THE PILKIPILDRIDAE, A NEW FAMILY AND FOUR NEW SPECIES OF ?PETAUROID POSSUMS (MARSUPIALIA: PHALANGERIDA) FROM THE AUSTRALIAN MIOCENE

MICHAEL ARCHER1, RICHARD H. TEDFORD2 and THOMAS H. RICH3

Collections made from the Etadunna Formation at Lake Palankarinna, Etadunna Station in northern South Australia from the Namba Formation at Lake Pinpa, Lake Yanda and Lake Tarkarooloo, Frome Downs Station, northern South Australia and from the newly discovered Miocene freshwater limestones of Riversleigh Station, northwestern Queensland, have revealed material referable to four previously unknown small Miocene possums. These cannot be referred to a known family-level group of diprotodont marsupials and are described herein as Pilkipildra handi (Namba Formation), Pilkipildra taylori (Etadunna Formation), Djilgaringa gil/espiei (Riversleigh) and Djilgaringa thompsoni (Namba Formation). All four of these possums are placed in a new family of marsupials, the Pilkipildridae. All appear to have been omnivores but some were probably more specialised as seed or hard fruit-eaters. They appear to have been Phalanger-like and/or Petaurus-Iike in diet. Structurally, pilkipildrids, most resemble petaurids but they also demonstrate resemblances to phalangerids, miralinids and ektopodontids. Although the precise phylogenetic interrelationships of the pilkipildrids within Phalangerida are uncertain, the tentative conclusion is that Pilkipildridae is the sister-group of Petauridae.

Key Words: Pilkipildridae; Pilkipildra handi; Pilkipildra taylori; Djilgaringa gil/espiei; Djilgaringa thompsoni; Phalangerida; Petauroidea; Marsupialia; Miocene. Pages 607-27 in POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION ed by M. Archer. Surrey Beatty & Sons and the Royal Zoological Society of New South Wales: Sydney, 1987.

INTRODUCTION demonstrate the distinction of these possums from all others. IN 1972, Archer, Woodburne and others dis- covered an isolated M2 of a very unusual possum Finally, a dentary fragment with M2 was found by Rich and others in 1984 at Lake Yanda from the Middle Miocene Tedford Locality (Namba Formation; Yanda Local Fauna), South (Etadunna Formation; Ditjimanka Local Fauna) at Lake Palankarinna, South Australia (Fig. 1). Australia (Fig. 1). The purpose of this paper is to describe and In 1973, Tedford and others discovered a phylogenetically analyse this new material. dentary of a clearly similar form from the Middle Although these new possumsare rare in all faunas Miocene sediments at Lake Pinpa (Namba in which they occur, they provide an opportunity Formation; Pinpa Fauna, Billeroo Creek Site), to relate the local faunas of northern and central South Australia (Fig. 1). Another South Aust- Australia and to test current conceptsof their rela- ralian isolated MJ. referable to this Pinpa form tive ages(e.g., Woodburne et at. 1985; Archer and was collected by Rich and others in 1976 at Lake Flannery 1985). Tarkarooloo (Namba Formation; Tarkarooloo Dental terminology used in this paper follows Local Fauna) (Fig. 1). Archer (1978, 1984), Tedford and Woodburne Early reference to the Tedford locality form (1987) and Woodburneet al. (1987). Nomenclature was given as a "Burramyid similar to species of of higher taxa follows Aplin and Archer ( 1987; this Cercartetus"(e.g., Rich et at. 1982) and to the Volume). Stratigraphic and faunal names for Pinpa taxon as a "large Cercartetus-Iike South Australia follow Woodburne et at. (1985). burramyid" (Tedford et at. 1977). SYSTEMATICS Discovery by Archer and others in 1984 at the Miocene Riversleigh fossil sites (Fig. I, unnamed SubclassMarsupialia (Illiger, 1811) formation; Last Minute Site, Last Minute Local Superorder Diprotodontia Owen, 1866 Fauna) of a dentary of yet another species Suborder Phalangerida Aplin and Archer, 1987 similar to the central Australian forms was Superfamily Petauroidea (Gill, 1872) followed by the finding at Riversleigh (unnamed formation; Gag Site, Dwornamor Local Fauna) Family Pilkipildridae new of the first upper molars referable to one of these Type gen1L5:PilkiPildra is selected as the type peculiar possums. These teeth further serve to genus of the family. lSchool of Zoology, University of New South Wales, PO. Box I, Kensington, New South Wales, Australia 2033. 'Department of Vertebrate Palaeontology, Atnerican Museum of Natural History, Central Park West at 79th Street, New York, New York, USA. sMuseum of Victoria, Russell Street, Melbourne, Victoria, Australia 3000. 608 POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION

Fig. I. Localities and local faunas from which pilkipildrids have been recovered: A, Frome Downs Station, Pinpa and Tarkarooloo Local Faunas, Pilkipildra handi gen. and sp. n.; B, Etadunna Station, Ditjimanka Local Fauna, Pilkipildra taylori gen. and sp. n.; C, Riversleigh Station, Last Minute and Dwornamor Local Faunas, Djilgaringa gillespiei gen. and sp. n.; D, Frome Downs Station, Yanda Local Fauna, Djilgaringa thompsonigen. and sp. n. (Line drawings by J .Taylor). ARCHE~, TEDFORD, and RICH: THE PILKIPILDRIDAE 609

Additional genera:Djilgaringa. and deep dentary , a paraconid on M2' prominent metastylids, extensively crenulated crown Range: The four new and only known species surfaces and a transversely compressed trigonid in the family range stratigraphically, geo- graphically and temporally as follows: Pilkipildra onM2. handi, Namba Formation, Frome Downs Station, They differ from tarsipedids in all aspects of South Australia, medial Miocene; Djilgaringa gross dental and dentary morphology . thompsoni, Namba Formation, Frome Downs Station, South Australia, medial Miocene; Djil- They differ from miralinids (see Woodburne, garinga gillespiei, unnamed freshwater lime- Pledge and Archer 1987) in having transverse stones, Riversleigh Station, northwestern rows of small cuspules on the upper molars, Queensland, medial Miocene; PilkiPildra taylori, reduced paracones and metacones, a short and Etadunna Formation, Etadunna Station, South deep dentary, steeply inclined Ii' wide P3' non- Australia, medial Miocene. linear M2 trigonid and large metastylids. Etymologyofthefamily name:Pilki is a Dieri word meaning "different" and pildra is a Dieri word They differ from macropodoids in not having meaning "possum" (Reuther 1901; as translated a masseteric foramen or a masseteric insertion by Scherer and published in 1981). The Dieri into the body of the dentary and in having a short Tribe occupied the Tirari Desert in which occurs and deep dentary , transverse rows of cuspules on Lake Palankarinna where the first pilkipildrid the upper molars, low-crowned bunodont molars fossil was discovered in 1972. posterior to M2 and distinct trigonid basinson the anterior lower molars. Family diagnosis:Pilkipildrids are phalangeri- dans that differ from ektopodontids in having distinguishable protocones and metaconules, a Djilgaringa new large buccally deflected P , a very steep molar gradient, a distinct trigoni~ and cristid obliqua on Genotypic species:Djilgaringa gillespiei is the type M2' and in lack.ing the pronounced transverse species of the genus. rows of cuspules that are the dominant features of the lower molars of ektopodontids. Additional species: Djilgaringa thompsoni. Pilkipildrids differ from phalangerids in Distribution: Last Minute Local Fauna and Gag having short and deep dentaries, a steeply Local Fauna, unnamed freshwater limestones, inclined Ii' reduced and cuspule-like paracones Riversleigh Station, northwestern Queensland; and metacones, a very steep molar gradient, Yanda Local Fauna, Namba Formation, Lake short and relatively wide molars, pronounced Yanda, Frome Downs Station, South Australia. metastylids, poorly-developed transverse ridges on the molars, poorly-indented medial buccal Age: Medial Miocene, ca 14-12 ma and lingual flanks of the molars, reduced en (Woodburne et at. 1985 and Archer and Flannery echeloncrest relationships, a distinct protostylid 1985). on M2' an extremely reduced M2 metaconid, a steeply inclined M2 trigonid, a simple or reduced Etymologyand gender:Djilga means "baby" and cristid obliqua on all molars with no "kink" and Garinga means "possum" in the Wanji language very low crown relief. as spoken by the late I vy George of Riversleigh Station northwestern Queensland. The name is They differ from petaurids in having a very in reference to the small sizeand presumed short large and sectorial P3' transverse rows of cuspules faces of these possums. The genus is here given on the upper molars, extremely reduced but feminine gender. distinct paracones and metacones and pro- nounced metastylids. Genericdiagnosis: Species of Djilgaringa differ They differ from pseudocheirids in their lack from the species of other pilkipildrid genera in of distinct selenodonty, steep molar gradient, the following combination of features: larger reduction of en echeloncrest relationships, reduc- sectorial and more buccally deflected p ; P lacks tion of the paracone and metacone and trans- posterobuccal and posterolingual cinguia; the M2 verse rows of cuspules on the upper molars. trigonid is higher; the M2 is proportionately shorter and wider; the crown base of M2 is pro- They differ from burramyids in their short and portionately more swollen; the talonid l>asin on deep dentary , extensively crenulated molars, M~ is less well-developed; termination of the transverse rows of cuspules on the upper molars cnstid obliqua of M2 occurs at the posterobuccal and trigonid basinson the anterior lower molars. base of the trigonid; the M2 has a poorly- They differ from acrobatids in having M5' a developed paracristid; and there is no notch in large sectorial and buccally oriented P3' upper the anterior cingulum to accommodate the molars with transverse rows of cuspules, a short posterior edge of P'!. 610 POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION

