New Genus and Species of Extinct Miocene Ringtail Possums (Marsupialia: Pseudocheiridae)

Home , Marlu, Phalangerida, Phalangeroidea, Pseudocheiridae, Pseudocheirus, Pseudochirops

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3560, 15 pp., 3 figures, 1 table March 8, 2007

KAREN K. ROBERTS,1 MICHAEL ARCHER,2 SUZANNE J. HAND,3 AND HENK GODTHELP4

ABSTRACT The first unique genus of ringtail possums from the Riversleigh World Heritage Area in Australia is diagnosed and described. Gawinga aranaea is the type and only species of the new genus and is known from nine isolated lower molars. It has been recovered from three Riversleigh deposits: two are of early to mid-Miocene age, while the age of the other has yet to be determined. The new possum is larger than Oligo-Miocene species of Paljara, Pildra, and Marlu, but smaller than most extant taxa. It is characterised by a distinctive lower molar cusp morphology of parallel ridges extending primarily from the cristid obliqua, filling the occlusal basins. Additional autapomorphies include: extended, shelflike protostylid cristids and a bisected posthypocristid on m1, and posterior molars that have a metaconid ridge posterobuccal to the metaconid and an anteriorly positioned protoconid relative to the metaconid. It also possesses an enlarged protostylid on m1, a feature otherwise known only in extant genera. The precise phylogenetic position of Gawinga within the pseudocheirid radiation has yet to be determined, but it is tentatively identified here to be a highly derived pseudocheirid, apomorphic with respect to Paljara and Pildra species, and with no known descendants.

1 School of Biological, Earth and Environmental Science, University of New South Wales, New South Wales 2052, Sydney, Australia ([email protected]). 2 School of Biological, Earth and Environmental Science, University of New South Wales, New South Wales 2052, Sydney, Australia; Research Associate, Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History ([email protected]). 3 School of Biological, Earth and Environmental Science, University of New South Wales, New South Wales 2052, Sydney, Australia; Research Associate, Division of Vertebrate Zoology (Mammalogy), American Museum of Natural History ([email protected]). 4 School of Biological, Earth and Environmental Science, University of New South Wales, New South Wales 2052, Sydney, Australia ([email protected]).

INTRODUCTION (Archer, 1984, 1992; Archer et al., 1989). These include new species of known Oligo- The ringtail possums and greater glider Miocene genera, the earliest representatives of family (Pseudocheiridae) comprise a group of extant Pseudochirops and the new genus and reclusive, nocturnal, arboreal marsupial foli- species described in this paper. vores. They form one of the most diverse groups within the broad radiation of diproto- dontians (possums, kangaroos, koalas, and METHODS AND MATERIALS wombats). The breadth of diversity within All described fossil material belongs to the the group was formally recognized in 1987 Queensland Museum palaeontology collec- with its elevation from subfamilial to familial tion, prefix QMF. Lower dental terminology status (Aplin and Archer, 1987). This follows Archer (1984; see fig. 1) and homology followed increasing evidence from molecular of molars and posterior premolar follows studies that pseudocheirids form a much Luckett (1993). Higher-level systematic termi- more distinct lineage than previously thought nology follows Aplin and Archer (1987). (e.g., Kirsch, 1977; Archer, 1984; Baverstock, Riversleigh site and system nomenclature 1984). follows Archer et al. (1989, 1995, 1997b). Extant pseudocheirids belong to six genera Measurements were made using a Wild throughout Australia and the New Guinea MMS235 Digital Length Measuring Set, region (Flannery, 1994; Strahan, 1995). These attached to a Wild 3MB stereomicroscope. genera had largely been classified as subgenera Length (L) represents maximum longitudinal of Pseudocheirus (e.g., Tate, 1945). Most distance; anterior width (AW), and posterior species are limited in distribution, inhabiting width (PW) respectively represent width of the high-altitude tropical rainforest in northeast- trigonid and talonid, perpendicular to the ern Queensland or New Guinea (Flannery, lengthwise axis. Scanning electron micro- 1994; Strahan, 1995). graphs were taken on an FEI Quanta 200 In addition to extinct species of living genera, ESEM at the Electron Microscope Unit fossil taxa have been referred to four extinct (EMU), University of New South Wales. genera (Bassarova and Archer, 1999; Crosby et al., 2004). The oldest pseudocheirid fossils, of the extinct genera Paljara, Pildra, and Marlu, SYSTEMATIC PALEONTOLOGY have been recovered from late Oligocene to SUPERORDER MARSUPIALIA ILLIGER, 1811 early Miocene sites in the Tirari Desert and Frome Basin in northern South Australia ORDER DIPROTODONTIA OWEN, 1866 (Woodburne et al., 1987; Bassarova and SUBORDER PHALANGERIDA APLIN AND Archer, 1999). Pseudokoala is the fourth extinct ARCHER, 1987 genus, known from Plio-Pleistocene deposits in South Australia, Victoria, and southeast FAMILY PSEUDOCHEIRIDAE WINGE, 1893 Queensland (Turnbull and Lundelius, 1970; Gawinga, new genus Archer et al., 1997a; Crosby et al., 2004). TYPE SPECIES: Gawinga aranaea n.sp. Paljara, Pildra, and Marlu have also been DIAGNOSIS: As for the type species until recorded from the Oligo-Miocene freshwater additional species are known. limestone deposits of the Riversleigh World ETYMOLOGY: Gawinga is a word meaning Heritage Area in northwestern Queensland ‘‘possum’’, as spoken by the late Ivy George of (Archer et al., 1989; Archer, 1992; Bassarova Riversleigh Station, northwestern Queensland. and Archer, 1999). However, the abundant Gender is considered to be feminine. pseudocheirid material from these mid- Tertiary sites at Riversleigh is largely unde- DISTRIBUTION AND AGE: As for the type scribed and unpublished, with the exceptions species. of Paljara nancyhawardae and P. maxbourkei (Bassarova et al., 2001). Nevertheless, pre- Gawinga aranaea, new species liminary studies reveal a great diversity of HOLOTYPE: QMF52173, isolated right m1 taxa, largely unrecognized beyond Riversleigh (figs. 2A, 3A). 2007 ROBERTS ET AL.: MIOCENE POSSUMS 3

