I Thc Bc,t.qlt,Rt,,'rJs,'f tht N,'nhrrn It,trtttr'\' llluscuntof Artsanr,/.Sr'icat r,.r. 199{) ?(:):51-80 l ALKWERTATHERIUMWEBBI. A NEW ZYGOMATURINE GENUSAND SPECIESFROM THE LATE MIOCENE LOCAL FAUNA. NORTHERNTERRITORY (MARSUPIALIA:).

PETERMURRAY NorthernTerritory Museum of Artsand Sciences, GPOBox 2109, Alice Springs NT 0871,.

ABSTRACT

Alkv'ertatheriumw,ebbi, gen. et sp. nov., possessescharacteristics structurally intermediatebetween the diprotodontinegenus Pyramios and the zygomaturine gents Plaisiodon of the family Diprotodontidae.In its expressionof a clearly differentiatedand well-developedparastyle on the Pr, Alky,'ertatheriumis aligned with the SubfamilyZygomaturinae. In its absenceof a hypoconeon the P3and its markedlyconstricted diastemal palate. Alkv,ertatherltrm resembles the membersof the Subfamily Diprotodontinae.Alkwertatherium was derivedfrom diprotodonti- nes at a structuralgrade similar to that of P)-romios.lt may haveshared ancestry with the primitive zygomaturinesPlaisiodon andNimbadon. P,-ramios, Alkuer- tatheriumand Plaisiodon exemplify a gradualstructural succession in cheektooth and cranial morphologyfrom the Diprotodontinaeto the Zygomaturinae.

KEywoRDS:Late Miocenemarsupials, Alcoota Local fauna,Diprotodontidae, zygo- maturinae,zygomaturine origins, Diprotodontinae,nototheriines, P '-ramios, Plaisiodon.

INTRODUCTION commonand therefore the inclusion of theodd molar of thesespecies would not seriously Primarilya descriptionof a new taxon,this influencethe statisticaldefinition of Plaisio- study also attemptsto addressthe character don. states of the Diprotodontidae in relation to The upper third premolarsof three of the Alkwertatherium,which is comparedwith four Alcoota generaare readilydistinguish- other Chehenhamian-Mitchellianequivalent able. forms in considerabledetail, incorporating a The P3of Pyramiosalcootense is character- brief review of the mid- to late Miocenedipro- ized in havinga weakly expressedor absent todontid genera. parastyle,absence of a hypoconeand presence At leastthree large generaand one smaller of a faint posterobuccalcingulum. Its broadly diprotodontidgenus are present in the Alcoota trilobateocclusal profile, large, conical proto- Local Fauna.The molar dentitionsof the three cone and equally large triangular,undivided largest genera: Pyramios a lcoot e nse parametaconewith a short,steeply descending Woodburne,P laisiodon centralisWoodburne postparametacristaare associatedwith dipro- and Alkwertatheriumwebbi, gen. et sp. nov., todontine(Diprotodontinae) diprotodorrtids. overlap in size and morphology. Isolated The large size of the Pi relativeto the molars molars of these genera are difficult to dis- is morein proportionwith thecondition in zy- criminate without the associatedthird premo- gomaturines.In Plio- Pleistocenediproto- lar. It is possible,judging from thesize distri- dontines,(eg. Eury:ygoma, and butions, that the tablesof measurementspro- ) the Pr is reducedrelative to the videdby Woodburne( 1967a)may containan molars. admixture of these forms. Sampling of the Plaisiodon centralis permanentupper pre- Alcootasite between 1985 and 1989indicates molarsare elongated. with a prominent.pos- that Pyramios and Alkwertatherium are un- teriorly curved parastyleand a long, blade-

53 P.F. l\lunay like postparametacrista.The posterobuccal Diagnosis.Crrnium narro\\!'r :.' .,r:rll,, cingulumis abscnt.The hypoconeis at least Iongerin proportionto rr'idth) thrn l' . .; '. incipiently prescnt.somctinlcs budding off Pluisiotlott.Kolopis or Ncolir'/r''. .: ..:. the posteriorside of the protocone.In some profile forming a distinct vertc\. .(.::- individual s the parametacone is weaklydiffer- weak frontal and low sagittalcrc'\l' :r.:::: entiatedinto two conjoinedcusps. but the bfing the type Plttisiodon t't'rttrulit (-?r' conspicuousvertical buccal sulcusthat ac- 6784). Constricted and elon,r.r:e,: companies such a division in the postsquamosallamina, similar to, but mtrrc zygomaturinesKolopsis torusY,l oodburne and extreme than in Neohelosor P/alsiorloa:oc- Zrgomaturusspecies is lessdistinct. ciput lower and narrowerthan any similar- lrrrs has a broad,Iow molariform,5-cusped sizeddiprotodontid. Rostrum narrower than in Pr with a divided parametacone.well-devel- Pyramios, Plaisiodon and Neoftelos.con- opedanterobuccal and posterobuccal cingulae stricted at the level of the infraorbital fora- anda low, but distinctmesostyle. men; diastemalpalate similar to. though While thesethree generacannot be mis- longerand morenarrowly constricted imme- takenfor any otherdiprotodontid, Alkv,ertath- diately anteriorto P: than in P_vranrios;later- erium v'ebbi upper third premolarshave a ally expandedpremaxillary palate, as in P.r'r- large parastylecombined with a P,-ramios- amios,but with a shallow.wide, as opposed to like absenceoithe hypocone;steep. triangular a narrow, deep,interincisival fossa. Nasals undivided parametaconeand large conical elevatedslightly and expanded anteriorly as in protocone.A weakposterobuccal cingulum is Plaisiodon andNeohe los. not downturnedand present.An indistinctmesostyle is confluent pointedas in P1-ramios. Zygomatic archlong, at its apex with the parametacone,as in P,r'r- as deepanteriorly as posteriorly,contrasting amios.The premolaris similarto thatof Py- with theshort. anteriorly narrowing zygomatic amios. but larger relative to the molars, and archesof Pyramios.Squamosal-jugal suture distinctive in its possessionof a massive. long, squamosalprocess extends to beneath stronglydifferentiated parasty'le. the orbit as in P_vramros:contour of archrela- The apparentabsence of unambiguousde- tively flat as in Plaisiodonand in contrastto scriminativefeatures in theupper molar denti- the strongly-bowedzygomatics of Ptrantios; tionr and the diprotodontine-z1gom;lturinemassetericprocesses broad and short as in continuityin thepremolar morphology result- ,in contrastto long.robust processes ing from the discovery of Alku'ertat heri unt in Pyramiosldeep, well-defined nasolabialis raisessome issuesin diprotodontidsys- fossasimilar to Plaisiodonand Neohelos. but tematics.On the basisof cranialcharacters. differing from Pyramios in which the fossais Alkv'ertatherium is very similarto Plaisiodon, poorlydeveloped. Trilobate, posteriorly broad but otherwiseexpresses affinities with Pyr- Pr composedof a large,slightly buccallyoff- amtos. setparastyle, pyramidal, undivided parameta- Abbreviationsof museumaccession num- coneand conical protocone; hypocone absent, bers: NTM, Northern Territory Museum; weakposterobuccal cingulum present, differ- NMV, Museumof Victoria(formerly National ingfrom Pyramlosin havinga well-developed Museumof Victoria): CPC, Commonwealth parastyleas Iarge or largerthan that of Plai sio- Palaeontological Collection (BMR); SGM, don. Upper molars more similar to P,-rantios Spencerand Gillen Museum (NTM Alice thanto Plaisiodonwith gradualprogression in Springs);VCMP, University of California molar width from Mr'ti wide interproximal Museumof Paleontology. contactbetween P3 and Mr, but differing from Pyramiosin having a more distinct,thicker SYSTEMATICS lingualcingulum, wider mouthof the lingual side of the interloph sulcus,more concave Family DiprotodontidaeGill posterior surfaceof the hypoloph, more dis- Subfamily ZygomaturinaeStirton, tinct "midlink", large metastyleon M1 and Woodburne and Plane much nanower hypoloph on M5. A conspicu- Gents Alkwertatherium gen. nov. ous obliquity of the lophs of M:'r resembles the condition of later diprotodontines,but Type species.Alkwertatherium webbi sp. Plaisiodon among the zygomaturines,has nov. similarly obliquity of the lophs.Dentary hori-

54 A new zygomalurlnegenus

/

Fig. l. Alkwerratheriumwebbi gen. et sp. nov. (holotype,SGM 888).A, lateralaspect of craniumiB, ventralaspect of cranium: C, dorsalaspect of cranium.Abbreviations: LC, lambdoidcrest; OC, occipitalcoodyle: GF, glenoid fossa;MP, massetericprocess; In, incisors;BOC, basioccipital;EG, entoglenoidswelling; PG. postglenoidprocess; NLF, nasolabialfossa: MPP, mastoid/paroccipitalprocess: MPS, maxillo-palatinesuture; FC, frontal crest;NFS, nasofrontalsuture; SC, sagittalcrest; SS, squamosalsulcus; SJS, squamosal-jugalsuture.

55 P.F.Murray

: :,-/:l -+ $\- ;!', r / \-'3

t3_ t? PP Lrl:

Fig.2. Plaisiodoncertralis Woodburne,1967 (SGM 871) for comparisonwith Alk*'ertatheriumt+ebbi. A,lateftl aspectof cranium;B, ventralaspect of cranium;C, dorsalaspect of cranium.Abbreviations not includedin Fig. l: FM. foramenmagnum; PP, paroccipitalprocess; PT, pterygoid;HTS, breachedhyporympanic sinus; PER, peiotic; PBS, paroccipital-basioccipitalsuture; FLP, foramer lacerumposterior; TW, vestigialsquamosal tympanlc wing; IPF. interpterygoidfossa; PLF, posterolateralpalatine foramina; PAL, palatine: IF, incisive foramina: SQ, squamosai:JU, jugal.

