Nimbadon, a New Genus and Three New Species Oftertiary Zygomaturines (Marsupialia: Diprotodontidae) from Northern Australia, with a Reassessment of Neohelos

Home , Diprotodontidae, Kolopsis, Neohelos, Ngapakaldia, Nototherium, Palorchestidae

NIMBADON, A NEW GENUS AND THREE NEW SPECIES OFTERTIARY ZYGOMATURINES (MARSUPIALIA: DIPROTODONTIDAE) FROM NORTHERN AUSTRALIA, WITH A REASSESSMENT OF NEOHELOS

S. J. HAND, M. ARCHER, H. GODTHELP, T.H. RICH AND N.S. PLEDGE

Hand, S.J.,Archer, M., Godthelp,H., Rich, T.H. & Pledge,N. S. 199306 30: Nimbadon,a new genusand three new speciesof Tertiary zygomaturines(Marsupialia: Diprotodontidae) from northern Australia, with a reassessmentof Neohelos. Memoirs of the Queensland Museum33(l): 193-210.Brisbane. ISSN 0079-8835.

Three new speciesof Oligo-Miocene zygomaturinediprotodontids ire describedfiom northernAusiralia. All are small,plesiomorphic and appearto comprisea distinctiveclade of zygomaturines, naqred here Nimbadon The clade is partly defined on the basis of the posteiiorlyi4clined P' parastyleand bladeextending from the parametaconeto the lingual half of the P' crown and then to the anterolingualcingulum. Two of the speciesare known from Oligo-Miocenelocal faunas of RiversleighStation, northwestern Queensland. The third is from the middle Miocene Bullock CreekLocal Faunaof Camfield Station,northwestern Northern Territory. Description of additional fossil material referableto Neohelos tirarensis Stirton, 1967,a middle Miocene zygomaturinefrom the KutjamarpuLocal Faunaof South Australia, enablesthe genus to be distinguished fiom Nimbadon. The chronostratigraphic significanceofthe new zygomaturinesis consideredand found to approximatelycorrespond to currentunderstanding of the relativeages of the depositsfrorn which the specimenswere obtained. I Diprotodontidae, Zygomaturinae, Nimbadon, Neohelos, Oligo-Miocene, Riversleigh, Bullock Creek Incal Fauna, Henk's Hollow Incal Fauna, Fig Tree I'ocaL Fauna.

SuzanneHand, M. Archer & H. Godthelp, School of BiologicaL Science, University of New South WaLes,PO Box l, Kensington,New South Wales 2033, Australia; T.H. Rich, Pakteontology, Museum of Victoria, Russell St,Melbourne, Victoria 3000, Australin; N.S. PLedge,PaLaeontology, South Australian Museum, Norlh Terrace, Adelaide, SouthAustra- Iia 5000,Australia;24 November,1992.

Specimens representing a very small zygoma- (Rich et al., 1982, l99l; Archer & Flannery, turine were collected between 1984 and 1986 by 1983; Archer & Hand, 1984; Woodburne et al., Archer, Godthelp and Hand from the Henk's Hol- 1985; Munay, l99Oa; Murray & Megirian, 19,90; low Site, in an as yet unnamed freshwater lime- Archer et al., 1989,1991). Recent reappraisal of stone on the Gag Plateau of Riversleigh Station the age of central Australian Tertiary mammalian (Archer, Hand & Godthelp, 1986; Archer & Flan- faunas, based on the study of foraminifera (Lind- nery,1987; Archeret al., 1989, 1991). Refened say, 1987), suggeststhat some of these faunas material includes maxillary and dentary frag- (e.g. the Ditlimanka, Pinpa and Ericmas l.ocal ments and isolated teeth. A second,. larger Faunas) are appreciably older than once thought Riversleigh species, represented by a maxilla, (e.9. Woodbume et al., 1985; but see Tedfbrd, was collected in 1986 by Pledge from Fig Tree 1966), possibly late Oligocene. By comparison, Site Locality adjacent to Godthelp Hill, the Bullock Creek Local Fauna is estimated to be Riversleigh Siation. ?middle Miocene in age, i.e. immediately post- A small Bullock Creek zygomaturine is known Wp-ajiri- (Munay, 1990a; Munay & Megirian, (Archer et al., l99l) of from a palare collecred i;"1981, by Rich and 1990). On-going ^studies the colleagu'es,from Horseshoc West Locality (WV the Riversleigh- fossil-faunas suggest -th.at I l3) i; the Camfield Beds of Camfield Stuiion, Henk's Hollow Lxrcal Fauna is ?middle Miocene northwestern Northern Territory (Rich et al., in age and the Fig Tree Local Fauna somewhere lgg1, lggl). between late Oligocene and early Miocene in age. Estimates of the age of the Henk's Hollow, Fig The new zygomaturines described here are Tree and Bullcrck Creek Local Faunas are based most similar to forms currently referred to the mainly on stage-of-evolution comparisons of par- genus Neohelos. Their generic distinction, how- ticular diprotodontian marsupials with those of ever, has been clarified by discovery at the type other northern and central Australian faunas lcrcality of new material referable to NeoheLos 194 MEMOIRS OF THE QUEENSLAND MUSEUM

TABLE L Measurements of Neohelos tirarensis P3 ing unchallengedconvention, is called the hypo- (AMF87625) and M'J (AMF87626) from rhe teaf cone.Cheektooth homology is that proposedby t-ocality,Lake Ngapakaldi,South Australia.In mm. Archer (1978). Higher level systematicnomen- Abbreviations: ant, anterior; post, posterior; paramet, claturefollows Aplin ( parametacone;protoc, protocone; parac, paracone. & Archer 1987).

Length 15.8 SYSTEMATICS width 13.9 c SuperorderMARSUPIALIA Illiger, l8l I width(paramet to Drotoc tiDS) 5.5 Order DIPROTODONTIA Owen, 1866 heisht(oaramet) t1.4 FamilyDIPROTODONTIDAE Gill, 1872 height(parastvh) 6.5 SubfamilyZYGOMATURINAE Stirton, length 18.8 Woodburne& Plane,1967 M] width(ant ) t].2 width(oost) 15.8 NeohelosStirton, 1967 height(parac.1 7.8 (Fig. l, Table l) tirarensis,the type andonly namedspecies ofthe Typespecies. Neohelos tirarensis Stirton, 1967 genus.The original description(Stirton, 1967) of this Miocenezygomaturine from the Kutjamarpu RevrssnGsNeRrc DrncNosrs Local Fauna of central Australia was basedon The following combinationof featuresappears five isolated teeth collectedin 1962at the teaf to distinguishspecies of Neohelosfrom all other Locality, Lake Ngapakaldi, Etadunna Slation, zygomaturines:P' with large,erect parastyle that South Australia.The holotype,a brokenP', pre- is well isolatedfrom the parametacone;parastyle serves posterior only the portion of the tooth. is conicalwithout tip developedas.a blade; an- Thoughless complete than the otherteeth, it was terolingualbasin well defined in Pr by distinct selectedas the holotype hcause of the impor- basalcingulum extending between parastylar cor tanceof premolar morphologyin diprotodontoid nerof toothto anterolingualbase of protocone;P' (Stinon, systematics 1967;Stirton, Woodbume parametaconewith an undivided tip; parameta- & Plane,1967). cone tip not developedinto anterobucallyori- In 1982 two isolatedteeth referableto N. rl- ented blade; line between protocone, rarensiswere collectedfrom the type locality by parametaconeand widest buccalpoint on crown Archer,Hand, T. Flannery,G. Hic^kie,J. Caseand is approximatelyrectilinear and dividescrown P. Bridge: a well-preservedRPr (AMF87625) either in half or leavesanterior division shorter and RM' (AMF87626). Theseadd considerablv than the posteriordivision; Pi with^well-devel- to knowledgeof this species.Additional materi- opedhypocone or hypoconeshelf; M'--'with well als referableIo Neohelosfrom the Bullock Creek developcdparastyle and metastyle. Local Fauna(Plane & Gatehouse,1968; Plane, 1971; Munay & Megirian, 1992) and various Nimbadon n.sen. Oligo-MioceneRiversleigh local faunas(Archer (Figs2-5. Table 2) et al., 1989,l99l) arepresently under study. lnstitutionalabbreviations used here are as fol- Type species. Ninbudon lavarackorunr t't.sp. lows: QMF, fossilcollection of the Queenslanc Additionol species. Nintbadon vyhitelawi n.sp., Nlrn- Museum; AMF, fossil collection of the Austra- badon scotton'orunt n.sD. lianMuseum; SAMP, palaeontological collection of the South Australian Museum; NMVP, pa- GnNrnrcDrAGNosrs laeontologicalcollection of the Museumof Vic- Speciesof Nitnbadondiff'er tiom those of all toria; AR, researchcollection of the School of other zygomaturines(with special referenceto Biological Sciences,University of New South Neohelos,the taxon to which they are otherwise Wales. Cusp nomenclature follows Archer most similar) in the following combinationof (1984) and Rich, Archer & Tedford (1978).The fcatures:small size (although they arelarger than poslerolingualcusp of theupper molars, conven- RaemeotherianRich, Archer & Tedford, 1978); tionally calledthe hypocone(e.g. Stirton, Wood- in havinga molar gradientthat does not apprecia- burne & Plane, 1961), is now called the bly increaseposteriorly (in contrastto all other metaconule following Tedford & Wqodburne zygomaturinesexcept Raemeotheriam); posteri- (1987)but theposterolingual cusp of Pj, follow- orly inclinedparastyle on P' (ratherthan conical Nts,WDIPROTODONTIDS FROM NORTHERN AUSTRALIA l9-5