Djilgaringa gillespiein. sp. suggests a semi-erect posture for this tooth, a posture in keeping with the apparently very short (Figs 2- 7) and deep dentary . Holotype: Queensland Museum fossil collec- tions F13028, a broken right dentary with P3' M2-5 There are three alveoli or alveolar remnants and alveoli for II' P2' ?PI and a partial alveolus for between p 3 and the alveolus for Ii. We suspect ?12.:!his specimen was collected by Archer et al. that each represents a distinct tooth because in May, 1984. there are no suggestions from the septal areas between the alveoli that a crown bridged any of Typelocality and ageof theholotype: The holotype the septa. The anterior alveolar remnant is in a was collected at Last Minute Site, from an position suggestive of 12,such as occurs in many unnamed freshwater limestone deposit (possibly phalaneridans (e.g., burramyids, phalangerids, a lateral equivalent of the Carl Creek Limestone ) petaurids etc.). The next alveolus in sequence on Riversleigh Station, northwestern Queens- probably represented a single rooted PI although land. The deposit is interpreted here to be the homology of teeth in this position even in approximately medi(1.lMiocene in age. living phalangeridans is in doubt (Archer 1984). Paratypeand its locality: A single isolated upper The alveolus anterior to p 3 probably represented right molar (Queensland Museum fossil collec- p 2. The relationships of tfie alveoli for this tooth tion No. FI4371), possibly an M3, appears to and p 3 indicate that p 2occurred at the baseof the represent this taxon. It was retrieved by anterobuccal corner of the p 3 crown. There is no H. Godthelp from blocks collected by Archer and wear facet in this position on the base of the p 3 others in May, 1983, from Gag Site, another crown thus suggesting that p 2 was a very small locality in the same unnamed but presumably tooth that functioned at the level of the gum. middle Miocene freshwater limestone deposits of Riversleigh Station. The p 3 is a massive sectorial tooth, being matched in height only by the trigonid ofM2. The Etymology:This speciesis named in honour of whole crown is obliquely set with respect to the Anna Gillespie, one of the principal Australian molar row, much as in the manner of the p 3 of Research Grants Committee preparators who some potoroids and burramyids. There was one worked on the Riversleigh Project at the Uni- relatively narrow cylindrical anterior root and versity of New South Wales unti11986. She was either one very wide posterior root or two also responsible for the discovery during posterior roots of uncertain width. The base of preparation of many of the new Riversleigh taxa. the crown is very swollen posteriorly and narrows Speciesdiagnosis: This speciesdiffers from Djil- anteriorly. At a position level with the junction of garinga thompsoni(new; see below) in that the P3 the anterior and posterior roots, the base of the was probably more buccally out-turned, the M2 crown is slightly indented on the buccal side. The (the only tooth of D. thompsoniknown) is pro- tall sectorial ridge is obliquely set within the portionately longer and narrower, the talonid is crown such that it forms approximately a 45° proportionately shorter, there is a protostylid, angle with respect to the molar row. There are the anteroventral face of the trigonid is less three cuspules along the crest corresponding to steeply inclined, the metaconid is better- the three prominent vertical ridges on the buccal developed, the cristid obliqua has distinct side and three of the four prominent ridges on anterior and posterior parts and the crenulations the lingual side. The fourth ridge on the lingual are coarser. side occurs between the first and the second. A Description:The dentary is deep and short. The short basally situated ridgelet occurs on the buccal side is badly damaged and reveals little buccal side anterior to the base of the second information. The lingual side preserves apart of prominent ridge. The anterior end of the crown the symphysis which was clearly very steep, is smoothly curved and anteriorly concave. The possibly rising at about 60° to the horizontal posterior end is a descending extension of the ramus. None of the dental foramina are pre- occlusal cutting crest. It descends abruptly away served other than a possible small mental from the main cutting crest, at an angle of about foramen on the buccal side below M2. A branch of 45° to the posterior end of the crown. The the dental canal is breached at the anterior end, posterior half of this descending crest underlies immediately adjacent to the steeply rising the comparably inclined trigonid of M2. The alveolus for II. The main portion of the dental anterior height of the crown markedly exceeds canal terminates in a large trabecular septum the posterior height. There are no basal cingula which forms the posterior wall of the II alveolus. or accessorybasal cusps. There is only a very slight ectalveolar projection The M has a high trigonid and broader of the dentary bey<:>ndM5 along the tooth row. talonid. nere is a short but wide anterior root The II alveolus suggests that this tooth was and along and wider posterior rooL The very robust. The alveolus rises at an angle of protoconid is displaced lingually such that it about 45° to the horizontal ramus and thus occurs lingual to the midpoint of the transverse

612 POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION

Fig. 3. Djilgaringa gillespiei, holotype, QM F13028, from Last Minute Site, Riversleigh Station, north- western Queensland. Stereophotographs of right dentary with alveoli for P2 (and ?P J and P3-M5 (anterior end up). (Photographs by H. Godthelp). width of the trigonid. The paraconid is end of the midvalley. The postmetacristid is represented by the anterior end of the anteriorly serrate, reflecting the pronounced enamel oriented preparacrista. The metaconid appears crenulations that occur on its posterobuccal to be a slight bump along the crest extending flank. The protostylid has two minor cristids, one posterolingually from the protoconid. Of these of which descends the trigonid flank in an three cusps, the protoconid is just taller than the anterior direction, to intersect the anterior metaconid which is about the same height as the cingulum, and the other of which abruptly paraconid. There appears to be a protostylid descends the flank of the protostylid to merge adpressed to the buccal flank of the protoconid with the flank of the trigonid buccal to the cristid below the level of the principal trigonid cusps. obliqua. There is also a distinct vertical cristid The paracristid appears to be continuous with that descends the buccal flank of the protostylid the lingual end of a short, somewhat poorly- to intersect the buccal cingulum of the trigonid. defined anterior cingulum. The cristid beyond The poorly-defined anterobuccal basal cingulum the metaconid and metacristid is a postmeta- passesaround the buccal side of the trigonid but cristid. It is more steeply inclined than the meta- extends no further posteriorly than the mid- cristid and connects the metaconid to the lingual valley. The whole trigonid rise steeply and rests ARCHER. TEDFORD, and RICH: THE PILKIPILDRIDAE against the posterior flank of p 3. The trigonid The M3 differs from the M2 as follows. Most of crest is continuous with, but at an angle to, the the differences pertain to the markedly different cutting crest of p 3. The two almost certainly trigonid. The trigonid and talonid are approxi- function as a unit to oppose p3. The talonid ofM2 mately the same height and width. The anterior has two cusps, a buccal hypoconid and a lingual root is longer than it is on M2. The whole crown entoconid. The whole of the talonid basin and is lower. The protoconid is anterobuccally posterior flank of the trigonid are strongly situated. There is no distinct paraconid. A pre- crenulated. These crenulations rise towards and protocristid connects the protoconid to the front interrupt the cristid obliqua, postmetacristid and of the tooth and merges with or becomes the pre-entocristid. The crenulations all converge to anterior cingulum. Two distinct crestsconnect to a point in the middle of the talonidt>asin, midway the large lingual metaconid, a postmetacristid along the transverse midvalley. The serrate and a premetacristid. The latter is continuous cristid obliqua extends from the hypoconid to the with the anterior cingulum. There is a low trans- base of the trigonid near its buccal flank, verse ridge raised among the crenulations that posterior to the protostylid. A prominent trans- links the protoconid to the metaconid. This ridge verse fissure demarcates its anterior end. is dorsally concave and highest where it contacts Another prominent transverse fissure occurs the metaconid. With wear this ridge could midway along its length. The cristid obliqua so become a functional serrated transverse lophid. divided has a descending posterior segment and Of the trigonid cusps, the metaconid is by far the an ascending anterior segment. There is no tallest, the smaller protoconid being subequal in actual transverse hypocristid but the talonid height to the talonid cusps. There is a small basin and its crenulations are raised along a trans- trigonid basin defined by the transverse ridge verse line between the entoconid and hypoconid. between the protoconid and metaconid and by With wear, this rise could have functioned as a the anterior cingulum. This basin is crenulated as serrated transverse ridge. There is a semilunar is the talonid basin. The cristid obliqua is posterior crest linking the posthypocristid and abruptly truncated at the midvalley by a pro- postentocristid around the posterior end of the nounced depression at the buccal end of the mid- talonid basin. There may be a small pre-entostylid midway along the pre-entocristid. The base of valley. A short postprotocristid which extends the buccal side of the crown is topographically posterolingually from the protoconid also much lower than the baseof the lingual side. The terminates at this depression. On the lingual side whole of the tall,' almost vertical buccal face of the of the crown, there is a large metastylid blocking talonid and parts of the buccal side of the the lingual end of the transverse median valley. It trigonid exhibit what appear to be rudimenta~ has short, inclined anterior and posterior connec- thegotic facets. This suggeststhat the M2 and p tions to the postmetacristid and pre-entocristid. were vertically honed against these surfaces.The The cristid obliqua posterior to the midvalley lingual side of the crown does not show this sort buccal depression is divided into two sections (as of wear. Thegotic facets are also developed in the it is in M2) the anterior one of which is short and transverse groove of the poseterior cingulum, on surmounts a small discrete swelling (the the posterobuccal flank of the entoconid, on the homologous swelling in M2 is relatively much crenulations ascending the posterior flank of the larger). The posterior segment of the cristid trigonid and on the posterior flank of the obliqua is anteroposteriorly oriented (whereas it hypoconid. is more oblique in M2). There are no buccal