56 r\ nc$ 1\g()llllllurlnc llcnu\

zonlal ramusdccp but re'lativclythin in sc'c- Prruntictsalcrnttens( - SGM 871:palate u'ith tion, intcrior borderstraight and proportion- completeright cheekdentition. Nt,ohclos ti- / ally sintilarto Pluisiodon:differing l'romthe rurensis- SGM 891:right and left dentaries short.deep. thick-sectioned ramus with con- from craniumof NTM P8695-38.Kolopsis vex "rocker" inl'criorborder profile of Plr- torrrs- SGM 889: cranium.Supplementary .rrlio.iistrai-qht. strong. high diastemalcrests specimensreferred to arenoted in thetext and expandedinto wide,flattened surfaces anteri- figures. orly and elongateddiastema resembling Diagnosis.As for the genus. Plaisiodonproportionally but moresimilar to Type Locality. Alcoota,Flinders Quany, Pyramios in its expressioni dentaries "...WaiteFormation.4 miles [6.4 km] south- unankylosedat the symphysis as in Plaisiodon west of Alcoota Station,2. I miles [3.4 km] and in contrastto Pyramios:symphysis ex- southwestof junction of Waite and Ongeva tremely long and horizontal,extending to Creeks, Northern Territory, Australia" posteriorM,. asopposed to P,-rantiosin which (Woodburne1967b). the symphysisis short and steeplyinclined. Age.The AlcootaLocal Faunais probably Sublingualfossa long, narrow and horizontal. CheltenhamianStage equivalent or slightly similar to Plaisiodon,much longerand more older (Woodburneet al. 1985).Kolopsls sp. horizontal than in P lower "-ramio.s; incisor andZ,- gomaturti.s gi /1lare reported from Beau- crownswide. thick, and spatulate, resembling maris. Victoria which is consideredto be thoseof Pt'ramiosand the New GuineaPlio- CheltenhamianStage (Stirton et al. 1967).A cene zygomaturine,Ko lopsoide s. Kolopsisspecies (Kolopsis rotundus Plane) is Et.v-mology.Alku erta (= A/coota) means describedfrom the radiometricallydated Oti- "native shield" in EasternArrente or Iliaura bandaFormation of New Guinea.at between language.AIkw,erta is the acceptedArrente 7.6-5.7million yearsB.P. (Everendene/ a/. orthographyof Alcoota.The areaaround Al- 1964;Stirton et al.1967).That age has subse- coota Homesteadwas namedafter a rocky quentlybeen adjusted to between3.5 and2.5 landmarkresembling a shie Id. As thisobject is myBP (Pageand McDougall1972: Hock and similar in shapeto the parastyleof the upper Holm 1986).Stirton et al. (1967)consider the thirdpremolar. reference is madeto thepromi- Awe Fauna to be a relict of mid-Tertiary nenceof thecusp which appears to standup in Australianfaunas and therefore not amenable front of the tooth like a shield.The generic to anoverall stage of evolutioncorrelation. On name Alkv'ertathcriunt also emphasizesthe the basisof the presenceof Z\gomaturusal uniquenessof the Alcoota Local Faunaby Beaumaris,the Alcoota Local Fauna is provi- designatinga form with the localityname. sionallyconsidered to be olderthan the Beau- marisLocal Fauna. Alkwertathe rium we bbi n,sp Description and comparison. General (Figsl-13) comparison:The cranium ofA lk:l'ertotherium n ebbi (Fig. I ) is more similar in overallap- " Plaisiodon" v,ebbi Murray. 1989:12 pearanceto Plaisiodon centralis (Fig. 2) and (nomennudem). somemorphs of Neohelostirarensis than it is Type material. HOLOTYPE - SGM 888: to either Pyramios alcootense or Kolopsis nearlycomplete, slightly crushed and asym- torus.The Alkv'ertatheriumr.r'ebbl cranium is metricallydistorted cranium missing the inci- smaller,more elongatedand laterallycom- sors, paroccipital processesand portions of pressed,more gracile and more prognathic the basicranium.PARATYPES - SGM 883: thanany known exampleof Plaisiodoncen- associateddentaries missing third premolars tralis or Pyramios alcootense(Fig. 3). The and posteriorportion of the ascendingrami. upper incisor arcade is broaderand more SGM P892:right dentaryfragment with with procumbent(Figs 4-5; Tables l-2); the ros- completecheek dentition (P,-Ms). trum is narrower and more elongated.The Comparative material. Plaisiodon cen- palateis narrower and the cheektoothrow is rralls- SGM 887:maxillary palate; SGM 881: straighter,narrower and shorter(Fig 6). right dentary: SGM 772: right dentary frag- The gracile, elongatedAIkw'ertatherium ment;SGM 885:left maxillaryfragment with webbi craniumis proportionallydissimilar to completecheek dentition; SGM 884: castof the type Pyramios alcootense(CPC 6749), holotype (CPC 6784); SGM 871: cranium. (Fig. 6), which has a broad,relatively short

57 P.F.Murray

Tsble l. \Icr\urcnr.nr\tmnr) ol A. uppcrin.i()r\. B. lowerIncrsor. advantageof neutralizingthe considerable In.lu'lrn!,mnlJnrJr" n Jn i l(.. rnJ(-. J(nrJ,' .1,r\'n'.'n' allometricdistorlions encountered in this

A. t:PPER I\CISORS family in relationto size,growth stage.and sexualdimorphism (Table 2). Allcolar lcnSth in)phnrlrionangle .4 a.hbt P t.dtdlts A a.hhi P ..ntrolts The rostrum of Alkv,ertathe rium v'ehbi is narrower, more uniformly tubular and about t.r5 :06 llo' l0.ll t15. ll5. thesame length as P. centralis,CPC 6784, but t50 16.5 175" I50' differs in being constrictedbilaterally at the level of the infraorbital foramen.and the na- B. LOWER I\CISOR salsare narrowest, about 30 mm acrossat this Thrckness Widrh lmplanr.tionan8le point, in relationto the arcingdorsal margin of (fronral.ftom horizo.ral) themaxilla. Each nasal terminationof A. *'ebbi A ,ehbt ll.0 ?9.0 20' is gently roundedand widestthere (46 mm) in P..enltolis ll.0 12.9 P dttootense I1.0 2E.0 40' contrast to P. centrolis in which the widest point of the combinednasal bones is immedi- C. DENTARYMEASUREMENT ately anteriorto thejugal eminence.Pyramios

P.enftdlis A. A'ebh P. al.oakase nasalsare narrowestdistally and combine to form a pyriform, decurved,overhanging nasal LenerhI ro P. 80.0 85.0 67.5 I48.5 r ll.0 ll2.: process. Deplh at V, 70.0 55.5 60.0 '71.5 Depth M,lV, 68.1 80.5 Table 2. Measuremen6(mm) of lhe A, lpper. and B, lower cheek DepthaI P, 51.5 60.0 65.0 den tit ions of A llB ?/tatft.riun B €rbi compared w nh Pvonios d lcootense 315.0 276.0 ?70.0 ^nd P hniodan.?ntrolis- Lengthsymphysis t2t.0 7 0 E8.0 l. aboveinieno. border 52.0 ll.0 50.0 A. UPPERCHEEK DENTITION cranium,longrobust masseteric processes and P\tunios Pldtsto.lon lacksthe postorbitaland postsquamosalcon- L888 R888 La7? R872 L88? R887

strictionsconspicuous in A. webbi and to a P.L 18.? r9.2 t8.0 1.1.0 lesserextent P. centralis.However in certain t1.1 17.6 l7.l 17.6 t7.7 specificfeatures, principally those relating to 13.3 ::.5 - ?0.0 :3.5 13.5 the trophic complex, P-r-ramiosalcootense I9.: t8.8 - 18.2 100 :0.0 l8.l l8.2 - IE.O :0.0 :1.0 shows some striking similaritiesto Alkwer- MIL 11_l 25.2 - 25.2. :r r 26.5 tatherium- These are seen in the narrowly 21.5 - 2!.0 :l.o ?2.5 constricteddiastemal palate, strongly devel- t9.7 21.2 19.0 ?l 6 2l l

oped diastemalcrests, flared premaxillary M'L 24.7 27.l 26.0 26.7 ]].0 30.l palate, broad. spatulate lower incisors and 22.5 ,:t :3.9 22.5 25.5 25.5 r8.3 20.5 210 21.2 length of cheektooth rows. There are no spe- Koldpsis torus expressed M'L 21.7 28.5 - 12.0 cific similarities to 20.1 21.9 2',12 in the cranium and dentariesof Alkwertath- 17.0 21.0 - l9.E ertum- Cranium: The lateralprofile of thecranium A. LOWER CHEEK DENTITION

of Alkwertatherium webbi is long and rela- Prrdnios Plaisiada. tively low, but with a definite vertex, unlike R892 LE63 R883 L89l R89r R88l that of the holotype of Plaisiodon centralis P,L 13.8 - 16.5 15.5 19.5 (CPC 6784) (Fig. l). A subsequentlyrecov- w 9.5 - 11.0 10.6 13.5

ered specimenof P . centralis (SGM 87 I ) also }T. L 2r.5 l9-9 r8.3 20.6 20.3 24.0 differs from the holotype in this respect(Fig. t4.5 l4.O - t4.3 l5.Z t5.2 r5.0 l5.l t3.7 t5.O t4.4 t7.o 2). It is possiblethat the holotype represents an extreme condition for the genusPlaisio- M'L 26.2 23.9 22_l 30.5 r9.0 t'1.3 15.5 '].0 ':.t 19.0 don. The basicranialaxis of Alkwertatherium 14.8 19.8 is however,less upward-flexed relative to the M.L 28.2 25.5 25.8 28.0 27.5 t5.0 occlusalplane than either the type specimenor 20.2 r8.7 20.5 20.0 23.0 SGM 871 Plaisiodon centralis. Alkwertat- lE.l 18.3 r8.8 19.0 23.O herium webbi's cranium is approximatelythe M.L 26.2 27.5 27.4 30.0 30.0 33_2 19.5 20.5 20.1 20.4 21.0 2.4.9 same length and has the same stateof tooth 16.6 t1.A l8-2 t9.2 19.0 2t.3 wear as the P. centralis type, which has the

58 A nc\r'zvSonlllunnc 8cnu\

I

Fig. 3. Dimensionsand comparisonof the ventralaspect of A/t r,r'erratherium uebbi with Plaisiodoncentralis. A, Plaisiodoncentralis (SGM 87l): B, Alk$ertatheriums.ebbi (SGM 888). Key ro abbreviarions(see Figs l-2). plus: GlC. groovefor internalcaro(id artery: FO. foramenovale: CF. condylarforamen. Scaled to equivalentcondyloba- sal lensth- In lateralview, the profile of thediastema is contoursof therostrum and particularly in the slightlymore elongated and less curved down- basicshape of lhe nasalbones. wards along with the profile of the incisors AIkv'ertatherium differs substantiallyfrom thanin P. centralis(Fig.5). AsinP.centralis, Plaisiodon ^nd P,\ramiosin the width of the the premaxillary-max illary sutureis nearly base,of the rostrumat the nasofrontalcontact. vertical. The dorsal profile of the nasals is In A. webbi,thewidth of thisregion, 50 mm,is gently concave.Though slightly crushed,a little more than half the width of the similar- natural-looking depressionlocated about 30 sizedP laisiodon,CPC 6784, and considerably mm behindthe end of thenasals indicates that lessthan half the width of that of Plaisiodon, they were \i,eaklyelevated. A small premaxil- SGM 871. Immediatelybehind the rostrum, lary-nasalnotch appearsto havebeen present. Alk*'ertat he rium resumesits proportional The narial apertureis trapezoidal.the nasals similaritieswith CPC6784. in whichthe inter- lying almost horizontal to the frontal plane. orbital width is only slightly greaterthan that Posteriorly,the nasalbones are gabled result- of the new genus. ing in a low, oval elevationsituated immedi- The frontal region of Alkw,ertatherium re- ately anterior to the frontal depression.A/k- tains the narrow aspect of the base of the v)ertatherium and P- centralis are similar in rostrum as it ascendsinto the frontal crests. this respect, and strong resemblancesto The frontal depressionis shallow and flat Neohelosare also Dresentin the dorsolateral comparedto the deeplyclefted fossaein CPC

