A new ektopodontid possum (Diprotodontia, Ektopodontidae) from the Oligocene of central Australia, and its implications for phalangeroid interrelationships

Abstract

The Ektopodontidae are an enigmatic group of phalangeroid marsupials known from the late Oligocene to the Early Pleistocene of Australia. Although represented to date only by isolated teeth and several partial dentaries and maxillae, their highly distinctive dental morphology has allowed three genera and nine species to be distinguished. Here, we describe possibly the geologically oldest ektopodontid, Chunia pledgei sp. nov., from the Oligocene Pwerte Marnte Marnte fossil locality of central Australia. Phylogenetic analyses of Phalangeroidea, using 80 primarily dental characters framed by a molecular scaffold, support placement of the new taxon in the genus Chunia. The analyses failed to recover species of the genus Durudawiri in a monophyletic Miralinidae, indicating that they require systematic review. We also transfer the purported basal phalangerid Eocuscus sarastamppi to Miralinidae (Miralina sarastamppi comb. nov.). Additionally, the M1 specimens used to describe the Early to Middle Miocene miralinid genus Barguru, and three species therein, are re-identified as deciduous third premolars from early macropodoids. These findings imply that the Miralinidae are known only from the late Oligocene, whereas the oldest named phalangerids are from the Early Miocene. From a functional consideration of ektopodontid dental morphology, we infer support for prior suggestions of a granivorous and/or frugivorous diet for them. The relative stage-of-evolution expressed by the new taxon is comparable to those in the lower faunal zones of the Namba and Etadunna formations, which supports a late Oligocene age for the Pwerte Marnte Marnte assemblage.

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A new ektopodontid possum (Diprotodontia,
Ektopodontidae) from the Oligocene of central
Australia, and its implications for phalangeroid
interrelationships
Arthur I. Crichton, Trevor H. Worthy, Aaron B. Camens & Gavin J. Prideaux
To cite this article: Arthur I. Crichton, Trevor H. Worthy, Aaron B. Camens & Gavin J. Prideaux
(2023): A new ektopodontid possum (Diprotodontia, Ektopodontidae) from the Oligocene of
central Australia, and its implications for phalangeroid interrelationships, Journal of Vertebrate
Paleontology, DOI: 10.1080/02724634.2023.2171299
To link to this article: https://doi.org/10.1080/02724634.2023.2171299
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ARTICLE
A NEW EKTOPODONTID POSSUM (DIPROTODONTIA, EKTOPODONTIDAE) FROM THE
OLIGOCENE OF CENTRAL AUSTRALIA, AND ITS IMPLICATIONS FOR PHALANGEROID
INTERRELATIONSHIPS
ARTHUR I. CRICHTON,
1
*TREVOR H. WORTHY,
1
AARON B. CAMENS,
1
and GAVIN J. PRIDEAUX
1
1
College of Science and Engineering, Flinders University, Bedford Park 5042, South Australia, arthur.crichton@flinders.edu.au;
trevor.worthy@flinders.edu.au; aaron.camens@flinders.edu.au; gavin.prideaux@flinders.edu.au
ABSTRACT—The Ektopodontidae are an enigmatic group of phalangeroid marsupials known from the late Oligocene to the
Early Pleistocene of Australia. Although represented to date only by isolated teeth and several partial dentaries and maxillae,
their highly distinctive dental morphology has allowed three genera and nine species to be distinguished. Here, we describe
possibly the geologically oldest ektopodontid, Chunia pledgei sp. nov., from the Oligocene Pwerte Marnte Marnte fossil
locality of central Australia. Phylogenetic analyses of Phalangeroidea, using 80 primarily dental characters framed by a
molecular scaffold, support placement of the new taxon in the genus Chunia. The analyses failed to recover species of the
genus Durudawiri in a monophyletic Miralinidae, indicating that they require systematic review. We also transfer the
purported basal phalangerid Eocuscus sarastamppi to Miralinidae (Miralina sarastamppi comb. nov.). Additionally, the M1
specimens used to describe the Early to Middle Miocene miralinid genus Barguru, and three species therein, are re-
identified as deciduous third premolars from early macropodoids. These findings imply that the Miralinidae are known only
from the late Oligocene, whereas the oldest named phalangerids are from the Early Miocene. From a functional
consideration of ektopodontid dental morphology, we infer support for prior suggestions of a granivorous and/or frugivorous
diet for them. The relative stage-of-evolution expressed by the new taxon is comparable to those in the lower faunal zones
of the Namba and Etadunna formations, which supports a late Oligocene age for the Pwerte Marnte Marnte assemblage.
http://zoobank.org/urn:lsid:zoobank.org:pub:8881FF3A-4B9F-4085-A5C2-1BBF976CFB65
SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP.
Citation for this article: Crichton, A. I., T. H. Worthy, A. B. Camens, and G. J. Prideaux. (2023) A new ektopodontid possum
(Diprotodontia, Ektopodontidae) from the Oligocene of central Australia, and its implications for phalangeroid
interrelationships. Journal of Vertebrate Paleontology.https://doi.org/10.1080/02724634.2023.2171299
Submitted: May 31, 2022
Revisions Received: December 19, 2022
Accepted: January 13, 2023
INTRODUCTION
The Australian Cenozoic terrestrial vertebrate record has an
almost 30 Ma gap from the early Eocene (55 Ma) to the late Oli-
gocene (25 Ma), during which most modern Australian marsupial
families are inferred to have originated (Vickers-Rich, 1991;
Black et al., 2012; Duchêne et al., 2018; Eldridge et al., 2019;
Beck et al., 2022). The little studied Pwerte Marnte Marnte
Local Fauna, Northern Territory (Fig. 1), may represent the
oldest Australian Oligocene terrestrial vertebrate assemblage
(Murray & Megirian, 2006; Megirian et al., 2010). Twelve ver-
tebrate taxa, including marsupials, dromornithids, and crocody-
lomorphs, have so far been reported from the fossil locality
(Murray & Megirian, 2006). All appear to represent undescribed
and as yet unnamed taxa unique to the site, with the exception of
the large crocodylomorph referred to Baru wickeni Willis, 1997
(Yates, 2017). Following recent new excavations and preparation
of bulk samples of fossil matrix, the remains of more taxa have
been recognized from the deposit, one of which is a new
species of ektopodontid possum.
The Ektopodontidae are an extinct family of enigmatic, pha-
langeroid possums known from the upper Oligocene through
Lower Pleistocene of mainland Australia (e.g., Stirton et al.,
1967; Rich, 1986; Woodburne & Clemens, 1986a; Pledge, 2016).
Ektopodontids are characterized by a highly complex, serrated,
lophodont dentition, a short face, and large anteriorly oriented
orbits (Pledge, 1982,1991,2016). The family comprises three
genera: Ektopodon Stirton, Tedford and Woodburne, 1967;
Chunia Woodburne and Clemens, 1986a; and Darcius Rich,
1986 (Table 1: for review see Pledge, 2016). Each genus is charac-
terized by a distinct molar morphology (Stirton et al., 1967; Rich,
1986; Woodburne & Clemens, 1986b). The species of Chunia,
known to date only from the late Oligocene, have been regarded
as the sister group to members of the remaining two genera
(Woodburne & Clemens, 1986a,b). Within both Ektopodon
and Chunia, clear trends of gradually increasing molar complex-
ity are manifested between species through time, which has led to
the recognition of ektopodontids as having use in constraining
the age of undated faunal assemblages through stage-of-
*Corresponding author.
Color versions of one or more of the figures in the article can be found
online at www.tandfonline.com/ujvp.
Journal of Vertebrate Paleontology e2171299 (17 pages)
© by the Society of Vertebrate Paleontology
DOI: 10.1080/02724634.2023.2171299
Published online 23 Feb 2023

