediately posteriorofjunctionbetweenhypoconidandentoconid;tworootspresentanteriorand posterior. M 3 .OnlyonespecimenQMF55625preservestheM 3 ;crownsub-circularinocclusal outline;protoconidandmetaconidfused,occlusalsurfacepeanut-shaped;posteriorloph small,directlyposteriorofmetaconid;appearstohaveonlyoneroot,butmaybifurcate withinthedentary. Remarks. Klinkhamer&Godthelp didnotdescribethelowerdentitionof L.macrodonta statingthatnospecimensfromthetypelocalitycouldbedefinitivelyassignedtothe species.However,fromourassessmentoftheavailable,andsomenew,fossilspecimens ofmandiblesandlowermolarsfromthetypelocality,weconsiderthatsuchmaterialis unequivocally Leggadina .Furthermore,consideringthatthisspeciesismorphologically distinctfromallknownspeciesof Leggadina ,andonlyasinglemorphospeciesof Leggadina hasbeenidentifiedinthedeposit,wereferthenewandpreviouslyundescribedlower dentitionto L.macrodonta .Additionalspecimenshavealsobeenrecoveredfromanother depositWoodbineCreekashortdistancefromthetypelocality.Although L.macrodonta wasnamedforitsbulkyM 1 andwasconsideredtobethelargest-knownmemberof thegenusatthetimeofpublication Klinkhamer&Godthelp,2015 , L.irvini sp.nov.is substantiallylargerFigs.5and6. DISCUSSION Dentalandfunctionalmorphologyin Leggadina TheenlargedaccessorycuspontheM 1 isprobablythemoststrikingfeatureofthe dentitioninmostspeciesof Leggadina .Itismuchless-developedintheoldest-known species L.gregoriensis ,suggestingthatitslargersizeinmostotherspeciesof Leggadina maybeaderivedtrait.Thedegreeofwearonmanyspecimenssuggeststhattheaccessory cuspishighlyfunctional,effectivelyformingananterior-mostfourthlophontheM 1 . Thetwoextantspecies, L.forresti and L.lakedownensis ,commonlyexhibitamedian constrictionoftheaccessorycusp,effectivelydividingitintwo.Thisfeatureisalso observedin L.macrodonta and L.irvini. Althoughitsfunctionisunclearitmaybethatthe constrictioncreatesanarrowercuttingedge,ausefultoolforprocessinginvertebrateprey. Phylogeneticrelationships Determiningtheprecisephylogeneticpositionofspecieswithin Leggadina isdifficultdue tothefragmentarynatureoftheknownfossilrecordofskeletalanddentalmaterial.Itis alsohamperedbyapoorunderstandingofmorphologicaldiversityincranialanddental charactersamongAustralianmuridsgenerally.However,weassumethattheoldestknown species, L.gregoriensis fromtheearlyPleistocene,islikelytopossessmoreancestraltraits Crambetal., PeerJ ,DOI10.7717/peerj.5639 17/27

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thanspeciesfoundingeologicallyyoungerdeposits.Threedistinctivefeaturesof Leggadina areless-developedin L.gregoriensis thanotherspecieswithinthegenus:thedevelopment oftheaccessorycusponM 1 ;theenlargementofM 1 relativetoM 3 ,andthedevelopment oftheT1supplementarycusponM 1 .Weinterprettheconditionofthesefeaturesin L.gregoriensis astheplesiomorphicstateforthegenus. L.webbi retainsseveralcharactersthatappeartobeplesiomorphicwithinthegenus. TheseincludetheenlargementoftheaccessorycuspandT1onM 1 ,andthereduction ofM 3 / 3 .Thisassociationofcharactersmayrepresentanevolutionarygrade,astheyare alsoseenintheoldestknownspecies, L.gregoriensis .While L.gregoriensis ,astheoldest knownspeciesofthegenus,isunsurprisinglyplesiomorphic, L.webbi ismuchyoungerand waslikelycontemporaneouswithspeciesthatarestillextanttoday.Wethereforesuggest that L.webbi representsaplesiomorphicspeciesof Leggadina andbasedonitsinterpreted palaeoecologylikelyrepresentsa`relic'lineagefromtheearlierdiversificationofthe genus.