I:IG.l.Neoltelostirurett.si.;,teaf[-mality,LrkeNgapakaldi,$outhAu.^ttaliaAMI;87625, I{I'}]:A-A',treltrsitl stereopair;B, buccal vicw; C, lingual view. AMF87626, I{M-': D-D', crcclusalstcrcopitir Brtrindiclrtcs l()rrtrtt andcrcct as in othcrzygomaturines exccpt posst- z-ygonralurincscxccpt Neohclo.v und Alkwu turlt- bly Plaisiodott centrali.sWoodburne, 1967); an eriutnMurray, 1990b);an_antcrobuccal blade on antcrolingualbladc on thc parastylcof P' that thc paramctaeortcof P' that sun)lout)lsan surmountsa posterolinguallyoricnted thegotic obliquelyoricntcd anterolingual thcgotic facette lacctte(in contrastto no apical bladc such as (in contrastto eitherno bladcor a poorlydcvcl- may[?]charactcrisc Neohelos): completcly undi- opcd antcriorlyorientcd bladc such as may[?l vidcdparametaconc on F (in contrastto all other charactcriseNcolrclos); vcry snrallto absenthy- 196 MEMOIRSOF THE QUEENSLANDMUSEUM

TABLE 2. Measurementsof Nimbadon lavarackorum n.sp.,N. whitelawin.sp. and N. scollorrorum n.sp. from Riversleighand Camfield Sta- tions, northern Australia. In mm. Brackets around figures indicate estimates. Abbrevra- tions: ant, anterior; post, posterior; *Gag Site specimens.

UPPER DENTITION N. Species Nimbadon lavurackorum whitelawr

NVM QMF 23r41 23t43 23rM 23t4s23146 23r41 23148 23r49 23150 23I 60+ PI 1t6506 2?t51 flsnl lcli L 12.1 14.l 12.4 12.9 l3.t) 14.3 P- 10.3 10.4) 10.9 ).{ L I 1.9 13.3 4.'l l3.l t3.2 1l M2 w{ant} t0.2 |0.9 t.1 (9.3) 5.0 r,v(Dost) 9.9 10.8 0.5 9.2 5.8 L tz.) 13.1 4.3 t-)-| 7.9 M3 w(ant) il.3 1.6 r0.9 w(post) 10.I 10.9 0.4 (9.5 L 13.8 14.3 13.5 18.5 MO w(ant) I 1.5 12.2 il.1 w(post) t0.7 t2.5 10.4 9.1 L 13.5 t8.t M5 w(ant) l 1.3 w{ Dost) 9.t3 Palatewidth \9.2 P--M5 L (84.4) P,-M" L 52.8 66.3 P"-M2 L 15.3 25.8 48.2 M2- L (71.s) M"' L 39.5 53.I NEW DIPROTODONTIDSFROM NORTHERNAUSTRALIA l9'7

FIG. 2. Nimbadonlavarackorurn n.gen, rLsp.,-Henk'sl-Iollow Site,fiversleigh Station A-A', QMF23l4l, holptype,left maxillaryfragment with M','M' and buccalhalf of P', occlusalstereopair B-D, QMF23l43, RPr:8, lingualview; C-C', crcclusalstereopair; D, buccalview Bar indicateslOmm poconeon P3(in contrastto Alkwertalheriumand developed);poorly developedto absentanterol- most but not all Neohelosand in contrastto all ingualbasal cingulum joining baseof parastyleto other zygomaturineP3s where this cusp is large, baseof protocone(in contrastto most other zy- including Maokopia Flannery 1992); pos- gomaturinesexcept some Neoheloswhere there terobuccalbasal cingulum on Pr (in contrastto may be only a very smallcingulum); an anterol- most other zygomaturinesexcept Alkwertath' ingualcrest on Pethat extends from theparameta- erium andNeohelos where this featureis variably cone towards the protocone but, veering 198 MEMOIRS OF THE QUEENSLAND MUSEUM

anteriorly, bypassesthe buccal crest from the Archer et al., l99l), Microsite(containing the protoconeand extendsto the anterolingualbasal Nooraleebal-ocal Fauna;Sig6, Hand & Archer, cingulum(in contrastto directlyconnecting to the 1982;Hand, 1993) and Gag Site (near the base of buccalcrest from theprotocone as occurs in most System C, containing the Dwornamor l.ocal if not all other zygomaturines);a line extended Fauna;Flannery & Archer, 1984;Hand, 1985; buccally through the protocone and parameta- Archeret al. 1991),but is closeto (thoughstill conepasses anterior to the positionof the widest above)the level of Two TreesSite (containing the point on the buccalbase ofthe crown (in contrast Two Trees Local Fauna Flannery & Archer, to intersectingthis point as it does in Neohelos 1987).On the basisof its stratigraphicposition and Allopertatherium, although this feature is and stageof evolution comparisonsof its fossil variablein Nimbadonwhitelawi n.sp.); this same mammals(work in preparation),the Henk's Hol- line dividesthe crown suchthat the anteriormoi- low l,ocal Faunais tentativelyinterpreted here to ety is longer than the posteriorone (as it doesin be middleMiocene in agc (Archeret al., 1989, Alkwertatheriutnbutin contrastto eitherdividine l99l ). the crown into approximatelycqual lengthso-r into shorteranterior and longer posterior moieties RsrenRgoSpgcrusNS AND THETR LocnLrtrss asit doesin Neohelos);poorly developedparasty- QMF23l42from the Henk's Hollow Locality, a left les andmetastyles on uppermolars (in contrastto dentarycontaining P:-Ms, is tentativelyrcf'cned to this speciesof Neohelosbut as in someanterior teeth species,as are the following isolated teeth fiom Henk's of other zygomaturinessuch as P. centralis). Hollow:QMF23l43, a {ght P'; QMF23l44,a leftP-; QMF23l45,a left Mj; QMF23146,a right Mj; Erylrolocy QMF23l47,a left M'; QMF23l48.a left ?Mlr Nitnba is a northwesternQueensland Aborigi- QMF23149. a rightMur QMF2Il50. a right M:: nal word (Wanyi language)meaning 'small';dbn 15l, a rightP3; a left P3; 'tooth'. QMF23 QMF23l52, is Greekfor The namealludes to thesmall QMF23153,a right P3;QMF23 154, a left ?M2. molars found in speciesof this genusand to the QMF23l55,a rightM2, and QMF23160, a right M'-', fact that the posterior molars do not increase werecollected from the Gag Site of thesame plateau, markedlyin size from M2 to M4 as they appear RiversleighStation. to do in the otherwise stmilarNeohelos tirarensis. Rsprnneo Locnlrrre,s ANDAGES Nimbadon lavarackorum n.sp. The stratigraphicrelationships of the Henk's (Figs2,3) Hollow Local Faunaand the Dwornamor Local Faunaare indicatedabovc. At present,both are Holoryps interpretedto be middle Miocenein age. The holotypeis QMF23l4l, a leftmaxillary liagment containingM', M'and thebuccal half of Pr. SpncresDrAGNosrs This speciesis distinguishedfrom Nimbadon ErylroLocy scottorrorumn.sp. from Riversleigh'sFig Tree The species is named after Sue and Jim locality(see below) by its smallersize, relalively Lavarackin recognitionof their invaluablesup- longerPe, better developcd hypocone on Pr, less port in the field at Riversleighand as founding well-developedparastyle on M' and probably membersand hard workins Councillors of the more elongateposterior uppcr molars and less RiversleighSociety. a supp6ngroup for Austra- well developedpostmetacristabut morc discrete lian palaeontologicalresearch. metastyleon M'. It is distinguishedfrom the similar-sizedN. Tvpe LocurrY ANDAcE whitelawi n.sp.by its almost square(rather than Henk's Hollow Locality (Archer & Flannery, rectangular)upper molars. 1987) occurs within the sequenceof Tertiary limestonesoutcropping on RiversleighStation, DgscRtrttott northwesternQueensland (Archer & Hand, 1984; F is representedby three specimens:a LP3 Archeret al., 1989,1991). It is stratigraphicallyfrom theholotype, QMF23l4l; an isolatedRP', nearthe top of the SystemC sequenceas defined QMF23l43: and an isolatedLP'. QMF23l44. by Archeret al. (1989,l99l). This is interpreted The tooth is widestacross the protocone,sharply to be stratigraphicallyhigher than Sire D (Sysrem pinching in anteriorlyand smoothly rounding A containing the Riversleigh Local Fauna; posteriorly.It is subtriangularand is comprised NEW DIPROTODONTIDSFROM NORTHERN AUSTRALIA t99

