A new genus and species of dasyuromorphian from the Miocene of Riversleigh, northern Australia STEPHEN WROE WROE, S.,2001:12:20. A new genus and species of dasyuromorphian fiorn thc Mioccnc of Riverslcigh, nofihem Australia. Menoirs of the Austrulian Associution of Pulueontologists 25. 53-59. ISSN 0810-8889 Jocttlttsiunt ntttizoni, new genus and spccies, is the least derived dasyuromoryhian yet described from the Oligoccnc-Miocene deposits of Riversleigh in northwestern Queensland. Within Dasyuromorphia,J. muizoni is plesiomorphic fbr all dcntal features examined excepting metacristid orientation. Oblique alignmcnt of this cristid with respect to the long axis of the dentary in./. tttuizoni is an apomorphy within Dasyuromorphia sharcd with some representatives of both Thylacinidae and Dasyuridae. Conscqucntly. placement of this new taxon at the family level is untenable. Analysis of the material draws attention to the absence of well supportcd synapomorphies for the dasyuromorphian order. Considcred together with temporal as well as geographic position, the prcscncc of a feature which is possibly synapomorphic with some Thylacinidae or Dasyuridae, is trcatcd as a reasonable basis for the placement of J. ntuittni within Dasyuromorphia. S. Wroe, (s.v:roe(cl,un,sw.edu.au) School o./ Biologit'al Sciences, Universitl, of'S.v"dne1,, Nev.'South Wales, 2006 and S<:hool o.f Biologic'alSc'ience, Universitl, o.f Nev South Wales, Nev'South Wales, 2052. Received I June 2000 Keywords: Joculu.s iuttt muizoni, Dasyuromorphia, Mioccne. Riversleigh DASYUROMORPHIANS havc been suggested to be structurally ancestral to the remainder of the Australian marsupial radiation (Bcnsley 1903, Ride 1964.Szalay 1994). Howcvcq the f-actor oftenflagged to suppoft a basal position for the clade, that is, the retention of essentially primitive marsupial rnorphology, hinders attempts to demonstrate a spccial relationship between dasyuromorphians and any specific South Amcrican clade. The discovery andinterpretation of new Australian fossil material has added new dimensions to debate on the topic of dasyuro- morphian cvolution (Wroe 1998. | 999a). Archer (1976b, 1982), Wroe (l 996, 1991a, I 997b, 1999b, in prcss),Wroe e/ al. (2000) and Wroe & Nasscr (2001) have denronstrated that cvcn generalised dasyurids, commonly thought to approximate the plesiomorphic australidelphian statc for many features, arc highly derived in their cranial morphology. Moreover, Wroe ( 1999b) argues that although thefamily Dasyuridae can not bc defined by thepresence ofdcntal synapomorphies. shared derived basicranial features demonstrate a special relationship between the middle Miocene dasyurid, Barinl:a wungala. and all 'modern Dasyuridae' (seir"su Wroe 1999b), with 'modern Dasyuridae' united by a furthcr suite of synapomorphic basicranial features. Recently discovered material from earlyTertiary deposits of Murgon, southcastern Queensland (Godthclp et al. 1999)has added further complexity to our understanding of dasyuromorphian evolution. Australia's oldest marsupicamivore, Djurthia mtu'gonensis, may bc refcrable to either Didelphidae (sensu Marshall et a\.,1990) or Australidelphia on the basis of dcntal evidence. If the latter is ultimatcly supported by the unambiguous association of D. mttrgonensi.v with australidelphian tarsal material, then it becomes more difficult to define Australidelphia, Dasyuromorphia or Didelphidae on the basisof dcntal morphology alone. A conservative approach is required in the taxonornic placernent ofgeneralised Australian fossil taxa, such as that described below, particularly in the absence of basicranial material. SYSTEMATIC PALAEONTOLOGY Order DASYUROMORPHIA Gill" I 872 Joculusium gcn. nov. T1'1tt' :pL'cit'.s..loctrltt.:itrnr nrtri:ttni sp. nov. Diagno.sis. Joculusiunt muizoni differs from all