Fig. 4. Djilgaringa gillespiei, holotype, QM F13028, from Last Minute Site, Riversleigh Station, northwestern Queensland. Composite scanning electron microscope photographs of lingual obliqua view of alveoli for ?P I and P 2 (or only for P2)' and P3-M5. (Photographs by H. Godthelp). 614 POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTIOr. cingula around the trigonid or on the antero- occlusal surface of ~5 faces dorsolingually while buccal face of the trigonid. the same surface of M2 faces dorsobuccally. The only known upper molar (FI4371) The M4 resembles M3 except as follows. The appears to be an M3 on the basis of size and crown is lower in height, narrower and shorter . occlusal patterns. There are only two distinct The talonid is distinctly narrower than the principal cusps, the protocone and metaconule. trigonid. The meta<.onid, although still the Assuming that there is a paracone and a highest cusp of the tooth, is proportionately metacone, the position of these cusps is in some shorter in height than that cusp on M .The doubt. Tentatively, we have assumed that they trigonid is only just taller than the talonia. The are not on the well-developed buccal margin of transverse trigonid ridge is less well-developed the crown. This is because there are two small and the trigonid basin lessdistinct. There is virtu- cusps lingual to the buccal crest in positions ally no development of the transverse talonid analogous to the paracones and metacones of ridge. Instead, a distinct sinuous but basically wynyardiids and other vombatimorphians and longitudinal median fissure divides the whole of some plesiomorphic petauroids (e.g., pseudo- the talonid into lingual and buccal sections. The cheirids). The protocone is the largest cusp, anterior segment of the cristid obliqua is very although the protocone, metaconule and buccal short and in fact little more than a slightly crests of the crown are subequal in height. The enlarged buccal end of one of the talonid basin buccal margin of the crown is formed by two adja- crenulations. cent occlusally convex crests. We think that this The M5 is similar to M4 except as follows. The large crest represents hyperdevelopment of a crown is smaller in all dimensions. The talonid is buccal cingulum. Between the peak of the much narrower than the trigonid. The posterobuccal crest and the protocone, occur metaconid and protoconid are subequal in height three cuspules aligned in a transverse row. and just taller than the talonid cusps. The Similarly, between the peak of the posterobuccal entoconid is extremely reduced and the crest and the metaconule, there are also three posterolingual corner of the tooth compressed. aligned cuspules. Of the anterior row of cuspules, There is no differentiation of the occlusal surface the most buccal is associatedwith minor cristae into a trigonid or talonid basin, the crenulations that appear to be homologues of a preparacrista forming a single pattern over the whole surface. and a postparacrista. For this reason, we The metastylid is only just distinguished as a interpret this cuspule to be the paracone. There slight prominence on the postmetacristid. There are no comparable cristae associated with the is no distinguishable cristid obliqua. The most buccal cuspule in the posterior row. The hypoconid is linked on the buccal side of the short preparacrista extends anterobuccally to tooth to the protoconid via the buccal ends of intersect the anterobuccal crest at the antero- transverse crenulations. Much of the occlusal buccal corner of the tooth. The longer postpara- surface of the crown exhibits small horizontal crista extends posteriorly from the paracone and thegotic facets that have sharpened the edges of then swings posterobuccally to intersect the the crenulations and crown margins. There is also a curious elongate depression worn in the middle of the rear half of the crown. Possibly it is the result of occlusion with the buccal edge ofM5. However, no analogous facet occurs on any of the other lower molars. Meristic gradients in the lower tooth row are as follows. Apart from the protoconid, all principal cusps decrease in size posteriorly. The protoconid of M2 is approximated to the tall metaconid but the protoconids of M3 to M5 also decrease in size posteriorly. The metastylids increase in size from M2 to M3 and then decrease to M5. The molars decreasein length, width and crown height from MI to M4.:.The whole tooth row is gently arcuate with M2 and M5 being topographically the highest posItioned teeth and M3 the lowest. This results in an occlusally concave tooth row when viewed from a lateral Fig. 5. Djilgaringa gillespiei. holotype, QM F13028, from Last point of view. Accordingly it may be presumed Minute Site, Riversleigh Station, northwestern that the curvature of the upper tooth row was in Queensland. SEM detail of occlusal view of alveoli for the opposite direction. There is also a sinuous ?P I and P2 (or only for P 2)' and P3-M2 (plus part of twist in the crown orientations such that the trigonid of M3). (Photograph by H. Godthelp). ARCHER, TEDFORD, and RICH: HE PILKIPILDRIDAE 615

Fig. 6. Djilgaringa gillespiei, paratype, QM Fl4371 , RM3, from Gag Site, Riversleigh Station, northwestern Queensland. Stereophotographs of occlusal view. (Photographs by H. Godthelp). posterobuccal crest. A preprotocrista extends cuspules in the posterior transverse row. The anteriorly and then swings buccally to become anteromost of the two buccal metaconule crests the anterior cingulum. This cingulum is con- bifurcates into crenulations that run to the centre tinuous around the anterobuccal end of the of the crown. The isolated median cuspule on the crown with the hyperdeveloped buccal posterior transverse crest is (with extreme cingulum. The postprotocrista extends caution) referred to here as the neometaconule. posteriorly then swings abruptly buccally and The surface of the crown is dominated by the terminates anterior to the premetaconulecrista. large central basin bounded on the anterior and The premetaconulecrista extends anteriorly and posterior sides by the transverse ridges. The low then swings anterobuccally to terminate opposite point of the occlusal surface of the crown is in the the postprotocrista. The postmetaconulecrista middle of this basin. Thegotic facets are not extends posteriorly and then swings buccally to apparent on the occlusal surface but the crown is become the posterior cingulum. This cingulum is almost unworn. The lingual side of the crown continuous around the posterobuccal corner exhibits very gentle crenulations on the flanks of with the buccal cingulum. A deep obliquely the protocone and metaconule but there is no oriented fissure interrupts the crown from near lingual cingulum. The anterolingual flank of the its lingual edge to pass between the pre- protocone exhibits a sharp corner extending metaconulecrista and postprotocrista thereby from the tip of the cusp to the baseof the crown. determining the boundary between these two The crown has three flattened roots. There is one crests. A similar transverse fissure extends in transversely compressed and elongate lingual from the buccal margin of the crown to divide the root and one posterior and one anterior buccal buccal cingulum into its convex crests. Both the root both of which are very wide and antero- lingual and buccal fissures lead to the centre of posteriorly compressed. the crown, as do the crenulations covering most of the occlusal surface of the crown. There is thus Discussion: Clarification should be given here a "point-focus" for the crenulations as there are of the reasons for concluding that the paratype on the lower molars. A small transverse crest links and holotype are conspecific. First, both speci- the protocone to the most lingual of the three mens represent a similar-sized species of cuspules in the anterior transverse row. Between phalangeridan with very low-crowned, similarly this cuspule and the paracone is the third and crenulated, bunoquadritubercular posterior longer isolated cuspule. With extreme caution, molars. Second, both represent a very rare taxon we refer to this medial cuspule as a paraconule. in assemblages of otherwise relatively well- There are two small transverse crests that leave represented species. The probability that the two the buccal tip of the metaconule. The postero- specimens represent different but similar-sized, most of these terminates in the slight swelling similar-shaped, rare and yet different taxa seems that represents the most lingual of the three remote. However, the most compelling reason 616 POSSUMS AND OPOSSUMS: STUDIES IN LVOLUTION