FlG.3. Nitnbadonlavarackor unr n.gen., n.sp., Henk's Hollow Site, Riversleigh Station. QMF23142, left dentary with Pr,Mz, M:, Ma andM5, occlusalstereopair. Bar indicateslOmm. of four cusps:the parastyle, parametacone, proto- toconeis lingual to the parametaconeand the cone and hypocone (the latter however being hypoconelies posterobuccalto the protocone. variably developed).The parametaconeis the The hypoconeis more sharplyseparated by deep highestcusp. lt is blade-likewith a strongshear- fissuresfrom the buccalcusps than is the proto- ing crest on the posterioredge and a short an- cone The parastylcis posteriorlyinclined with a terobucallyoriented apical crest.The protocone shortanterolingually oriented apical blade This and parastyleare subequalto eachother in size. largeconical cusp forms a stronganterobuccal The hypocone is the smallestcusp and is even projectionin theocclusal outline o[ thecrown. lt absentin onespecimen (QMF23 lzl4).There is no is separatedfrom adjacentcusps by a chevron- suggestionof a division in the parametacone shapedtransverse cleft that is better-developed which is pyramid-shapedhaving relatively flat- linguallythan buccally. Posterior to thiscleft, and tenedanterior, buccal and lingual faces.The pro- on the anteriorflank of the parametacone,a con- 200 MEMOIRS OF THE QUEENSLAND MUSEUM

spicuousridge extendsanterolingually from the tip of themetacone to theposterior cingulum with tip of the parametaconeto the anterolingualcin- which it merges.A weakly developedpostparac- gulum at a point anterobuccalto the baseof the rista on the posteriorflank of the paraconeex- protocone. From the tip of the protocone, a tends toward the midvalley but stops short of poorly-definedtransverse crest runs buccally un- contacting similar premetacristaethat extend til it almostmeets (but does not) theparametacone from the metaconeand from just lingual to the ridge,its counterpart,at the commisurethat sepa- metaconetowards the midvalley. From the proto- ratesthe protoconeand parametacone. Anterolin- cone and metaconule,wide but very faint crests gually, a very poorly developed (to ?absent) extend posterobuccally across the posterior cingulum extendsfiom the anterobuccalbase of flanks of the protolophand metaloph.From the the protoconeto the lingual baseofthe parastyle protocone,this crest extends to the transverse but doesnot continue up theflank of theparastyle. valley nearthe midline; from the metaconulethis A cingulum is also developedposterobuccalli crestextends to the posteriorcingulum also near from the buccalflank of the parametaconeto the themidline of thetooth. most posteriorpoint of the crown (but is better- Wearfacettes on thesecrests exhibit oolish and developedin somespecimens in than others)and parallelstriations (particularly in QMF23l45) appearsto be developedposterolingually from suggestingthat their function was maintainedby this point to at least the baseof the hypocone. thegosisagainst (respectively) the entoconidof There is no evidenceof an anterobuccalcinsu- Mz andthe metaconidof M:. The antcriorcingu- lum. From thetip of the paramctacone.a proili- lum extendsfrom theparastyle around the lingual nent crest runs to the posterior margin of the baseof the protoconewherc it is intenuptedand tooth, dividing the posterolingual and pos- thencontinues across the lincual endof the trans- terobuccalcingula. A small crestruns posteriorly versevalley to thcanleroling-url base of thc meta- from the tip of the protoconeto a swelling or conulewhcre it is interruotedand then continues cuspule.Another thin creston the posteriorface aroundto the llctastyle.There is no buccalcin- of the hypocone appearsto convergewith the gulum. The M'may havebeen three-rooted with posterolingualcingulum (at least in QMF23144). a cylindrical root beneaththe paraconeand an- The toothis two-rooted.The antcriorroot is coni- otherbeneath the protoconc and a singlewide root cal and slightly anteriorlysloping; the largerpos- beneaththe metaloph.hecise thegotic facettes terior root is anteroposteriorlyflattened and occur on the anteriortrailing edgesof the pro- anteriorlyconvex. Many of the medial surfaces toloph and rnetalophbladcs. The anteriorflanks of the four crowns are covered in fine, poorly of the protoloph and mctaloph are "hollow- developedcrenulations. There are two roots:one ground"in anticipationofthe thegotic sharpening anterior oval one beneaththe parastyle;and a of the blades.Fine verticalcrenulations on the much longer anteroposteriorlycompressed root flanks of the protoloph and metaloph produce thatextends transvcrsely beneath the whole width secondary,vertical ?betathegotic bladesas the of th"eposterior part of the crown. tooth sustainsabrasive and thegoticwear. -s M'. The first upperadult molar is known from M3'5. M3 are similar to M2 in basic morohol- the holotype,QMF23l4l, and ?anisolated left ogy but are slightly largcrand higher-crowncd. M', QMF23l45. h is a low-crownedalmosr The paraconeis largcr and more buccally- situ- squaretransversely lophodont tooth that is only atcdthan the metaconc. Thc protolophand,mcta- slightly longer than wide. It is comprisedof an loph increaseslightly in width frornM'-". The anterior moiety, the protoloph, and a posterior parastylcand postrnetacrislaarc markedly re- moiety,the metaloph.Both areanteriorly convex. duccdin M'-'suchthat in M'lhcy arereprescnlcd The paraconeand metaconeare similar in sizeas by tcrminalswellings in lhc arrterior arrd posterior arethe slightly shorterprotocone and metaconule. cingularespectively and are absent in Muand Mt. The metaconuleis slightly higherthan thc proto- In slomespecirnens-(e.g. M3in QMF23l60),how- cone and more lingually-situated.The metaloph cver,there is a very tiny cuspuleon thc posterior is thus wider than the protoloph.The paracone flank of the mctaconeof posterior molars. Thc andmetacone are slightly closertogether than are postparacristais lcss well-developcdas are the the protoconeand metaconule.In the anterobuc- crestsfrom the protoconeand metaconule.Thc cal comer of the tooth a weak parastyleis devel- mesostyleappcars to be lacking.Thc partof the oped at the buccal end of the short anterior crownanterior to theprotoloph is shorterand the cingulum.There is no mctastylealthough thcre is swellingin thetransverse valley bctter developed. a prominentpostmetacrista that extends from thc The melalophis much morc itrongly curvetlin NEW DIPROTODONTIDS FROM NORTHERN AUSTRALIA 201