`Relic'or`Ghost'lineagesareknownfromtheMiddlePleistoceneMt.Etnafauna includingplesiomorphicbandicoots,possums,koalas,andmarsupial`lions' Hocknull, 2005 ; Hocknull,2009 ; Hocknulletal.,2007 ; Price&Hocknull,2011 .Wehypothesisethat therodentfaunareflectsanearlyradiationofmuridsintoclosedrainforestenvironments andsubsequentextinctionintheseenvironmentsduringthelateMiddlePleistoceneand LatePleistocene.Similardiversificationandbiasedmesicextinctionhasbeensuggested withinthedasyuridmarsupialsfromMt.Etnaalso Cramb,Hocknull&Webb,2009 ; Cramb &Hocknull,2010b . Isitpossiblethat L.webbi representssomethingclosetotheactualancestorofthe genus? Klinkhamer&Godthelp suggestedthat Leggadina evolvedfromarainforestinhabitingancestor,andindeedthemostbasalextanttaxaintheAustralo-Papuanmurine radiationoccurinNewGuineanrainforests Roweetal.,2008 .However,basedon molecularevidencethegenus Leggadina isnestedwithinacladewhoseextantmembers Pseudomys , Notomys , Mastacomys ,and Zyzomys arenotcurrentlyfoundintropical rainforesthabitats Roweetal.,2008 .If,then, L.webbi representstheancestralcondition of Leggadina bothmorphologicallyandecologicallyitsuggeststhat Leggadina diversified withinmesicrainforesthabitatsfirst,withsubsequentsecondaryxeric-adaptationofits derivedendmemberspeciesandsubsequentextinctionofthemesic-adaptedplesiomorphic forms. Alternatively,itmayindicatethatthepredominatelyxeric-adaptedAustralianmurid cladeshaveallexperiencedmesicradiationssometimeinthepastandtheselineagesarenow missingduetotheoverridingextinctionbiasofthesehabitatsthroughouttheQuaternary duetointensifyingariditye.g., Hocknulletal.,2007 ; Price,2012b . L.irvini istheleast-knownspeciesofthegenusduetoalackoffossilspecimens. Onthebasisofgrossmorphology,therelativelylargeaccessorycuspandT1onthe M 1 appeartobederived,indicatingthatitisprobablyclosertothecrownspeciesof Leggadina thanto L.gregoriensis .Theoveralllargesizeof L.irvini couldpossiblyindicate amorphoclinederivedfromthesmallestspeciesthrough L.macrodonta to L.irvini .Apart from L.gregoriensis and L.webbi ,theremainingmembersofthegenusallshareasimilar levelofdevelopmentofcharacterssuchastheenlargementoftheaccessorycuspandT1on Crambetal., PeerJ ,DOI10.7717/peerj.5639 18/27

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Figure9Temporaldistributionofspeciesof Leggadina . Full-size DOI:10.7717/peerj.5639/fig-9 M 1 ,andthepresenceofaT1supplementarycusponM 1 .Thisprecludestheconstruction ofaclearerevolutionarynarrativefortheendmembersofthisgenus. Spatialandtemporaloccurrence Leggadina hasalonghistoryinnorthernAustraliawiththeoldestdescribedspeciesof thegenus, L.gregoriensis ,occurringindepositsdatingtotheEarlyPleistoceneFig.9; Klinkhamer&Godthelp,2015 .Alackofwell-datedfossildepositsbetween1.8.5Ma limitsourunderstandingoftheradiationwithinthegenus.BytheMiddlePleistocene,at leastthreespeciesof Leggadina occur,namely L.webbi and L.forresti fromtheMt.Etna region,and L.macrodonta fromFloraville.Anadditionalspecies, L.irvini fromChillagoe, isinterpretedasprobablybeingofmiddlePleistoceneage.Thefateof L.macrodonta is unclearasitissofarknownfromonlytwodeposits,however, L.webbi appearstohave persisteduntilca.280ka. Apaucityofradiometricdatinglimitsourunderstandingofthetimingoftheorigin ofspeciessuchas L.lakedownensis and L.irvini .Bothtaxalackfirmgeochronological control,butwerepresentbytheMiddle-LatePleistocene.Thepresenceof L.lakedownensis withinfossildepositsoftheChillagoeregionisnotsurprising,asthetypelocalityofthe speciesLakelandDownsisrelativelyclose<150kmtotheNorth-Eastandextant populationsoccurintheregiontoday Moro&Kutt,2008 .Interestinglythough,the absenceof L.lakedownensis fromolderMiddleLatePleistocenedepositsintheChillagoe areamayindicatethatitisageologicallyrecentarrivalinthearea. L.irvini issomethingof apuzzle.Onlyasinglespecimenisknownfromasiteofuncertainage.Whyitwasreplaced bythesmaller L.lakedownensis intheChillagoeareacannotbeascertainedwithoutbetter understandingofitsageandcontemporaryfaunas. Leggadinawebbi isacommonelementoffossilassemblagesfromtheMt.Etnaregion thataredominatedbyrainforest-adaptedtaxa Hocknull,2005 ; Hocknulletal.,2007 . Itslossfromtheregionislikelyassociatedwithintensifyingariditythatbeganduring themid-BruhnesclimaticeventthatsawamajorfaunalturnoveratMt.Etnawhereby Crambetal., PeerJ ,DOI10.7717/peerj.5639 19/27