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Fig. 7. Measurements (mm) of Djilgaringa gillespiei. Tooth lengths and widths are maximum dimensions of crowns. Paratype. lower left. Holotype, above (buccal view) and right (occlusal view). for concluding that they represent the same chitinous insects such as beetles or even small taxon comes from consideration of occlusal vertebrates. patterns. Djilgaringa thompsoni new The paratype occludes perfectly with the (Figs 8-9) holotype ..even to the extent that the unusual metastylid of the M3 perfectly occludes along the Holotype:The holotype and only known speci- anterior flank of the distinctive transverse men is South Australian Museum SAM P24918, "crista" formed by the transverse alignment collected by a joint expedition of the Royal of the protocone, buccal protocone crest, Australian Electrical and Mechanical Engineers protoconule and reduced metacone. Similarly, (RAEME) of the Australian Army and the the metaconule perfectly occludes within the Museum of Victoria on 23 August, 1984. It is a short but distinctive trigonid basin of M4" left M2 in a fragment of a dentary that also retains parts of the alveoli of C1' P?2' P 3 and M3. Because this taxon is the only one for which Type locality: The holotype was collected from upper teeth are known, it is the best one to use in the upper 10 centimetres of lake surface sedi- attempts to determine occlusal mechanics. con- ment, approximately 5 metres east of the western sidering the transverse alignment and similar size edge of Lake Yanda (31001'S, 140°19'E), of the principal upper cusps and cuspules and approximately 63 km northeast of Frome Downs the incipient or slightly developed transverse Station Homestead, Frome Downs Station, South cristids of the lower molars, it seems probable Australia. that there was a significant transverse grinding phase in the chewing cycle. Local Fauna and Age: The faunal assemblage collected at the type locality has been named the The elaborate crenulations covering the sur- Lake Yanda Local Fauna. The unconsolidated face of the crown would have acted as a very surface material comprising the sample collected effective grating device during a transverse for processing was not demonstrably in situ. It grinding phase as well as added to the durability could represent: 1, an erosional wash from the of the crown surface. The wide bases of the western edge of the Lake Yanda outcrops and crowns, much narrower occlusal surfaces and hence from an unknown horizon within the short, deep dentaries suggest that, whatever was Namba Formation; or 2, a natural lag deposit being comminuted, it required considerable remaining in situ after the finer sediments from force. The powerfully built shearing premolar the originally fossiliferous layer were removed. and combined M2 paracristid- P3 shearing crest unit also suggest that this possum was cutting Tedford et al. ( 1977) suggest that this fossil- something hard and resilient. Possibly it was iferous deposit at Lake Yanda is part of the lower seeds with a hard husk or seed coat, very unnamed member of the Middle Miocene ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 617

Fig. 8. Djilgaringa thompsoni,holotype, SAM P24918,left M2' from Lake Yanda, Frome Downs Station, South Australia. Upper, SEM stereophotographs of occlusal view (anterior towards top). Lower, SEM photograph of oblique buccal view (anterior to left). The pale area on the buccal flank of the hypoconid is damaged enamel. (Photographs by H. Godthelp).

Namba Formation and that the Yanda Local Tertiary Australian mammals. She has also been Fauna is probably equivalent to the Pinpa Local a mainstay in the preparation and curation of Fauna. Rich et at. (1982), however, suggest that the Tertiary collections of the Museum of the fossiliferous unit may be at the base of the Victoria. upper unnamed member of the Namba Forma- SpeciesdiagnosiS': This speciesdiffers from Djil- tion. Further comments about this locality are gan:ngagilles~iei in that 1he P~ was prob~bly less given in Archer (1982: 404) but the precise oblIquely oriented, the M2 IS proporuonately stratigraphic position of the Yanda Local Fauna shorter and wider, the talomd is proportionately within the Namba Formation is at present uncer- longer, there is no protostylid, the anteroventral tain. face of the trigonid is more steeply inclined, Etymology:This speciesis named in honour of the metaconid is less distinct, the cristid obliqua Betty Thompson who was involved in the col- appears to consist of a single uninterrupted lection of the holotype as well as many other cristid and the crenulations are more delicate. 618 J'OSSUMS AND OPOSSUMS: STUDIES IN EVOLU [ON

Description:This description will confine itself "\ to aspects that differ from those of Djilgaringa gillespiei. The disposition of the alveoli in the dentary fragment indicate that the premolar row was much less irregular than that of D. gillespiei.The T posterior (and possibly only) root of p 2 occurs 3'44 2.7 anterior to the anterior root of p 3' ratDer than lingual to it. There is also a suggestion from the -1- 3'06 alveolar margins that p 2 was two-rooted with a much smaller anterior root. This conclusion is reached becauseof the sharp rise in the alveolar borders between what is therefore interpreted Fig. 9. Measurements (mm) of the holotype of Djilgaringa here to be an anterior and a posterior root. In D. thompsoni. Tooth lengths and widths are maximum gillesPiei, p 2 appears to have had only one root dimensions of crown. becausea comparable rise in the alveolar margin is not evident. The Yanda species is relatively more specialised than the Riversleigh species in its The M of D. thompsonidiffers from that tooth shorter, stockier molars. However, there are in Do gillespiei as follows. It is proportionately other characters that suggestthat the Riversleigh shorter and wider. Its talonid is also proportion- species is relatively more derived. For example, ately wider and shorter than the trigonid. The its p 3 is markedly oblique and was probably cristid obliqua is not interrupted by a transverse hyperdeveloped with respect to the Yanda fissure. The posthypocristid forms a gentle angle species, its p appears to have had only a single as it passes lingually to become the posterior root, its posfuypocristid is rounded and unlike cingulum (in contrast to the continuous curve the shape more typical of other phalangeridans present in DogillesPiei). The posterior flank of the and the protoconid is more buccal in position. talonid is vertical such that the posterior Each species, therefore, appears to be cingulum is the most posterior extension of the autapomorphically specialised and unsuitable as crown (in contrast to Dogillespiei where the most an ancestor for the other. They are regarded posterior portion is the posteriorly swollen base here as each other's sister-group. of the cro~n). Despite the proportionately short talonid, the posterior cingular "basin" (the area between the posthypocristid-postentocristid and Pilkipildra new the poorly-developed transverse ridge) is larger Genotypic species:Pilkipildra handi. than it is in D. gillespiei. The trigonid is propor- tionately more massive but lacks any trace of a Additional species:Pilkipildra taylori. protostylid or buccal vertical crest on the flank of Distribution: Tedford Locality, Etadunna the protoconid. There are no coarse vertical Formation, Etadunna Station, South Australia; crenulations on the buccal flank of the trigonid Billeroo Creek (Site 3) and Tom D's Quarry on and no anterobuccal basal cingulum. The para- the western side of Lake Tarkarooloo, Namba cristid is proportionately .longer. The protoconid Formation, Frome Downs Station, South Aust- is situated in a more buccal position. The ralia. metaconid is not distinct and appears to be Age: Medial Miocene (Woodburneet al. 1986). smaller than that cusp in DogillesPiei. Discussion:This speciesis unusual but not only Etymology and gender: The etymology of Pil- becauseof its peculiar morpholoy. On the apical kiPildra is the same as that given above for the buccal face of the trigonid, just below the family. The genus is here given feminine gender . protoconid, there is a thegotic facet that does not Generic diagnosis: Species of Pilkipildra differ appear to have a counterpart in DogillesPiei. It dis- from those of the only other pilkipildrid genus, plays some microstriations that are parallel to Djilgaringa, as follows: they have a smaller and those which occur on other parts of the M2 and less buccally out-turned p 3; posterobuccal and which indicate an oblique vertical shearing phase posterolingual cingula on p 3; lower trigonids on as the teeth approach the centric position. How- M2; proportionately longer and narrower M2; ever, in this facet there are many more micro- less swollen M2 crown base; continuation of the striations at right angles to these which suggest cristid obliqua up onto the posterior flank of the that the trigonid of M2 was being forced in an trigonid; a relatively well-developed paracristid anteroventral direction to hone the postero- on M2; a notch in the anterobasal cingulum of M2 lingual flank of p3o for receipt of the posterior edge of p3; a less A wear facet in a similar position on M2 of D. serrate and buccally poorly-developed transverse gillespieidoes not appear to be a thegotic facet, its cristid on the talonid of M2; less well-developed surface being irregular rather than polished and transverse cristids on the talonids of M3-4; less covered by pits and multidirectional scorings. crenulated crowns; a single pronounced vertical ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 619 crenulation on the posterior face of the M2 Etymology:This speciesis named after Suzanne trigonid below the metaconid; and proportion- Hand (formerly of Macquarie University and ately shorter and wider posterior molars. now of the University of New South Wales) who, besides being a research colleague and the prin- Pilkipildra handi new cipal research worker to make sense of the (Figs 10-12) myriad bat fossils from Riversleigh, has spent four field seasonsin the Riversleigh area (sup- Holotype: The holotype is South Australian ported in part by ARCS funds) and two in South Museum palaeontoloical No, P27909, a left Australia helping to collect many of the new dentary fragment with damaged P3 and M2' mammals that have been found in these areas. complete M3,.1.and alveoli or parts of alveoli representing LI' P?1' P ?2 and M5' DiagnosiS':This species differs from PilkiPildra Typelocality: The holotype was collected at Bil- taylori (which is known only from an isolated M2) leroo Creek, Site 3 (31°9'S, 140°14'E), Frome as follows: the M2 is shorter; the trigonid is pro- Downs Station, South Australia. It was obtained portionately shorter and wider; the posterior from low outcrops of the Namba Formation cingular basin of the talonid is shorter and less exposed on the north side of the Creek 2.4 km well developed on the buccal side; the posthypo- northeast of the north end of Lake Pinpa. The cristid is less crenulate; the vertical crest below sediments at this locality consisted of green clay- the metaconid is less extensively developed; the stones overlaying dolomitic claystones, buccal segment of the transverse talonid cristid is Paratypeand locality:An almost unworn isolated less well developed; the anterior basal notch is left M2 (NMV P157570) appears to represent this narrower because the buccal side of the notch is less well developed; and the postentocristid is taxon. It was collected in 1976 by a joint expedi- tion of the Queensland Museum, Museum of better developed. Victoria and Monash University from Tom 0's Description:This description is based on a com- Quarry (31°8'30"S, 140°6'20"E), on the western side of Lake Tarkarooloo, Frome Downs Station, parison with the only other reasonably complete pilkipildrid dentary known, the holotype of Djil- South Australia, garinga gillesPiei and, in large part, will be an Localfaunas and age range: the Billeroo Creek annotation of the differences between the two. type locality h':ls produced an unnamed local fauna evidently roughly equivalent to the Pinpa The dentary is broken posterior to the alveoli Local Fauna in terms of stratigraphic level within for M5 and anterior to the posterior wall of the Ii the Namba Formation; Tom O's Quarry appears alveolus. There are at least two small alveoli to be stratigraphically above the sites at Lake anterior to p 3.Although their homology is uncer- Pinpa and Billeroo Creek, The Namba Forma- tain, their similarity to the alveoli in the holotype tion is interpreted (Woodburne et al, 1985) to be of D. gillespiei suggests that they represent a medial Miocene in age. single-rooted PI and p 2' The root of the lower