59 P F. M urray

6784 and SGM tl7l. Plaisiotlonccntralis. In relativelyfonger than in eitherPlaisiodon or Pyrantios dlc()otcnsethe frontal crests are Prramios.The masseteric process in A. v'ebbi large,rounded swellings in markedcontrast to is relativelydelicate and short, not extending the long narrow. crisply delineatedand more than a few millimetresbelow the oc- straight crestsof Plaisiodon and Alku,ertath- clusalline. The processes are missing from the eriunt. As in P. t'entralis. the frontal crests holotypeof P. t'entralisbut its brokensurface convergein a low sagittalcrest and the flat indicatesthat a muchmore robust process was lateralwall of the braincasedescends steeply present.The extentto which the masseteric towardsa long, narrowsquamosal sulcus. In processwas developed in P. centralisis dem- Pvramios the frontal crestsdo not converge onstratedby SGM 87l. The massetericproc- into a sagittalcrest. remainingas separate essesof Pyramios are also much longer and temporaliscrests for the length of the neuro- more robust than in Alkwertatherium. The cranium.The basicshape of the neurocranium nasolabial fossa is deeper, more inferiorly of Alkv'ertathe rirm differs linle from that of directed and more sharply delineatedin A1ft- P. centralis. exceptfor its greaterlength and wertatherium than in Plaisiodon or Pyramios, narrownessposterior to the squamosalroot, more closely resemblingthat of Neohelosti- and the extentto which it is elevatedabove the rarensis. tooth row. The latter difference however, Palate: The diastemalpalate of A lkwertath- amountsto only aboutten degrees. erium webbi is markedlyconstricted immedi- A larger discrepancyin cranial shape atelyanterior to thePr andattains a minimum betweenAIku'ertat herium webbi andPlaisio- width of only about28 mm at l5 mm anterior don centralis is the nasofrontalangle. which, to the tooth. Anterior to the Pr. at 25 mm. the as measuredat the nasofrontalsuture, regis- palate begins to flare laterally to attain a ters a differenceof abouttwenty degrees(Fig. maximumwidth of 52 mm immediatelyposte- 6). As in P. centralisthe parietalsof Alkwer- rior to the Ii alveoli. ln P. centralis,the dias- tatherium are long and narrow and the tema is moderatelynarrow, relatively more squamosal lamina is broad. The constrictedthan in most Neohelostirarensis postsquamosal arch in Alkv,ertat herium is aod Kolopsistorus craniain which the maxi- considerablylonger and more deeply concave mum interincisivalwidth is approximatelythe thanin comparableP. t'entralisspecimens. sameas the interdiastemalminimum (Figs5- The zygomatic arch of Alkv,ertathe r ium 6l Tablesl-2). In conjunctionwith theanteri- webbi is deep and long. The contourof the orly expandedpremaxillary palate, the incisor undistortedleft zygomaticarch is flatter than alveoli openmore laterallythan ventrally and in P. centralis,closely resembling the condi- theimplantation angles of theincisor roots are tion in Neohelos tirarensis (Fig. 6). The closer to horizontal.A more graphic expres- squamosalprocess is long and sustainsa con- sionof thiscomplex is seenin the positionof siderablewidth, extendinganteriorly to lie the Ir alveolusimmediately in line with 12in beneaththe orbit. The squamosojugalsuture Plai siodonc e ntra lis,N eo he lo s tirarens is and alsocontributes to theposterior orbital margin Kolopsis /oras in contrastto the laterally off- in Pyramios.Both CPC 6784 and SGM 871 set Ir alveoli in Alkwertatherizm.In the mor- have much shorter squamosalprocesses that phology of the diastemal and premaxillary terminate 30 mm or more posterior to the palate,Alkwertatherium is a bit different from distal orbital margin. Consequently,in A/,t- zygomaturines,more closely resemblingthe h,ertatherium,the zygomaticarch is at leastas nototherePyramios alcootense.However, in deep anteriorly, immediately posteriorto the Pyramios, the interincisival fossa is a deep, orbit, as it is immediately anterior to the gle- spoon-shapeddepression. ln Alkwertat h- noid fossa. erium, the interincisive region is a shallow, ln P . centralis andPyramios alcootense,Ihe wide concavesurface. zygomaticarch is narroweranteriorly than it is Although no upperincisors have been iden- posteriorly. Although the squamosalprocess tified for the species,the implantationangles does not extend as far anteriorly in Neohelos of theteeth indicate that the crownswere more as in Alkwertatherium, the anterior depth of procumbent than in P. centralis, Neohelos the arch is approximately the same as the tirarensis or Kolopsis torus. The diastemal posteriordepth, and the squamosalprocess is palateis alsorelatively longer than in P. cen-

60 A new zygomalurinc genus

c

Fig. 4. Comparison of the anrerior palatal and dertary diastemal regions in Altwertatherium webbi and Plaisiodon celtralis. A, vental aspect of nnte;or palatal region of P. centralis (SGM 871); B, ventnl asPectof symphysial rcgion of the dentary of P. ce ralisi C, ventral a;pect of anlerior palatal rcgion of A. webbi (SGM 88t); D, ventral aspect of the symphysial region of the dentary of A. weDbi.Not to scale'

6l t

P.F. Murray

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At EREST SUBORB I It sfi8tF s0IJl||osIl,slJtcus Fig. 5. Restorationsof Alkwertatherium webbi get et. sp. nov. Opposite, restorativesketch of lateral aspectof skull, scale 50mm; A-C, diagrammatic restorationsof cranium.

62 A new zygomaturincgenus

trdlis.The incisor implantation in Pyramiosis andAlkwertatherium is the sharedfeature of more similar to that of Alkwertatherium,thin postglenoidprocesses. thoughalso less procumbent. The occipital regionof Alkwertatheriumis The maxillary palaleof Alkwertatheriumis conspicuouslynarrower than in Plaisiodon, slightly narrowerthan in P. centralis,made Pyramiosand Kolopsis, but is similarin width less visually apparentperhaps, by the nar- though lower than in someNeohelos speci- rowerand shorter cheek tooth rows (Figs 1-3, mens(eg. NTM P8695-38).The occipital 6). The palateis otherwisesimilar to thatof condyles,which are the most posterior struc- Plaisiodon,particularly in the shapeof the turesof thecranium, are comparatively small, cheektootharcade and moderateextent of transverselyelongated and narrow, in contrast posteriordivergence. Pyramios alcootense to the large, widely separatedoccipital hasa relativelybroader, shorter, more domed condylesof Pyramios.The condyles are sepa- palatewith more posteriorlydivergent tooth rated ventrally by a deep,V-shaped inter- rows(Fig. 6). T.bf.3. Cr.nilf mc.sur.m.Dls (mm) ot /altr.r.artr.riLn *cbbi ltta) com- Cranial base:The internalnares and in- parcd*irh Ptdisodon.. ^calis /6a4.871).nd Prranios olcookns. \a't2\. terpterygoidfossa appear to be shallowerin Alkwertatheriuzr than in P. centralis.in which Crrnirl |[ci!uramants an exceptionallydeep, cavernous excavation L€ngth.lI to occipirrlcondylc 415.0 - 520.0 L.n8th'lamMoid crcst to outcr lr - 525.0 is a conspicuousfeature of SGM 871. The L.ngth-zygomatic.rch 204.0 t95.0 243.0 cranialbase is poorly preserved in Alkwertath- Lcnrth-t.mponl is foss. 122.0 125.0 155.0 L.n8th-dilskmal prlatc 73.0 52.O 7t.0 erium.Sufficient surface contour is presentto IrrSrh-uppcr ch..k toolh row t22.5 120.0 - 149.0 L!ngth-int.rplcrygoid fos - 138.0 definethe extremely wide, obliquely oriented Lcngth-massctcricproccss 65.2 - l{x.5 glenoid fossae, ventrolaterallydirected LensthlamMoid crcstto nrslls 395.0 HciShFbasioccipilrl-sa8ilhl crcs ?0.0 122.0 r 2r.0 pterygoidfossae and low, wide, but appar- Dcpth.v.ncr to ptcrySoid 145.0 - 175.0 ently thin, delicate postglenoidprocesses. Dcplh-post.riorzygomrlic .r! h 50.0 52.1 t4.5 D.pth.rntcriorzy8omrticarch 50.0 - 56.6 SGM 871, Plaisiodon centralis,preserves Distancc-molarsabovc mas*Icric pr <5.0 - 35.0 manybasicranial features of thegenus and the D.oth-marilla rbov€ P' 57.0 54.0 D.pth-from M" to lop of frontal | 10.0 l(X.o l15.0 majorityof thoseportions visible in .\lkwer- Widlh-occrput 98.0 - 130.0 widrh.acrcssmd Dorntoforbrts 95.0 l r0.0 140.0 tatheriumappear to correspondclosely to it. Width-frontalabovc orbits 5t.0 t8.0 t21.o ln Pyramios,exceptionally wide glenoidfos- Widlh.cranrumal fronlrl conv.rg. 60.0 61.0 60.0 widrh.PMX ,cross nlrr.l apcnurc 69.0 60.0 92.O saeare oriented at right anglesto theaxis of widlh-zySomaio sagirralcr.sr 120.0 $-0 t67.0 the cranium.There is, moreovera highlydis- Widrh-antcriorto lambdoidcrcn 102.0 - | 90.0 widlh-premarillrc bcrw€cnIr 4l.0 26.0 30.0 tinctive lateral profile of the glenoidnotch widrh-pafarcanrcrior to P\ 21.8 39.0 3't.1 54.5 whichis narrowlyV-shaped, as opposed to the widrh'narillrc lrbid sidcsPr 6?.0 72.O 75.5 91.4 widrh-palat€lingu.l M" 52.0 62.0 - 64.0 broadlyU-shaped profile of A//