evolution biochronology (Pledge, 1986; Woodburne & Clemens,
1986a; Megirian et al., 2004,2010).
Our primary aim in this paper is to describe and compare new
ektopodontid material from the Pwerte Marnte Marnte fossil
locality in the southern Northern Territory, because the taxon
represented is perhaps the oldest in the family, and so may
shed light on the origins of this enigmatic group. We then re-ex-
amine ektopodontid intra- and interfamilial relationships, reflect
on the affinities of some related taxa, and draw dietary inferences
from observations of dental morphology.
MATERIALS AND METHODS
Terminology
The dental terminology follows Woodburne and Clemens
(1986a) and Woodburne et al. (1987), with the exceptions of:
molar serial homology, which follows Luckett (1993); m1 trigonid
homology, and that of the cingula spanning the anterior and pos-
terior margins of the molars, which is newly defined below. Hom-
ology of the buccal-most cusps on the upper molars in
phalangeriforms and thylacoleonids is also discussed.
The structures on the m1 trigonid of ektopodontid species
have ambiguous homology to those in other phalangeroids. Pre-
vious authors have regarded, on the basis of their relative place-
ment: the buccal- and lingual-most cuspids on m1 as the
protoconid and metaconid, respectively; the anterolingual
cuspid as a parastylid; and the cingulid spanning the anterior
margin to be a precingulid (e.g., Pledge, 1986; Rich, 1986; Wood-
burne & Clemens, 1986a). We consider it more parsimonious that
the buccal-most cuspid is instead a protostylid because: (1) the
protoconid in other basal phalangeroids is more lingually posi-
tioned, and (2) the structure does not link caudally to the
remnant lingual kink to the cristid obliqua in the new ektopodon-
tid taxon described below. Consequently, we propose two
hypotheses for the homology of the remaining trigonid struc-
tures. (1) Cuspid 2 represents the protoconid, and the cingulid
spanning the anterior margin of m1 corresponds to the paracris-
tid. (2) Cuspid 3 represents a lingually displaced protoconid that
is linked to the parastylid by a short paracristid, and the cingulid
spanning the anterior margin of the tooth corresponds to a
TABLE 1. Distribution and age of ektopodontid taxa. Ages of Local Faunas from the Namba and Etadunna formations following Woodburne et al.
(1994), Megirian et al. (2010), and those of Riversleigh Faunal Zones following Woodhead et al. (2016). Abbreviations:?, uncertain; E, Early; Fm,
Formation; FZ, Faunal Zone; L, late; LF, Local Fauna.
Taxon Distribution Age
Chunia illuminata Woodburne and Clemens, 1986a Ditjimanka LF, Etadunna Fm L. Oligocene (24.9
Ma)
Chunia sp. Chunia cf. illuminata in Woodburne and Clemens (1986a) Pinpa LF, Namba Fm L. Oligocene (≥25.2
Ma)
Chunia omega Woodburne and Clemens, 1986a Tarkarooloo LF, Namba Fm L. Oligocene (≥24.1
Ma)
Chunia pledgei sp. nov. Pwerte Marnte Marnte LF ?L. Oligocene
Chunia sp. in Archer et al. (2006) Dirk’s Towers and Upper Site, FZ B, Riversleigh E. Miocene (18.2–
16.5 Ma)
Darcius duggani Rich, 1986 Hamilton LF and Nelson Bay Formation,
southwestern Victoria (Rich et al., 2006)
E. Pliocene–?E.
Pleistocene
Darcius-like form in Long et al. (2002), reported as a new genus by
Crosby et al. (1999) and Archer et al. (2006)
Creaser’s Ramparts and Neville’s Garden, FZ B
Riversleigh
E. Miocene (18.2–
16.5 Ma)
Ektopodon tommosi Pledge, 2016 Tarkarooloo LF, Namba Fm L. Oligocene (≥24.1
Ma)
Ektopodon stirtoni Pledge, 1986 Mammalon Hill, Lake Palankarinna, Etadunna Fm L. Oligocene (24.1
Ma)
Ektopodon ulta Megirian, Murray, Schwartz and Von Der Borch, 2004 Kangaroo Well LF E. Miocene
Ektopodon serratus Stirton, Tedford and Woodburne, 1967 Kutjamarpu LF, Wipajiri Fm E. Miocene
Ektopodon sp. cf. E. serratus in Pledge et al. (1999) Wayne’s Wok LF, FZ B, Riversleigh E. Miocene (18.2–
16.5 Ma)
Ektopodon litolophus Pledge, 1999 Kutjamarpu LF, Wipajiri Fm E. Miocene
Ektopodon paucicristata Rich, Piper, Pickering and Wright, 2006 Childers Cove and Dutton Way, Whalers Bluff Fm ?Pliocene
FIGURE 1. Location of the Pwerte Marnte Marnte fossil deposit, southern
Northern Territory, Australia. Aerial image from Bing Maps, taken 3 Feb-
ruary 2022. Microsoft product screen shots reprinted with permission from
Microsoft Corporation, ©2022 Microsoft: Earthstar Geographics SIO.
Crichton et al.—New ektopodontid possum from Australia (e2171299-2)

lingually displaced precingulid (similar to that of Djilgaringa gil-
lespiei Archer, Tedford and Rich, 1987). Given that structural
homology cannot be unambiguously demonstrated we opt to
be conservative and refer to the primary protolophid cuspids
on m1 only by their relative position number. We consider
that, due to the way in which ektopodontid cusps develop (i.e.,
budding and partitioning), the relative position number of a
given cusp on a loph does not necessarily reflect homology
between taxa. The anterolingual cuspid is referred to as a para-
stylid. The cingulid spanning the anterior margin of m1 is
referred to as a precingulid, while that of more posterior
molars is referred to as the paracristid. The cingulid spanning
the posterior margin of the molars is referred to as part of the
posthypocristid (see Beck et al., 2022).
We interpret that the buccal-most cusps on the upper molars of
ektopodontids have ambiguous homologyto those in other phalan-
geriforms, and consequently refer to them only by their respective
cusp position number. For the purpose of scoring the morphologi-
cal character matrix, we interpret that, in non-ektopodontid pha-
langeriforms, the primary buccal cusp on the anterior moiety of
upper molars rep resents the paracone, and the cus pate ridge poster-
obuccal to it represents stylar cusp C. This interpretation of hom-
ology has been followed with respect to basal macropodoids (e.g.,
Flannery & Rich, 1986; Black, Travouillon et al., 2014; Travouillon
et al., 2014; Den Boer & Kear, 2018). Wenote that this arrangement
of cusps on the anterior moiety of M1 is also present in the phalan-
geroids Burramys wakefieldi Pledge, 1987 and Durudawiri inusita-
tus Crosby and Archer, 2000. For the posterior moiety of upper
molars, we interpret that the primary buccal cusp (or “metacone”)
represents stylar cusp D, and the central cusp (or “neometaco-
nule”) represents the metacone. This is consistent with the
interpretations of Woodburne et al. (1987), Crosby and Archer
(2000), and Case et al. (2009), as well as the cusp terminology
used by Beck et al. (2022). With respect to thylacoleonid molar
cusp homology, we tentatively follow Murray et al. (1987) and Gil-
lespie et al. (2020), wherein the primary buccal cusps represent the
paracone and metacone, and the longitudinally ridged structure
buccal to them on M1 derives from stylar cusps C + D. This
interpretation of homology is followed on the basis that, on the
M1 of the referred Lekaneleo roskellyae (Gillespie, 1997) specimen
QM F23442 (see Gillespie et al., 2020:fig. 4), the anterior moiety has
a cuspate structure (stylar cusp C) posterobuccal to the primary
buccal cusp (paracone), and, on the posterior moiety, a cuspate
structure (stylar cusp D) buccal to the primary buccal cusp (meta-
cone). The presence of a more longitudinally ridged structure span-
ning the buccal face of M1 in the holotype of L. roskellyae (QM
F23453: see Gillespie et al., 2020:fig. 1) is interpreted here as
derived, reflecting that QM F23442 was recovered from the
upper Oligocene White Hunter Site, Riversleigh World Heritage
Area, while QM F23453 was recovered from the Lower Miocene
Upper Site at Riversleigh (see Gillespie et al., 2020).
Higher-level systematic nomenclature follows Woodburne
(1984) and the refinements made by Aplin and Archer (1987),
with the exception of the use of the suborder Phalangeriformes
Szalay, 1982, sensu Woodburne (1984), and the later referral of
the family Burramyidae to the superfamily Phalangeroidea by
Kirsch et al. (1997). Biostratigraphic nomenclature follows
Woodburne et al. (1994), Archer et al. (1997), Travouillon
et al. (2006), and Megirian et al. (2010).
Specimen Preparation
The specimens were recovered from c. 2 tons of limestone
quarried from the Pwerte Marnte Marnte fossil beds on
expeditions in 2014 and 2020, led by Aidan Couzens and
Arthur Crichton, respectively. The fossiliferous rock was pro-
cessed from 2020–2022 at Flinders University using a combi-
nation of acetic acid (5–10%) etching and mechanical
preparation, building on the methods of Murray and Megirian
(2006). The fossil locality preserves heavily fractured and dis-
torted partial skeletal elements in a well-cemented calcareous
limestone conglomerate of densely concentrated non-diagnostic
bone fragments and well-rounded, mainly quartz pebbles. Mech-
anical preparation with pneumatic micro-jack tools was largely
ineffective because the bone material is typically softer than
the limestone, as well as being more firmly cemented to the lime-
stone than the bone is to itself. Similarly, even low concentrations
of acid quickly separated the bone material into smaller frag-
ments along their internal laminae and fracture planes. As a
result, preparation of individual specimens of interest required
many relatively short acid treatments. Between acid treatments,
the thin layer of porous corroded limestone at the newly
exposed rock–fossil juncture was carefully brushed away using
acetone, in association with the extensive removal and reapplica-
tion of protective plastic (Paraloid B-72) coats. This process was
accelerated by reducing the bulk matrix surrounding focal speci-
mens using mechanical approaches (e.g., involving rock saws and
pneumatic micro-jack tools).
Comparative Specimens
The collection of modern and fossil phalangeriform cranioden-
tal material at SAMA was used for wider comparisons, under
magnification using an Olympus SZX12 microscope. Measure-
ments were made using Mitutoyo digital calipers (model No
CD-8”C) and rounded to 0.01 mm (Fig. 2A;Table 2). Below
we only list specimens of key taxa that were examined for the fol-
lowing descriptions. Ektopodontidae: Chunia illuminata,M1
SAMA P29081, M2 SAMA P17997, M2 metaloph QM F10641,
M3 SAMA P33944, m2 SAMA P19903 (cast of UCMP
315228), m3 SAMA P19902 (cast of UCMP 315227); Chunia
sp. cf. C. illuminata, m3 SAMA P19905 (cast of AMNH 95584);
Chunia sp. cf. C. illuminata, m4 SAMA P22721; Chunia omega,
half of ?M3 SAMA P23065. For the following taxa, where
access to specimens was not possible, we used published descrip-
tions and figures: Darcius duggani;Ektopodon ulta;Onirocuscus
silvacultrix Crosby, 2007;Trichosurus dicksoni Flannery and
Archer, 1987;Eocuscus sarastamppi Case, Meredith and
Person, 2009;Durudawiri inusitatus;Durudawiri anfractus
Crosby, 2002;Lekaneleo roskellyae;Djilgaringa gillespiei
FIGURE 2. Reconstruction of right m1 (NTM P11992) of Chunia pledgei
sp. nov., from A, occlusal view showing orientation of measurements, and
the angle of the pre- and post-cuspid-cristids from the longitudinal axis of
tooth; B, anterior view showing the orientation of the cuspids relative to
the parasagittal plane.
Crichton et al.—New ektopodontid possum from Australia (e2171299-3)