(') 3

Fig. 10. PilkipildrQ handi, holotype, ~ AM P27909, from Lake Pinpa, Frome Downs Station, South Australia,left dentary with alveoli for P 2 and Ms plus P 3-M .P 3 and M2 are significantly damaged. A, lingual view (anterior towards bottom). B, buccal view (anterior towards top). a, stereophotographs of occlusal view (anterior towards top). (Photographs by ~. Tarka). 620 ;POSSUMS AND OPOSSUMS: S- DIES IN EVOLUTION

Fig. 11. PilkipildrQ handi, paratype; NMV P157570, LM2' from Lake Tarkarooloo, Frome Downs Station. South Australia. Left, SEM photograph of occlusal view (anterior towards top). Right, SEM photograph of buccal view (anterior to left). (Photographs by H. Godthelp). incisor was very large judging from the dimen- paratype. Otherwise there are no cingula on the sions of the alveolus that remains. It extended buccal, lingual or anterior sides of the crown. posteriorly to at least the level of M2. The mental There is no protostylid. The buccal face of the foramen occurs at about mid-depth down the trigonid is smooth (rather than vertically dentary and opens just behind the anterior root crenulated), although there is a prominent verti- of p 3. A groove begins at this opening and con- cal swelling that extends ventrally beyond the tinues steeply upward acrossthe anterior root of steeply sloping metacristid. The cristid obliqua p 3 to the alveolar margin. A tiny posteriorly runs smoothly in a sinuous curve from the opening foramen occurs between M2 and M3 on hypoconid to the posterior flank of the trigonid the buccal side of the dentary at about mid-depth. in a position immediately lingual to the posterobuccal end of the metacristid. An oblique The p 3. is damaged but enough remains to wear facet connects the end of the two cristids. demonstrate its distinctive shape. It was narrower Apart from the single prominent vertical crenu- than the p 3 of D. gillesPieiand had posterobuccal lation that extends down the posterior flank of and posterolingual cingula. A steep but well- the trigonid from the metaconid, there are no developed thegotic facet extends along the prominent vertical crenulations on this part of buccal side of the posterior remnant of the the trigonid. The metaconid is relatively promi- median longitudinal crest and down onto the nent and curved. It extends anteriorly from the posterobuccal cingular crest. The remnants of protoconid and then, about halfway along its the buccal and lingual flanks of the crown suggest length, it swings anterolingually and continues to that there was a basal swelling and that the shear- the basal anterior end of the crown where it ing portion of the tooth was narrower than that forms the lingual flank of the anterior basal region of the p 3 in D. gillespiei. The remnant notch. The lingual flank of the trigonid is con- slopes of the tooth suggest that it was shorter- cave because of the curvature of the paracristid. crowned and there is no indication of vertical The hypocristid is sinuous rather than evenly ribs. Altogether, it appears to have been a more curved. It gently swings posterolinually and then slender, shorter and less sectorially specialised tranversely from the hypoconid until it reaches tooth. the mid-point along its length where it bends for- There are two M2's known (the holotype and ward, then backwards and then curves antero- the paratype). The anterior end of M2just over- lingually to gradually merge with the postento- laps the posterolingual basal cingulum of the p 3 cristid. This inflexion in the hypocristid corres- (rather than the posterior part of the median ponds with the anterior end of M3 and probably longitudinal crest). The base of the trigonid is helped to reduce independent transverse move- only gently inclined with respect to the baseof the ments of the teeth. The talonid basin is less talonid. The M2 crown is relatively long for the crenulatedthan it is in the speciesof Djilgaringa.The tooth row, in part because the trigonid is less talonid basin is proportionately longer, narrower, compressed anteroposteriorly. The anterior deeper and lesscrenulated. The transversetalonid basal portion of the crown is developed into two cristid is not serrateand is lesswell developedthan in swellings that define a small median basal notch. the speciesof Djilgaringa.It extends buccally from A tiny anterobuccal basal cuspule or cingular the entoconid to the midline of the talonid where remnant occurs on the anterobuccal flank of the it vanishes at the base of the lingual flank of the paracristid near the anterior notch on the hypoconid. The posterior cingular pocket ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 521

(between the transverse talonid cristid and the suggests that the bite was not as powerful. The posthypocristid) is relatively small and restricted significance of the difference in orientation of to the lingual half of the talonid. The walls of this the p 3 is unclear although it must reflect a pocket are not crenulated. differently shaped p3 and perhaps a lessrounded face. The dentary is certainly less arcuate and The M is only represented in the holotype. suggeststhat the lower jaw was relatively longer . Comparea with the M3 of Djilgaringa gillespieiit is The smaller and less extensive crenulations on proportionately shorter and wider although the molar surfaces and the relatively more longer in absolute dimensions. The basal buccal prominent and non-serrated cristids suggest that inflexion between the trigonid and talonid occurs P. handi spent relatively less time transversely in a more posterior position. There is no grinding hard foods and more time shearing and posterior cingular pocket and no transverse cris- grinding softer foods. The relative reduction tid on the talonid. The talonid basin is relatively of the cingular pocket on the talonid suggests less crenulated. The trigonid basin is not clearly that the metaconule of the as yet unknown crenulated. The metastylid is smaller. The upper molars was smaller (or less distinct} hypocristid is less curved and gives the posterior and that a less significant break occurred end of the tooth a more rectangular (rather then between the premetaconulecrista and the post- round) appearance. protocrista. The presence of the trigonid basin, The M4 is only known in the holotype. Com- however, suggests that the metaconule was pared with that tooth in D. gillespiei,it is relatively present even if it was smaller than that cusp in p . much shorter, wider and lesscrenulated. There is handi. no clear longitudinal groove in the talonid. The metastylid is very poorly developed. The trigonid Pilkipildra taylori new basin is not crenulated. (Figs 13-14) The M5 is unknown but its anterior alveolus in Holotype:The holotype and only known speci- the holotype suggeststhat it was also proportion- men is South Australian Museum Palaeonto- ately wider than that tooth in D. gillespiei. logical collections No. P27910. It is an isolated Discussion:This speciesis the best-known of the LM2. genus. The relatively unworn isolated LM2 Type locality: The holotype was collected by (NMV P157570) from Lake Tarkarooloo adds Woodburne, Archer et al. in 1972 from Tedford important information lacking in the holotype. Locality, Lake Palankarinna, Etadunna Station, Fortunately, enough of M remains in the South Australia. holotype to demonstrate the aimost indistinuish- Local fauna and age: Tedford Locality is the able shape and size of the paratype and hence its type locality for the Ditjimanka Local Fauna conspecificity with the holotype. which is interpreted (Woodburne et al. 1985) to Compared with the dentition of Djilgaringa gil- be medial Miocene in age. lespiei,the teeth of PilkiPildra handi suggest that Etymology:This speciesis named in honour of this possum used its cheekteeth in a slightly Jenny Taylor who spent almost seven years as a different way. The smaller and less swollen P3 distinguished part-time preparator, sorter , photographer, drafts person and artist connected with the vertebrate palaeontological research programme at the University of New South Wales. ~2.52i ( 3.54 Diagnosis: PilkiPildra taylori differs from P. T handi as follows: M2 is longer; the trigonid is 4.51 proportionately longer and narrower; the r 13"40 posterior cingular basin of the talonid is longer ~ 4.37 and better developed on the buccal side; the post- hypocristid is more crenulate; the vertical crest ~ below the metaconid is better developed; the 3,42 buccal segment of the transverse talonid cristid is better developed; the anterior basal notch is wider; and the postentocristid is less well ~ 2,87 developed. Description:The holotype is similar to the M2 of 1/ P. handi except for the features noted above in II the diagnosis. Overall, it is a larger tooth than the M2 of P. handi. It also exhibits a slightly corru- Fig. 12. Measurements (mm) of Pilkipildra handi. All measurements are maximum crown widths, lengths gated buccal protoconid flank in contrast to the and heights. Left, paratype. Right, holotype. smooth buccal flank of P. handi. 622 ;POSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION

Although it is unfortunate thatP. taylori is only known from M2' this tooth is the most distinctive of the lower molars and, judging by the differ- ences in M2 morphology in other pilkipildrids, a good basis for recognition of species. Considering the many tonnes of matrix that have been processedfrom Tedford Locality since 1971, there seems little point in putting off description of P. taylori on the chance that additional material would turn up in the future.