63 P.F.Munay condylarnotch. The foramenmagnum is trans- proportionallysmall occipitalsurface was versely wide and distinctly oval in shape. deeplyexcavated for theattachment of nuchal Immediatelyabove the foramenmagnum, the musculature. Upper cheekdentition: The Pr is a short, Trbf. 4. Summary of c har^cr.ts ol Alkv athetiun||.rbigcn..tsp. nov.atrd t.y to cornparisons shown in Fi8urcs 6. L l l. ll. broadlytrilobate tooth composed of a large, high, transverselyoval-sectioned parastyle Sunnrrt of chrrrcteristica ot A ltv. rloth.rium t.b bi with a slightbuccal offset of theapex, a high, 1.0Dorsum €rrnii pyramidal,undivided parametaconeand a l.l hi8hslecp frontal robust,conical but lower protocone 1.2consrricr.d pr€orbilally slightly 1.3conslrictcd poslsquarnosally (Figs7-9; Table4). The hypoconeis absent. 1.4upwqrd basicranial ncxion 1.5high, thin nanow frontslcrcsts The apexof the parastyleis setcloser to the 1.6antcriorly .rpandcd nasrls parametaconethan in Plaisiodon, but closely 1.7trapczoidal narial ap.nur€ l.E low. narrowocciput resemblesit proportionally. The buccal 1.9\ridc, oval foramcnmaSnum grooveseparating the parastyle from thepar- 2.0 ZySomalicofacial ametaconeis deeper,longer and morecleft- 2.1 lon8,dccp squamosal proccss ofzygomatic arch 2.2 zygomaticarch flartcnedin larcralasp€cr like than in any other zygomaturinegenus. 2.3 zySomalicarch dc.p anteriorly 2.4 shon,dclicarc mass.r.ric p.occsscs The anterolingualbasin is deeper,more con- 2.5 d.cp. wcll-dcfincdnasolabial fossa fined and formsa moredefinitive horizontal 2.6high, distincr sinuous f.cialcrcsr 2.? lon8, pcll dcfincdbuccinaror sulcus shelf than in Neohelosor Plaisiodon.The 2.8lon8 sq'ramosals lcus anterolingualcingulum is shortbut distinct, 2.9 shallowlyarcin8 diasrcmal profilc commencingfrom themid-lingual base of the 1.0 Palatc 3.1 nal, narrowand long parastyleto ascendthe anterolingual aspect of 3.2 ncrrly straightarcad€s. sliShr postcrior divcrgcnce protocone, 3.3diastemal palat. markcdlyconslrictcd the formingnear its base,a minute 3.4 narin8 prcmaxillarypalarc. shallow IC fossa protostyle.A disti4ctsecondary basin, slightly 3.5 Ir llteral to 11,alv.oli oFn mtcrclat.Ellly elevatedabove the parastylarbasin, lies im- .1.0Basis cranii 4.I Narrow,shrllow intcrptcrySoidfossa mediatelyanterior to the baseof the proto- 4.2 small.shallow pterygoid fossac cone.This preprotoconal basin is incipientin 4.3 widc obliqu. glenoidfossac 4.4 d..p. V'shap€dinrcrcondylar notch Neohelos,distinct but smallin Kolopsisand 5.0 Upp.. third (p.mancnr) premola. variablyexpressed in Plaisiodon,in whichits 5.1larS€ paraslylc 5-2 hypoconcabscnt presenceis associatedwith a reductionof the 5.3 undividcdparamctacon€ parastylarbasin. A protostyleis presentin 5.4buccal cin8ulum prcscnl 5.5hrth clcarly.xprcsscdm.sosltl. someNeohelos and Kolopsis specimens, but 5.6 wid€.d..p postcriorfossa. distinctivcly *om appearsto beabsent in Plaisiodon.The proto- 6.0 Upp.r molar! 6.1 wcakparastylc, strong postparaconal crcsr coneis large,though slightly smaller than the 6-2 strong,shon. round.d linSullcinSulum parametaconeand higher, relative to thepar- 6.3 smallprotostylc M1 6.4 Mr in lin€ with M' linSullly ametaconelhan in Neohelos,Plaisiodon and 6.5 Pr wid€ly contacrsMr intcQroximllly Kolopsis. 6-6 m€lalophssharply rcduccd M'r 6.7 mcBstylcslow on PMC, slrcn8on M' In section,the protoconeof Alkwertath- 6.8 labialcingulac shon, thick. risingcorfincd to MV erium approximatesa rounded trapezoidal 7.0 D.n6ry 7.1 body dccp,tapcrs antcriorly shapecompared to thedistinctly rounded sec- ?.2 dirslcrnalc.csls. tonS high, artcriorly cxpandcd tionofthe cusp it PlaisiodonandPyramios. A 7.1 nc.r horizont symphysis,termindcs b.hind M, 7.4 shon, shallowdiSasrric fossa short,thick postprotocristaascends the cusp 7.5 Scnialpits in vcnrralbord€r ofsynphysis nearvertically, becoming indistinct immedi- atelyshort ofthe lingual portion ofthe postcin- E.l widc,lhickcrowns 8.2 ncarly horizontalimplanlation gulum.The postcingulumis well-developed 8.3 cnamclon all surfaccs 8.4 thick ccmentumbasc nis.d abov. cnah.l lingually, becomingindistinct interproxi- 9.0 Low.r third prcmolar mally and distobuccally.The posteriorsur- 9.1 small rclariveto nolars facesof the parametaconeand protoconeare 9.2 narrow,ovalcrown 9.3 w€akbuccll cingulumprcscnt steepand delineatethe sidesof a deep,oval 9.4largc centralcuspid, shon postcriormoicly distalbasin, exaggerated to someextent per- 10.0Lowcr molars wear. l0.l paralophidcr.st wcat, prorolophidfac€ srccp haps,by Althoughthere is ampleroom lO.2 protolophidsM:_r hiSh rclativ. ro hypolophids onthe posterolingual shelf for a hypocone,not lO.3 midvall.ys V-shapcd l0-4 linSualoffsct of Pr-M: somuch as athickening ofthe cingulum can be 10.5wcaL, shan prccidSulid foundto betraya phenotypicexpression of the 10.6rcduccd sizc of MJ structure.

64 A new zySomatunneScnus

lr.2l

mid- to Fig. 6. Characterdistribution compalison of the cfanium of Alkwertatherium t)ebbi rtith crania of the lalger B' taie Miocene diprotodontid genera.A, Plaisiodon cerrrolir, (holotyPecPc 67E4, restoredfrom cast sGM 884); Neohelos tirarinsis (NTM FS695-38); C, Alkwertatherium webbi, (SGM EE8) restored; D' Pyramios alcootense (holotype cranium CiC 6749, paltially restofed) (after Woodburne 1967); E, dorsal aspectof snout of P. centralis SGM 884); F, A. w;bbit G, N. tirarensis: H, P. alcootense(after Woodbume 1967); I, ventral aspectof ifro. (restored) (after i. centralis""rt SGM 8?l (rcstored); J, A. webbi (restored); K, N. rirarezsis; L, P. alcootense, woodbume 1967).Numerical referencesto charactersare given in Tabl€ 4. Correspondingnumbers indicate a strong similarity; brackers indicate a variable condition or lesa distinct, though simila! features. Abbreviations: FRC' DC, irr.i"i Jr"rt; FAc, facial cresti BF, buccinator fossa; MP, masseteric process; ICF, Interincisive fossa: diastemal constriction; NLF, nasolabial fossa.

65 P.F. Murray

PS PMC

B a D

rrlttl cm

Fig. 7. Upper cheek denlition of A/klter tatherium webbi. (A-C) comparisonof Pt-Ml of Plaisiodon centralis with (D\ Alkwertatheriumwebbi. A-C, range of morphologicalvarialton in cusp morphologyof Plaisiodon centralis:C, "hypoconelessvariant" which has a thickeningin the lingual cingulum;in B, the plrastyle is exceptionallywom. Noie the narrow labiad interproximalcontact of the Pr with Mr in Plaisiodon: E, upper cheel toorh row of Alkwertatheriumwebbi; F,lower cheektooth row of Alkwerratheriumwebbi. Abbreviati;ns: PS, parastylelpMC, parametacone;PRc, protoconelHYC, hypocone;PPC, postparaconalcrest: MTS, metastyle;BC, buccalcingulum; ML, midlink; PAC, paracone;MS, mesostyle;MEC, metacone;MED, meraconid;END, entoconid;ACD, anrenor cingulid; PRD, protoconid;HYD, hypoconid;BCD, buccal cingulid; PCD, posrcingulid;MLD, metalophidor cristid obliqua.

66 A new zygomatunnegenus

Apparently "hypoconeless"variants of cies, and indeedamong zygomaturinesin Neohelosusually show a thickeningof the general.There are two otherconsistent differ- cingulumin theposition of thehypocone. The encesin the morphologyof the arcade:in posteriorportion of the toothis moresimilar to Alkv,ertatherium the interproximalcontact thatof Pyramios,both structurally and thegoti- betweenthe Pr andM2 is wide andcentered, cally, exceptthat the posterolingualportion of andthe M5 is aligned with the Ma on the lingual the postcingulumis more generousin Alkwer- side.In P/aisiodoncentralis the Pj is offset tatherium. The low, interproximallyindistinct buccallyleaving a large V-shapedgap be- postcingulumcommences on the distobuccal tweenthe teethon the lingualside, and the M5 corner of the parametaconeafter which it is offsetlingually creating a step-likecontour ascendsthe posterolabialmargin ofthe cuspin of theocclusal profile on thelingual side. The the form of a steep,thick, slightly irregular primary differencesin molar morphology postparametacrista,nanowing gradually as it betweenAlkwertatherium and P . centralisarc approachesthe apex of the cusp. The par- in thedegree of developmentin thebuccal and ametaconeis steepand triangular in section lingualcingulae and crests related to thepos- with theanterior face presenting a transversely teriormargins of the lophs. flattened,apically taperingsurface. A distinct The secondmolar in Alkwertatheriumis cuspuleis presentimmediately lateral to and distinctivein havinga wider mid-valleybu- below the apex of the parametacone.This ccally and in possessinga well-developed mesostyle(possibly homologouswith stylar buccalcingulum, continuing anteriorly into a cusp C of primitive vombatiform molars) is short postparaconalcrest. The parastyleis continuouswith the posterobuccalcingulum, poorly developedon all molars.The molar which in Alkwertatheriumdefines a distinct, crown morphologyis otherwisevery similar oval fossetteon the distobuccalflank of the in the two speciesand the descriminationof parameracone. isolatedmolars is complicatedby a high de- The P3of SGM 872,Pyramios alcootense, is greeof morphologicalvariability. similar to A/kpertatherium in the shapeof the The M2 of Alkwertatheriumhas a weakly parametaconeand the degreeof development developedparastyle, but a distinct, short, of the postparametacrista.A posterobuccal postparastylarcrest. A short postparaconal cingulum is presentbut does not establisha crestascends the base.ofthe paraconeand is fossette.The mesostyleis largerbut lessdis- continuouswith a thick buccalcingulum tinctly defined.There is a faint postparastylar whichspans the mouth of theinterloph valley sulcus separatinga small parastylefrom the to the base of the hypocone,where it is parametaconeand definingthe anteriorextent transectedby a faint sulcus.The cingulum of the mesostyle.None of the Pyrazios third bulgesslightly as a presumptivemesostyle. premolars show a tendencyto develop more The protolophis slightly wider and more than an incipient parastyle,although the ante- massivethan the metaloph.A low, short, rior crown baseis moregenerous than in other midlink is presentand a second,faint crest nototheriines,being more comparableto that transectsthe interlophvalley just lingual to of zygomaturines,and a faint buccal crease, the longitudinalmidline of the crown. The delineatingthe base ofthe parastyle,is present postcingulumis wideand rounded. Buccally it on some specimens.The large size of the Pl ascendsthe metacone as a distinctpostmetac- and the incipient parastyledevelopment gives rista,at thebase of whichis developeda low, the impression that Pyramios is structurally indistinctmetastyle. Lingually, the postcin- intermediateto nototheriines(Diprotodonti- gulum terminatesnear the baseof the hy- nae) and zygomaturines. poconeand is separatedby the lingual sideof The upper molars of Alkwertatherium,in the metalophfrom a shortlingual cingulum comparison with similar-sized CPC 6748, that flares out aroundthe mouth of the inter- Plaisiodon centralis, are smaller relative to loph sulcus.At its anteriorextreme, a small the splanchnocranium, particularly M4-5, protostyleis present.The anterior cingulum is which do not abruptly widen behind the third wide linguallyand slightlythickened on the molar as in P. centralis.This marked transi- midline. tion in the molar gradientin P. centralis is a TheM3 is largerthan the M2 with a distinctly distinctive and consistent feature of the spe- widerlingual interloph sulcus and correspond-

6'1 v

P.F. Munay

aa a ,' /a .a a a/a

/a P3 LXW M2 LXAW aa a M2 LXPWt aa . t'j.'. ^ 8t ' r' l or- a a+ al L.' a I a,-

"lI

T E M3 LXPT{

t l1 a I I'l a a z

,1

I 1l M5 LXPW I lo llt ,

vitrDTH n lr/r

Fig. E. Scatterdiagram of lhe dimensions of upper cheek teeth compa ng A/kwertatherium (triangles) with plaisio- don (dots) ar:.d.Pyramios (squares);data from Woodbume (196?a) with the addition of new ssecimenslisted under ComParativeMaterial of A. webbi. Note the relatively clear separationof genera with the premolar compar€dto the large degreeof overlap with the molar dimeosiotrs.Alkwertatherium webbi aligns with Pyramios alcooiense, Scale is in millimetres, X axis = width, Y axis = length; regressionswere not calculated due to to small sample size.