Fig. 1. Right m1 diagram of Gawinga aranaea. Abbreviations as follows: abcm anterobuccal cingulum; bprcd buccal protocristid; bprsdr buccal protostylid rib; cora cristid obliqua ridge A; corb cristid obliqua ridge B; corc cristid obliqua ridge C; end entoconid; ensdr entostylid ridge; hyd hypoconid; hyld hypoconulid; med metaconid; pacd paracristid; pad paraconid; pcdprsd precristid of the protostylid; pencd preentocristid; pmcd premetacristid; pocdprsd postcristid of the protostylid; poencd postentocristid; pohycd posthypocristid; pomcd postmetacristid; poprcd postprotocristid; prd protoconid; prsd protostylid. Scale bar is 1 mm.

PARATYPE: QMF52174, isolated left m1 Arachnea Ridge Site, but an early Miocene (fig. 3B). age is also possible given the presence of this TYPE LOCALITY: Arachnea Ridge Site, new species. Riversleigh World Heritage area, Lawn Hill DIAGNOSIS: Gawinga aranaea is character- National Park, northwestern Queensland, ized by a distinct, lower molar cusp morphol- Australia. ogy as follows: a reticulated occlusal surface of REFERRED SPECIMENS: QMF52175 (fig. robust ridges, predominantly normal and 3C) right m2; QMF52176 (fig. 2D, 3I) left lingual to the cristid obliqua; a hypoconid base m4 from Arachnea Ridge Site. QMF52177 that is enlarged posterobuccally; an anteriorly (fig. 2B, 3D) right m2; QMF52178 (fig. 3E) placed protoconid with respect to the metaco- left m2; QMF52179 (fig. 3F) right m2; nid on posterior molars; and a bisected post- QMF52180 (fig. 2C, 3G) right m3 from hypocristid on m1. The lower molars of G. Upper Site. QMF52181 (fig. 3H) right m3 aranaea are narrower and longer than in most from Wayne’s Wok Site. extinct pseudocheirids, with the exception of ETYMOLOGY: From the Latin aranea mean- Marlu kutjamarpensis Woodburne et al., 1987, ing ‘‘spider’’ or ‘‘spider’s web’’. In reference to Pildra magnus Pledge, 1987, and all species of the Riversleigh site, Arachnea Ridge. Pseudokoala. It differs from known species of DISTRIBUTION AND AGE: Riversleigh World the other extinct genera by having a shorter, Heritage Area, northwestern Queensland. weaker, and more posteriorly oriented m1 Upper Site and Wayne’s Wok Site are inter- buccal protocristid; by having a large cuspate preted to be part of Riversleigh’s System B protostylid; and a larger entostylid and ridge strata (Archer et al., 1995, 1997b; Creaser, (entostylid completely absent in species of 1997). Biocorrelation of the Riversleigh fossil Marlu and Pseudokoala). Posterior molars also assemblages, and of Upper Site in particular, exhibit a prominent metaconid ridge and an suggests an early Miocene age for System B elongate preentocristid that is transversely sites. No age has been determined for buttressed at its anterior end. 4 AMERICAN MUSEUM NOVITATES NO. 3560

enlarged; metastylid progressively more complex along tooth row; narrower notch between preentocristid and metastylid; entostylid ridge forms a continuous crest with hypoconulid; larger hypoconulid on posterior molars; more lengthwise orientation of lingual cusps, particularly entoconid; wider buccal cusp angles; buccal cusp apices less lingually curved; shallower trigonid and talonid basins. Features shared with species of Paljara include: m2 longer than m1; reduced or absent anterior margins between paraconid and paracristid; paraconid on posterior molars positioned on lengthwise axis; elongate, bladed metacristids; equidistant positioning of the entostylid ridge between posthypocristid and entoconid; and lack of buccal protostylid or cingulum on posterior molars. G. aranaea differs further from Pildra spp. by the following features: stronger and broader anterior cingula (except P. magnus); anterior margins on posterior molars reduced or absent; m1 paraconid extended further anteriorly; paraconid on posterior molars positioned much closer to longitudinal axis; m1 metaconid relatively lower cusped; wider distance between apices of m1 metaconid and protoconid; narrower notch between metastylid and preentocristid; preentocristid less steep and more bladed; entoconid less conical; entostylid ridge forms a continuous crest with the hypoconulid which is separate from the postentocristid; larger hypoconulid. Features shared with species of Pildra include: m2 longer than m1; presence of a lingual rib extending from the m1 paraconid; lingual enlargement of the protoconid on posterior molars; progressively more complex metastylids along the tooth row; similar orientation of the posthypocristids on m1–2. G. aranaea differs further from Marlu and Pseudokoala spp. by the following features: stronger anterobuccal cingula; larger m1 Fig. 2. Stereo occlusal view of m1–4 of Gawinga paraconid; m1 protoconid more lingually aranaea. A. QMF52173 (holotype), right m1; B. positioned; m1 metaconid relatively larger QMF52177, right m2; C. QMF52180, right m3; D. and separated from protoconid by a deeper QMF52176, left m4. Scale bars 5 1 mm. notch; greater distance between apices of m1 metaconid and protoconid; metastylids pro- G. aranaea differs further from Paljara spp. gressively more complex along the tooth row; in the following features: m1 anterobuccal larger, more distinct hypoconulid. G. aranaea cingulum reduced; m1 paraconid smaller; differs further from all species of Marlu protoconid on posterior molars buccally and Pseudokoala, except M. praecursor 2007 ROBERTS ET AL.: MIOCENE POSSUMS 5