DISCUSSION Four aspects of pilkipildrids invite discussion: their interfamilial relationships; their intra- familial relationships; their ecological role; and their chronostratigraphic significance. The interfamilial relationships of the Pilki- pildridae within Diprotodontia are somewhat ambiguous. There are three most reasonable, hypotheses: I, either the pilkipildrids are most closely related to the Petauridae (Fig. 15A; the hypothesis favoured here); or 2, they are more closely related to a cluster of families that includes the Phalangeridae, Ektopodontidae and Miralinidae (Fig. 15B-C); or 3, they form a dis- tinct major group of phalangeridan possums, one which is no more closely related to phalangerid-like forms than it is to petaurid-Iike forms (Fig. 15D). Fig. 13. Pilkipildra taylori, holotype, SAM P27910, LM2' from Lake Palankarinna, Etadunna Station, South Pilkipildrids and petaurids share many Australia. A, SEM photograph of occlusal view features of molar morpholoy including the (anterior towards top). B, line drawing of same tooth: occlusal (upper left); buccal (upper right); anterior following: 1, bunodonty; 2, quadritubercular (lower left); posterior (lower centre); lingual (lower molar shape; 3, extensive fine crenulations; 4, right). Bar scale = 2 mm. The occlusal view in 13B point focus of the crenulations of the lower is more directly overhead; the occlusal view of 13A is molars into the centre of the crown; 5, a relatively an oblique view from a more posterior position. (Photograph by H. Godthelp; drawings by M. Wood- simple cristid obliqua; 6, a comparably modified burne). trigonid on M2; 7, a similar trigonid basin on the M3-4;8, low transverse cristids on the talonids of M2-3and trigonids ofM3-4; 9, reduced dimensions 2.94 and almost flat occlusal surface of M. ; 10, a simi- lar dentary shape; 11, relatively s~all medial indentations on the buccal and lingual surfacesof the lower molars; 12, narrow posterior halves of the upper molars; 13, a strongly curved paracris- 4'77 tid on M2; and 14, reduction of en echeloncristid relationships. ~ However, pilkipildrids also share with phalangerids, miralinids end ektopodontids several features (Fig. 15B-C) including: 1, a ~3.06 tendency to elaborate conules and crenulations Fig. 14. Measurements (mm) of Pilkipildra taylori. All into cuspidate transverse crests; 2, presence of a measurements are maximum crown length and vertical cristid below the metaconid on the widths. posterior flank of the trigonid; 3, quadri- Discussion: The two species of PilkiPildra are tubercular molars; 4, point focus of the crenula- much more similar to each other than are the tions of the lower molars; 5, a comparably modi- species of Djilgaringa leaving little doubt that they fied trigonid on M2 (ektopodontids differ and are are congeneric. On the other hand, they exhibit unique here); 6, afunctional M2 paracristid-P 3 such different proportions that there can also be shearing unit (again ektopodontias differ here); little doubt that they represent distinct-species. 7, a very large and sometimes buccally deflected ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 623 p 3 (and again ektopodontids display an suggest that the similarities of upper molar autapomorphic condition here, one that appears morphology between phalangerids and pilki- to converge on that seenin petaurids); 8, cuspsof pildrids are based on symplesiomorphy. In turn, the upper molars arranged into transverse rows that suggests that the albeit low and poorly- with the buccal cusps being subequal in height to formed transverse crests of petaurid upper the lingual cusps; 9, reduction of the paracone molars are autapomorphic developments of the and metacone; 10, development of trigonid transverse rows of low cusps that would have basins on M3-4.with their associated transverse been present in a petaurid-pilkipildrid common trigonid cristids (phalangerids have also done ancestor. Phylogenetic transition of this sort may this on all of the lower molars and on the talonids have occurred several times in diprotodont as well, features not present in the lower molars marsupials such as in phalangerids, macro- of pilkipildrids or petaurids). podoids and possibly wynyardiids (e.g., see Archer 1976; Tedford et at. 1977; Rich and The third major phylogenetic hypothesis, an Archer 1978; Archer 1984 and Pledge 1987). unresolved trichotomy (Fig. 15D), depends for its defence on the inability to confidently recognise Accepting petaurids to be the group most dichotomies. closely related to pilkipildrids has other con- sequences. Petaurids are clearly related to Choice between the three phylogenetic pseudocheirids among families of phalangeri- hypotheses must depend to a certain extent on dans with living representatives (e.g., see McKay preconceptions about which dental features are 1984). They may also be related to acrobatids and more reliable indicators of relationship. At tarsipedids (Aplin and Archer 1987) but the present, we have no other guide such as basi- evidence for this is ambiguous. If pseudocheirids cranial morphology . are accepted as the sister-group of the pilki- Perhaps the best evidence for phalangerid pildrid-petaurid sister-group, they may serve as relationship is the upper molar morphology. The the outgroup for interpretation of the probable incipient but incomplete transverse lophs and the plesiomorphic states of polymorphic characters evidently reduced metacone and paracone are in the pilkipildrid-petaurid sister-group. In this features found in some phalangerids (albeit the case, the following features of pilkipildrids more derived taxa; see Flannery et at. 1987) but would probably be autapomorphic rather are not known to occur in petaurids. Added to than symplesiomorphic pilkipildrid-petaurid this is the well-developed phalangerid-like M2 features: The steeply inclined Ii; the large, some- paracristid- P3 shearing crest unit. Again, nothing times out-turned and sometimes serrated P ; the like this develops in petaurids but its absence prominent and isolated metastylids (which do not could be the result of the marked reduction of P3 appear to be the same as the metastylids of in petaurids. This possibility is significant pseudocheirids in that they are not part of or because a comparable functional unit occurs defined by a postmetacristid); the very narrow in some macropodoids, miralinids, some posterior half of M5 (this feature occurs also in burramyids and even thylacoleonids. Although it miralinids); the gently sloped lingual flanks of is possible that this two-tooth shearing-unit the upper molar; the well-rounded corners of the evolved independently in these groups, it is also upper molars; the very prominent, tall and possible that it represents a symplesiomorphic swollen buccal cuspsof the upper molars; and the feature of diprotodontians. very reduced paracones and metacones. The best evidence for petaurid relationship Similarly, autapomorphic petaurid dental seems to be the strikingly similar morpholoy of features would include: marked reduction of P3 the posterior lower molars, These are very low- and incorporation (with loss of identity) of the crowned, have reduced or absent transverse intermediate conules of th~ upper molars into talonid cristids, a very reduced M5, a longitudinal low transverse crests. median groove on the posterior lower molars, reduction of en echelon crest relationships, Other non-pseudocheirid-like features in barely indented buccal and lingual margins on pilkipildrids and petaurids are noted above as the lower molars and marked transverse con- hypothetical synapomorphies. striction of the posterior half of M5' These We should consider whether the Pilkipildridae features are unknown in phalange rids which all might be paraphyletic and more properly include have well-developed transverse crests on all of within it the Petauridae. In other words, isjustone the lower molars, large M5s, strongly indented of the pilkipildrids or pilkipildrid g~nera the crown margins and marked en echelon crest sister-groupof Petauridae? Although possible, it relationships, particularly in the lower molars, seems improbable. Among the diagnostic Tentatively , pending discovery of more com- features of the Pilkipildridae are the large P3 and plete material, we are inclined to favour the isolated metastylids, features that do not appear hypothesis of petaurid relationship and to to be plesiomorphic within the Petauroidea (they 624 J'OSSUMS AND OPOSSUMS: STUDIES IN EVOLUTION

~ w Macropodoipea Ma(ropodoiQea A B

~ y .(V'

f2f ( fj)