M3-5and is more lingually offset with respectto apex of the protoconid. Taken together, these the protoloph. flanking cuspulesand their associatedvertica- comprisea transversestructure that inter- Dentary. a dentarycontaining P3, cristids QMF23I42, the crown at its apex at right angles to the Mz-s,is tentativelyreferred to this species.It is of sects shearingcristid. The posterior a size appropriatefor some of the referred upper main longitudinal is much betterdeveloped than the ante- molars of this speciesand in its suite of plesio- cingulum which is presentonly at theanterol- morphic zygomaturinefeatures (e.g. its lack of a rior cingulum the crown. The posteriorcingu.lum posteriorly increasing molar size gradient), is ingual tip of extendsfrom the lingual baseof the protoconid to analogousto the phylogeneticstate of the upper posteriorcuspid where it is met by the buccal molari of N. lavarackorum.However, because the protoconidbut is bestdeveloped in the the specimenappears to be approximatelyl0% baseofthe of the posteriorcuspid where it is met by largei than the holotype,there is still someslight region longitudinalcrest of the crown. In this doubtabout the proprietyofreferring this dentary the main the posterior cingulum is to N. Iavarackorutn. area of intersection, conspicuouslycrenulated in somespecimens (i.e. The dentaryis badly fracturedand is missing QMF23l52 andQMF23l53) andslightly less so medialsymphysis, angle and ascend- theincisor, in others(i.e. QMF2315l). In QMF23I52,awear ing ramus.It is deepestbelow the hypolophidof facetteon lhe postgrobuccalcingulum, possibly M+.The ventralborder slopes posteriorly upward producedby the P'parametacone,is developed from this point and anteriorlyupward to at least which is not seenin otherspecimens. In this same the hypolophid of Mz. The anterioredge of the specimen,just anteriorto thecrenulated posterior coronoid processleads posterodorsally from the cingulum, a transversecrest extendsanterolin- body of the horizontal ramus.The postalveolar gually from the tip of the posteriorcusp to the processis missing.There is no distinct digastric posterolingualcingulum. In all specimens,a wear fossaand the areabeneath the leadingedgc of the facettefor Mz is devclopedat the tallestpoint of coronoid processis smooth suggestingthat the the posterior cingulum. The tooth is double- fora- masseteriafossa was not deep.The mental rooted,the anteriorroot bcing conical in shape, a men is locatedapproximately 4mm in front of the posterior root being anteroposteriorlyflat- vqrticalline markingthe mostanterior edge of the tened. Pr crown. It is round in lateral view and opens and al- anterodorsallyonto the buccalsurface of the di- SpecimensQMF23l52 QMF23I53, similar in morphology,are considerably astemalregion. Although the mandibularfora- though thanthe P: preservedin the dentary.The men is not preserved,the mandibularcanal is smaller in this speciesmight bc sexuallydimorphic. representedby a sulcusat about the level of the P: tooth row. Mz. The Mz, known from QMF23I42 and I 54?(and the Gag Site 155),is an The P: is preservedin QMF23I42 as well as QMF23 QMF23 elongate,subrectangular tooth that is narrower an isoiatedLP:, QMF23l53,an iso- QMF23152, anteiiorlythan posteriorly.Thc trigonid of Mz is latedRP: and an isolatedRPr. The QMF23l5l, by a transverseprotolophid and an tooth is longer than it is wide and more nanow represented arcuateanterolingually directed paracristid that anteriorlythan posteriorly. It bearsa centralprin- to the anteriormargin of the tooth. Frorn cipal cusp, the protoconid,and a much smaller extends a shortindistinct crest (?protocris- medially positioned posterior cingular cusp. theprotoconid posterobuccallyto termi- These arc joined by a prominent longitudinal tid) appearsto extend in a slight swelling which is perhapsthe shearingcrest that also extendsanteriorly from nate protostylid.From the metaconid,a crestextends theprotoconid to terminateas a cuspuleor cingu- a shofi distancc.Frorn the entoconid,a lar swelling at the anterior edge of the crown. anteriorly entocristidcxtends anterolingually. Lingual to the principle central cusp there is a short variablydistinguished cuspule (stylid or vertical In txclusalview, the paracristid is convexbuc- cristid). This structureis the apex of a vertical cally. the protolophid is transverscor very llanking crestthat extends ventrally to a pointjust slightly postcriorlyconvex and the hypolophidis posterior to the lingual baseof the protoconid. marteitly posteriorlyconvex. The protolophidis This crestis most conspicuousin posteriorview. narrowcrthan thc hypolophid.An anteriorcingu- A posterolingualcingulum leads posteriorly from lum is presentboth buccal and lingual to thc the baseof this crestto the baseof the posterior anteriorend of the paracristid.The cingulum on cusp.A similar but much less well-developed thebuccal side is not prescrvedin QMF23l42, is veriical cristid extendsventrally from the buccal distinct (betwccn the protolophid and hypolo- 202 MEMOIRSOF THE QUEENSLANDMUSEUM

phid)in QMF23l55 butnot in QMF23l54.There TYPEI-OCALITY AND AGE is no lingual cingulum or cristid obliqua in The type locality is fossil vertebratelocality QMF23I42 but there is a lingual cingulum in WV l13 in Bultitude(1973) (17'7'5, 131"32'E), QMF23l55 (againbetween the protolophidand theHorseshoe West locality of theCamfield Beds hypolophid). The posterior cingulum connects at Bullock Creek,Camfield Station, northwestern the posteriorbase of the hypoconidto that of the Northem Territory. The Bullock Creek Loca. entoconid.A wear facette is developedat the Fauna (Plane & Gatehouse.1968: Archer & midpointof theposteriorcingulum. Distinct wear Bartholomai.1978: Rich et al.. l99l: Archer & facettesextend along the posteriorlengths of the Hand, 1984;Murray & Megirian, 1990,1992)is protolophidand hypolophid.In lingual view, the currentlyinterpreted to be ?middleMiocene, i.e. floor of the transversevallev is U-shaoed.The immediatelypost-Wipajiri, in age(Woodburne et protoconidis taller than the subequalmitaconid, al., 1985;Murray, 1990a;Munay & Megirian, hypoconid and entoconid.The tooth is double- 1990,1992). rooted but these are not well preservedin thc isolatedteeth QMF23154 and QMF23l55. Spr,cresDIAGNosrs QMF23I54 (Mz?) has a paracristidand pre- This speciesis distinguishedfrom N. lavarack- metacristidthat are much lessdistinct than those orutn and N. scottorronln bv its markedlv more preservedin the dentaryand Gag Site specimen. elongate(i.e. lesssquare) upper molars and rela- Only theparacristid extends to theanterior cingu- tively moreanteriorly situated buccal swelling on lum of the tooth. In this specimen,the enamelon P'. It is alsodistinguished frorn N. scottorrorum the posteriorface of the protolophidhas promi- by its relativelymuch longer Pr and markedly nent vertical crenulations.The cristid obliqua is convexanterior and posteriormolar crown mar- alsodistinct although low andextends as a minor gins such that theseteeth have a much reduced verticalcrenulation on to theposterior flank of the areaof interdentalcontact. protolophid. M:-s. Unlike Mz, trigonidsof the posteriormo- DsscnrprroN lars lack a prominent paracristidand are more The spccics is describedinsofar as it differs rectangularin appearancewith the protolophid from Nitn badon lavarctc ko rutn. being slightly wider than the hypolophidin M:-s. The palatepreserves most of the right and a In M:, the protolophidand hypolophidare ap- largepart of theleft maxillaeand srnall fragments proximately the same width. The paracristid of theleft andright palatines.Anteroventrally, the forms a poorly-definedvertical crest that extends palateis fracturedat or behind the premaxillo- only partly down the anteriorface of the protolo- maxillary suture. Posterovcntrally,it preserves phid. The premetacristidis also poorly defined the maxillo-palatinesuture. The latter extends and extends approximatelythe same distance. anteriorlyto a point medial to the posteriorpart Protolophidsand hypolophids become more pos- of M'. Palatalridges extcnd longitudinally and teriorly convex from Mz to M:. In Ma-s,the pro- anteriorlya"long the lengthof the palatefrom the tolophids are markedly wider and the level of M'. The right diastemalcrest runs an- hypolophidsare lingually displaced.M+ and Ms terolingually. The tooth rows are parallel to arelarger than M:. slightly convex buccally. Anteriorly, doming of the median region of the palate is marked. TI Nimbadonwhitelawi n.sp. extendsposteriorly to the level of the rear of M' (Fig.a) and, though shallowingpcrhaps, anteriorly to at leastjust behindthe premaxillo-maxillary bound- Holorvpe ary. There is a pair of nutricnt foramina on the The holotypeand only known spec^imen is rigtrtslOe of thepalate medial to P3and on the left NMVP.I86506. lt preserveslhe palate.RP'-M) and sidea singleforamen. Mcdial to the hypolophof LPr-Mr.AII teethixcept LPr aredama[ed and LM:] M', is anothertiny foramenon each side of the andRM' aremissing parts of theirposterior halves. palate.The infraorbital foramen canal is about 30mmin length.The infraorbitalcanal opens onto the face 14mm abovc the anterioredse of the P' ETYMoLoGY alvcolus.Sulural relationships ol t[c palatinc. This speciesis namedafter Michael Whitelaw lacrimal,jugal and maxillarybones are unclear. who assistedin the collectionand processingof Therc is no evidence for rnaxillary or Dalatal specimensfrom Bullock Creek. vacuilicsalthough the anterior an.l postcrior ex- NEW DIPROTODONTIDSFROM NORTIIERNAUSTRALIA 203