Archer, Tedford and Rich, 1987; species of Barguru Schwartz,
2006;Strigocuscus celebensis (Gray, 1858); and Ailurops ursinus
(Temminck, 1824) (Rich, 1986; Archer et al., 1987; Flannery &
Archer, 1987; Flannery et al., 1987; Crosby & Archer, 2000;
Crosby, 2002,2007; Case et al., 2009; Gillespie et al., 2020).
Institutional Abbreviations—AMNH, Department of Ver-
tebrate Paleontology, American Museum of Natural History,
New York, NY, U.S.A.; FUR, Palaeontology Laboratory, Flin-
ders University, Adelaide, Australia; NMV P, Palaeontology,
Museums Victoria, Melbourne, Victoria, Australia; NTM P,
Museum of Central Australia, Museum and Art Gallery of the
Northern Territory, Alice Springs, Northern Territory, Australia;
UCMP, University of California Museum of Paleontology, Ber-
keley, CA, U.S.A.; UCR, Department of Earth Sciences, Univer-
sity of California, Riverside, CA, U.S.A.; SAMA M, Mammals
(modern), South Australian Museum, Adelaide, Australia;
SAMA P, Palaeontology, South Australian Museum, Adelaide,
Australia.
Phylogenetic Analysis
Morphological Matrix—A largely novel morphological dataset
of 80 characters (75 dental and 5 cranial) was constructed for
members of the superfamily Phalangeroidea to assess ektopo-
dontid intra- and interfamilial relationships, drawing in part on
characters developed in previous phylogenetic assessments
(e.g., Archer et al., 1987; Flannery et al., 1987; Woodburne
et al., 1987; Crosby & Archer, 2000). Seventeen multistate mor-
phological characters perceived as representing morphoclines
were specified as ordered. Descriptions of all morphological
characters and assessed states can be found in Supplementary
Data 1. Morphological characters 72–75, relating to the number
of cusps per molar loph, comprise up to ten states; however,
ordered characters cannot exceed six states in MrBayes 3.2.7a
(Ronquist et al., 2012). Therefore, in the Bayesian analyses,
each of characters 72–75 were concatenated down to five states
(see Supplementary Data 1). The complete morphological char-
acter matrices (nexus format), with standard and concatenated
states for characters 72–75, can be found in Supplementary
Files 2 and 3, respectively. Thirty-two taxa were scored (9
extant and 23 extinct). Phalangeroidea was represented by 25
taxa: 10 ektopodontids, 4 miralinids, 9 phalangerids, and 2 burra-
myids. The extinct pilkipildrid Djilgaringa gillespiei Archer,
Tedford, and Rich, 1987, was also coded. Pilkipildrids are cur-
rently regarded as Phalangeriformes incertae sedis but are con-
sidered to be within either Phalangeroidea or Petauroidea
(Archer et al., 1987; Brammall, 1999). Six outgroup taxa were
included; namely, two macropodoids, three petauroids, and one
thylacoleonid. Justification for taxon inclusion can be found in
Supplementary Data 1.
Molecular Matrix—Nearly complete sequences of mitochon-
drial genomes were obtained from GenBank for representatives
of the six modern phalangerid genera, the two burramyids, and
the petauroid taxa. GenBank accession numbers can be found
in Table S1, Supplementary Data 1, and the molecular character
matrix (nexus format) in Supplementary Data 4. The sequences
were aligned in Mesquite using the program MUSCLE.
Manual adjustments were made, wherein sites with ambiguous
homology were excluded. The adjusted sequences were
15,500 bp in length.
Phylogenetic Inference—Maximum parsimony analyses were
performed on the morphological dataset, in TNT version 1.5
(Goloboff et al., 2008). In parsimony, one analysis was per-
formed, which included all 32 taxa, wherein the thylacoleonid
L. roskellyae was specified as the deepest outgroup member
(for readin file see Supplementary Data 5). Unequivocal
relationships between the outgroup taxa, as well as extant pha-
langerids, were enforced using a “skeleton”constraint. The
tree search involved an initial “new technology”search with sec-
torial search, ratchet, drift and tree fusing that was run until the
same minimum tree length was found 10,000 times. From these
saved trees a “traditional”search was applied using the tree
bisection resection (TBR) swapping algorithm, with the resulting
most parsimonious trees combined into a strict consensus tree.
Support values for branch nodes were calculated using 2000 stan-
dard bootstrap replicates, implemented using a “traditional”
search, which results in output as absolute frequencies.
Undated Bayesian analyses of the combined morphological
and molecular matrices were carried out in MrBayes 3.2.7a
(Ronquist et al., 2012), using the Markov Chain Monte Carlo
(MCMC) approach, with gamma rate variability implemented
for morphological data maintaining the assumption that only
variable characters were scored. A time reversible model of
DNA substitution, and invgamma distribution rate variation
across sites (nst = 6, rates = invgamma), was implemented for
the mitochondrial protein first and second codon positions, fol-
lowing the approach taken by Mitchell et al. (2014) for the
same mitochondrial sequences. For the third codon position,
transitions and transversions were allowed different rates of vari-
ation across sites (nst = 2, rates = gamma). Four phylogenetic
analyses were performed. Three analyses were polarized by
TABLE 2. Measurements (in mm) of lower dentition from members of
the genera Chunia and Darcius as well as plesiomorphic representatives
of Ektopodon. Measurements of D. duggani from Rich (1986), and
E. tommosi and E. stirtoni from Pledge (1986), in which the former is
reported as E. sp. cf. E. stirtoni.Abbreviations:L, length; AW, anterior
width; PW, posterior width.
Specimen number Tooth L AW PW
Chunia pledgei sp. nov.
NTM P11992 (holotype) Rp3 4.01 - 3.21
Rm1 6.70 4.76 5.00
Rm2 6.55 4.30 4.33
Rm3 6.18 4.02 3.91
NTM P11993 (paratype) LM2? - - 6.96*
Chunia sp. cf. C. illuminata
AMNH 95584 Lm3 5.91 3.77 3.51
SAMA P22721 Lm4 6.14 4.06 3.97
Chunia illuminata
UCMP 315228 Lm2 5.96 3.96 3.87
UCMP 315227 Lm3 5.86 4.31 4.04
SAMA P29081 LM1 7.49 6.31 7.03
SAMA P17997 RM2 5.50 6.83 6.16
Darcius duggani
NMV P54185 (holotype) Rp3 4.2 - 3.0
Rm1 8.3 3.0* 5.1
Rm2 7.8 5.0 5.2
NMV P54184 Rm3* 6.7 4.9 4.7
NMV P156981 Rm4 6.7 4.9 4.6
NMV P150060 Lm1 8.2 4.8 4.8
Ektopodon tommosi
NMV P48759 Lp3 3.70 - 2.95
SAMA P19965 Rp3 3.70 - 2.80
SAMA P19950 Rm1 7.25 7.20 7.65
NMV P48764 Lm2 7.65 7.45 6.80
NMV P48765 Lm3 6.45 - -
SAMA P19966 Rm4 5.75+ 5.70 4.10
NMV P48766 Rm4 6.30 5.50 4.80
NMV P160517 Rm4 5.80 4.95 4.00
Ektopodon stirtoni
SAMA P19509 (holotype) Rp3 4.10 3.3* -
Rm1 7.80 8.45 9.20
Rm2 8.00 - 7.65+
Rm3 7.10 6.30+ 6.20+
SAMA P23988 Lm4 6.80 5.95 5.00
Crichton et al.—New ektopodontid possum from Australia (e2171299-4)