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rainforest-adaptedfaunawerereplacedbyextantspeciesthatpresentlyliveinxeric habitats Hocknulletal.,2007 ; Price,2012b .Significantlythough,thisfaunalturnover eventbrought L.forresti tothearea.Indeed,fossilsfromMt.Etnaitselfaretheoldest recordca.280kaforthisspeciesandcanthereforebeutilisedasacalibrationpointin futurephylogeneticassessmentsusingmolecularclocks. L.forresti survivedlocallyuntil atleastthelateHolocene,beingrecordedfromdepositssuchasthePleisto-Holocene ColosseumChamber Priceetal.,2015 .Wearecurrentlyunawareofanyextantrecords of L.forresti intheMt.Etnaregion,butthelocalsmall-bodiedextantmammalfaunais likelytobeincompletelyknownwithadditionalrecordsofrodentsthatmayeitherstillbe presentintheregionorveryrecentlyextinct Cramb&Hocknull,2010a .Forexample,the mostcommonsmall-bodieddasyuridmarsupialfoundwithintheColosseumChamber depositistheStripe-facedDunnart, Sminthopsismacroura Cramb,Hocknull&Webb, 2009 ,aspeciesthatwasonlyfoundextantintheareaasrecentlyas2007representedby specimenQMJM18420.Itisthuspossiblethatextantpopulationsof L.forresti mayyetbe discoveredinthearea. Acautionarynoteregardingpalaeoecology Extantspeciesof Leggadina areomnivoresthatdigsimpleburrows Moro&Kutt,2008 ; Reid,2008 .Theyarefoundinavarietyofhabitatsrangingfromdesertstotropical woodlands Kutt&Kemp,2005 .Thediscoveryof L.webbi infossildepositsinterpreted asrepresentingclosedrainforestpalaeoenvironmentsindicates Leggadina hadaneven broaderhabitatrangeinthepast.Thismaybetakenasacautionarynoteforany researcherattemptingtoreconstructpastenvironmentsonthebasisofthepresumedhabitat preferencesofsinglefossiltaxausingonlyextantrelatives.Palaeoecologicalreconstructions shouldideallybebasedonmultipletaxawithcongruenthabitatpreferences,with considerationofanatomicalspecialisations,ecologicalguildsandrelevantpalaeoclimatic data. Forexample,extantTreeKangaroos Dendrolagus spp.arecommonlyassociatedwith rainforesthabitats,yetfossilTreeKangaroos Bohra spp.evidentlyhadbroaderecological tolerances,beingfoundinassemblagesinterpretedaswoodlands Dawson,2004 ; Prideaux &Warburton,2009 aswellasrainforests Hocknull,2005 .Similarly,recentlyextantBilbies Macrotis spp.areexclusivelyfoundinxerichabitats,yetfossilBilbies Liyamayidayi inhabitedrainforests Travouillonetal.,2014 . Itmustberememberedthatthelongspanofgeologicaltimewillincludemanyhabitats hostinglineageassociationsthathavenoanaloguetoday LundeliusJr,1989 . Interestingly, Leggadina ispartofthe` Pseudomys division'ofhydrominerodents,a groupwhichisnotablyabsentfromextantrainforestcommunities.Incontrast,middle PleistocenedepositsatMountEtnae.g.,QML1311Hcontainsixspeciesof Pseudomys divisionmurines.Atleastfiveoftheseappeartohavebeenendemictorainforesthabitats, astheyareonlyfoundindepositswithothermoretypicalrainforest-inhabitingtaxa.This suggeststhatmodernassemblagesofrainforestmurinesarenotagoodanalogueforthose ofthemiddlePleistocene. Crambetal., PeerJ ,DOI10.7717/peerj.5639 20/27