FlGo4. \imbadon whitelawi n.sp.,Bullock Creek,Northern Territory. NMVPI86506, palatewith RP3-M5and LPr-Mr, occlusalstereopair. Bar indicatesl0mm. tremities of the palateare missing. The maxillary badoninbeinglonger relative to Ppand in appear- processnear the roof of the zygomatic arch, al- ing to be-rectangularrather than square. though damaged,is down-turnedand conspicu- Thel ne M'M- appears toIo differolller frolnlrom theme RiversleighI ous but doesnot extendventrally below the level specresspecies rnin a stmllarsimilar way as M-,M', but lt!t appealsto of the palate. There appearsto have been a very be relativelyeven more elongate. M'and M'are reduced orbital wing of the maxilla, although approximatelyequal in length. boneboundaries in this regionare unclear. The Ma differs less from that tooth in the other Upper dentition. The Pe differs from most speciesof Nirnbadon. specimens(all exceptQMF23lzt4 AR55l3) ofN. All of the cheekteethof N. whitelawl appearto lavarackorum in the greater degree of develop- differ from those of N. scottorrorun in having ment of the hypocone. ln N. whitelawi the anteriorly and posteriorly markedly convex tooth parastyle appearsto be less posteriorly inclined margins so that the crowns abut with limited contact. and the anterolingually-directedcrest that extendsfrom the parametaconeto the anterolingual cingulum is less distinct although it is possibly Nimbadon scottorrorum n.sp. (Fig. diminished by wear. It neverthelessapproaches s) the buccal crest from the protocone at a steep angle rather than perpendicular. Holorvpe' The M' on both sidesof the holotypeis dam- Theholotype and only known specimen is QMF23157 agedbuccally and lingually. However,it appears (formerlySAMP278l5). a rieht maxillaryfrasment to differ from both Riversleighspecies of Nim- conrainingt', v2, M3,M4 un-dM5. whil;p3 uio v2 204 MEMOIRSOF THE QUEENSLANDMUSEUM

are intact, M3-5are missing the buccalmargins of the and is subroundedin shape.Unlike N. lavarack- crown. orum,inwhichP3 is equaiin lengthor longerthan any adult upper molar, in N. scottonorum this Ervuor-ocv tooth is the shortestin the tooth row. The hypo- The speciesis namedafter Sueand Don Scott- coneappears to havebeen very poo^rlydeveloped. Orr, in recognition of their long-term support for The anterobuccalcorner of M' has a much the RiversleighPalaeontological Research Pro- squarerappearance due to greaterparastylar de- ject. With the Lavaracks,they are also founding velopmentin the anteriorcingulum. This is true membersand Councillorsof the RiversleishSo- also of the posterobuccal corner of the tooth ciety. where metastylardevelopment occurs mid-way alongthe postmetacrista. TYPEI-OCALITY AND AGE Parastylar development in M' is relatively The type locality, Fig Tree Site, is adjacentto marked compared with its condition in N. GodthelpHill, RiversleighStation, northwestern lavarackorum. The teethare buccally fractured in Queensland.It is laterally adjacentto units re- Ml-5 makingit impossiblelo determinethe de- gardedby Archer et al. (1989, 1991)to be part of greeof deve-lopmentof the buccalcusps in Ma-s. SystemB although it may actuallybe from the basal part of System B or even upper part of DISCUSSION SystemA, hencestratigraphically below Henk's Hollow (upperpart of SystemC; Archer,Hand & The threediprotodontids described here appcar Godthelp, 1986) and Gag Site (lower part of to comprisea new clade of zygomaturines.As SystemC; Flannery& Archer,1984; Hand, 1985) speciesof the new genusNirnbadon', they may and possibly above or equivalent to Microsite be distinguishedfrom other zygomaturinesby, (?SystemA; Sig6,Hand & Archer, 1982;Archer among other features,a combination of upper eral., 1989, l99l)and SiteD (SystemA; Tedford, premolar attributes.Premolar morphology was 1967;Archer et al., 1989, l99l ). On thisbasis and extensivelyused by Stirton (1961) and Stirtonet stageof evolutioncomparisons of tiremarsupials al. (1961) to help resolve distinctionsbetween in these faunas, the Fig Tree Local Fauna is diprotodontidlineages and has subsequently been interpretedto be ?lateOligocene-early Miocene usedby most workers.Few other charactersys- ln age. tems have been found to bc as useful in distin- guishing probable inter-relationshipsamong SpecresDracNosrs Tertiarydiprotodontids. This speciesis distinguishedfrom Nitnbadon SinceStirton et al.'s (1961)rcview of Tcrtiary lavarackorum andN. whitelawi by its larger size, diprotodontids,diverse diprotodontoid materials anteroposteriorlycompressed Fe (which is much have been collectedfrom Oliso-Miocene fossil shorter than any upper molar), its more robust sitesat Riversleigh.Bullock Crcck, Alcoota and cingulaon all chee[t^eethand its greaterparastylar Beaumarisand from Pleistocenesites in New developmentin M'-' (contributingto the squarec Guinea(e.g. Flanncry, 1992)and many areasof appearanceofthese teeth). It alsohas less convex Australia.This materialincludes specimens rep- anterior and posterior molar crown margins resentingnew generaand probablynew diproto- which thereforehave much wider interdentalcon- dontoidsubfamilies. Murray (1986, 1990a,b) has tact with eachother. namedseveral ncw Tertiary taxa but the bulk of It is further distinguishedfrom most (but not the material,particularly from Riversleighsites, all\ N. lavarackorumbv its much smallerhvpo- is yet to be described.As a result of the new coneon P3. discoveries,the superfamily Diprotodontoidea is in needof majorrevision. Descntpttott At present(e.g. the reviewsof Archer, 1984; Nimbadon scottorrorum differs from N. Aplin & Archer,1987; Marshall, Case & Wood- lavarackorwn andN. whitelawl as follows: burne,l989; Murray,1990b) two diprotodontoid The P3 is markedly anteroposteriorlycom- families are recognised:the Palorchestidac;and pressedsuch that it is almostas wide as it is long the Diprotodontidaewith two subfamilies,the ' The generic name Nimbadon was used by Munay (1990b) in a cladograrnof hypotheticalphylogenetic inter-relationshipsamong Miocene diprotodontids. However Murray did not dcsignatea spcciesof Nimbadon in the cladogramor in the ensuingdiscussion, irnd, as outlined in Article l3B of the Codc of Zoological Nomenecfature,'Nimbadon' was thus usedas a mtmemnudtun. NEW DIPROTODONTIDSFROM NORTHERNAUSTRALIA 205

F1G.5. Nilnbalon scottorrorum n.sp., Fig Tree Site, Riversleigh Station. QMF23l57, right maxillary fragmenl with RP'- M', A-A', occlusalstereopair; B, buccalview. Bar indicateslOmm.