outgroup taxa from one of Thylacoleonidae, Macropodoidea, or
Petauroidea to assess their respective topological influence (for
readin files see Supplementary Files 6–8, respectively). The
fourth analysis included all aforementioned outgroup taxa,
wherein the thylacoleonid L. roskellyae was specified as the
deepest outgroup (for readin file see Supplementary Files 9).
Unequivocal relationships between outgroup taxa were enforced
using partial and hard constraints. The Bayesian analyses were
run for 10 million generations, using four independent runs of
four chains (one cold and three heated chains, with temperature
of the heated chains set to the default value of 0.2). Trees were
sampled every 1000 generations with a burn-in fraction of 25%.
Post-burn-in trees were summarized using a majority rule con-
sensus of all compatible groups, with Bayesian posterior prob-
abilities as support values.
SYSTEMATIC PALEONTOLOGY
Order DIPROTODONTIA Owen, 1866
Suborder PHALANGERIFORMES Szalay, 1982, sensu
Woodburne (1984)
Superfamily PHALANGEROIDEA Thomas, 1888, sensu
Aplin and Archer (1987)
Family EKTOPODONTIDAE Stirton, Tedford and
Woodburne, 1967
Genus CHUNIA Woodburne and Clemens, 1986a
Revised Generic Diagnosis—Species of Chunia are distin-
guished from those of Darcius and Ektopodon by: the presence
of a shelf-like, rather than cuspate, posterobuccal structure on
p3; a p3 length that is c. 60% versus 50% that of m1 length;
three or more anterior and posterior struts on the upper molar
cusps; and prominent transverse linking of cristids on m2–4.
They differ from species of Darcius by having: pre- and post-
cuspid-cristids oriented anterobuccally at a lower angle from the
longitudinal axis of tooth, c. 10–20° compared with c. 25–30°, and
an m1 that is rhomboid from occlusal view, rather than acutely tra-
pezoidal. They differ from species of Ektopodon by having a pre-
cingulid on m1 that is not subsumed by terminating cristids.
CHUNIA PLEDGEI sp. nov.
(Figs. 2–5)
Holotype—NTM P11992, partial right adult dentary contain-
ing p3, m1–3.
Paratype—NTM P11993, posterior half of left upper molar
(probably M2).
Referred Specimen—NTM P11994, small fragment of indeter-
minate molar.
Locality—Pwerte Marnte Marnte fossil locality (24°21’S, 133°
43’E), on the southern flank of the James Range, Northern Ter-
ritory, Australia (Fig. 1).
Stratigraphy, Local Fauna, and Age—Pwerte Marnte Marnte
LF (Murray & Megirian, 2006). Initial biochronological assess-
ments suggested that this assemblage is probably from an unde-
scribed geological formation of late Oligocene age (Murray &
Megirian, 2006), but may pre-date those of the Etadunna and
Namba formations of the southern Lake Eyre Basin, and thus
correspond to an as-yet-unnamed land mammal age immediately
preceding the Etadunnan (Murray & Megirian, 2006; Megirian
et al., 2010).
Etymology—Named for Neville S. Pledge, whose research on
ektopodontids over the last four decades has greatly extended
our understanding of this family.
Species Diagnosis—Referred to the genus Chunia mainly on
account of the prominent transverse-linking of cristids on the
lower molars, and the presence of three or more anterior and
posterior cristae descending from the cusps on the upper molars.
The new species is distinguished from C. illuminata and
C. omega in that the M2 metaloph has a postcingulum on the pos-
terolingual face of the metaconule; and in lacking cristae that
transversely link the pre- and post-cusp-cristae, with the exception
of the central link spanning between the apices that is also
observed in species of Ektopodon. The lower molars are distin-
guished from those of C. illuminata in having: lophids that bear
generally fewer cuspids, with thicker pre- and post-cuspid-cristids
FIGURE 4. Chunia pledgei sp. nov. paratype metaloph from left (prob-
ably) M2 (NTM P11993) in occlusal view with associated line drawings
and annotations. The brackets around cusp 6 denote that this terminol-
ogy is informal, referring only to the relative position number of the
cusp. Abbreviations:a, anterior; b, buccal; lc, lingual cingulum; mcl,
metaconule; poc, postcingulum; pomclc, postmetaconulecrista. Scale
bar equals 2 mm.
FIGURE 3. Chunia pledgei sp. nov. holotype right dentary (NTM
P11992), preserving p3 and m1–m3. A, occlusal view; B, lingual view;
C, buccal view. Scale bar equals 5 mm.
Crichton et al.—New ektopodontid possum from Australia (e2171299-5)