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CONCLUSIONS Thetwonewspeciesof Leggadina describedinthispaper, L.irvini and L.webbi ,demonstrate thatthegenusoncedisplayedgreaterdiversityofmorphologyandecology.Moreover,with sixspeciesof Leggadina nowrecognisedfourextinctandtwoextantitisclearthatspecies diversitywithinthegenuswasgreaterinthepast.Whiletheextinctionof L.webbi appearsto betiedtoclimate-changedrivenhabitatloss,thecausesforthewiderdeclineofthegenusin recenttimesisunclear.Itis,however,apatternalsoapparentinotherAustralianmammal groupssuchaskoalas Price,2008a ; Blacketal.,2014 ; Price,2012a .Thispresentstudy addstothegrowinglistofsmall-bodiedmammalextinctionsthatoccurredinAustralia, alongsidetheextinctionofthemegafauna,throughoutthelateQuaternary.Itdemonstrates thattheQuaternaryextinctionsincludedrepresentativesfrommanyofthemostsuccessful extantlineages,suchasmurids,peramelids,dasyuridsandphascolarctids.Wecontend thatdeterminingthechronological,palaeoecologicalandpalaeoclimaticcontextforthe extinctionofthesesmall-bodiedfaunaisofequalimportancetothatofthemegafauna extinctiondebate. ThefossilrecordofAustralasianrodentshasreceivedrelativelylittleresearchattention, butrecentworkby Klinkhamer&Godthelp ,coupledwiththisstudy,hasgreatly enlargedourunderstandingofatleastonegenus.Thetaskmustnowbetoextendthis worktothe35othermurinegeneraknownfromAustralo-Papua. Institutionalabbreviations QMF QueenslandMuseumfossilspecimen QMJM QueenslandMuseummodernspecimen QML QueenslandMuseumfossillocality ACKNOWLEDGEMENTS WearegreatlyindebtedtothesupportofDouglasandMaryAnnIrvin,GregoryWebb,the ChillagoeCavingClub,ErnieandKylieCampandfamily,MichaelArcher,SueHand,Noel Sandsandfamily,CliveCavannahandmembersoftheCentralQueenslandSpeleological Society,AnnAugustynandAmandaJenningsHintonaswellasthestaffofCapricornCaves, JohnAugustynoftheQueenslandNationalParksandWildlifeService,PaulTierney,Shona Marks,MathewNg,RochelleLawrence,JoanneWilkinson,KristenSpring,Jian-xinZhao andYue-xingFeng.WealsoextendourappreciationtothestaffandvolunteersofThe UniversityofQueenslandandQueenslandMuseumfortheirkindassistanceinpreparing fossils.ThanksalsotoHenkGodthelpandFredFordfordiscussionsaboutthetaxonomy of Leggadina .WethankMattMcDowell,KevinRowe,andananonymousreviewerfor helpfulcommentsthatimprovedthemanuscript. Crambetal., PeerJ ,DOI10.7717/peerj.5639 21/27

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ADDITIONALINFORMATIONANDDECLARATIONS Funding ThisresearchwasfundedbyAustralianResearchCouncilgrantsLP0453664,LP0989969, DP120101752,andDE120101533andagrantfromtheIanPotterFoundation.Thefunders hadnoroleinstudydesign,datacollectionandanalysis,decisiontopublish,orpreparation ofthemanuscript. GrantDisclosures Thefollowinggrantinformationwasdisclosedbytheauthors: AustralianResearchCouncil:LP0453664,LP0989969,DP120101752,DE120101533. IanPotterFoundation. CompetingInterests Theauthorsdeclaretherearenocompetinginterests. AuthorContributions JonathanCrambconceivedanddesignedtheexperiments,performedtheexperiments, analyzedthedata,contributedreagents/materials/analysistools,preparedfiguresand/or tables,authoredorrevieweddraftsofthepaper,approvedthefinaldraft. GilbertJPriceconceivedanddesignedtheexperiments,analyzedthedata,contributed reagents/materials/analysistools,preparedfiguresand/ortables,authoredorreviewed draftsofthepaper,approvedthefinaldraft. ScottAHocknullconceivedanddesignedtheexperiments,analyzedthedata,contributed reagents/materials/analysistools,authoredorrevieweddraftsofthepaper,approvedthe finaldraft. DataAvailability Thefollowinginformationwassuppliedregardingdataavailability: ThemolarmeasurementsofLeggadinawebbisp.novareprovidedinAppendixS1. NewSpeciesRegistration Thefollowinginformationwassuppliedregardingtheregistrationofanewlydescribed species: PublicationLSID: urn:lsid:zoobank.org:pub:3C34C73B-4800-4256-BC9E-0E7B50689024 LeggadinairviniLSID: urn:lsid:zoobank.org:act:06906882-7329-45DD-BCC8C3474DC925BE, LeggadinawebbiLSID: urn:lsid:zoobank.org:act:E420DF0C-C7BD-421A-B7A27E3EDC598588. SupplementalInformation Supplementalinformationforthisarticlecanbefoundonlineathttp://dx.doi.org/10.7717/ peerj.5639#supplemental-information. Crambetal., PeerJ ,DOI10.7717/peerj.5639 22/27

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