68 A ncw zygomalurine gcnus ingly longerlingual cingulum. The protostyle alcootense.Although the dentary was found in is reducedto a low bulge. The "midlink" associationwith the craniumof Alkwertath- (whichdoes not appear to behomologous with erium, which was isolatedfrom other fossil a cristaobliqua), is a teardrop-shapedenamel concentrations,direct association of fossilsin bossdeveloped on the baseof the paraconal the Alcootaassemblage is no guaranteethat sideof the protoloph.The interlophvalley is the remainsrepresent a single individual. sinuous,deep and narrow. Both moietiesare approximatelyequal-sized. The postmetac- rista is indistinct.The postcingulumis re- ducedlingually but remainswide and low on the posterobuccalcorner of the metaloph, wherea low metastyleis present. The Ma is larger than M3 and is distin- guishedby its narrowermetaloph, wide pro- tolophand buccally expanded paracone, wider midvalley,less well-developed postcingulum and lessdistinct though broader "midlink". The M5closely resembles Ma in sizeand shape, but the metalophis relativelynarrower, the postcingulumis confinedto theposterobuccal side of the crown, the midlink is reducedto a faint swelling and the buccalcingulum is absent. Although the molarsare indeed distinctive, thereare no individualcharacters of thecrown morphologythat can invariably separate them from Plaisiodon centralis or from Pyramios alcootense.Except for their smaller size, slightlygreater apparent obliquity of thelophs of M2'3and the differencein the molar gradi- ent, the degreeof variabilityin Plaisiodon crownmorphology, and indeed, even the dif- "F ferencesbetween the right and left sidesof the Alkwertatheriumcheek dentition, render the distinctionof isolatedteeth somewhat dubi- ous,given that the size rangeof Alkwertath- erium ts unknown.Worn molars,particularly "w M2,have a distinctivethegotic character which Fig. 9. Comparisons of the upper cheek dentitions of with larger mid- to late Miocen€ diprotodontid genera with will be discussedin conjunction the Alkwerthatherium webbi. A, Neohelos tirdrensis (N"IM lowers.The molargradient, dimensions, and P8690) "hypoconeless variant"; R, Pyramios al- the low dispositionof the metasyleon M2 of cootense (SGM [R]872); C, Alkwertathefiurn u'ebbi Alkwertatheriunmore closely resembles Pyr- (SGM [R]888); D, Plaisiodon certralis (SGM [R]887); amios, but the proportionalwidths of protol- E, Plaisiodon cenrralis (SGM 885); F, lingual occlusal profie Neohelos (NTM P8690) compared metalophfor molar,the occlusal of tirarcnesis oph to each ,tith G, Pyramios a/coolezse(SGM [R1872):H, Alkwer- contours,particularly M4r, with a markedre- tatherium webbi (SGM 888): I, Plaisiodon centralis ductionof the width of themetaloph, are more .(SGM [RlEE7)l I' Plaisod.ol ceatralis (SGM 885). similarto Plaisiodon. Abbreviatio-ns:MS, mcsostyle; PS, parastyle; PR, protocone: MT, metastyle; PC; postcingulum; HY, Dentary: The associateddentary of A/k- hypocone;BC, buccal cingulum; ML, midlinki AC, wertatheriumsuperficially resembles that of anterior cingulum; LC, lingual cingulum; ME, Palorchestesin having an extremely long, metacone; PA, paracone.Nurnerical references to the kangaroo-like,horizontally disposedsym- charactersare listed in Table 4. The lingual profiles of physis,containing broad, spatulate, procum- the molars show the st€plik€ offset of Ms in Plaisiodon, in comparison to the oth€r gencra. There is a tcndency bentlower incisors(Figs l0-l l). The molars towards this condition in someNeohelos and some Pyr- aretypical of diprotodontidsand most closely amios (F, G); but the trait is appa!€ntly not present in resemblethose of the nototheriine.Pyramios Albeertatherium vtebbi.

69 P.F. Murray

However,there are occasionallyisolated To the extent that the somewhatdistorted pocketsin whichpartially articulated material lower toothrows can be physicallyoccluded is recovered.A / kv'ertat heriunt occurred in one with theuppers, they match closely in termsof of thesesituations. The dentarylay slightly occlusalsurface angles of the similarly worn aboveand at the posteriorend of thecranium lophsand lophids,the distancebetween them, with thedentitions of bothfacing upwards. As and in terms of the individual variations of the excavationaround the dentaryprogressed, each tooth in the degreeof wear, pattern of the cranialbase of SGM P888 was partially attrition and thegoticconespondence. exposed immediately beneath the posterior The dimensions of the individual molar end of the inferior border of the dentary,the teeth are also within the expectedtolerances anteriorends of thejaws andcranium pointing for the sameindividual which rangesnormally away from one another,as thoughthe dentary between0.85 and 1.0. The lengthof the right had been dislodsedbackward from the skull. uppersfrom front to backare: 23.3, 27.1. 28.7,

Fig. 10. Dentaryof Alkwertatheriumwebbi gen. et sp.nov. (SGM 883,paratype). A, occlusalaspect; B, latemlaspect. Note the extremeprocumbency of the lower incisors,anteriorly tapering horizontal ramus, high long diast€malcrests and their bony expansions,long deep,sublingual fossa and short, weak transversetorus penetratedby genial pits. The symphysis,which is unfused,extends to the posteriormoiety of M,. Abbreviations:SLF, sublingualfossa; DC, diastemalcrest; AF, anreriorlyflattened surfaces of diastemalcrests; GP, geoial piti TT, transversetorus; PS, posralveolarshelf; PA, postalveolarprocess; MF, mandibular foramen; PME, posterior massetericeminence; FM, mental foramen.

70 A new zygomatunne genus

.1 ,l t_..*> (

(-L-':F-\'^/'.1Y \ := ll 1.?E,4 Fig. 11. Comparison of the dentariesof larger mid- to late Miocene diprotodontids with Alkwertatherium webbi. A, Plaisiodon cerrrclis (SGM 881); B, medial aspect (left) and occlusal aspect (right) of Neohelos tirarersis (CPC 2253O):C, Alkwertatherium webbi (paratypeSGM 883)',D, Pyramios alcootente, (SGM 891). Numerical character definitions are given iu Table 4. Abbreviations:DC, diastemalcrest; DF, digastric fossa;DS, dentarysymphysis; GP, genial pit.

7l P.F. Munay

27.7. The right lowers are 18.3,22.1, 25.8, physisand Plaisiodon,in which they aresitu- 27.4;resulting in a proportionalcongruence of ated on the ventral surface. ln Alkv'ertath- 0.87. The distancebetween the lophs and erium, the genial pits penetratethe ventral lophidsfor eachoccluding pair areas closely surfaceof the symphysis,but extendonto the matched as can be determinedby simple posteriorsurface as well. measurements.The congruenceof the lower Lower dentition: The lower incisors are incisorswith the upperincisor sockets appears extremely wide, thick, spatulatehorizontally to be close. Presumablythe low angulation implanted teeth that repose with the lateral and buccaloffset of the emptyupper incisor margin of the crown at aboutten degreesfrom socketsis disposedto the accomodationof the horizontal(Figs 5, l0-11; Table l). Plaisio- broad,procumbent lower incisors. don centralis incisors are only moderately The dentary of Alkwerratherium differs spatulate,with the crowns orientedabout 55 from that of the nototheriine Pyramios al- degreesfrom horizontalin frontal aspect,and cootensein having a nearly straightinferior lying at about 35 degreesfrom horizontalin border of the horizontal ramus,an anteriorly lateral aspect, being considerably less tapering and more slender as opposedto a procumbent than in Alkwertatherium. The more massive, anteriorly deep, posteriorly lower incisor implantation of Pyramios is tapering body; much shorter and vertically nearly horizontal,as in Alkwertutherium,bvt narrower, more horizontal diastemalportion, the symphysial angle is substantiallymore and a much longer and more horizontallydis- steeplyinclined and extendsfar deeperbelow posedsymphysis that extendsto behindM, as the alveoli. The frontal implantationangle of opposed to behind the Pr. In Pyramios al- the incisor crowns in Pyramios is acute.The cootense,the dorsalcontour of the symphysis intemal angle of the paired incisors of Pyr- (sublingualsulcus) is nearlyvertical in SGM amios is V-shapedat between80 and 85 de- P891. Ventrally, in Pyramios,a distinct men- grees.In Alkwertatheriumthe internal angle tal eminenceis developedimmediately below (dorsal surfaces)of the paired incisorspres- the incisoralveoli. This is alsoevident in the ents an obtuse surfaceof approximately120 paratypeUCMP 69784.The dentaryis similar degrees. to, though much smaller than any mature The enamel extends entirely around the specimen of Plaisiodon centralis, differing crown of the lower incisors of Alkwertath- principally from that genus in the more erium, as in Pyramios,in contrastto its being procumbent incisor alveolus and relatively confinedto a narrowstrips on eitherside ofthe longer diastemalportion of thejaw. The sym- dorsal surface of the crown as in the physial outline is more similar to Plaisiodon zygomaturinePlaisiodon centralis. The se- than it is to Pyramios. verely worn tips of the crownsof Alkwertath- The horizontalramus is relativelydeeper in erium lower incisors precludesa description proportion to length than in Plaisiodon,but it of their original shape,but there can be little is also proponionally less thick in section doubt that they were very similar to thoseof below the molar alveoli. The diastemalcrests Pyramiosalcootense. The transversewidth of of Alkwertatherirm are much thicker, higher the crown is at least28 mm and about 10 mm and less sinuousthan in P. centralis. Anteri- thick medially,near the base of thecrown. The orly, the diastemal crests become laterally crownsare thicker medially,tapering towards expanded, flat surfacesparalleling the sub- the externalmargins. The cementumis raised horizontally implanted incisor crown bases. abovethe enamelon the dorsalsurfaces form- The dia$temalcrests of Pyramiosare similar, ing a continuationwith the broad,bony dias- though more arched dorsally, much shorter temal platform. and less expandedanteriorly than in Alkwer- The P, of the paratype dentary SGM P883 tatherium. Internally, the digastric sulcus is was broken off, then placed in a small box slightly deeper than in either Pyramios or which was subsequentlymislaid during trans- Plaisiodon and extends further anteriorly than portation of the specimensfrom the field. It in the latter but not as far anteriorly as in the wasexceptionally small relative to the molars. former genus.The positionof the genialpits is Fortunatelyit is well preservedon SGM P892, also intermediate betweenPyrarnios, in which a right dentary fragment of Alkwertatherium they are on the posterior surface of the sym- (Figs 12-13).The P, has a small, oval crown