and less transverse-linking between them; and the lingual kink of
the cristid obliqua on m2 is merged with the principal pre-cuspid2-
cristid, where it is partitioned into smaller cristids, rather than
being separated from the apex of cuspid 2 by a small but distinct
cuspate structure with short and fine radiating cristids.
Description
Dentary—The partial right adult dentary (NTM P11992) pre-
serves p3, m1–3, the posterior margin of the alveolus of i1, and an
alveolus in the i2 position (Fig. 3A–C). The specimen, which
measures 30.9 mm in length, is fragmented and held together
by matrix. A relatively large anterior mental foramen (diameter
>1 mm) is situated 2.5 mm anteroventral to the exposed anterior
root of p3; it has sediment infill and slight damage to the dorsal
margin. A smaller posterior mental foramen is 5.6 mm ventral
to the anterior root of m2 (Fig. 3C). A longitudinal line spans
the mesial face of the dentary, representing the mylohyoid line.
The cross-sectional shape of the ramus is largely distorted. Due
to post-depositional distortion, the m1 is out of its original align-
ment relative to m2–3(Fig. 3A–C). The axis of m2 and m3 is pre-
served in original alignment and is offset from the longitudinal
axis of the dentary by an angle of c. 15°. The alveolus of i1 has
a steeply inclined posterior surface and is abutted posteriorly
by a relatively small, single-rooted alveolus, which is tentatively
referred to as being for i2 on the basis of its presence in other
phalangeroid taxa. The i2 alveolus is slightly ovate in cross
section, with a greater anterior than posterior width (anteropos-
terior width c. 1.5 mm). The diastema between i2 and p3 is rela-
tively short (c. 2 mm), with a small foramen situated slightly
anterolingual to the p3.
The dentary of Chunia pledgei is narrower than those of other
ektopodontids for which this element is known (specifically
Chunia sp. cf. C. illuminata SAMA P22721 and Ektopodon stir-
toni SAMA P19509). This is evident in the undistorted width
ventral to the m2 at the mylohyoid line, which is 5.7 mm in
C. pledgei, 7.1 mm in C. sp. cf. C. illuminata, and 8.2 mm in
E. stirtoni. As a result, the tooth row is closer to being in line
with the axis of the dentary, such that the p3 only partly over-
hangs the lateral margin of the dentary in dorsal view (as
opposed to completely overhanging in E. stirtoni), similar to
that seen in phalangerids.
Lower Dentition—The height of p3 is less than that of m1,
being roughly level to the m1 parastylid, though this may be
due to distortion as both are somewhat displaced as preserved
(Fig. 3A–C). The p3 is oriented anteriorly at an angle of c. 25°
from the dorsoventral axis of m1 (Fig. 3A–C). The lingual face
is relatively flat, bearing a weakly convex longitudinal expansion
near the base of the crown. The whole buccal surface is strongly
convex. The tooth has a crest that is aligned posterolingually to
anterobuccally relative to the longitudinal axis of the molar
row (Fig. 3A), though again this orientation may not be original
if the tooth is incorrectly positioned as a result of post-deposi-
tional distortion. The crest bears three cuspules, with the pos-
terior two being weakly developed (Fig. 5A). The apices of the
cuspules appear subequal in height from the dorsal mandibular
margin, though the apex and buccal extremity of the second
cuspule is missing. From the first cuspule, the crest continues
anterobuccally almost to the base of the crown, sweeping
weakly lingually before terminating. The first cuspule also
bears ridgelets that descend the lingual and buccal surfaces.
The ridgelet on the lingual surface sweeps posteriorly near the
base of the crown, whereas the ridgelet on the buccal face termi-
nates midway down the crown. The third (posterior-most)
cuspule has a buccal ridgelet that is continuous with a shelf
that descends anteriorly, which is reported as a posterobuccal
shelf (Fig. 5A).
The p3 is not yet known for other species of Chunia. The p3 is
proportionately larger than those of ektopodontids in other
genera, being 60% of m1 length, compared with 51% in species
of Ektopodon and Darcius (Table 2). If the anterobuccal orien-
tation of the crest is not a preservational artefact, it represents
a point of difference from the only other ektopodontid known
from the p3 in situ,E. stirtoni, in which this tooth is oriented ante-
rolingually. Species of Miralina also exhibit an anterolingually
oriented p3, whereas in other phalangeroids the p3 may be
oriented anteriorly or anterobuccally. The p3 differs from other
ektopodontid species in that it lacks subsidiary cusps on the
lingual or buccal faces. In the p3 of E. tommosi and
D. duggani, a single cusp is situated on the posterobuccal face,
whereas in E. stirtoni, three cusps occur on the buccal face and
one on the posterior lingual surface. The posterobuccal cusp in
these taxa appears to be the structural homolog of the postero-
buccal shelf in C. pledgei. In common with E. stirtoni and
E. tommosi, the anterior (first) cuspule on the crest is subequal
in height to the posterior (third) cuspule. These species also
share ridgelets that descend from the cuspules in unworn speci-
mens. In common with many phalangeroids, the lingual ridgelet
descending from the central cuspule is considerably less promi-
nent than those of the anterior- and posterior-most cuspules
(the buccal extremity of the second cuspule is damaged).
The m1 is roughly rhomboid in occlusal view, bearing a rela-
tively-flat lingual face with angular anterior and posterior
corners of 75° and 115°, respectively, whereas the buccal face
has well-rounded corners and is constricted at mid-length
towards the transverse valley. The crown is also rhomboid from
anterior view, wherein the buccal face is ventral relative to the
lingual face. The m1 is markedly wider than m2, but m2 is only
slightly wider than m3 (Table 2). The trigonid comprises
c. 40% of the length of the crown and the talonid c. 60%. The
tooth is bilophodont, with the protolophid separated from the
hypolophid by a deep transverse valley. The lophids are them-
selves composed of cuspids with cristids extending anteriorly
and posteriorly from each, situated parallel to one another
across the width of the lophid.
The protolophid on the m1 has four cuspids, which are referred
to as cuspids 1–4 (see Terminology section). The cuspids are
oriented buccolingually at an angle of c. 25° relative to the para-
sagittal plane of the tooth (Fig. 2B). Cuspid 4 is displaced more
posteriorly relative to the axis of the protolophid by roughly
half its width. Cuspids 2–3 have cristids that descend radially,
together forming sub-pyramidal structures that are only slightly
greater in length than width. A precingulid extends from the
buccal pre-cuspid2-cristid to the lingual margin. It is slightly
concave anteriorly and raised medially. The precingulid rises lin-
gually to meet a parastylid that is positioned directly anterior to
cuspid 4. The transverse valley is weakly excavated in the basin
between the termini of the pre- and post-cuspid-cristids. The
transverse valley is not crossed by any structures, though the
central post-cuspid2-cristid on the protolophid abuts the lingual
pre-cuspid2-cristid on the hypolophid, possibly deriving from
the cristid obliqua.
The hypolophid on m1 also has four cuspids, with cuspids 1 and
4 representing the hypoconid and entoconid, respectively (Fig.
5A). Compared with their equivalents on the protolophid,
cuspids 2 and 3 are oriented lingually at a lesser angle of c. 15°
relative to the parasagittal plane of the tooth. The entoconid is
less than half the width of the hypoconid, with the latter having
a width several times greater than the other cuspids on the hypo-
lophid. The pre- and post-cuspid2–3-cristids are more anteropos-
teriorly elongate than their equivalents on the protolophid. The
pre- and post-cuspid-cristids are together oriented anterobuc-
cally at an angle of 20° from the longitudinal axis of tooth (Fig.
2A). These pre- and post-cristids also bifurcate and become
very fine towards their ends, terminating on the transverse
Crichton et al.—New ektopodontid possum from Australia (e2171299-6)

valley and posthypocristid respectively. The three small cristids
bifurcating from the primary pre-cuspid2-cristid appear to
derive from a merged lingual kink in the cristid obliqua. The
posthypocristid is strongly curvilinear, descending steeply poster-
iorly from the hypoconid, then forming a right angle as it turns
lingually and continues along the posterior margin (postcingu-
lum sensu Woodburne & Clemens, 1986a), terminating at its
juncture with the postentocristid posterior to the entoconid.
The lingual margin of the hypolophid is sharply delimited by a
pre- and postentocristid. The preentocristid descends anteriorly
with four cristids arising from its buccal side and terminating at
the transverse valley, the two most posterior of which are dis-
tinctly thicker and longer than the two anterior.
The m1 is not yet known for other species of Chunia.The
noticeably greater width of the m1 relative to m2 in C. pledgei
differs from species of Ektopodon and Darcius (Table 2).
Unlike in species of Ektopodon, the m1 of C. pledgei and
D. duggani is narrower than it is long, though that of the latter
is over a third proportionately narrower still (Table 2). Both
C. pledgei and species of Ektopodon share a rhomboid m1 in
occlusal view, whereas that of D. duggani is acutely trapezoidal.
In C. pledgei, the precingulum extends from cuspid 2, whereas
in Darcius duggani it extends from cuspid 1. In species of Ekto-
podon, the precingulid is completely subsumed by struts. The
protolophid and hypolophid of C. pledgei each have four
cuspids, whereas D. duggani has four on the protolophid and
three on the hypolophid. By comparison, E. tommosi bears six
cuspids on each of the proto- and hypolophids. In both
C. pledgei and E. tommosi, cuspid 1 is roughly a third narrower
and shorter than the hypoconid, while in D. duggani they are sub-
equal. Both C. pledgei and E. tommosi bear protolophid cusps
that are oriented lingually, whereas those of D. duggani are
oriented buccally. Unlike the radiating cristids from cuspids 2–
3 on the protolophid, those of the species of Ektopodon and
D. duggani are more anteroposteriorly oriented and elongate.
On the hypolophid, the pre- and post-cuspid2–3-cristids are
similar in relative width to E. tommosi, and narrower than
D. duggani.
The m2 is 13% narrower and 2% shorter than m1 (Table 2).
The m2 trigonid and talonid are subequal in length. A distinct
protoconid and hypoconid demark the buccal ends of the
protolophid and hypolophid, respectively. A small, isolated
cusp lies anterior to the metaconid in the paraconid position.
The protolophid is composed of five cuspids, with the weakly dif-
ferentiated cuspid 2 budding from the lingual face of cuspid
1. The cristids extending from the cuspids on the protolophid
are more anteroposteriorly elongate than their homologs on
the m1 trigonid. The pre- and post-cuspid-cristids are together
oriented anterobuccally at an angle of 20° from the longitudinal
axis of tooth. The somewhat cuspate structure at the terminus of
pre-cuspid2–3-cristids appear to derive from the paracristid and
is referred to as the lingual apex of the paracristid. The structure
descends anterolingually to the paraconid anterior to the
metaconid. Anterior to the lingual apex of the paracristid is a
precingulid. The lingual apex of the paracristid is separated
from the protoconid by a deep valley, representing the antero-
buccal notch sensu Archer et al. (1987)(Fig. 6A–D). Alterna-
tively, the pre-cuspid2-cristid may represent the remnant of a
continuous paracristid between the protoconid and the lingual
apex of the paracristid. As for the m1, no structures cross the
weakly excavated basin of the transverse valley with the excep-
tion of the juncture between the posterolingual cristid to
cuspid 1 on the protolophid and the anterolingual strut to
cuspid 2 on the hypolophid, together possibly deriving from the
cristid obliqua.
The hypolophid is composed of four cuspids. As in m1, the
entoconid is relatively disjunct from the other cuspids, with five
pronounced cristids that radiate from the buccal face. The
remnant lingual kink of the cristid obliqua is distinct and
V-shaped on m2, composed of the three cristids descending ante-
riorly towards the transverse valley, which are bifurcated from
the primary pre-cuspid2-cristid (Fig. 5A). The posthypocristid
is similar in morphology to that of m1.
The m2 of C. pledgei has similar dimensions to those of
C. illuminata (UCMP 315228, formerly UCR 15228), being mark-
edly narrower than in species of Ektopodon and slightly broader
than D. duggani (Table 2). The crown height is c. 25% taller than
that of C. illuminata. The crown morphology differs most
obviously from that of C. illuminata in its thicker pre- and
post-cuspid-cristids that have less prolific anastomosing
between them. The m2 protolophid of C. pledgei is composed
of five cuspids compared with six in C. illuminata and seven in
E. tommosi. The m2 of D. duggani (NMV P54185) is relatively
worn but the protolophid appears to have been made up of
four or more cuspids. In common with C. pledgei, a small cusp
in the paraconid position is present in C. illuminata, though it
is not clearly distinct from a cristid descending anterolingually
from cuspid 5 (Fig. 5C). Directly lingual to the anterobuccal
notch, the discretely identifiable lingual apex of the paracristid
in C. pledgei has been replaced by a series of finer anastomosing
cristids in C. illuminata (e.g., Fig. 6A–D). Unlike C. pledgei,in
which a single cristid weakly abuts the proximate structure on
the opposing lophid, the transverse valley in C. illuminata is
crossed by up to five cristids (Fig. 5A, C). In D. duggani, the
transverse valley is crossed by cristids in some specimens,
seeming to be variable within the species. In no species of Ekto-
podon is the transverse valley crossed by any structures.
Both C. pledgei and D. duggani have four cuspids on the hypo-
lophid, whereas C. illuminata has six, and species of Ektopodon
have seven or more. In C. pledgei, cuspid 3 seems to be structu-
rally homologous to cuspids 3 + 4 in C. illuminata, with the
latter derived through the subdivision of the former in accord-
ance with the pre- and post-cuspid-cristids (Fig. 5A, C). The
lingual kink of the cristid obliqua on the m2 is similar to that
in E. tommosi and E. stirtoni, wherein the structure has been
merged with the anterior end of the pre-cuspid2-cristid, and in
turn forms three bifurcating cristids: one branching midway up
the hypolophid and the other two branching weakly near the
base of the transverse valley. By comparison, the structure
remains largely independent of cuspid 2 in C. illuminata, being
separated from the apex by a small but distinct cuspate structure
with short and fine radiating cristids (Fig. 5C). In D. duggani, the
structure deriving from the lingual kink of the cristid obliqua on
m2 is not clearly discernible.
The m3 is 10% shorter, but only slightly narrower than m2
(Table 2). The tooth is more distinctly rhomboid in occlusal
view than m2 and slightly wider anteriorly than posteriorly
(Fig. 5A). The lingual apex of the paracristid is more uniform
than that of m2, lacking a valley incised into it or the associated
precingulid (Fig. 5A). As in the m2, the protolophid has five
cuspids, with the weakly differentiated cuspid 2 budding from
the lingual face of the protoconid. Anterior to the metaconid is
a small, isolated cusp in the paraconid position, differing from
that of m2 in that the cusp is connected to a short and fine
cristid descending anteriorly from the metaconid. No structures
cross the transverse valley.
The hypolophid has four cuspids, differing from the m2 in that
the pre-cuspid3-cristid bears three successively diverging struts
that are directed towards the lingual extremity of the lingual
kink of the cristid obliqua and the post-cuspid3-cristid is not
divided posteriorly into two subequal cristids. The structure
deriving from the lingual kink of the cristid obliqua is only
weakly connected to the pre-cuspid2-cristid and is not parti-
tioned into further cristids. Consequently, the structure is more
distinctly V-shaped than its homolog on the m2. As in the m2,
the strength of expression of the lingual kink of the cristid
Crichton et al.—New ektopodontid possum from Australia (e2171299-7)

