A PRE-NEOGENE PHALANGERID POSSUM FROM SOUTH AUSTRALIA JUDD A. CASE, 1 ROBERT W. MEREDITH, 2 AND JEFF PERSON 3 1 College of Science, Health & Engineering, Eastern Washington University, Cheney, WA 99004-2408; jcase@mail.ewu.edu 2 Department of Biology, University of California, Riverside, CA 92521; rmere001@student.ucr.edu 3 North Dakota Geological Survey, 600 East Boulevard, Bismarck, ND 58505; jperson@nd.gov ABSTRACT--Phalangeridae is one of the most widely dispersed families of possums (Marsupialia, Dirprotodontia) in the Australasian region, extending from Tasmania in the southeast to Sulawesi of the Greater Sunda Islands of Indonesia in the northwest. Yet this one family of possums has generated the most morphological and biochemical phylogenetic uncertainties of any family within Order Diprotodontia. The various phylogenetic relationships for the family have led to different biogeographic models in regard to the site of origin and directions of dispersal for taxa within the family. The recovery of a maxilla from faunal zone B of the late Oligocene Etadunna Formation at Lake Palankarinna, South Australia (ca. 25 mya), results in the oldest known phalangerid to date, some ten million years older than the numerous Middle Miocene fossil phalangerids described from Riversleigh, Queensland. Whereas the Riversleigh phalangerids are similar enough to modern taxa to have originally been included in modern genera, the Etadunna specimen has morphologies that are very plesiomorphic for the family. These include a bladed P3 with a central main cusp that has denticles posteriorly, but no ridges; P3 aligned with tooth row; M1 with parastyle shear aligned with blade of P3; and M2 and M3 more square in occlusal outline. Autapomorphic character states include an infraorbital canal anterior to the second premolar, lack of an intraorbital groove, and the opening of the lacrimal canal inside the orbit. With substantial molecular time-of-divergence data now available, plus the addition of this new pre-Neogene phalangerid from South Australia, a new biogeographic model for site of origin and dispersal can be offered where phalangerids originate in Australia, diversify and give rise to the cuscus subfamilies, which disperse to New Guinea and then to Indonesia. INTRODUCTION The Australian possum family Phalangeridae, which includes cuscuses and brush-tailed possums, is the most widely distributed Australasian marsupial family with approximately two-dozen recognized extinct and extant species that range over most of Australia (including Tasmania), New Guinea, and northwestward to the Celebes Islands (Flannery, 1994; Hamilton and Springer, 1999; Osborne and Christidis, 2002; Springer et al., 1990; Fig. 1). This one family has generated the most phylogenetic and taxonomic uncertainties of any family within Order Diprotodontia, whether those phylogenies are based on morphological data or on biochemical data (e.g., Flannery et al., 1987; George, 1987; Groves, 1987a; Norris, 1994; Springer et al., 1990; Kirsch and Wolman, 2001; Ruedas and Morales, 2005). The various phylogenetic relationships for the family have led to different biogeographic models in regard to the site of origin (Australia or Sulawesi in the Celebes) and directions of dispersal (Australia to the Celebes or from the Celebes to Australia), for taxa within the family (e.g., Flannery et al., 1987 or Ruedas and Morales, 2005). Late Oligocene deposits in South Australia from the Etadunna and Wipajiri formations in the Lake Eyre Basin, and from the Namba Formation in the Frome Basin, have produced a wide range and the earliest records of most of the extinct and extant possum families (Fig. 2). Burramyidae, Ektopodontidae, Miralinidae, Pilkipildridae, and Pseudocheiridae have all been recovered from deposits of the Etadunna Formation, yet there had been no positive sign that Phalangeridae was present at all (see the series of papers in Archer, 1987, or those cited in Woodburne et al., 1993). The absence of phalangerids in the late Oligocene had been confusing considering that the earlier molecular studies (e.g., Springer et al., 1990; Springer, 1997), which produced divergence time data from molecular sequences, indicated that the phalangerid lineage should be present by the Eocene.