Fig. 3. Buccal views of Gawinga aranaea. A. QMF52173 (holotype), right m1; B. QMF52174 (paratype), right m1; C. QMF52175, right m2; D. QMF52177 right m2; E. QMF52178, left m2; F. QMF52179, right m2; G. QMF52180, right m3; H. QMF52181 right m3; I. QMF52176, left m4. Scale bars 5 1 mm. 6 AMERICAN MUSEUM NOVITATES NO. 3560

Woodburne et al., 1987, in the absence of an metacristid not linear with very weak post- overlapping or joined metastylid and preen- protocristid; anterior protocristid on posterior tocristid. G. aranaea also differs from species molars reduced or absent; larger entostylid of Pseudokoala in having relatively conical and ridge, forming a continuous crest to the lingual cusps, with steeper cristids; shorter hypoconulid apex; entostylid ridge equidistant postprotocristid on posterior molars; posthy- from entoconid and posthypocristid (except P. pocristid extending further lingually and archeri Collett, 1884, and P. winteri Mackness absence of a buccal protostylid or cingulum and Archer, 2001); wider hypoconid cusp on posterior molars (except P. curramulkensis, angle. G. aranaea differs further from originally described as Corracheirus curra- Petropseudes dahli as follows: m1 metaconid mulkensis Pledge, 1992). Features shared with much larger and separated from protoconid Marlu and Pseudokoala species include: dis- by a deeper notch; m1 cristid obliqua connects tinct anterolingual cingula; and broad buccal with metaconid; much shorter postprotocris- cusp angles. G. aranaea also shares with Marlu tid on posterior molars; entoconid more a longer m2 than m1. conical; entostylid present; less compressed In comparison with extant taxa, G. aranaea lingual cristids. Features shared with is smaller than all known species except Pseudochirops and Petropseudes species in- Pseudochirulus mayeri Rothschild and clude: lingual rib extending from m1 para- Dollman, 1933, and P. canescens Water- conid and a cuspate protostylid on m1. It also house, 1846, and is very similar in size to shares with species of Pseudochirops an m1 Petauroides ayamaruensis Aplin et al., 1999. It protostylid basin. also differs from extant taxa (species of With the exception of Pseudocheirus stirtoni Pseudocheirus, Pseudochirulus, Petropseudes, and P. marshalli (Turnbull and Lundelius, Pseudochirops, Petauroides, and Hemibeli- 1970), which are compared alongside species deus) as follows: m1 shorter than m2 (except of Petauroides and Hemibelideus, G. aranaea Petropseudes); m1 precristid of the protostylid differs further from Pseudocheirus spp. as joins anterior end of the anterobuccal cingu- follows: stronger and broader anterior cingulum; m1 postcristid of the protostylid well- la; anterior margins of posterior molars re- defined and shelflike, terminating at the cristid duced or absent; paraconid on posterior obliqua; distinct and strong metaconid ridge molars positioned much closer to longitudinal present on posterior molars; metastylid pro- axis; greater distance between apices of m1 gressively more complex along the tooth row; protostylid and protoconid; m1 metaconid metastylid and preentocristid do not overlap relatively larger and separated from proto- or join; posthypocristid more obliquely ori- conid by a deeper notch; premetacristid on m1 ented. does not align linearly with the very weak G. aranaea differs further from species of postprotocristid; wider protoconid cusp angles Pseudochirops and Petropseudes as follows: on posterior molars; protoconid on posterior stronger anterior cingula (anterior cingula molars more lingually swollen, forming a slight absent in Pseudochirops cupreus Thomas, anterior protocristid in some specimens; much 1897, and Petropseudes dahli Collett, 1895); shorter postprotocristid on posterior molars anterobuccal cingulum present on posterior that does not unite with the metastylid; molars; m1 buccal protocristid shorter and entostylid present; hypoconulid on m1–2 is weaker; flat lingual face of metastylid; hypo- not ribbed posterolingually, and is perpendic- conulid relatively larger and more distinct ular to hypoconulid cristids; cristid obliqua from postentocristid and posthypocristid; terminates at same height as postprotocristid; buccal cusp apices less lingually curved; buccal lingual cristids on posterior molars less steep; protostylid or cingulum on posterior molars buccal cusps less lingually curved; shallower absent. G. aranaea differs further from trigonid and talonid basins. Features shared Pseudochirops spp. as follows: flat lingual face with species of Pseudocheirus include: lingual on m1 protoconid; greater distance between rib extending from m1 paraconid; a cuspate apices of m1 metaconid and protoconid protostylid on m1; and absence of a buccal (except P. corinnae Thomas, 1897); m1 pre- protostylid or cingulum on posterior molars. 2007 ROBERTS ET AL.: MIOCENE POSSUMS 7