obliqua parallels the morphology of the anterobuccal notch in
the paracristid.
The m3 is subequal in relative width to that of C. sp. cf.
C. illuminata (AMNH 95584) and comparatively narrower than
in C. illuminata (UCMP 315227) and D. duggani (NMV
P157248) (Table 2). As in m2, the crown height is about 25%
higher than that of C. illuminata, though comparable to that of
C. sp. cf. C. illuminata. As with m2, the crown morphology
differs most obviously from that of C. illuminata in its thicker
pre- and post-cuspid-cristids, with less anastomosing between
them (Fig. 5A, C). The crown morphology of C. sp. cf.
C. illuminata is of intermediate complexity between that of
C. pledgei and C. illuminata. The thick and anteroposteriorly
elongate pre- and post-cuspid-cristid morphology in C. pledgei
bears some similarity to D. duggani and species of Ektopodon,
though differing in that these taxa lack prominent struts that
transversely link cuspids. Ektopodon tommosi does, however,
bear linkages between pre- and post-cuspid-cristids on m3 and
m4, with those on the m3 restricted to the lingual-most cuspids.
As in m2, the small cusp anterior to the metaconid in the para-
conid position is present in C. illuminata and C. sp. cf.
C. illuminata, in which the structure is similarly connected to a
pre-cuspid5-cristid (Fig. 5A–D). This small cusp anterior to
the metaconid is also present in D. duggani and E. stirtoni.The
lingual apex of the paracristid is more uniform than that of C.
sp. cf. C. illuminata and C. illuminata, being more structurally
independent from the terminating pre-cuspid-cristids (Fig. 5A–
D). Remnants of the lingual component of the paracristid
FIGURE 5. Occlusal view of lower cheek teeth from species of Chunia, with associated line drawings and annotations depicting key intrafamilial
homologies. A,Chunia pledgei (right p3, m1–m3, NTM P11992); B,C. illuminata (SAMA P19903, cast of UCMP 315228, left m2: image reversed);
C,C. illuminata (SAMA P19902, cast of UCMP 315227 left m3: image reversed); D,Chunia sp. cf. C. illuminata (SAMA P19905, cast of AMNH
95584, left m3: image reversed). The bracketed cusp numbering denotes that this terminology is informal. Abbreviations:a, anterior; abn, anterobuccal
notch; b, buccal; cdo, cristid obliqua; end, entoconid; hyd, hypoconid; lkcdo, lingual kink of cristid obliqua; med, metaconid; pacd, paracristid; pastd,
parastylid; pbs, posterobuccal shelf; pohyd, posthypocristid; prcd, precingulid; prd, protoconid; tv, transverse valley. Scale bar equals 5 mm.
Crichton et al.—New ektopodontid possum from Australia (e2171299-8)