Diprotodontinae and the Zygomaturinae. Al- siderablevariability in cranial morphology has though zygomaturineshave traditionally (e.g. beenobserved in some zygomaturines(e.g. in a Stirtonet al.,1967)been considered to be among Neohelos sample from the Bullock Creek Local the most primitive of diprotodontoids,it is by no Fauna; P. Munay, pers.comm.),and the molar meanscertain that this is so (Munay, 1990b).It dentitionsof the zygomaturinesPlaisiodon cen- is not clear what might be usedas an appropriate tralis Woodburne, 1967 and Alkwertatherium outgroupin a phylogeneticanalysis of zygoma- webbi Munay, 1990b and the diprotodontine turinesnor, consequently,are polaritiesof char- Pyratnios alcootense Woodburne, 1967 have acter state morphoclines within the been found to overlap in size and morphology Zygomaturinae confi dently determined. (Munay, 1990b). Murray ( 1990b)has discussed other difficulties It is perhapsa measureof the difficulties en- in analysing diprotodontid phylogenetics.He countered in determining species and generic notes that despite the fact that many Tertiary boundariesfor diprotodontidsthat Nimbadon is diprotodontidsare representedby almost-com- one of few non-monotypicTeniary zygomaturine plete skull and dentarymaterial, discontinuities genera, the others llr.ing Kolopsrs Woodburne, in some charactercomplexes and the continu- 1961andZygomaturus Owen, 1859. ously varying natureof otherstend to obfuscate Recognitionof the genusNitnbadon has been clarificationof relationshipsbetween taxa. Con- facilitated by re-diagnosisof NeohelosStirton, 206 MEMOIRS OF THE QUEENSLAND MUSEUM

1967based on new materialobtained by Archer is moreclosely related to Allovertatheriumwebbi and colleagues20 yearsafter the original material thanto any otherzygomalurine. was collectedby Stirtonand colleaguesfrom the A phylogenetichypothesis of diprotodontidin- Leaf t-ocality of Lake Ngapakaldi, South Austra- ter-relationships,including the three new Nirn- lia. This provides novel infgrmation about the badon speciesand broadly based on Murray's anterior morphology of Pp, which exhibits, cladisticanalysis of dentalcharacters, is givenin among other distinctive features,a large, erect Fig. 6. The polarity of somecharacters has bccn parastyle.This featureis also presentin speci- int lrcted differently from Murray (1990b)but mens referred to Neohelos from the Bullock basic intergeneric relationships remain un- Creek and Riversleigh Tertiary faunal assem- changedexcept for the position of Plaisiodon blages(Plane & Gatehouse,1968; Plane, 197 l; centrulis. Rich et al., 1982: Murray & Megirian, 1990, In Fig. 6 and Murray (1990b),the Zygomaturi- 1992;Archer et al., 1989,l99l). naeare clustered on the basisof a largeparastyle In his review of Oligo-Miocenediprotodontid on F which is separatedfrom the paiametacone taxa,Murray (1990b)postulates a numberofphy- by a deep cleft. The Kolopsoides-Plaisioclon' logenetichypotheses, only one of which is ex- N i mb ado n -N eo he lo s - Ko Io p si s-Zy g, o tnat u r us pressedin his cladogram(fig. l4). The latter is cladeshares as i.! synapomorphy developmeqt ol' basedprimarily on analysisof dentalcharacters a hypoconein P'. Thc basicproportions o[ P'are (in particular, P"), using speciesof the Oligo- apomorphicallyshared by speciesof the Nin- Miocene paforchestidgenera Ngapakaldia and badon,Plttisiodon, Neohelos and Kolopsisclade Pitikantia as outgroups.In it, Murray identifies (but seeMurray, 1990b),with a divisionin the speciesof KolopsisandZygomaturus as the most parametaconeinterpreted to have occuned sub- derived diprotodontidsand NeoheLostirarensis scqucntlyin the Kttlopsislincage. Retraction ol- as their closest relative. Speciesof Nimbadon themesostyle lowrrds thc cingulum in P'cluslcrs form the sister-groupro the Neohelos-Kolopsis- species of Neolrclos and Kolopsis (Munay, Zygomaturus clade, with Plaisiodon centralis 1990b). being the sister-groupof a Nimbadon-Neohelos- In both cladograms,tlre postcriorly inclined (or Kolop sis-Zy g omatu rus clade, Kolopsoide s cul- hooked)parastyle of P' in spcciesof Nimbadon tridens Plane, 196l the sister-group of a is regardedto be apomorphic.Only one othcr P lai sio don-N irnbad on-N eo he I o s -Ko Io p si s- zygomaturineexhibits this fcature- Plaisiodott Zygomaturus clade and Alwertatheriunrwebbi centralis. Although species of Nimbadon are the most plesiomorphicof zygomaturines.Spe- readilydistinguished from P. centralisby aspects ciesof Pyramios, Euryzygoma,Bematheriutn and of upper premolar morphology (including in I']. Diprotodon form a separatc (diprotodontine) centraListhe very largehypocone and the lingual clade.Raemeotherium yatkolai Rich, Archcr & crestfrom the pararnctaconclinking to the proto- Tedford, 1978 from the ?lateOligocene Namba conerathcr than the anterolingualcingulum) as Formation of Lake Pinpa, South Australia, is well as by their smallsize, lack of a postcriorly interpretedto be the mostplesiomorphic membcr increasingmolar gradicnt and absence of metalo- of thefamily Diprotodontidae. phids on lowcr nrolars,sharing of thc distinc- On the basisof his broaderstudy of dentaland tively shapedparastyle rnay indicatean albeit cranial characters,however, Murray (ibid.) con- distant phylogenetic relationship. cludesthat therc are probably two minor zygoma- Althoughthe three taxa describcd hcre as spe- turine lineages:onc reprcsentedby speciesof ciesof Nintbadonmay , whenbetter known, prove Nimbadon, Neohelos and Kolopsis, a group he notto bc monophyletic,all exhibitthe distinctive suspectsmay consist of taxa rclated largely by creston P'running linguallyfrom the paramcta- symplesiomorphies;the other lineage possibly conc to thc protoconethen anteriorly to the an- containingspecies of Alkwertatheriwn,Plaisio- terolingualcingulum, a feanlrenot previously don and Kolopsoides,although for this clade he noted in any othcr diprotodontoid taxa. Othcr canfind evenless concrete evidencc. Hc suggests featuresthat charactcrisethe new taxa include that thesetwo lineagesmight be relatedthrough thcir smallsize and an Mz:M+lcngth ratio which commonancestry in Nitnbadon.He alsosuggcsts approaches1.0. The latter are interprctcd hcrc and in the text,but not the cladogram,thatNitnbndon gencrally (see below) to be plesiomorphicfea- speciescould representbasal zygomaturincs with tures among diprotodontids,but they rnight somespecific affinity to Plaisiodoncentralis and equallybe interpretcdto rcprcscntaponrorphic Neohelo s tirarens is,andthat P/cis i odon ce nt ral is reversalswithin ccrtainzygomaturine lineages. NEW DIPROTODONTIDS FROM NORTHERN AUSTRALIA 207

Ngapaknldia& Pitiknntia sPP. Rae meo ther ium ya tko la i

Diprotodontines

Alkwertatheriumwebbi

K olop soide s cultridens Plaisiodancentralis

8- Nimbadon scottorrorum 7----aI I rlo - N. lavaracktrum L-gJ I 11_ N. whitelawi

N eohelos tirarensts ," : KoloPsis sPP'

FIG. 6. A phylogenctichypothesis of zygomaturines,broadly bascd on Murray's (1990b) cladisticanalysis ot' dentalcharacteis in the biprotodontidae.Apomorphies are as follows: l, loss,incorporation or supp-res.sionof stylarcusps C ;1ndD with iespectto the lophson uppermolars; 2, reductionof paralophidcrest on IQ; 3,large pirastyleon P{ separatcdliom paranrctlConehy a dcgpcleftl 4. developrncntof a_hypocong gn P'.:5. busic lnd dilgqnrrlcrcsl on P': [1.sht-rrlenirlg prop.ortionalsimilirity ol'P'16,hookcd parastyle on P'l 7. apicalblude ' bf P': 9. elongltionof posteriormolars (i.e. irt lcastM3-4); 10,hypertrophy of P hypoconql| | , elongrttionol antcriormolais,i.e.M2;l2,mcsostyleonPiretractedtowardscingulum; l3,divisioninP''parametacone,