1a A new zygomaturinegenus

P3 LXW M2 LXPW a a a M2 LXAW a ao aa a a f. a a O a t alo o' ll r: r,rf I

a M3 LXAW aa M3 LXPW M4 LXAW T I ta E t ta lt aa ll aa loot' fo lao H a fh t z

a a I I M5 LXPWa a a a a a a a

YllI f>TH ryIryI

Fig. 12. Scatter diagram of the dimensions of lower cheek teeth of Albeertatherium webbi (triangles), plaisiodon centralis (dots) al0.dPyramios alcootense(squares), As with the upper dentitions, Alkwertatheriui is more closely aligned with Pyramios alcootense. Data from Woodbume (1967a) and new specimens given in materials list, Regressionswere not calculated due to small samvleof Alkwertatherium.

'13 P.F. Murray composedof a large central cuspid and a mediancristid which extends back to theinter- proximalcontact with M, and is conjoinedby a weak buccal and a more distinct lingual cingulum. The buccal cingulum trends obliquely towards the anterior edge of the posteriorroot, then faintly ascendsthe flank of the central cuspid to define a shallow,U- shapedfossa. The posterolingualcingulum surroundsa kidney-shapedbasin. Structurally the P, crown is more similar to that of a zygomaturine(e.g. Plaisiodon centralis) and differs from thatof Pyramiosin being smaller, relatively narrower, shorter posterior to the central cuspid, in possessinga buccal cin- gulum and in lacking a clearly definedtrans- versecrest from the central cuspid. The lower molars are similar to those of Pyramios alcootense(Fig. l3). Alkv,ertath- erium has a distinct but low paralophidcrest and a steep,high protolophidon the M". This high protolophidrelates thegotically io the correspondinglylow protoloph of the upper and the deeply wom posteriorfossa of the Pr and anteriorcingulum of Mr. With the excep- tion of M/ the protolophidsare wider thanthe hypolophids.The M, is relatively small, and the gradientis that of a gradual front to back increasein size.The lophids of M,., are more obliquelyoriented than the othermolars. The protolophidof M, is alsomuch higherthan the hypolophid.The interlophidvalleys of the first two molars are more sinuousand steeply Fig. 13.Comparison of the lower cheekdentitions of the V-shapedthan in the last two. A short,low larger mid- to lare Miocenediprotodontid genera with precingulumis presenton the lingualside of Alkwertatheriumwebbi. A, Kolopsistorus (SGM E93); ',eebbi(paratype protolophid. B, Albrenathe um SGM E92); C, Pyr- the anterior base of the Its ex- omios alcootense(SGM 891); D, Plaisiodoncentalis pression diminishes gradually from front to (SGM 881); E, labial aspectof dentition of Kolopsis back. A low cristid obliqua is presenton all rorrs (SGM 893);F, Alkwertatheriumwebbi (SGM 892); molars, extending from the hypoconid down G, Pyramios alcoorense(SGM 891): H, Plaisiodon cen- (SGM the anteriorface of the hypolophidto the base rralis 881). Numerical referencesto character definitionsare given in Table 4. Abbreviations:END, of the posteriorface of the protolophidin the entoconid;MED, metaconid;HYD, hypoconid;PRD, approximatelongitudinal midline of thetooth. protoconid;CO, cristidobliqua; PLC, paralophidcrest; Weak cingulaeoccur in the buccaland lingual BC; posterobuccalcingulid; AC, anterobuccalcingulid; mouths of the interloph sulcus.The postcin- MV, midvalley (U-shaped ir Rolopsis toras, as consid- ered typical of zygomaturines):HLD, hypolophid, PLD, gulum is thick, relativelydeep and rounded.It protolophid. is elevated slightly near the longitudinal midline of the tooth,commencing on the labial Analysisof characters.The morphological side proximally and swinging gradually to- descriptionofA lkwertatheriumwebbi broadly ward the lingual side distally. samplescomparable morphological features, Etymology. The species designation of whichonly a few arespecifically useful in "webbi" is made in gratitude to Thomas and diprotodontidsystematics (Tables 3,5; Figs6, Wendy Webb of Alcoota Station, Northern 8, 11, l3). Many importantfeatures (suture Territory, for their valuedsupport in palaeon- configurations,upper incisor morphology tolosical researchat Alcoota. etc.)could not be considereddue to thepoor

'74 A new zygomalu ne genus stateof preservationof thespecimen. Though teriorly divergentmolar arcades.However, inconrplete.this constellation of charactersis the IIs in Euryzygomaand Diprotodon arein adequateto formulatean hypothesisof the line with the I:'s and the zygomaticprocesses approximatesystematic position of Alku,er- areflat-sided. tatherium. The lower incisormorphology, relatively Basedprimarily upon the work of Stirtoner wide thoughV- shapedinterlophid valleys, al. (1967) and subsequentlyArcher and weakcristid obliquae and comparatively low Bartholomai( 1978). Aplin andArcher ( 1987), the Diprotodontidaecan be dividedinto two Tablc 5. Drsrributionofcha.acl.rs in Gp..scntarivesof four diprolodonroid subfamilies,the Zygomaturinaeand the No- fanilics. I, wyny,ldiid lMuotnutu rt//idnjt): 2, prlorchcstid' (Nsapakoldia l , d i, p^lotth.srin (P.opolotch.st. r) . ramplcsrcpEs.nt thc totheriinae or Diprotodontinae.Recent revi- ourgroupi 4, diprorodontinc(Pyanios alcoot.nt.\i 5, zygomaturinc(A/tp.r- sionshave sunk tath.riun w.bbi\', 6, z\!go''l,a'l!i^. lN.ohclos tiatsnrir)i 7, zy8omrturinc the Nototheriinae.Consensus (Plaisiodo, .. nltalis\:8, zyEon^r\tin \Kotopsistotqr). Symttols:o=ab6€nt; purports that the two groups of diprotodon- +=pr€s€nt:t:mor! or lcsspr.scntt -=not obs€rvedi?=unsurc of homoloSy: AP=apomoAh. tids, the Zygomaturinae,with a well-devel- PL=plesiomorphy. opedparastyle on theupper third premolarand I 2 3 4 5 6 7 8 CHARACTERDISTRIBUTION r. the Diprotodontinaewhich eitherlack or have ?:-.l I:- ! ANDSTATE - small parastyles,are monophyletic.It is as- I I o o o long.hrgh stccp frontal rAP) sumedthat the largezygomaturine parastyle is l.2oooconstriccdprcorbitally(AP) l.l + o o poscquamosal constric tion /,(PL) a synapomorphiccharacter. However, in the 1.4 o t o upwardBC flcrion (AP)y' 1.5 + + o thin fronralc.csrs (PL) r case of the Diprotodontinae,the absenceor 1.6 o o o nasalscipand antcriorly (AP) small sizeof the parastyleis a symplesiomor- 1.7 o o o trapezoidnrrial ap.nurc (AP) l.E + o o low.nanow occipur (PL) phic state. 1.9 o + + wid€, oval foramenmagnum (PL) Diprotodontinesare also descriminated 2.1 o o + long squamosalproccss (AP) 2.2 o + + narr.nd zygomaticarch {PL) from zygomaturineson the basis of tighter, 2.3 o o o zy8om.tic d..plrercriorly {AP) . 2.4 + + o shon mass€rcricproccsses (PL)./ more V-shaped interlophid val ley s; 2.5 + + o de€pn.solabisl fossa (PL) "cleaner", less complex internal loph faces; 2.6 o o o disrinctfacirl cr€sl (AP) 2.1 o o o distinclbuccinalor foss. (AP) high, steepprotolophid of the M'l suppression l.E + + + longsquamosal sulcus (PL) of the paralophidcrest: weak-anteriorcin- :9 o + ? shalloe di.st.nal profil€ (AP) + (AP) Ll o o lon8. narrowpalarc / gulid; strongpostparaconal crest on the upper J2 + + + o 1 + + + arcadcsparallcl. slraight (PL),, molars;reduced size of the upperand lower i.l o o + cotrstricrcddiastema (AP) V l.:l o o + fiaredprcmrxillary palarc (AP) premolars relative to the size of the molars, 3.5 o o + + + o o o Ilatcraltol: (AP) 4.1 + o o nanow.shallow lPfossa (PL) and a greaterobliquity of the molar lophs and ,1.2 + + (PL) smallprcrySoid fossac , lophids. In derived forms (Diprotodon), the .1.3 o o o obliqoc8lcnoid fossac (AP)./ 4.4 o o : dccp.V-shaped condylar notch, AP) lophs (-ids) of the molars are hypsodont. 5.1 ? o o larScparastylc on Pr (AP) / This charactercomplex may succeedin 5: + . + trypoconcaUscnr rPLr / 5.1 + + + undivrdcdparamctaconc {PLr r' distinguishingthe laterTertiaryDiprotodonti- 5.4 o o o buccalcin8ulum pr.s€nr (PL) y' nae from the Zygomaturinae,but Pyramios 5.5 ? I + hi8h,larScm€sosrylc (PL) 5.6 o o + + + o o o functionrl poslcriorbasin (AP) alcootensevariably expresseszygomaturine- 6.1 + + + + + o t o wcrt p.rlstylc, slronSPPC (PL) 6.2 o o o i + o I o thick. shon. round€dLC (AP) like midlinks, complex interloph shapesand 6.3 o o o o + o i o protoslylcon Ml (AP) cingulum configurations,as well as possess- 6.4 + + + t + o o o M.-MJ in linc lingually (PL) 6.5 + + + P3widcly conhcts M: (PL) ing an upperthird premolarthat is consistently 6.6 o o o o t + + + M€ralophr.duclion M'r (A?) as large relative to M2, as in for example,the 6.7 o o o larScmct.rrylc low on M. (AP) 6.8 o o o shon. thick buccalcin8ulum (AP) zygomaturine,N eohe lo s. 7.1 + + + o + + + + dccpramus tapcrs antcriorly {PL) Pyramios alcootensealigns with 7.2 o o + srronSdirsrcmal crcsrs (AP) diproto- 7.3 o o + o + o 1 o long, horizontalsymphysis (PL) /, dontines in having a steep,high protolophid 7.4 o o + shon,ecak di8astricfoss! (AP) r 7.5 + + + + ! + + + gcnial pirs vcntralsurfacc (PL) on the M2, a suppressed,practically nonexis- 8.1 o o . spatulatcI, crown rA?r / tent, paralophidcrest; in the molar gradientof E.2 o o ' horizonlllly implartcd I, (A?)',/ E.3 o o + cnamclall sufaccsI, crown (AP) the uppers,in which thereis a simplefront-to- 8.,1 o o o €clnenrumraiscd abolc cnamel (AP) back enlargementand in which the metaloph 9.1 o + o Pr sftall relativ€to |nolars (PL) 9.2 o + o o + o o o ndow, ovll crown of Pr (PL) is not asreduced relative to the protolophas in 9.3 o o o o + + + + buccalcinSulum prcscnt on Pr (AP) zygomaturines,and of 9.4 o o + shon posrcriornoicry Pr (PL) course,the upperthird l0.l o o + ste€pprotolophid, wcak crcst (AP) premolar, which lacks a well-developedpar- 10.2o o+++o o o protolophidshiSh€r (AP) 10.3 + + + ++ o o o v'shap€dmid vlll€ys (PL) astyle. In cranial characterc, Pyramios 10.4 o o o linsual offsct Pr (AP) resemblesEuryzygoma in its diastemalcon- 10.5 o o + w.at, shofl prccingulid (AP) + + + (A?) striction, deep,broad cranium and short,pos- 10.6 o o o o i rcduccdMJ

