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STEPHEN WROE,1 JENNI BRAMMALL,1 AND BERNARD N. COOKE2
ABSTRACT-The near-complete skull of the Giant Rat-kangaroo Ekaltadeta ima is described from a middle Miocene deposit at Riversleigh, north western Queensland. Surprisingly, the results of phylogenetic analysis indicate no special relationship with the only other hypsiprymnodontids for which substantial cranial material is known (Hy=psiprymnodon moschatus, H. bartholomaii), but within Macropodoidea, a number of derived features present in E. ima are found only in another extinct taxon, the Balbarinae. Recent studies have suggested that Balbarinae may not represent a basal macropodid clade as thought by most previous authors and furthermore that the subfamily is perhaps distinct from all other kangaroos. In light of these findings an interesting possibility is noted, i.e., that Propleopinae and Balbarinae may represent a monophyletic clade to the exclusion of all other taxa. Preliminary results of investigation into dietary habitus indicate that Propleopinae represents a radiation of medium- to large-sized omnivorous kangaroos. Within this clade it is reiterated that a tendency toward carnivory might be inferred from the relative importance of high amplitude vertical shearing versus horizontal shearing and/or crushing elements in the dentition.
INTRODUCTION
UNTIL RECENTLY the propleopine (Giant Rat-kangaroo) subfamily has represented an interesting but highly enigmatic element of the macropodoid radiation. The first material attributable to Propleopinae (Propleopus oscillans) was described by De Vis (1888) who considered it to be a sister taxon to the extant Hypsiprymnodon moschatus. Giant Ratkangaroo material representing an additional species, P. chillagoensis, was described by Archer et al. (1978) from the Pleistocene Chillagoe Formation. Archer and Flannery (1985) added a further two new species, P. wellingtonensis, from Pleistocene deposits of Wellington Caves in New South Wales and the first pre-Pliocene propleopine, Ekaltadeta ima, from middle Miocene deposits of Riversleigh in northwestern Queensland. A new Pliocene genus and species, Jackmahoneyi toxoniensis, was described by Ride (1993) from Bow, N. S. W. A second Ekaltadeta species, jamiemulvaneyi, from early-late Miocene deposits of Riversleigh (Archer et al., 1995; Wroe, 1997a), was described by Wroe (1996a). Ride and Wells (1995) and Ride et al. (1997) introduced the first cranial material for a propleopine, consisting of a maxillo-premaxilla fragment, representing a juvenile P. oscillans. The skull of an adult E. ima, described below, constitutes the most complete cranial material...