are identified in D. duggani and species of Ektopodon; however,
in the latter they are concealed almost entirely in occlusal view
by terminating cristids. The protolophid on the m3 of
C. pledgei and C. sp. cf. C. illuminata has five cuspids, with
cuspid 2 poorly separated from cuspid 1, whereas that of
C. illuminata has six, with cuspids 2 and 5 poorly separated
from cuspids 1 and 6, respectively (Fig 5). By comparison, that
of D. duggani has five cuspids, and that of E. tommosi—though
incomplete—appears to have seven cuspids. Unlike C. pledgei,
in which the transverse valley on the m3 is not clearly crossed
by any structures, the transverse valley in C. sp. cf.
C. illuminata and C. illuminata is crossed by two to three cristids
(Fig. 5A–D).
In common with C. sp. cf. C. illuminata and C. illuminata, the
hypolophid bears four cuspids. In C. sp. cf. C. illuminata and
C. illuminata, cuspid 3 on the hypolophid bifurcates anteriorly
and posteriorly into two roughly equal cristids, whereas in
C. pledgei the post-cuspid3-cristid remains undivided and the
pre-cuspid3-cristid bears three successively diverging struts that
are oriented towards the lingual extremity of the lingual kink
of the cristid obliqua. The remnant lingual kink of the cristid
obliqua is distinct and V-shaped on m2, composed of the three
cristids descending anteriorly towards the transverse valley,
which are bifurcated from the primary pre-cuspid2-cristid. On
m3, the cuspate structure deriving from the lingual kink of the
cristid obliqua is similar to that of C. sp. cf. C. illuminata and
C. illuminata with respect to its relative size and distinction
from proximate cristids (Fig. 5A–D). As in m2, both C. sp. cf.
C. illuminata and C. illuminata differ from C. pledgei in that
the lingual kink of the cristid obliqua is separated from the
apex of cuspid 2 by a small but distinct cuspate structure with
short and fine radiating cristids (Fig. 5A–D). The apex of
cuspid 3 on the hypolophid does not link to the apex of the ento-
conid (cuspid 4), but rather a cristid on the posterior margin
spans to the postentocristid, also present in C. illuminata and
C.sp. cf. C. illuminata.
Upper Dentition—NTM P11993 is the posterior half of an
upper molar, that is closest in width to the M1 (SAMA
P29081) of C. illuminata (Table 2,Fig. 4A), though its mor-
phology is more congruent with that of the M2 (SAMA
P17997). NTM P11993 bears a metaloph with three principal
cusps and three much smaller buccal cusps (Fig. 4). Cusps 2
and 3 have three prominent cristae descending anteriorly
and posteriorly, with cusp 2 also bearing struts that radiate
from the lingual face. These cusps are oriented buccally, par-
alleling the morphology of the metaconule. The posterior face
of the metaconule bears a crescentic postcingulum. A promi-
nent lingual cingulum descends the anterolingual face of the
metaconule, arching anteriorly. Buccal to the lingual cingulum,
three short cristae rise from the anterolingual face of the
metaconule. The cusp in the metacone/stylar cusp D position
(cusp 6) is relatively small. We interpret that the metacone
may be structurally homologous to the apex of cusp 4, or
even cusp 3, following a similar manifestation of morphologi-
cal change to that evident on the anterior and posterior faces
of the metaconule. No cristae transversely link the cusps with
the exception of a central crista. None of the pre-cusp-cristae
are broken at their termini, indicating that no structures
crossed the transverse valley. The postmetaconulecrista (or
posterior cingulum) is strongly curvilinear, descending
steeply posteriorly from the metaconule, then forming a
right angle as it turns buccally and continues along the pos-
terior margin, terminating at its juncture with post-cusp6-
crista.
NTM P11993 shares with the upper molars of species of
Chunia three cristae descending posteriorly from cusps 2 and
3. NTM P11993 differs from all other ektopodontids in bearing
a postcingulum on the posterior face of the metaconule. It also
differs from Chunia spp. in lacking cristae that transversely link
the cusps on M2, with the exception of the central link spanning
the loph shared by species of Chunia and Ektopodon but not
D. duggani. If NTM P11993 is from an M1 rather than an M2,
it differs from that of C. illuminata in that the structural
complex putatively deriving from the metacone (cusps 4–6)
does not form a selene.
Phylogenetic Analysis Results
Parsimony analysis of the morphological dataset, with
implementation of constraints on macropodoid and petauroid
taxa, and Lekaneleo roskellyae as the specified outgroup, gener-
ated a strict consensus of 558 most parsimonious trees of 242
steps (see Supplementary Data 10 for a .tre file containing the
most parsimonious trees). The strict consensus tree had a consist-
ency index of 0.53, and a retention index of 0.78 (see Fig. S1). The
resulting topology under parsimony is, for the most part, consist-
ent with that under Bayesian inference, though with lower
support for most nodes.
Analysis under Bayesian inference of the combined morpho-
logical and molecular dataset with inclusion of all outgroup
taxa resulted in the Burramyidae as sister to the pilkipildrid
Djilgaringa gillespiei with weak support (BPP = <0.50), which
were together sister to all remaining phalangeroids (BPP =
0.81) (Fig. 7D). Monophyly of Phalangeridae + Miralinidae +
Ektopodontidae was weakly supported (BPP = 0.54; BS =
31%). The miralinids Miralina doylei Woodburne, Pledge,
and Archer, 1987 and M. minor Woodburne, Pledge, and
Archer, 1987 formed a strongly supported clade with the pur-
ported basal phalangerid Eocuscus sarastamppi (BPP = 0.96;
BS = 86%). This clade is moderately supported as the sister
to Ektopodontidae (BPP = 0.71; BS = 67%) by state changes
in characters 72–75 relating to the number of cusps per
molar loph, in addition to three synapomorphies: P3 aligned
anterolingually relative to longitudinal axis of the molar row
(C.I. = 0.40: char. 15); enamel surface crenulations form well-
developed crests (C.I. = 0.30: char. 19); and parastylid present
on m1 in anterolingual most corner (C.I. = 1: char. 54). Ektopo-
dontid monophyly was also strongly supported (BPP =0.97; BS
= 88%), with Chunia as the sister group to a weakly supported
Darcius +Ektopodon clade (BPP = 0.62; BS = 46%). Mono-
phyly of Chunia received strong support (85%) in parsimony
and weak support under Bayesian inference (0.52), united by
three synapomorphies: cristids transversely-link between the
pre- and post-cuspid-cristids on m2 and m3 (C.I. = 0.1: char.
25); generally three cristae descend anteriorly and posteriorly
per cusp on upper molars (C.I. = 0.67: char. 27); and presence
of a precingulid buccal to paracristid on m2 (C.I. = 0.17: char.
51). Chunia pledgei emerged as the sister taxon to a weakly
supported C. sp. cf. C. illuminata +C. illuminata +C. omega
clade (BPP = 0.61; BS = 50%). The species of Ektopodon
formed a strongly supported clade (BPP = 0.97; BS = 81%),
with E. tommosi sister to remaining species (BPP = 0.90; BS
= 76%). Ektopodon stirtoni branched next, then E. ulta,
which was the sister taxon to E. litolophus +E. serratus.
The purported miralinid Durudawiri inusitatus was recovered
with low support as the sister group to either the miralinid +
ektopodontid clade (BPP = <0.50) or to the miralinid + ektopo-
dontid + phalangerid clade (BS = 31%). Phalangerid monophyly
was strongly supported (BPP = 0.80; BS = 72%). Under Bayesian
inference, Trichosurus dicksoni formed a Trichosurinae clade
with T. vulpecula (Kerr, 1792) and W. squamicaudata Alexander,
1918 (BPP = 0.54). This clade emerged as sister to Ailuropinae
(Ailurops ursinus and Strigocuscus celebensis) + Phalangerinae
(Spilocuscus maculatus (Desmarest, 1817) and Phalanger orien-
talis (Pallas, 1766)). The extinct Onirocuscus silvacultrix is
embedded within Ailuropinae with low support (BPP = <0.50),
Crichton et al.—New ektopodontid possum from Australia (e2171299-9)

FIGURE 6. Occlusal view of lower molars of selected phalangeroids, with associated line drawings and annotations depicting key interfamilial hom-
ologies. A, holotype right m1–3ofChunia pledgei (NTM P11992). B, composite lower molar row of Miralina doylei: SAMA P29065, cast of UCR
15824, left m1 (image reversed); SAMA P32399, cast of UCR 15819, left m2 (image reversed); SAMA P29082, left m3 (image reversed); SAMA
P32400, cast of UCR 15823, right m4. C, composite lower molar row of Trichosurus vulpecula: FUR 399, right m1–3; FUR 401, right m4. D, composite
lower molar row of Spilocuscus maculatus: SAMA M1691, right m1–3; SAMA M1689, right m4. Abbreviations:abn, anterobuccal notch; cdo, cristid
obliqua; end, entoconid; hyd, hypoconid; med, metaconid; pacd, paracristid; pastd, parastylid; poend, postentocristid; pohyd, posthypoconid; pomed,
postmetacristid; poprc, postprotoconid; prc, precingulid; prd, protoconid; prend, preentocristid; prmed, premetacristid; prstd, protostylid. Scale bars
equal 5 mm.
Crichton et al.—New ektopodontid possum from Australia (e2171299-10)

FIGURE 7. Phylogenies of Phalangeroidea that result from Bayesian analyses of the combined morphological and molecular data, when using differ-
ent outgroup taxa, between which unequivocal relationships are enforced. Topology Awas polarized by the thylacoleonid Lekaneleo roskellyae;B,by
macropodoid representatives; C, by petauroid representatives; and D, by all aforementioned outgroup taxa, wherein L. roskellyae was specified as the
deepest outgroup. Each is presented as a majority rule consensus with numbers at nodes representing Bayesian posterior probabilities (BPP). In A–C,
black circles at nodes represent BPP of ≥0.95, dark gray circles represent BBP of 0.75–0.94 and light gray circles present BBP of 0.5–0.74. Nodes
without circles or numbers represent retained compatible partitions with BPP <0.5.
Crichton et al.—New ektopodontid possum from Australia (e2171299-11)