zi\rlo w- 75 / ,^ tt &'"{r-\i'6'S P.F.Munay

Iophsand lophidsof P_rrantiosare not sugges- incorporationor suppressionof stylarcusps C tive of a closerelationship to Euryzygomaor andD intothe lophs (Fig. l4 [ ]).The absence any other laterTertiary notothere(Woodburne of theparastyle on thePr is plesiomorphic.A 1967a.1967b). symplesiomorphicdiprotodontid character is Havingnoted these discrepencies in combi- the presenceof a largeepitympanic fenestra, nationwith thegeologically late occurrence of whichdecreases in sizein thederived diproto- Pyramios, Woodburne (1967a, 1967b) dontids,but remains more highly expressed in characterizedPyramios as a primitive nototh- the zygomaturinesthan in the nototheres.In ere residingnear the baseof subsequentdipro- Pyramiosthe epitympanicfenestra is small todontine radiations. Although Woodburne and simple(Woodburne 1967b) whereas in ( 1967a)does not make the point explicit, the Neohelos,the fenestra is usuallylarge, though odontological similarity of Pyramios with sometimessubdivided and narrowedtrans- cenain Alcoota zygomaturinesis difficult to versely.The ventral squamosal tympanic wing ignore, and some of the ambiguities in is virtuallyabsent in plesiomorphicdiproto- differentiatingPyramios from the zygomatur- dontidsso thatthe tympanic cavity is a mere inesare implicit in his conclusions. hollowingof theposterior wall of a bulla-like Among the zygomaturines,some Plaisio- hypotympanicswelling that also forms the don centralis specimenshave strong postpara- entoglenoideminence. In Pyramios,a secon- conalcrests, as in Alkwertatherilm. The molar daryventral tympanic process is derivedfrom parastyles of both Alkwertatherium and themastoid (Woodburne 1967b). The polarity Plaisiodon are relatively small; and the inter- of thismorphological complex appears to bea loph valleysare proportionally similar in these progressivereduction of thealisphenoid tym- genera. The thick, short labial cingulae that panic process,present in Propalorchestes arisealong the anteriorends of the midvalleys (Murray1986) to a short,entirely squamosal are alsopresent in someP/ais jodon specimens tympanicprocess (e.g. Vombatidae).The and are especially prominent in Alkwertath- diprotodontidconditon is accompaniedby a ertum. hypertrophyof a hypotympanicsinus immedi- Assuming monophyly for the Diproto- atelyanterior to the tympaniccavity and the dontidae, Pyramios and Alkwertathe rium tympanicprocess is furtherreduced.ln Pyr- could representremote descendants of the two amios,the reduced anterior processes are re- respectivesubfamilies (Fig. l4). An alterna- placedby a mastoidtympanic wing. ln Dipro- tive hypothesis is that Pyramios, Alkwerta- todonthe tympanic cavity is partiallyfloored therium, Plaisiodon and perhapsKolopsoides by fusionand hypertrophy of othersurround- representan intermediateclade of diprotodon- ing elements.In all known zygomaturines, tids into which a degreeof parallel evolution exceptperhaps, ,in which secon- (i.e. independentdevelopment of the parastyle dary bony fusionsare evident, the tympanic and hypocone)must be introduced.The reality cavityis openventrally. is, given the degreeof morphologicalvariabil- The deriveddiprotodontids show a more ity (ie. absenceof hypoconein someNeohelos distinctfront to backmolar gradient than in specimens)and difficulty in establishingclear palorchestidsand primitive diprotodontids complementary distributions in character (Fig.1a t2l), (Richet a|.1978). Plesiomorphi- complexesin thesegenera (correlation of the cally a strongparacristid (paralophid crest of presenceor absenceof a featurewith another), Stirtonet al. 1967)is present. combinedwith the extraordinarilylong period Thesynapomorphic basis for cladestem [3] of time sincetheir inferreddivergence from a is inferredto be the reductionof the paralo- parentclade or their respectiveparent clades, phid creston M2. Thereis a plesiomorphic that few "pristine" characterstates of a pre- retentionof the srnallparastyle, high mes- cisely comparablenature are present for com- ostylarcusp and simple, undivided parameta- parlson. coneon the P3. The cladogram(Fig. 14) is basedprimarily Pyramiosalcootense retained or developed upon dental morphology, particularly the a P3of largesize relative to themolars [4] with upper third premolar. The family Diprototo- a small,though in someindividuals (SGM dontidaeis distinguishedfrom the Palorches- P872)at incipientlyzygomaturine-like, par- tidae on the basisof the synapomorphicloss, astyle.Symplesiomorphically the uppermo-

'76 A ne!\' zygomalurlne genus

IZYCO|{ATURUS] {DrPRqToD0i{l I KAL I MFTAIV / I --l d=

].io;; I =;= = l--..----*-AM r A...r =3=-I ==d== ? ====F =:-dl :.--:----^* I t----I BAIFIF.IS;E)AI-IAI.I z U - BAI-COF,IBIAl.I H E

BA-T'ESFOFTf)IAI!

LOI\IGFC)RDI AIV

JANJIJ T< T AFJ

Fig. 14. Hypothesisof phylogeneticbranching in Miocene diprotodontidsbased primarily upon a cladistic assessmentof odontologicalcharacters (Table 5). depicledwith minimum circuitry. The approximateLyellian equivalencyof the includedgenera is relatedto pan-continentalstages (Woodburne et a/. (1985).The discussion containsa more detailedinterpretarion. ul loss.incorporation or suppressionof stylarcusps C and D in relationto the lophsi[2] disrinctfront to back molargradient: [3] reductionof paralophidcrest: [4] Pr largerelative to molars; [5] reductionof sizeof permanentpremolars relative to molars;[6] largeparastyle, separated from the parametacone by a deepcleft: [7] developmentof a hypoconeon the Pr: [E] "hook-like"parastyle on P' (Hand?t a/., in preparation):[9] basicproponional similarity of the Pr in Nimbadonand Neohelos (nanow posterior fovea of Pr.etc): [10] mesostyleretracted towards cingulum; ull parametaconein kolopsisdivided into two dislinct cusps. larsdevelop midlinks to theextent of Plaisio- Plesiomorphicallythe genusKolopsoides rc- don and Alkwe rtathe rium. The paralophid tainsa poorly differentiatedparastyle, though crest is weak or absentand the protolophidof interpretedby Plane (1967) to be a derived M'?is high and steep. feature.Autapomorphically, the hypoconeis Charactercomplex [5] setsthe othernototh- as large or even larger than the protoconein eriines apart from Pyramios: synapomorphic Kolopsoides. Kolopsoides and Plaisiodon reductionof the sizeof the permanentpremo- appearto be united by a lengtheningof the lars relative to the molars and tendency to- parametaconein which however,the paracone wards higher, steeperlophs and lophids. and metaconeremain essentially undifferenti- The developmentof a largeparastyle on the ated, the mesostylarcusp remains high and P3 [6] unitesall zygomaturinediprotodontids. poorly defined labially, and a posterobuccal Plesiomorphically it lacks a hypocone,is cingulum is absentin thesetwo genera.Phen- broadposteriorly and retains a high stylarcusp etic similarity in the long, nearly horizontal on the labial sideof the apexof the parameta- dentary symphysisof Plaisiodon, Kolopsoi- cone. A marked narrownessof the metaloph des and Alkwertatheriumcombined with the relative to the protolophon Ma and especially large, deep, almost fully enamelled lower M5 is also characteristic. incisors in (young only) Kolopsoides(Plane Subsequentzygomaturines are united by 1967) suggesta minor clade grouping, but the developmentof a hypoconeon the Pr l7l. evidenceis thin.