We can, howevcr,find no pressingevidcnce to yatkolai but is tentativelyconsidercd by Tedford closely align individual speciesof Nitnbadon et al. (197-5)to be a palorchestid.Apart from its withany previously known zygomaturinc laxa. slightly largersize, Nimbadon lavarackorutn, the Most zygomaturines- including speciesof only speciesof thc genusso f'ar representcdby Zygctnnturus, Kolopsis, Kolopsoides and lower molars,like all otherzygomaturines differs Plaisiodon- exhibit a markedincrease in molar from R. yotkolai in its reductionof antcrior en- sizefrom M2 to M4 (with an Mu-M+length ratio trcristids. Nitnbatlctnspccies fufthcr differ fiom of 0.85 or less)with M5 gcncrallydecrcasing in Raemeotheriuttr,vatkoltti in being larger;in hav- size (seealso Rich, Archer & Tedford, 1978). ing a morcmassive clcntary which, in transversc Whctherthis is alsotrue of topotypicalNeohelos width,is approximatelytwicc thewidth of M:; in tirarensisis not known but Neohelosspecimens havingless wcll developcdcristids obliqua; rela- from Bullock Crcck and most lrom Riverslcigh tively widcr trigonidson all molars;trigonid of exhibitthis featurc. Mz nearlythc sanrewidth as thetalonid (in con- yatkolai wherc it is markedly nar- A molargradient of M2:M4 lcngthapproaching trast to R. protoconid 1.0is regardedby tuch, Archcr & Tedfbrd( I 978) rower);mctaconid of Mz ashigh as thc to be plesiomorphicin zygomaturines.Rde- andassociatcd with a prominent,steeply inclined, meotheriumycttkolai,commonly considcred to be swollenanterior buttress: mctacristid of Mz trans- the most primitive of known zygomaturines(but versolyoriented (in contrastto R. yarftolalwhcrc seeMurray, 1990b,and bclow) and rcpresented it is postcrobuccallyoriented); "arcuate" (rather by a dentary,isolated lowcr teeth and an upper thananteroposteriorly rcctilinear) paracristid on incisor from thc Oligo-MioceneNamba Forma- Mz; and lophidsof lower molarsless occlusally tion of Lake Pinpa,also hasuniformly sizedmo- concavc. lars (with a ratio of Mz:M+ length of 0.96). It is possiblethat molar size gradicntsin zy- Palorchestidsand diprotodontinesvariably cx- gomaturincsare allomctricallyrelatcd to body- hibit this f'eatureand one of thc oldestknown size, with larger anin'ralsexhibiting rclatively diprotodontoids,representcd in the carly Mio- largerpostcrior molars. Frorn Oligo-Miocctrc de- cenc GeilstonBay .LocalFaurra by u rtraxilla ;xrsitson RiverslcighStation, small diprotoclon- prcservingpart of Mr andM', alsohas uniformly tines havc been found with M2:M4 length sizedmolars. The latter is similar in sizc to R. gradicntsapproaching 1.0. Equally, however, thc 208 MEMOIRS OF THE QUEENSLAND MUSEUM

larger of the Riversleigh speciesof Nimbadon all membersof other lineageswith ubiquitously describedhere (N. scottorrorum) appearsto have small members(e.g. burramyids and acrobatids). been similar in overall size to at leastone unde- Becauseso few dentalcharacter systems have scribed Riversleigh Neohelos that shows a been found to be useful in diorotodontid svs- markedprogressivc increase in molar size from tcmatics.polarity swings of tniskind greatly in- M2 to M4.It seems,therefore, that the featureis fluencethe interpretedrelationships of taxa and not always dependenton absolutesize although thcir biostratigraphicsignificance. If elongation it may vary allometricallywithin lineages.In Fig. is plesiomorphicamong diprotodontoids, then N. 6 it has been interpretedto be autapomorphic whitelawiwould be themost plesiomorphic of the within variousclades. IhreeNintbadon species. Its presencein the mid- Intragenericrelationships w tthinN i mb atl o n are dle MioceneBullock Creek Local Faunaand the not much easierto interpret.Nimbadon whitelawi presenccof what would then bc interprctcdto be differs fronr both N. liwtrackorutn anclN. .rc.o/- the most apomorphicin the older Fig Trce Local torrorum in its markedly more elongateuppcr Fauna, would not be support for the currently mofars (particularly with respcctto N. scottor- understoodstratigraphic relationships. If, on thc rorwn) and relatively nlore anteriorlv situated otherhand, clongation is interprctedto be apo- buccalswelling on P1. Nimbttclonlctviracktrum morphic, then the most dcrived species (N. differs from N. scottorrorarnin its smallersize. whitelawi) occursin one of the youngcr faunas lesswcll-developcd parasrylc on Mr and proh- and the mostpfesiornorphic (N. scottorrorutn)in the oldestof thc faunas(Fig Tree). ably more elongateposterior uppcr molars and 'fhe lesswell developcdpostmetacrista but moredis- stratigraphicrelationships of thefossil as- crete metastyleon M'. Nimbttdonscottorrorltm scmblageshave been discussed in thc Systemat- is larger than both N. lavarackorum and N. ics section above. Thc Fis Trec Site occurs whitelawi,has more robustcingula on all chec! adjacent to units regarde-dto be part of teethand greaterparastylar development in Mr-' Rivcrsleigh'sSystern B scquenceas definedby (contributingto thc squaredappearancc of thesc Archcretal. (1989, 199 l), thoughit rnayactually teeth). Within Nitnbcldon,fcatures such as the be basal System B or upper System A, and is hypcrtrophytrl'lhe P' hypoconcin somespcci- interpretedto bc lateOligocene to early Miocenc m-ensof N. lavaruckorutnand thc shorteningof in age.The Henk's Hollow Site occursnear the P3in N. scottorrorumappcarto beautapomori'hic top of Riversleigh'sSystem C sequenccand the featuresunique to thosespecies. The moststrik- Gag Site nearits base.Both lie stratigraphically ing differencesbetween the taxalic in the degrce above the Fig Trcc level. On the basis of their of squaring(or converselyelongation) of the up- positionsand stageof evolutioncomparisons of per molars. their fossil mammals,they are interprctedto be middlc Miocene in age and are probably similar There are two quite different phylogencticin- in age to the Bullock Creek assemblage.The terpretationsof Ninbadon species,depending on Bullock CreekLocal Faunahas beeninteroretco whetherelongation (versus squaring) ofthe upper by Woodbumeet al. ( 1985),Munay l990a)and molarsis consideredto be plesiomorphicor apo- I Murray & Megirian( I 990)to be middleMiocenc, morphic. Commonality would indicate squarcd i.e.immt'diately post-Wipajiri. in agc. upper molars to be plesiomorphicamong dipro- todontianmarsupials including phalangeridans, On balance,we considcrthe phylogenetic rcla- tionships of Nimbatlon (Fig. vombatimorphiansand cven plesiomorphic kan- species 6) to ap- proximatclycorrcspond to current garoos.However, within the Diprotodontidae the understanding 'plesiomorphic' of therelativc ages of thc othcrwise (i.e. simple) Rae- depositsfrom whichthe specimcnswere obtained meotherium yatkolai has relatively elongate butconclude that forthc momcnlat least lower molarsand, although no upp"ri,t.tolars"are caulionis appropriatc in allernpts to use zygomatunnes yet known, they too would probably have been to correlatenorthern Aus- tralianTcrtiary relativelyelongatc, using as a guidethe relative mammal-bearing faunas. proportionsof the upperand lower molarsof M lavarackorum.It should be noted that the pre- ACKNOWLEDGEMENTS sumptionthu R. ycttkolaiis the mostplcsiomor- phic diprotodontidis basedon its simplicity. Grantsto P.V. andT.H. Rich from theAustra- Simplicity, however, often characteriscsthe lian ResearchCouncil and the National Geo- smaller membersof some diprotodontianline- graphicSociety made possiblc the collection and ages(e.g. pseudocheirids and macropodids)and preparationol Nintbctdonyvhitelawi. The South NEW DIPROTODONTIDSFROM NORTHERN AUSTRALIA 209