G. aranaea differs further from Pseudo- TABLE 1 chirulus spp. as follows: anterior margins of Length (L), Anterior Width (AW), and Posterior posterior molars reduced or absent; m1 para- Width (PW) of Gawinga aranaea conid smaller and less conical; paraconid on Measurements in millimeters. posterior molars positioned much closer to longitudinal axis; m1 metaconid larger and QMF L AW PW separated from protoconid by a deeper notch; m1 52173 3.18 1.51 1.7 shorter, weaker m1 buccal protocristid; ante- 52174 3.16 1.48 1.72 rior protocristid on posterior molars absent or m2 52177 3.51 1.82 1.81 very reduced; entostylid and ridge present; 52178 3.29 1.78 1.84 hypoconulid on m1–2 is not ribbed or curved 52179 3.23 1.57 1.63 on the posterolingual surface, and cristids are 52175 3.38 1.77 1.73 oriented lengthwise; posthypocristid less m3 52180 3.13 1.68 1.72 curved at lingual termination; lingual cusps 52181 3.13 1.57 1.67 less conical (except m1 protoconid); buccal m4 52176 3.31 1.73 1.69 cusp cristids higher crested (except anterior protocristid); cristids are less steep; shallower trigonid and talonid basins. Features shared m1; and flat lingual surfaces of metaconid/ with species of Pseudochirulus include: broad, protoconid and entoconid on m1–2. distinct anterior cingula and a cuspate protostylid on m1. DESCRIPTION G. aranaea differs further from Pseudo- cheirus stirtoni, P. marshalli and Petauroides All lower molars are relatively narrow and and Hemibelideus spp. as follows: anterior low cusped with shallow basins. Their occlusal margins of posterior molars reduced or surfaces appear reticulated due to the presence absent; paraconid on posterior molars posi- of enlarged ridges off the cristid obliqua and tioned much closer to longitudinal axis; m1 in posterior molars, also off the paracristid. metaconid is a more distinct, independent Tooth homology of posterior molars was cuspid (except P. marshalli and P. ayamar- determined by differences in morphology and uensis); shorter, weaker m1 postprotocristid; morphometrics (table 1). much shorter postprotocristid on posterior m1: The holotype QMF52173 and para- molars; entoconid buccally compressed; larger type QMF52174 are virtually identical entostylid and much stronger, continuous (figs. 3A, 3B) although the latter is slightly entostylid ridge on all molars (H. lemuroides damaged. Lingual margin of the tooth is Collett, 1884, has no entostylid or ridge); almost flat, and paraconid is low cusped and hypoconulid more peaked and distinct and positioned slightly buccally to the lingual lacks a ribbed or curved posterolingual margin. A lingual rib runs halfway down the surface; wider hypoconid angles; cristid ob- crown from the paraconid, ending in a short, liqua terminates at same height as postproto- horizontal shelf. Paracristid is weakly arcuate cristid (except P. ayamaruensis); buccal cusp and extends down the anterior flank of the apices less curved lingually; cristid obliqua paraconid. Protoconid is subconical (missing and paracristid higher crested; buccal proto- in QMF52174), with steep, moderately bladed stylid or cingulum on posterior molars absent; cristids that both curve lingually, and a steep, shallower trigonid and talonid basins. It very weak, buccal protocristid. Protostylid is differs further from species of Hemibelideus pyramidal and located midway down the as follows: buccally enlarged m1 protostylid; protoconid; a flat, sloping lingual surface m1 paraconid less conical, and independent of forms the protostylid basin. Protostylid cris- paracristid (P. ayamaruensis also differs in this tids are long and form a shelf around the feature). Features shared with P. stirtoni, P. buccal protoconid face. Precristid of the marshalli and species of Petauroides and protostylid descends concavely, curving back Hemibelideus include: distinct anterolingual up slightly to form a small peak, a short cingula; an enlarged cuspate protostylid on distance before connecting with the anterior of 8 AMERICAN MUSEUM NOVITATES NO. 3560 the anterobuccal cingulum. Postcristid of the Posterior end of protostylid postcristid joins protostylid travels posterolingually toward the cristid obliqua at base of this lingual section. metaconid, following the contour of the The midsection of the cristid obliqua, con- protoconid and hypoflexid, and terminates at necting the buccal and lingual sections, is the cristid obliqua. Buccal protostylid rib is linear and supports three ridges, separated by kinked midway; basal half of the rib is equally wide notches. Ridge B is lowest in enlarged and crested, almost reaching the base height; ridge C is broadest. Anterior end of of the hypoconid. Metaconid is pyramidal each ridge is slightly behind the anterior end of with a vertical, lingual surface, defined by each adjacent notch; all are joined by the straight, moderately sloped cristids. cristid obliqua in a zigzag shape, so that the Premetacristid joins the posterolingually ori- anterior face of each ridge is flat and leans ented postprotocristid in a notch. The notch posterolingually. Crest of ridge A curves continues posterobuccally, forming the hypo- lingually as it descends, terminating at the flexid, which is traversed by the postcristid of metastylid. Ridge C is linearly aligned with the the protostylid. Metastylid is virtually absent, entostylid ridge. Talonid basin is reduced to comprising a very small cusp posterior to, and a narrow, obliquely oriented valley, parallel to independent of, the postmetacristid; the tri- the cristid obliqua. angular lingual surface of the metastylid is m2: Paraconid and anterior point of tooth obliquely oriented and vertical, and its apex is extended on the lengthwise axis so the continues anterobuccally, merging with the trigonid