Fig. 15. Most-supported cladograms involving the Pilki- condition and there is commonly a notch in the pildridae. Character states for ektopodontids are anterobuccal corner of the anterior cingulum of the based,where possible,on Chunia cf C. illuminata Wood- lower molars (the condition varies intraspecifically but burne and Clemens, 1986 (e.g., AMNH ,95584), the the tendancy occurs only with the three families for most plesiomorphic of known forms. Those for which it appears to be a synapomorphy); 5, the trans- phalangerids are based on the "simple" -crowned verse crests are relatively smooth rather than denticu- forms such as Phalangerursin1L5 (see Flannery, Archer late, the P3 is markedly out-turned and the lower and Maynes 1987). Those for petaurids are based on molars exhibit a pronounced transverse constriction Petaurus alL5tralis (e.g., AM M9550). Those for between the trigonid and talonid; 6, there is an elab- pilkipildrids are mainly Pilkipildra handi. Those for oration of conules on the lower molars, an elaboration pseudocheirids are based on the "simple" species of of the M2 parastyle, markedly serrate transverse crests, Pseudocheirussuch as P. peregrinlL5.Tarsipedidae, etc., a modification of the "kink" in the cristid obliqua such refers to the apparent relationship between tarsi- that a small part becomes lingually isolated from the pedids with acrobatids (see Baverstock, Birrell and rest of the crest and the P3 is inturned (i.e., the crown Krieg 1987). Potential synapomorphies and is oriented anterolingually); 7, there is a steep molar autapomorphies (the hypothetical phylogenetic sig- gradient reducing posteriorly, a very narrow talonid nificance of these features depends on the position of on M5' a highly compressed M2 trigonid with a distinct the taxon in the alternate cladograms) are as follows: I, anterobuccal swelling, a very narrow P3 and steep and a combined shearing unit involving the M2 trigonid buccally displaced paracone crestson M2; 8, many con- and the posterior crest of P3; 2, the ectotympanic is ules comprise horizontal transverse crests, premolar solidly fused to the surrounding bones of the middle size is reduced and the molars are short and wide; 9, ear; 3, principal crests (the prehypocristid/postproto- biochemical affinity of living members (e.g., Kirsch cristid, preentocristid/postmetacristid and pre- 1977 and Baverstock, Birrell and Krieg 1987) and metaconulecrista/postprotocrista oppositional pairs) reduction of MI; 10, the protoconid is displaced to the meet in an en echelonpattern, there is a tendency to lingual side of the trigonid of M2' the cristid obliqua of enlarge the conules (intermediate cuspules between M2 extends to the top of the metaconid, the the principle cusps) and the metacone is enlarged; 4, hypoconids and posterior protoconids are markedly the cristid obliqua has a "kink" near its anterior end angular and the postprotocristids extend across the (after leaving the hypoconid, the cristid obliqua turns tooth to the lingual side of the crown; 11, molecular sharply lingually, sometimes even intersecting a short affinity of living forms (e.g., Baverstock, Birrell and anterolingual crest from the hypoconid, before meet- Krieg 1987);12, selenodonty is reduced and there is an ing the posterolingual end of the postprotocristid), the elaboration of a bunodont quadritubercular pattern, conules are arranged into high transverse ridges on the posterior molars are very low crowned, there the upper and lower molars, the ancestral selenodont is a steep molar gradient which reduces posteriorly, oattern is modified into a bunodont semi-selenodont the M. is reduced with a verv reduced talonid width. ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 625

Fig. 15 cont. -the transverse cristids on the talonids of the do not appear to be any potential synapomorphic posterior molars are reduced, there is a longitudinal states that would support a hypothesis that the median groove on the posterior lower molars, the en echelon crest relationships are reduced as are the pilkipildrids were actually the sister-group ofjust median transverse constrictions on the lower molars; one subgroup of the Petauridae (e.g., species 13, the II is steeply inclined, the P3 is large, the meta- of Gymnobelideus, Dactylopsila-Dactylonax or stylids are prominent and isolated, the lingual flanks of Petaurus).There are, in contrast, shared-derived the upper molars are small and vertically sloped as are the buccal flanks of the lower molars, the comers of the states that support the hypothesis of petaurid upper molars are well rounded, the M3 talonid is monophyly including the gross reduction of P3 narrow, the buccal cusps of the upper molars are and the loss of distinction of the conules on the prominent, tall and swollen and the paracones and upper molars. metacones are very reduced; 14, there is a marked reduction of P3 and a loss of distinction of the conules Relationships among the known pilkipildrids of the upper molars; 15, there is a tendency to develop transverse crests with cuspules, the cristid obliqua of are less obscure. Clearly there are two clades, M2 runs to the posterior flank of the protoconid (or each presented here as a new genus (Fig. 16). Of protostylid) rather than the metaconid or between the these, the species of PilkiPildra appear to be the protoconid and metaconid and there is a small vertical more plesiomorphic if Petauridae is accepted as cristid on the lingual posterior flank of the trigonid of M2; 16, see 9; 17, there are prominent and isolated the sister:.group of Pilkipildridae. They retain metastylids, a loss of the "kink" in the cristid obliqua, a what appears to be the plesiomorphic states for loss of the anterobuccal notch in the lower posterior lower molar morphology (e.g., less well- molars, well-rounded corners on the upper molars, the developed transverse talonid cristids). Of the talonid of M has a very narrow talonid, the molars speciesof Djilgaringa, D. thompsoniappears to be show a mar[ed decline in size posteriorly and the paracones and metacones are reduced; 18, see 10; 19, the more plesiomorphic in its lack of a protostylid see12 and 14 except that here the low transverse molar on M2' its apparently two-rooted P2' its smaller P3 crests and <;ristids are autapomorphic; 20, the M5 is and in its less elaborate crenulations. The differ- very reduced, the buccal sides of the lower and lingual ences between the species of Pilkipildra are less sidesof the upper molars have gentle slopes,the upper molars have rounded comers and there are semi-Iophs significant but the short proportions, small formed by small cuspules; 21, see17 but here the well- talonid cingular basin and poorly developed rounded comers of the upper molars are transverse talonid cristid of P. handi are more symplesiomorphic; 22, there are prominent and Petaurus-Iike than the corresponding states in P. isolated metastylids, reduced posterior molars, markedly reduced and low-crowned M5, a vertical taylori. lingual cristid on the posterior flank of the M trigonid, well-rounded'comers on the upper molars, low trans- The intrafamilial phylogenetic relationships verse crestson the lower molars, transverse rows oflow may have chronostratigraphic significance. First, cusps on the upper molars, reduced paracones and it is clear that Pilkipildra handi (Pinpa Local Fauna metacones, prominent anterobuccal cusps on the and Tarkarooloo Local Fauna) and P. taylori upper molars, a steeply inclined II and gently inclined li!lgual flanks on the upper molars and buccal slopesof (Ditjimanka Local Fauna) are very similar to each the lower molars; 23, the cristid obliqua has a "kink" at other and probably comparable in age. There is its anterior end and there is a tendency to develop a no way of confidently determining which (if notch in the anterobuccal comer of the posterior lower either) of the two is the older, although P. handi molars. appears to be structurally a bit more plesio- are absent in petaurids and pseudocheirids) and, morphic. therefore, evidence against the hypothesis of In contrast, Djitgaringa gillesPiei (Riversleigh Pilkipildridae being a paraphyletic taxon. Addi- local faunas) exhibits several features that tional autapomorphic and non-petaurid features suggest it is more derived than D. thompsoni(the in pilkipildrids that argue against inclusion of the Yanda Local Fauna) and hence that it is probably Petauridae within the Pilkipildridae include the younger in age. This hypothesis is supported by relatively short anteroposteriorly compressed accumulating evidence that suggests closer trigon ids on the lower molars, the relatively wide chronologic ties between the Riversleigh Gag and and short lower molars and the highly Last Minute local faunas and the Kutjamarpu autapomorphic morphology of the upper molars Local Fauna of South Australia (Archer in prep.), including the reduced paracone and metacone the latter generally being regarded (e.g., and relatively very deep transverse fissure which Woodburne et at. 1985) as younger in age than bisects the crown. In all of these characters, the Ditjimanka, Pinpa, Tarkarooloo and Yanda all known petaurids display plesiomorphic local faunas. It should be pointed out here that conditions. other more recently discovered Riversleigh local As a final consideration regarding interfamilial faunas (e.g., Mike's Menagerie) appear to have relationships of the pilkipildrids, we should closer ties to the older local faunas of central consider the possibility that the Petauridae as Australia (e.g., the Tarkarooloo Local Fauna) on treated here may be paraphyletic because the the basis of other taxa (e.g., species of Pilkipildridae may actually belong within that Namitamadeta).However, these apparently older family rather than outside it as its sister-group. Riversleigh local faunas have yet to produce Against this view, however, is the fact that there pilkipildrids. 626 POSSUMS AND OPOSSUMS: STUDIES IN EVOLU [ON