Australian Museum enabled N. Pledge tcl collect Mineral Resources,Geology and Geophysics and prepare the holotype of N. scottorrorutn. Australia,sheet SE/52-8. Work ai Riversleigh has been supported by the FLANNERY, T.F., 1992.New Pleistocenemarsupials Australian Research Council, the Department of (Macropodidae,Diprotodontidae) from subal- the Arts, Sport, the Environment and Territories, pine habitatsin Irian Jaya,Indonesia. Alcheringa National Estate Programme Grants (Queens- 16:321-331. land), the Australian Geographic Society, ICI, the FLANNERY, T.F. & ARCHER, M. 1984.Revision of Queensland Museum and the University of New the extinct gigantic rat kangaroos(Potoroidae: South Wales. During the course of this work, S. Marsupialia),with descriptionof a new Miocene Hand and H. Godthelp were supported by a Uni- genusand species,and a new Pleistocenespecies versity of New South special research grant. The of Propleopus. Journal of Palaeontology 89: authors thank Dr Peter Murray for his construc- ll3l-1149. tive criticism of the manuscript, and Dr David 1987a. Stri gocuscu s reidi andTr ichosurus dic kson i, who provided helpful nomenclatural advice. Ride two new lbssil phalangerids(Marsupialia: Pha- The photos were taken by Ross Arnett of thc langeridae)tiorn the Miocene of northwestern University of New South Wales. Queensland.Pp.527-536. In Archer(1987). 1981b.Bettongia moyesi, a new and plesiomorphic LITERATURE CITED kangaroo(Marsupialia: Potoroidae) tiom Mio- cenesediments of northwcsternQueensland. Pp. APLIN, K. & ARCHER,M. 1987.Recent advances in 759-161.In Archer(1987). marsupialsystematics with a new syncreticclas- HAND, S.J.1985. New Miocenemegadermatids (Chi- sification.Pp. xv-lxxii. In Archer(1987). roptera: Megadermatidae)from Australia with ARCHER, M. 1978.The natureof the nrolar-premolar commentson megadcrnratidphylogenetics. Aus- boundaryin marsupialsand a re-interpretationof tralianMamrnalogy 8: 5-43. the homology of marsupialcheekteeth. Memoirs 1993. First skull of a speciesof Hipposideros l8: 157-164. of the QueenslandMuseum (Brachipposideros)(Microchiroptera: Hip- 1984.The Australianmarsupial radiation. Pp. 633- 'Verte- posideridae),from AustralianMiocene sedi- 808. In Archer, M. & Clayton,G. (eds), ments.Memoirs of the QueenslandMuseum 33: brate zoogeography and evolution in 179-192. Australasia'.(Hesperian Press:Perth). 'Possums MARSHALL, L,G., CASE, J.A, & WOODBURNE, 1987. and opossums:studies in cvolu- M.O. 1989. Phylogeneticrelationships of the tion'. (Surrey Beatty and Sons and the Royal familiesof marsupials.Current Mammalogy 2: Walcs: Syd- Zoological Society of New South 433--502. ney)' Prinritivernarsupial tapirs ARCHER,M. & BARTHOLOMAI, A. 1978.Tertiary MURRAY, P. 1990a. (P Idc epftalas Murray and mammals of Australia: a synoptic review. Al- ropalorc lrc st e s no\tacu front the mid-Miocencof cheringa2: 1-19. P. ponticulussp. nov.) north Australia(Marsupialia: Palorchestidae). ARCHER, M., GODTHI]LP, H., HAND, S.J. & The Beaglc,Records of the Northern Territory MEGIRIAN, D. 1989. Fossil mammalsol Museumof Arts and Scicnces1: 39-51. Riversleigh,northwestern Queensland: prelimi- nary overviewof biostratigraphy,corrclation and 1990b.Alkwertatheriurn webbi, a new zygomatur- environmentalchange. The AustralianZoologist ine genus and speciesfrom the late Micxene 25 35-69. Alcoota Local Fauna,Northern Territory (Mar- ARCHER,M. & HAND, S.J.1984. Background to the supialia:Diprotodontidae). The Beagle,Records searchfor Australia'soldest mantnrals. Pp. 517- of the Northern Territory Museum of Arts and 'Vcrte- 565.In Archcr,M. & Clayton,C. (eds), Scicnces7: 53-80. brate zoogeographyand evolution in MURRAY, P. & MEGIRIAN, D. 1990.Furtherobser- Australasia'.(Hespcrian Press: Perth). vationson thc morphologyof Wakaleovander- ARCHER,M., HAND, S.J.& GODTHELP,H. I986. /elri (Marsupialia: Thylacoleonidae)from the 'Uncovering Australia's dreamtime'.(Surrey mid-Mimene Camfield Beds. No(hem Terri- tory. The Beaglc,Records of the NorthernTcni- Beattyand Sons: Sydney) '7: ARCHER,M., HAND, S.J.& GODTHELP,H. I99I. tory Muscum of Arts and Sciences 9l-102 'Riversleigh'.(Reed Books: Sydney). l992. Continuityand contrast in the middle andlate BULTITUDE, R.J. 1973.Wave Hill, NorthernTerri' Miocenevertebrate communities from theNorth- tory - 1:250,000Geological Series. Burcau of ern Territory.The Beagle,Records of the North- 2to MEMOIRS OF THE QUEENSLAND MUSEUM

ern Territory Museum of Arts and Sciences SIGE, B., HAND, S.J. & ARCHER, M. 1982. AN 9:195-218. Australian Miocene Brachipposideros(Man-r- OWEN, R. 1859.On someoutline-drawings and pho- malia, Chiroptera) related to Miocene repre- tographsof the skull of the Zyg o mat u r us t r ilo b us sentatives from France. Palaeovertebrata12: Macl,eay (Nototherium Owen?). Proceedingsof 149-l'72. theGeological Society of l,ondonl5: 168-176. STIRTON, R.A. 1967.A diprotodontidfrom the Mio- PLANE, M. 1967.Two new diprotodontidsfrom rhe ceneKutjamarpu fauna, South Australia. Bulletin PlioceneOtibanda Formation, New Guinea.Bul- of theBureau of Mineral Resources,Geology and letin of the Bureau of Mineral Resources,Geol- Geophysics,Australia 85: 45-51. ogy and Geophysics,Australia 85: 105-128. 1971. The genusNeohelos (Marsupialia:Diproro- STIRTON, R.A., WOODBURNE, M.O. & PLANE, M.D. 1967.A phylogeny dontidae).ANZAAS, Zoology, 43rd Congress, of the Tertiary Dipro- Sydney.Abstract. todontidae and its significance in correlation. Bulletin PLANE, M. & GATEHOUSE, C.c. 1968. A new of the Bureau of Mineral Resources, vertebrate fauna fiom the Tertiary of Northern Geologyand Geophysics, Australia 85: 149-160. Australia.Australian Journal of Science30 272- TEDFORD, R.H. 1967.Fossil mamnal remainsfronr z I J. theCarl CreekLimestone, northwestem Queens- RICH, T.H., ARCHER, M., HAND, S.J.. land. Bulletin of the Bureau of Mineral Re- GODTI{ELP, H., MUIRHEAD, J., PLEDGE, sources,Gcology and Geophysics, Australia 92: N.S., , FLANNERY, T.F., WOODBURNE 217-23'7. M.O.W,,CASE, J.A., TEDFORD, R.H., TURN- TEDFORD, R.H., BANKS, M.R., KEMP, N.R., BULL, W.D., LUNDELIUS, E.L. JR, RICH, MCDOUGALL, T. &. SUTHERLAND, F.L. L.S.V.,WHITELAW, M.J.,KEMP, A. & RICH, 1975. Recognition of the oldest known fossil P.V. 1991.Australia's mammal record: Austra- marsupialsfrom Australia.Nature 225: 141-142. lian Mesozoic and Tertiary terrestrialmammal TEDFORD, R.H. & WOODBURNE, M.O. 1987.ThC localities. Pp. 1005-1070In Vickers-Rich, P., Illariidae,a new family of vombatilbrmmarsupi- Monaghan,J.M., Baird, R.F. & Rich,T.H. (eds), 'Vertebrate als from Miocene strataof South Australia and palaeontologyof Australasia'.(Pio- an evaluationof the homology of molar cusps neerDesign Studio and MonashUniversity Pub- in thc Diprotodontidae.Pp. 401-418.In Archer licationsCommittee: Melbourne). ( | e87). RICH, T.H., ARCHER, M., PLANE, M.D.. FLAN- NERY, T.F,, PLEDGE, N,S., HAND, S.J. & WOODBURNE,M.O. 1967.Three new diprodontids RICH, P.V. 1982.Australian Tertiary mammal from theTertiary of the NorthernTerritory, Aus- localities.Pp.525-12In Rich, P.V. & Thompson, tralia. Bulletin of the Bureau of Mineral Re- 'The E.M. (eds), fossil vertebraterecord of Aus- sources,Geology and Geophysics,Australia 85: tralasia'.(Monash University OlTsetPrinting 53-r 03. Unit: Clayton,Victoria) WOODBURNE,M.O., TEDFORD, R.H,, ARCHER, RICH,T.H., ARCHER,M. & TEDFORD,R.H. I978. M.,]'URNBULL,W.D., PLANE, M.D. & LUN- Raemeotheriumyatkolai gen.et sp.nov., a primi- DELIUS,E.L. 1985. Biochronology of thecon- tive diprotodontidliom the medial Miocene of tinentalmammal record of Australiaand New SouthAustralia. Memoirs of the NationalMu- Guinea.Spccial Publication, South Australian seumof Victoria39: 85-91. Departmentof Mines and Energy 5: 347-363.