is pointed. Paraconid is distinct anterior crest of ridge A. (damaged in QMF52175). Paracristid sup- Entoconid is subconical; preentocristid is ports one or two posterolingual, triangular anterobuccally oriented and swings trans- ridges, similar to the cristid obliqua ridges. In versely lingual at the end. Postentocristid is QMF52178 and QMF52177 (reduced in straight, running posterolingually to the lin- QMF52179) a small ridge extends posteriorly gual margin at a constant slope. Hypoconulid from the paraconid. A buccal rib descends is also on the lingual margin and has a vertical, from the premetacristid in all except triangular lingual face and forms a peak QMF52177, typically joining a paracristid directly posterior to the end of the postento- ridge. An anterobuccal cingulum descends cristid. Hypoconulid merges with the large, low on the buccal enamel, either proceeding anterobuccally directed entostylid ridge, from the paraconid or a short distance below; flanked by two V-shaped valleys. The ridge a buccal parastylid is present, except on crest turns anteriorly following the entostylid. QMF52178. A slightly shorter anterolingual Posthypocristid is bisected and runs parallel to cingulum, sometimes featuring a lingual para- entostylid ridge; posterolingual terminus brief- stylid, extends horizontally from the lingual ly deflects lingually to join postcristid of the side of the paraconid, often in conjunction hypoconulid, forming the posterolingual cor- with anterior end of the premetacristid. ner. Hypoconid has a flat, anterolingual Protoconid is shorter and positioned anterior surface, and is slightly shorter than the to metaconid; it is a conical, lingually enlarged anteriorly positioned entoconid. cusp, taller than the hypoconid. A small, short Viewed posterolingually, the cristid obliqua posterobuccal shelf is positioned midway appears zigzagged. Three broad, triangular down the cusp (on QMF52175), and a thin ridges run in a posterolingual direction, posterobuccal rib runs to the protoconid base perpendicular to the cristid obliqua. The (QMF52175 and QMF52178), possibly as anteriorly directed buccal section of the cristid a vestigial protostylid. Lingual surface of obliqua, before the ridges, runs from the protoconid is enlarged, particularly in hypoconid apex and is broadly bladed and QMF52179 and QMF52175. The poorly slightly concave, like the buccal half of the bladed postprotocristid weakly curves poster- posthypocristid, but shorter. Lingual section olingually, toward the end of the postmeta- of the cristid obliqua is straight and of equal cristid. Termination of the postprotocristid length to buccal section, and joins metaconid varies: in QMF52178 it joins the cristid apex perpendicular to the metacristids. obliqua in a continuous crest; in QMF52177 2007 ROBERTS ET AL.: MIOCENE POSSUMS 9 it buccally joins the metaconid ridge; in steeper than preentocristid, extending to the QMF52175 and QMF52179, cristid obliqua lingual margin. Entostylid ridge is similar to and metaconid ridge are joined, postproto- m1, gradually ascending anterobuccally to the cristid in the former is detached marginally entostylid before receding anteriorly, termi- from this junction and connected in the latter. nating buccal or slightly anterobuccal to the Metaconid has elongate, bladed cristids; pre- entoconid. Entostylid ridge in QMF52177 is metacristid slopes gradually to lingual edge of damaged anteriorly. Hypoconulid and hypo- the paraconid or slightly short of it. conid are similar to that in m1 (hypoconid is Postmetacristid is shorter and steeper than damaged in QMF52175 and QMF52177). premetacristid; it has a small lingual deflection Posthypocristid is not bisected and is almost at its end and either joins the metastylid straight with a slight posterior curve on the (QMF52179, QMF52178) or is separated by lingual half. Cristid obliqua is similar to that a notch (QMF52175, QMF52177). in m1, but the three ridges are lower in height Metastylid forms a lengthwise crest (except and in QMF52179 curve in toward the base of QMF52178, which divides into two pyramidal ridge B instead of running parallel. Ridge C is cusps) with a small buccal rib extending from smaller than the entostylid ridge; ridge B splits its posterior. Immediately posterobuccal to into two ridges on QMF52178 and the metaconid, a triangular ridge extends QMF52177; ridge A splits in all except anteriorly from the metastylid (not always QMF52177. Talonid valley in m2 tends to joined). Links between the ridge and sur- widen posteriorly. Anterior termination of the rounding features are variable: in QMF52179, cristid obliqua is variable, but is usually either perpendicular links at anterior end of the ridge joined to or separated by a minor notch from connect it to the metaconid and postproto- the metaconid ridge and postprotocristid cristid; in QMF52175, it is joined midway by junction. QMF52178 is the only specimen in a buccal link to the cristid obliqua–postpro- which the cristid obliqua connects solely to the tocristid junction; in QMF52177, the ridge postprotocristid. joins the anterior end of the metastylid and m3: m3 trigonid is slightly more rounded forms a perpendicular buccal link with the than in m2. Anterior cingula are similar to m2, postprotocristid; the ridge in QMF52178 is except the anterobuccal cingulum is much not connected anteriorly and is bifurcated narrower and buccal parastylid is absent. posteriorly, of which the anterior crest joins Paracristid is smoothly curved in QMF52181 the anterometastylid while the posterior crest but