77 P.F. Munay

Nimbadon and Plaisiodon are tenuously vertical profile of Pyramios,yet the procum- united by a "hook-like" shapeof the par- bentincisor implantation and morphologyof astyleof Pr (Handet ai. personalcommunica- the incisors suggesta closer relationship tion) [8]. The shapeand proportionsof the between Pyramios and Al kwe rtat he r i um. cusps the Pr are also similar in Neohelosand Conversely,the deep, spatulate lower incisor Nimbadon[9 ]. However,Neo&e/os usually has crowns of the zygomaturineKolopsoides are a prominentbuccal cingulum with a smallbut more similar to thoseof A /tlr ertatheriumand fully differentiated mesostyle located well Pyramios than to those of other zygomatur- below the apex of the parametaconeI l0]. In ines. Kolopsis the parametaconeis divided into two The constricteddiastemal palate in Alkwer- distinct cusps [1] and an anterobuccalin tatherium is very similar to the condition in addition to a posterobuccalcingulum, some- Pyramios and other nototheres.It is one of a times with a defined mesostvle.is usuallv few consistentapomorphic features that could present. unite the diprotodontinae(nototheres) and, wereit not for theprominent parastyle-bearing DISCUSSION Alkwertatherium, a monophyletic grouping might be supported with this character. The similarities betweenAlkwertatherium Plaisiodon centralisalso has a more extreme andPyramios on theone hand and Alkwertath- constriction of the diastemal palate than in erium and Plaisiodon on the other, are not other zygomaturines,except perhapsfor Z_v- easyto reconcilebecause of discontinuitiesin gomaturus.The conditionvaries continuously someof the charactercomplexes and the con- from Pyramiosto Alkwertatheriumto Plaisio- tinuously varying natureof others.My initial don (Fig. 6). A numberofotherfeatures (Table impression of Alkwertatherium was that it 5) align thecraniumof Alkwertatheriumtothe might belong to the genusPlaisiodon, (Mur- zygomaturines,especially to that of Plaisio- ray 1989),impetuously resulting in a nomen don. nudem status for the name "Plaisiodon" The zygomaturinesNimbadon, Neohelos webbi. Although the type Pyramios descrip- and.Kolopsis appearto form a distinct sub- tion seemedmore remote relative to Alkwer- clade, largely through a retention of ple- tatherium than that of Plaisiodon. there are siomorphiczygomaturine features. I surmise also both generaland specific similarities to that they separatedfrom theAlkwertatherium- Pyramios.Inorder to include Alkwertatherium Plaisiodon- Kolopsoide s subcladeat the point within one or the other genus,either generic of the expressionof the hypoconeon the Pr. In diagnosiswould haveto be revisedto accomo- order to expressthis phenomenonon a cla- date the specimen.If the differencesamong dogram,I would be compelledto postulatea Plaisiodon, Pyramios and Alkwertatherium series of dichotomiesfor which there is no were to be sunk to the specific level, the concreteevidence. A similar seriesofdichoto- subfamilial diagnosesas well as the generic mies would be entailedto resolvethe relation- diagnoseswould require revision due to the ship betweenPy ramios andAlkwertatherium. higher level systematicemphasis placed upon I have not expressedthese palaeontologically the presenceof a large, differentiated par- unsupportedbranchings on the cladogram. astyle on the P3 of Alkwertatherium and all It hasnot beendirectly demonstratedin the other zygomaturines. The least disruptive fossil record that the zygomaturinesarose option is to differentiate the new form at the from a parastyle-lessancestor. The condition generic level. is inferred from the plesiomorphicalignment Alkwertatheriun showsdivisions of certain of palorchestidswith the diprotodontids.The character complexes that are perceived as earliest recognizeable diprotodontids (e.g. interrelatedcharacters in other Alcoota gen- ) lack the prominentparastyle of era. For example, the protolophid of M. is zygomaturines(Murray in press;Murray and steep in Alkwertatherium but the paralophid Wells, in press). crest is more differentiated than in Pyramios, The preferredhypothesis is that zygomatur- suggestingthat the two charactersare geneti- inesarose from a notothere-likeform in which cally independent.The long, horizontal sym- the parastylewas reduced,as in primitive physial profile in Alkwertatheriarn is more palorchestids.It is thereforemore compelling similar to that of Plaisiodonthan to the nearlv to view PyramioJas a structuralintermediate

78 A new zygomatu ne genus betweenthe diprorodontinesand zygomatur- it isaccepted that Pyramios is a diprotodontine ines, than to place the genusin a position rather than a primitive zygomaturine.The anceslralto later diprotodontines.The mor- Alcootaform, P laisiodon centralis, appears to phologl of Alku'ertatheriam is resolved as be more closelyrelated to Alkwertatherium being largely symplesiomorphic with Pyr- thanto any otherknown zygomaturine. It is arnios. but in possessionof the zygomaturine postulatedthat there were two minor zygoma- apomorphyof a large,differentiated parastyle. turinelineages, one represented by Nimbadon, As yet, thereare no recognizableannectent Neohelosand, Kolopsis, and the other repre- forms for either Alkwertatherium or Pyramios sentedby Alkwertatherium,Plaisiodon and in any of the pre-Cheltenhamianlocal faunas. Kolopsoides.Thetwo minorlineages could be The Bullock Creek Neohelos tirarensis ap- unitedthrough the ancestorof Nimbadon. pears to be closely related to Kolopis torus This assumes.of course.that I have not (Stirton et al. 1967). Nimbadon spp could describedone of the extremeends of two represent basal zygomaturines with some highlyvariable generic clines (Plaisiodon and specific affinity to Plaisiodon and Neohelos Pyramios)as anew genus. Ijustify thegeneric (Hand et a/., in preparation)but there is no distinctionof Alkwertatheriamon thebasis of firm evidenceto supportthis observation.It is its possessionof a characterthat is alsoem- not likely however,that the apomorphicchar- ployedto distinguishthe two subfamiliesof actercomplexes in Alkwertatheriumand Pyr- theDiprotodontidae. The systematic emphasis amios evolvedentirely within the intervening of thischaracter depends upon the assumption periodbetween the mid- andlate Miocene. It is that Alkwertatheriumis more derived than reasonableto assumethat theancestors ofboth Pyramiosandmor'e primitive than Plaisiodon. of thesedistinctive generawill eventuallybe Shouldit eventuallybe shown that Alkertath- recognizedin one of the early to mid-Miocene erium is an extremevariant of eithergenus, faunas. this accountwould be no less informative, The presence of Alkwertatherium, becauseit will havedrawn attention to a de- Plaisiodon, Pyramios and other unique non- greeof morphologicalvariability sufficient to diprotodontid forms such as the primitive seriouslyquestion current diprotodontid sys- macropodidHadronomas puckridgi, sets the tematics. Alcoota Local Fauna apart from the mid- Meanwhile,I submitthat Alkwertatherium Miocene and early to mid-Pliocenefaunas. It accountsfor someof the anomaliesin the appearsto representan assemblageof ple- cheektooth measurementsof Pyramiosand siomorphic relicts, the ancestorsof some of Plaisiodonprovided by Woodburne(1967a). which must antedatethe Bullock CreekLocal Its morphology,though derived, provides a Faunaand which must have evolved in rela- glimpseof theantecedents of the two subfami- tive isolation.Of the diprotodontids,only i(o/- liesof diprotodontidsand gives some indica- opsis is suggestiveof later annectents(Zygo- tion of the polarityof certaincharacters as maturus). I suspecttherefore, that a signifi- well as documentingstructurally, the stages cant portion of the Alcoota Local Faunamay transitionalbetween diprotodontines and zy- represent a relict of early to mid-Miocene gomaturines. radiationsanalogous to the New GuineaPlio- cene local faunas.Although there is no obvi- SUMMARY ous geographic feature that would explain suchan isolation,it may be thatthe isolationof Alkwertatheriumwebbi exhibits a unique drainagepattems and associatedhabitats oc- combinationof diprotodontine(= ne1s1h- curred earliestin the centre,severely limiting eriine) and_zygomaturine characters in its population movements by mid-Miocene cranium,dentition and dentarymorphology. ttmes. Although the upperthird premolarhad devel- opeda largeparastyle as in thezygomaturine CONCLUSIONS diprotodonts,it retainsa weak posterobuccal cingulum,lacks a hypoconeand otherwise Alkwertherium webbi get et sp. nov. estab- resemblesthe P, of the notothere,Pyramios lishes a close relationship between diproto- alcootenseWoodburne. The craniumof A/t- dontines(= nototheres)and zygomaturines,if wertatheriumisbasically similar to thatof the

79 '| P.F. Murray I zygomaturinePlaisiodon centralis Woo- Murray, P. 1986.Propalorchestes novaculacepha- dburne,differing principally from thatgenus /asgen. et sp.nov., a new palorchestid(Dipro- in havingan extremelyconstricted diastemal todontoidea:Marsupialia from the Miocene palate,expanded interincisival fossa and inci- CamfieldBeds, Northern Territory, Australia. sor angulationmore characteristic of nototh- The Beagle, Occasional Papers of the North- ern Territory Museum of Arts and Sciences eriines.The dentaryresembles some nototh- 3(l):195-21t. eriinesand especiallypalorchestines in hav- Murray, P. 1989 (unpublished). "Plaisiodon ing a long,narrow sublingual fossa and spatu- webbi" anew zygomaturinespecies (Marsupi- late incisors,but is more similar to the alia: Zygomaturinae) from the late Miocene zygomaturinePlaisiodon in overall shapeand Alcoota Fauna of Central Australia. Conler- proportions.Alkwertatheriura can be ex- ence on Australian Vertebrate Evolution and plainedas a relict form whichevolved from an Syst ematic s, Sldne). (Abstract): I 2. ancestralclade structurally intermediatebe- Page,R. andMcdougall, I. 1972.Ages of minerali- tweenzygomaturines and nototheriines. It is zation of gold and porphyry copper depositsin concluded that Alkwertatheriumwebbi is a the New Guinea Highlands. Economic Geology 67'.1034- 1048. late survivingrepresentative of a plesiomor- Plane,M. 1967.Two new diprotodontidsfrom the phic zygomaturineclade ancestral to Plaisio- Pliocene Otibanda Formation, New Guinea. don centralisand Neohelos tirarensis. Tertiary Diprotodonridae from Australia and NewGuinea.ln: Bureauof Mineral Resources ACKNOWLEDGEMENTS Geologyand GeoplhysicsBulletinSS:105- 128. Rich,T. Archer,M. andTedford, R. 1978.Raemeo- I thankRod Wells andTom Rich for their theriumyatkolai, gen.et sp. nov., a primitive commentson themanuscript. Thanks also go diprotodontid from the Medial Miocene of to theFlinders University Students who helped South Australia. Memoirs of the National dig out the extensiontrench and to Danny M useumof Victoria 39:85-91. part Stinon, R. 1967. The Diprotodontidae from the Tumer who spent the better of a week Ngapakaldi Fauna, South Australia. In: Terti- excavatingthe specimen. ary Diprotodontidae from Austalia and New Guinea.Bureau of Mineral ResourcesGeol- REFERENCES ogy and GeophysicsBulletin E5:3-35. Woodburne,M. 1967a.The Alcoota Fauna,Cen- Aplin,K. andArcher, M. 1987.Recent advances in tral Australia an integrated palaeontological systematicswith a new syncretic and geological study. Bureau of Mineral Re- classification.In: M. Archer (ed.\ Possums sources Geology and Geophysics Bulletin and oppossums:studies in evolution.xv-lxxii. 87:l- 175. Surrey Beatty and Sons and the Royal Society Woodbume,M. 1967b.Three new diprotodontids of New SouthWales: Sydney. from the Teniary of the Northem Territory, Archer, M. and Bartholomai, A. 1978. Tertiary Australia. ln: Tertiary Diprotodontidae from mammalsof Australia:a synopticreview. Australia and New Guinea. Bureau of Mineral Alcheringa 2:l-19. Resources Geology and Geophysics Bulletin Everenden,J., Savage, D., Curtis,G. andJames, G. 85:53-104. 1964. Potassium-argondates and the Ceno- Woodbume, M. Tedford, R. Archer, M. Tumbull, zoic mammalian chronology of North W. Plane, M. and Lundelius, E. 1985. Bio- America. American Journal of Science chronology of the continental record 262:145-198. of Australia and New Guinea. Special Publi- Hoch, E. and Holm, P. 1986. New IVAr age deter- cation of the South Australian Department of minations of the Awe Fauna Gangue, Papua Mines and Energy.5:347 -363. New Guinea: Consequencesfor Papuaus- tralian late Cenozoic stratigraphy. Modern Geology lO:181-195. Accepted6 September1990

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