Q. thompsoni Q. qiltespiei research possible. Archer's 1983, 1984 and 1985 ""' / fieldwork at Riversleigh was supported by the Australian Research Grants Scheme (Grant No. >Jf E7915864). Additional aid was provided by the Queensland Museum and anonymous donors. Woodburne's and Archer's work in South Aust- y ralia was supported by a National ScienceFound- ~ ation Grant to Woodburne (Grant No. GB- 35488) and Australian Research Grants Scheme ~ ~ Petauridae support to Archer, T. Rich and P. Rich (Grant

y No. E76/15122). Tedford's work in the Frome Basin was supported by a National ScienceFoun- ~ Pilkipildridae dation Grant (Grant No. GB-18273X1). Other ~ financial support for South Australian work was provided to Archer by the University of New ,(1)' South Wales and the Queensland Museum and to Rich by the National Georaphic Society (Grant Fig. 16. The most-supported cladogram of hypothetical No.1562). intrafamilial relationships within Pilkipildridae. Invaluable field and other support was Potential synapomorphies are as follows: 1, see provided by many colleagues (in alphabetical character-states No.12 in Fig. 15; 2, see character- order): K. Aplin, E. Archer, R. Beale, R. Brown, statesNo.14 in Fig. 15; 3, the II is steeply inclined, the P3 is large, there are prominent and isolated meta- F. Bussat, G. Clayton, C. Cleeland,J. Courtenay, stylids, the lingual flanks of the upper and buccal T. Flannery , A. Gillespie, H. Godthelp, K. flanks of the lower molars are gently inclined, the Gollan, K. Grimes, C. Hann, S. Hand, W. Head, corners of the upper molars are well rounded, the Mg Q.Jones, R. Langford, P. Lawson, D. Marina, M. talonid is narrow, the buccal cusps of the upper molars are prominent, tall and swollen, there are very reduced Macdonald, W. Moore, P. Morrison, M. Plane, N . paracones and metacones, transverse rows of cuspules Pledge, P. Rich, I. Stewart, J. Taylor, E. are developed on the upper molars and there are very Thompson, R. Wells, M. Whitelaw, M. Wood- short trigonid basins; 4, there are posterobuccal and burne and many undergraduate students of the posterolingual cingula on Pg' there is a well-developed notch on the anterobasal cingulum of M..2and there is University of New South Wales. an overall reduction of crenulations; -', the talonid Particular thanks are extended to Ken Grimes basin on M is well developed as is the vertical cristid on (and the Geological Survey of Queensland) for the posterolingual flank of the trionid of M2' there is a relatively well-developed posterior transverse cristid his part in the discovery of the new Riversleigh on the talonid of M2; 6, the trigonid of M2 is short and sites, to John Courtenay (and the Burke Shire) wide, the M2 is shortened and the postentocristid is for his role as co-ordinator of Probe Scientific reduced; 7, the P3 is large and obliquely oriented, Expeditions in organising most of the logistics there is a loss of the posterior cingula, the M trigonid is elevated, the molars are short and wide, the crown and support for the 1984-85 Riversleigh expedi- basesof the lower molars are more swollen, the cristid tions and for helping to discover many of the best obliqua and paracristid on M2 are shortened and the sites and to Henk Godthelp for his vital role in notch on the anterobasal flanK of M! is reduced; 8, the discovering and preparing (via A.R.G.S. support) M2 is proportionately short and wide, the M2 trigonid is very steeply inclined and the metaconid of M2 is most of the Riversleigh material. Critical logistic barely distinct; 9, the P9 is very obliquely oriented, the support for the Riversleigh work was also talonid is proportionately short, the M2 has a small received from the Wallaby Task Force of the 35th protostylid, the cristid obliqua is divided into anterior Squadron of the RAAF based in Townsville and posterior segments and the crenulations of the crowns are pronounced. during 1984-85. They performed the seemingly miraculous task of shifting 12 tonnes of pilki- Overall, the upper and lower crown mor- pildrid-bearing rocks from the remote and phology of pilkipildrids is reminiscent of, but less almost inaccessibleoutback of Riversleigh Station eleborate than, that exhibited by some of the to the nearest point of road transportation. The omnivorous phalangerids (e.g., Phalanger Burke Shire Council then provided much- maculatus) and petaurids (e.g., Petaurus breviceps). appreciated support in transporting the rocks to Perhaps pilkipildrids were phalangerid- and Mount Isa. Personnel of the 4th Base Workshop, petaurid-Iike in diet; i.e., opportunistic omni- RAEME, Bandiana, Victoria, not only provided vores. Their small size (relative to phalangerids; the logistic support essentialto reach Lake Yanda comparable-sized petaurids being as yet but also had a crucial role in the collection of the unknown from this time) suggest that they may fossil vertebrates from this remote area of central have exploited the smaller range of this omni- Australia. vorous habitus which was otherwise unoccupied The manuscript was typed by T. Deguara and by phalangerids. the figures prepared by J. Taylor, P. Watkins and H. Godthelp (University of New South Wales). ACKNOWLEDGEMENTS Photographs were taken by H. Godthelp and R. The greatest debt of gratitude we owe is to the Arnett (University of New South Wales) and C. various funding bodies that have made this Tarka (American Museum of Natural History). ARCHER, TEDFORD, and RICH: THE PILKIPILDRIDAE 627

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ARCHER, M., 1978. The nature of the molar-premolar bound- Sydney. ary in marsupials and a reinterpretation of the homology REUTHER, J. G., 1901. "The Diari". Translated (as "A Diari of marsupial cheek-tooth. Mem. Qd Mw. 18: 157-64. Dictionary") by Rev. P. A. Scherer. Awtralian Institute of Aboriginal Studies Microfiche No.2 (1981). ARCHER, M., 1982. Review of the dasyurid (Marsupialia) fossil record, integration of date bearing on phylogenetic RICH, T. H. AND ARCHER, M., 1979. Namilamadeta snideri, a interpretation, and suprageneric classification. Pp. 397- new diprotodontan (Marsupialia, Vombatoidea) from 443 in "Carnivorous marsupials" ed by M. Archer. Royal the medial Miocene of South Australia. Alcheringa 3: Zoological Society of New South Wales: Sydney. 197-208, ARCHER, M., 1984. The Australian marsupial radiation. Pp. RIcH,T. H., 1982. Monotremes, placentals, and marsupials: 633-808 in "Vertebrate zoogeography and evolution in the record in Australia and its biases. Pp. 386-477 in "The Australasia" ed by M. Archer and G. Clayton. Hesperian fossil vertebrate record of Australasia" ed by P. V. Rich Press: Penh. and E. M. Thompson. Monash University Offset Print- ing Unit: Clayton. ARCHER, M. AND FLANNERY, T. F ., 1985. Revision of the extinct gigantic rat kangaroos (Potoroidae: Marsupialia), RIcH,T. H., ARCHER, M., PLANE, M., FLANNERY, T., PLEDGE, with description of a new Miocene genus and species N., HAND, S. AND RICH, P., 1982. Australian Tertiary and a new Pleistocene species of Propleopu.s.J. Paleo. 89: mammal localities. Pp. 525-72 in "The fossil vertebrate 1131-49. record of Australasia" ed by P. V. Rich and E. M. Thompson. Monash University Offset Printing Unit: BAVERSTOCK, P. R., 1984. The molecular relationships of Australasian possums and gliders. Pp. 1-8 in "Possums Clayton. and gliders" ed by A. P. Smith and I. D. Hume. Surrey TEDFORD, R. H., ARCHER, M., BARTHOWMAI, A., PLANE, M. Beatty & Sons and the Australian Mammal Society: D., PLEDGE,N. S., RICH, T. H., RICH, P. V. AND WELi$, R. Sydney. T., 1977. The discovery of Miocene vertebrates, Lake Frome area, South Australia. Bur. Min. Res. J. Awt. Geol. BAVERSTOCK,P. R., BIRRELL,J.AND KRIEG, M., 1987. Albumin Geophys. 2: 53-57. immunologic relationships among Australian possums: a progress report. Pp. 229-34 in "Possums and opossums: WOODBURNE,M. 0., TEDFORD, R. H., ARCHER, M., TURNBULL, studies in evolution" ed by M. Archer. Surrey Beatty & W. D., PLANE, M. D. AND LUNDELIUS, E. L., 1985. Bio- Sons and the Royal Zoological Society of New South chronology of the continental mammal record of Aust- Wales: Sydney. ralia and New Guinea. Spec. Publ., S. Awt. Dept. Mines and Energy 8: 347-63. FLANNERY, T. E., ARCHER, M. AND MAYNES, G., 1987. The phylogenetic relationships of living phalangerids WOODBURNE, M. 0., TEDFORD, R. H. AND ARCHER, M., 1987. (Phalangeroidea: Marsupialia) with a suggested new New Miocene ringtail possums (Marsupialia: taxonomy. Pp. 477-506 in "Possums and opossums: Pseudocheiridae) from South Australia. Pp. 639-79 in studies in evolution" ed by M. Archer. Surrey Beatty & "Possums and opossums: studies in evolution" ed by M. Sons and the Royal Zoological Society of New South Archer. Surrey Beatty & Sons and the Royal Zoological Wales: Sydney. Society of New South Wales: Sydney.