more like m2 in QMF52180. Two para- attenuates toward the posterometastylid. cristid ridges are present; anterior ridge is Entoconid is subconical and taller than the shorter and oriented anteroposteriorly, both posteriorly positioned hypoconid; it has mod- terminate in the trigonid valley, buccally of erately sloped, bladed cristids that are oriented premetacristid blade. Form of the metaconid parallel to the metacristids. Preentocristid is and protoconid is similar to that in m2, as is anterobuccally oriented but bends anterolin- relative height and position of cusps. gually at the base, where it either levels or rises Postprotocristid is poorly bladed and joins slightly before terminating. Just after inflec- cristid obliqua in a continuous curve on the tion, the cristid forks widely, forming a steep, longitudinal axis. Premetacristid terminates on flat, triangular anterior surface. The entoconid the lingual edge of the paraconid (QMF52181) narrows progressively away from apex but or fails to join (QMF52180). widens again from the inflection point, so Metastylid is bicuspid and anterometastylid there is a small, transverse, pyramidal buttress is larger. In QMF52181, the anterometastylid anterior to the preentocristid. Opposing this continues into the metaconid ridge but in preentocristid buttress is the flat, posterior QMF52180 is separated by a notch. face of the metastylid, separated by a narrow Posterometastylid has a short buccal crest notch. In QMF52175 (reduced in and is pyramidal. Metaconid ridge of QMF52179), a buccal rib in descends from QMF52180 is joined to the metaconid and the preentocristid, swinging posteriorly at the postprotocristid by shallow, perpendicular entoconid base. Postentocristid is concave and links on either side. 10 AMERICAN MUSEUM NOVITATES NO. 3560

Entoconid resembles that in m2 but is paracristid. The ridge is swollen centrally and relatively smaller, and constriction between a second, buccal blade extends from a right the entoconid and anterior preentocristid angle; this second blade runs posterolingually, buttress is reduced. Entoconid on QMF52181 parallel to the metaconid ridge, and ends is damaged, but there is a buccal rib descending opposite the preentocristid buttress. from the preentocristid, as in QMF52175 (m2). Entoconid and hypoconid resemble that in Compared to m1–2: hypoconulid is obliquely m3. Entostylid ridge is as large as in m2, but is oriented so the flat lingual face forms the more curved. It ends adjacent to the lingual posterolingual corner; entostylid, entostylid preentocristid rib and almost forms a complete ridge, posthypocristid, and hypoconid are crest around the buccal entoconid surface, as relatively smaller; entostylid is positioned in QMF52175 (m2). Hypoconid has a steeper closer to hypoconulid. Cristid obliqua is anterolingual surface than m1–3. Both trigo- oriented slightly less obliquely than m1–2; nid and talonid basins are completely filled by cristid obliqua ridges are reduced in height reticulated ridges off the cristid obliqua and and progressively widen from ridge A to C. On paracristid. Cristid obliqua ridges are more m3 specimens, only ridge A bifurcates, and the sinuous than m1–3. Ridge C is largest and divergence occurs at the start of the ridge, on rather swollen while anterior ridges become the cristid obliqua. progressively thinner. No ridge is divergent, m4: QMF52176 is here considered an m4. but ridge B has a slightly bifurcated crest at its It has a wider and longer trigonid than posterior end. talonid, and the margins are curved so the COMMENTS: QMF52176 is a damaged tooth appears anteriorly bulbous. Relative specimen and is tentatively identified as m4, cusp position and heights are as in m2–3. because it differs significantly from other Anterobuccal cingulum is reduced to a very specimens identified as m2 or m3 (figs. 2, 3). short and stout parastylid-like protrusion near It is possible that QMF52176 is incorrectly the enamel base, below the paracristid. assigned as m4 but will remain thus until further material is recovered. Anterolingual cingulum, also short, has a lingual parastylid and runs horizontally from anterior end of premetacristid. The arcuate DISCUSSION paracristid is disrupted by two paracristid Gawinga aranaea exhibits the following ridges, enlarged in comparison to m2–3. pseudocheirid synapomorphies: narrow, sele- Protoconid is conical with unbladed cristids; nodont lower molars; a distinct entostylid and a short posterobuccal ledge occurs on the metastylid; m1 cristid obliqua connecting with protoconid, similar to that in QMF52175 the metastylid, as opposed to the protoconid (m2). Lingual expansion of the protoconid or protostylid; and a lingually displaced m1 observed in m2–3, is developed further into an protoconid (Archer, 1984; Woodburne et al., unbladed, anterior protocristid, directed 1987). However, the distinct ridges on the slightly posterolingually. Protoconid angle is lower molars of G. aranaea represent an very wide, more similar to m2 than m3. autapomorphic feature that immediately se- Postprotocristid descends gradually, joining parates it from all other pseudocheirid taxa. the cristid obliqua in a continuous crest. The form of the ridges is such that the Postmetacristid is slightly steeper than m2–3. cristid obliqua and paracristid on the posterior Metastylid is bicuspid and crested length- molars are raised and the depth of the trigonid wise. It features short, transversely extended and talonid basins reduced, particularly as the blades from each apex and a lower, parallel ridges themselves fill the basins. This creates blade running the same distance from the relatively shortened cusp height compared to posterior base of each cusp. The blades are other pseudocheirid genera, but no apparent separated by small notches and the cusps, decrease in the overall relative height of crown postmetacristid and preentocristid are respec- enamel. The ridges show some resemblance to tively separated by deeper notches. Metaconid crenulations present in species of Pildra and ridge is almost straight, extending between the Pseudochirops, but the phylogenetic signifi- posterometastylid and the posterior end of the cance of these similarities is uncertain. 2007 ROBERTS ET AL.: MIOCENE POSSUMS 11

Interestingly, the ridges appear morpholog- stylid, which are not present in any other ically similar to those found in ektopodontids genus. The first lower molar also has an (particularly Darcius Rich, 1986), an enigmat- unusually long postcristid of the protostylid, it ic family of extinct possums allied with extends across the hypoflexid, obstructing the phalangerids (Pledge, 1986; 1991). The molar shearing plane between the trigonid and morphology in ektopodontids is characterized talonid and potentially restricting transverse by multiple ridges arranged in two trans- motion of the m1 paracone and protocone. versely oriented lophs. The ridges often bi- Bisection of the posthypocristid is another furcate and feature smaller, accessory ribs that unique feature of m1. G. aranaea exhibits the anastomose and reticulate at the base of the first evidence of a cuspate m1 protostylid in lophs (Stirton et al., 1967; Archer, 1984; extinct pseudocheirids, a feature that until Woodburne and Clemens, 1986; Woodburne, now had been regarded as a synapomorphy of 1987). However, the similarity of cusp detail extant genera. Further autapomorphies in- between ektopodontids and G. aranaea is clude the metaconid ridge, a cristid located more likely to be the result of convergence posterobuccally to the metaconid on all of the than close ancestry, as there is little besides the posterior molars. The form and position of enlarged ridges to unite the two groups. The this ridge is similar to the anterolingual unusually wide molars and transverse ‘‘lophs’’ protocristid found in species of Pseudo- of the species of Ektopodon are very much chirops. However, in G. aranaea, there is no opposite to the characteristics of G. aranaea or strong link between the protoconid and any species of pseudocheirid. Comparison is metaconid ridge besides occasional small links more appropriate with species of Darcius to the postprotocristid (there is only an (although the oldest material is Pliocene in incipient anterior protocristid in most speci- age), due to their relatively narrow, obliquely mens). The ridge is variable in its connection slanted molars with reduced number of ridges with adjacent features, particularly at the (Rich, 1986), and to a lesser extent with the anterior end and in QMF52176, in which it more plesiomorphic (ridges are weaker and forms an additional crest. Paljara nancyha- reticulated) Oligocene species of Chunia wardae shows a very small stylid or cuspule at (Woodburne and Clemens, 1986). However, the posterobuccal base of the m2–4 metaco- the ridges exhibited by ektopodontids form nid, which could be homologous to the a disjointed crest or loph, independent of the metaconid ridge of G. aranaea. cristids of the main cusps, whereas G. aranaea The anterior placement of the protoconid has unpeaked ridges that extend away from relative to the metaconid on posterior molars these main cristids, such as the cristid obliqua. is also a unique feature of G. aranaea, as is the Without the ridges, the molar detail of G. swelling of the posterobuccal base of the aranaea is unquestionably pseudocheirid in hypoconid. However, as the only identified nature (e.g., the oblique, selenodont cusps, the material of this species is a number of isolated lingually shifted m1 protoconid and the teeth, often lacking roots, it is difficult to enlarged m1 protostylid). Furthermore, the determine the precise orientation within the accepted phylogenetic affinities of pseudo- dentary. cheirids and ektopodontids is to separate The many autapomorphic characteristics of superfamilies — Petauroidea (Baverstock, the lower molars justify the erection of the 1984; Baverstock et al., 1987; Westerman et genus, although referable premolars and al., 1990; Kirsch et al., 1997; Osborne et al., upper molars have yet to be identified. 2002) and Phalangeroidea (Archer, 1984; Characteristic extra ridges should be expected Woodburne and Clemens, 1986; Woodburne, in them, especially the upper molars. The 1987; Pledge, 1991), respectively—with an morphology of the lower molar dentition, estimated divergence date of ,45 m.y. particularly the m1, is highly distinctive within (Springer and Kirsch, 1991). pseudocheirids and provides one of the best Besides the ridges, G. aranaea exhibits diagnostic tools in the identification of species. a number of other autapomorphies. The m1 Currently, G. aranaea is identified as one of has extended, shelflike cristids of the proto- the most derived species of the extinct 12 AMERICAN MUSEUM NOVITATES NO. 3560 pseudocheirids with an intriguing a number of approximately 16–23 m.y. (Archer et al., 1989, plesiomorphies shared with extinct taxa, sy- 1995, 1997b). Upper Site in particular has napomorphies with extant taxa and a suite of produced a very diverse local fauna and has autapomorphies as outlined briefly below. been biocorrelated with the Kutjamarpu Local Woodburne et al. (1987) identified species Fauna of northern South Australia (Archer et of Paljara and Pildra as the two most plesio- al., 1989, 1995, 1997b). Although Woodburne morphic pseudocheirid groups. Symplesio- et al. (1993) argued that the Kutjamarpu LF morphies shared with G. aranaea include: m1 was late Oligocene in age, Archer et al. (1997b) shorter than m2 in length; absence of over- argued it was early Miocene. Upper Site lapped or joined preentocristid and metasty- includes species in the three Oligo-Miocene lid; and presence of an entostylid and ridge. pseudocheirid genera Paljara, Pildra, and The first symplesiomorphy is also shared with Marlu, representatives of the modern genus species of Marlu and the last with species of Pseudochirops, an additional undescribed pseu- Pseudochirops. The ancestral form of the docheirid group, and G. aranaea. Wayne’s Wok talonid (entostylid is present; the hypoconulid Site has also produced taxa of the three Oligo- and posthypocristid are independent of each Miocene genera in addition to Gawinga and other; and the posterolingual corner extends shares many taxa with Upper Site Local Fauna further posterior than the end of the post- and other local faunas attributed to System B entocristid) is shared by G. aranaea and (Travouillon et al., MS.). Numerous other species of Paljara, but is also found in species petauroid and phalangeroid taxa have been of Pseudochirops. recognized from both sites (Crosby et al., Generic-level synapomorphies with other 2004). Many System B localities have produced pseudocheirids include: a progressively complex local faunas with relatively high levels of metastylid along the tooth row (shared with diversity and relative abundance of arboreal Pildra); an elongated preentocristid (shared animals. It has been suggested by Archer et al. with Marlu, Pseudokoala, and extant genera); (1989, 1995, 1997b) that such an ecological a lingual rib extending from the m1 paracristid community indicates a rainforest climate sim- (shared with Pildra, Pseudochirops, Petro- ilar to that found in montane New Guinea, pseudes,andPseudocheirus) and an enlarged Borneo, or the Amazon of South America. m1 protostylid (shared with extant genera). Arachnea Ridge Site is poorly sampled in Based on these features, G. aranaea appears comparison to Upper and Wayne’s Wok sites. particularly apomorphic in contrast to other Aside from the pseudocheirid material de- Oligo-Miocene pseudocheirid taxa, and the scribed here, only balbarine kangaroo materi- many autapomorphic features make reference al has been recovered from Arachnea Ridge to a particular group difficult. At present, it Site. Therefore, at the present time little can be also appears unlikely that any of the modern determined with confidence about the relative genera were derived from species of Gawinga. age of this site other than a possible early The relationships of Gawinga to other pseu- Miocene correlation with Upper and Wayne’s docheirid genera are yet to be fully assessed Wok sites. and will be investigated as part of a larger Broad changes in faunal composition be- project on the systematics and phylogeny of tween the early to mid-Miocene and late Oligo-Miocene pseudocheirids, incorporating Miocene, with a general reduction in arboreal a number of new taxa in preparation (Roberts taxa, including pseudocheirids, are well docu- et al., in prep.). mented by the Riversleigh fossil deposits TEMPORAL AND SPATIAL DISTRIBUTION: (Archer et al., 1989, 1995, 1997b; Myers et Gawinga aranaea is a relatively rare species, al., 2001). This is thought to correlate with found to date in only three of the hundreds of changes in paleoclimate at the time, relating to local faunas in the Riversleigh World Heritage the formation of the New Guinea Highlands area. Two of these deposits, Upper Site and and the onset of reduced rainfall on the Wayne’s Wok Site, are considered to be part of Australian continent (Kemp, 1984; Archer et Riversleigh’s System B deposits, which have al., 1995; Martin, 1998). This has been been interpreted to be early Miocene in age, or suggested as the cause of a shift from a closed 2007 ROBERTS ET AL.: MIOCENE POSSUMS 13 forest or rainforest vegetation structure to Queensland Parks and Wildlife Service, the a more open structure that would be less able University of New South Wales, the Queen- to support a high number of sympatric sland Museum, the Australian Museum and arboreal taxa (Archer et al., 1989, 1995, Zinnifex. We thank M. Bassarova, R. Beck, 1997b; Myers et al., 2001). Five genera of K. Black, P. Brewer, A. Gillespie, J. Louys, K. pseudocheirids are now recognized in the early Travouillon, and V. Weisbecker for discus- Miocene deposits of Riversleigh, lending sion, technical advice, and assistance. T. further support to this interpretation. Ennis, S. Ingleby, and N. Pledge kindly DIET: Extant pseudocheirids are one of the allowed access to comparative specimens from most strictly folivorous possum groups in the Australian Museum and South Australian Australia and New Guinea (Flannery, 1994). Museum. We also thank an anonymous The energy benefits of eating leaf matter are reviewer and W.D. Turnbull for valuable low, requiring the ingestion of large quantities, comments and suggestions. and therefore an efficient masticatory and digestive system (McNab, 1978; Hume et al., 1984; Foley and Cork, 1992). Strict folivory is REFERENCES most sustainable in mammals of 700 g mass or Aplin, K.P., and M. Archer. 1987. 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