while the putative miralinid D. anfractus is embedded within
Phalangerinae (BPP = 0.87; BS = 60%), well distant phylogeneti-
cally from D. inusitatus.
Under Bayesian inference, phalangeroid interrelationships
remained largely consistent irrespective of changes to the out-
group taxa used, though with some variation in associated
support values (Fig. 7A–C; for unconcatenated trees with BPP
values see Figs. S2, S3, S4, Supplementary File 1, or .tre files in
Supplementary Files 11–14). Exceptions include the relative pla-
cement of the pilkipildrid Djilgaringa gillespiei and purported
miralinid Durudawiri inusitatus. Specifically, there was weak
support for: D. gillespiei as sister to either the phalangeroid
clade comprising miralinids, ektopodontids, and phalangerids
(Fig. 7A, B) or the Burramyidae (Fig. 7C, D); and D. inusitatus
as sister to either Phalangeridae (Fig. 7A, B), or the miralinid
+ ektopodontid clade (Fig. 7C, D).
DISCUSSION
Chunia pledgei sp. nov. is the first taxon named from the
Pwerte Marnte Marnte locality of the southern Northern Terri-
tory. Dental comparisons with other ektopodontids and a parsi-
mony analysis shed light on relationships within the family and
Phalangeroidea, more broadly. In addition, the new taxon
allows for further inferences about the potential diet of ektopo-
dontids and provides insights into the relative age of the Pwerte
Marnte Marnte LF due to the long-noted biochronological utility
of ektopodontids.
Phylogenetic Interrelationships
Chunia pledgei is resolved as the sister taxon to other species
of Chunia within the Ektopodontidae, with low support under
Bayesian inference (Fig. 7A–D) and high support under
maximum parsimony (Fig. S1). Chunia pledgei is referred to
Chunia rather than Ektopodon chiefly on the basis of the promi-
nent transverse-linking of cristids on the lower molars, and the
presence of three or more anterior and posterior cristae descend-
ing from the cusps on the upper molars.Our placement of Chunia
as the sister taxon to Ektopodon +Darcius is consistent with the
original hypothesis of Woodburne and Clemens (1986a, b),
though support values remain low (Fig. 7A–D). This poor resol-
ution is, in large part, due to the apparently considerable phylo-
genetic distance between ektopodontids and other
phalangeroids, which makes polarization of key dental attributes
in the family problematic. Darcius duggani, in particular, pre-
sents an anomalous combination of seemingly plesiomorphic
and derived traits (Rich, 1986; Rich et al., 2006). It will likely
only be possible to robustly assess the affinities of D. duggani
with the recovery of further specimens, especially, the complete
upper dentition.
Ektopodontids are deeply nested within Phalangeroidea, and
were already highly distinctive by the late Oligocene, so it is
likely that they and other phalangeroid lineages had an exten-
sive, prior evolutionary history. Our phylogenetic analyses recov-
ered Ektopodontidae as sister to Miralina +Eocuscus
sarastamppi with moderate support (BPP = 0.71; BS = 67%). A
sister relationship with Miralinidae is consistent with earlier
hypotheses about these groups (Archer et al., 1987; Woodburne
et al., 1987), but differs from a later analysis that recovered ekto-
podontids as sister to Pilkipildridae + Miralinidae (Crosby &
Archer, 2000). Robust resolution of the affinities of pilkipildrids
would require discovery of the M1.
Previous osteology-based analyses of phalangeroid inter-
relationships have separated burramyids (pygmy possums) at
the superfamily level (Burramyoidea), outside of Phalangeroi-
dea + Petauroidea (Archer et al., 1987; Woodburne et al., 1987;
Crosby and Archer, 2000). However, molecular studies have
supported a sister relationship between Burramyidae and Pha-
langeridae within the Phalangeroidea (Kirsch et al., 1997;
Beck, 2008; Meredith, Westerman, Case et al., 2008; Meredith,
Krajewski et al., 2009; Meredith, Westerman et al., 2009; Mitchell
et al., 2014; Westerman et al., 2010; May-Collado et al., 2015;
Duchêne et al., 2018; Eldridge et al., 2019; Beck et al., 2022).
Our Bayesian analyses, in which petauroids and macropodoids
were constrained, recovered the Burramyidae as sister to the
other included phalangeroid families, with Pilkipildridae poorly
resolved as sister to either the former or the latter. Molecular evi-
dence indicates the split between Burramyidae and Phalangeri-
dae occurred roughly 40–47 Ma ago in the Eocene (Beck, 2008;
Meredith, Westerman, Springer, 2008; Meredith, Krajewski,
et al., 2009; Meredith et al., 2011; Mitchell et al., 2014;
Duchêne et al., 2018). More recently, Beck et al. (2022) recov-
ered a considerably younger divergence estimate of 29.9 Ma
though this was driven in part by their use of an effective prior
of 25.7 Ma (95% Highest Posterior Density = 23.6–32.0 Ma).
We consider that the degree of morphological distinction
evident between phalangeroid families by the late Oligocene is
more congruent with earliest Oligocene or Eocene divergence
estimates.
In our phylogenetic analyses the placement of several key fossil
taxa differs from those presented in previous studies (Crosby &
Archer, 2000;Crosby, 2002; Case et al., 2009). Eocuscus saras-
tamppi, though originally deemed a basal phalangerid, formed a
strongly supported clade with species of Miralina (Fig. 7A–D;
Fig. S1). The phylogenetic placement of E. sarastamppi was
initially assessed (Case et al., 2009) using a morphological charac-
ter matrix created for, and comprising, exclusively phalangerid
taxa (see Flannery et al., 1987), and its referral to the family was
not justified by any synapomorphies. In this study, the sister
relationship between E. sarastamppi and the species of Miralina
is supported by five synapomorphies: a cuspate ridge near base
of crown on P3, formed by the raised anterior terminus of the
crista that descends anteriorly from the first cuspule (C.I. = 1.0:
char. 10); preprotocrista not continuous with preparacrista on
M1 (C.I. = 1.0: char. 22); cuspule between paracone and parastyle
on preparacrista on M1 (C.I. = 1.0: char. 39); cuspule on crista des-
cending anteriorly from stylar cusp D on M1 (C.I. = 0.5: char. 41);
and parastyle/stylar cusp A on M2 (C.I. = 1.0: char. 44). The attri-
butes used by Case et al. (2009) to describe Eocuscus and differen-
tiate it from genera in Phalangeridae are consistent with those of
Miralina. Species of Miralina and E. sarastamppi are of similar
geological age, with all three taxa described from the Ditjimanka
LF of the Etadunna Formation, southern Lake Eyre Basin. On the
basis of its smaller size and the presence of a double rooted rather
than single rooted P2, we consider E. sarastamppi to be dis-
tinguishable from the type species M. doylei only at a species
level, and thus view Eocuscus Case, Meredith and Person, 2009
as a junior synonym of Miralina Woodburne, Pledge and
Archer, 1987.Miralina sarastamppi (Case, Meredith & Person,
2009) nov. comb., cannot be readily compared with the similarly
sized M. minor, because the former is known only from a
maxilla with relatively worn dentition (Case et al., 2009), and
the only upper dentition attributed to the latter is an M1 (Wood-
burne et al., 1987). As such, the possibility remains that
M. sarastamppi may be a junior synonym of M. minor. A conse-
quence of the referral of this taxon to Miralinidae is that the
oldest named phalangerids derive instead from the early
Miocene Faunal Zone B of Riversleigh (e.g., see Flannery &
Archer, 1987; Crosby et al., 2001; Crosby, 2007). From Riversleigh,
an undescribed phalangerid (new genus 2 sp. 1) has also been
reported from several upper Oligocene sites (Faunal Zone A):
e.g., Boles’Bonanza, Lee Sye’s Outlook, and Quantum Leap
Site (see Archer et al., 2006).
This study also failed to recover a sister relationship between
the miralinid genera Miralina and Durudawiri. The type
Crichton et al.—New ektopodontid possum from Australia (e2171299-12)

species of Durudawiri,D. inusitatus, was referred to Miralinidae
on the basis of: an anterior cingulum that rises steeply to meet the
parastyle on M1; a large central cusp on the posterior moiety on
M1; elongate i1; curvilinear cristid obliqua on the lower molars;
lingually displaced protoconid on m1; well-defined anterior and
posterior cingula on the lower molars; and a hypolophid of m2
that meets the postentocristid (Crosby & Archer, 2000). In the
present study, D. inusitatus was recovered with low Bayesian
support (<0.50) as sister to either the Phalangeridae (Fig. 7A,
B) or to the miralinid + ektopodontid clade (Fig. 7C, D), and
under Parsimony, with similarly low support, as sister to the mir-
alinid + ektopodontid + phalangerid clade (Fig. S1). This poor
resolution reflects that at least some of the aforementioned attri-
butes shared between species of Miralina and D. inusitatus
appear to be symplesiomorphies. Most notably, a large central
cusp (“neometaconule”) on the posterior moiety of M1 is also
present in the late Oligocene burramyid Burramys wakefieldi
(unpublished specimen, SAMA P40931). The specimen
(SAMA P40931, preserving P3, M1–M2) was referred to
B. wakefieldi by Pledge (pers. comm., 2022) based on comparison
with the holotype (SAMA P24570, preserving p3, m1); both are
of similar relative size, share generally similar morphology to
species of Burramys, and were recovered from Mammalon Hill
(Ngama LF), Etadunna Formation. The incidence of a large
central cusp on the posterior moiety of M1 in a further species
of basal phalangeroid is interpreted as support for the hypothesis
that, in phalangeriforms, this structure may represent the meta-
cone, while the “metacone”may represent stylar cusp D (see
Woodburne et al., 1987; Crosby & Archer, 2000; Case et al.,
2009; Beck et al., 2022).
The second species of Durudawiri,D. anfractus, is more pha-
langerid-like, and was consistently recovered deeply nested
within Phalangeridae, in a clade with the phalangerines
S. maculatus and P. orientalis.Durudawiri anfractus was linked
with D. inusitatus and differentiated from phalangerids on the
basis that the hypolophid meets the posthypocristid rather than
the hypoconid on m3, as for the m2 in D. inusitatus (Crosby,
2002). However, we note that this attribute is also present on
m3–4ofS. maculatus (Fig. 6D) and on m4 of P. orientalis.
These observations highlight that Durudawiri may require
further study: not only may the two referred species fall
outside of Miralinidae, but D. anfractus likely also belongs in a
different genus.
None of the three species of the purported miralinid genus
Barguru were included in this analysis. The three species are rep-
resented by a total of five specimens identified as representing
M1 from the Early Miocene Kangaroo Well and Middle
Miocene Bullock Creek deposits of the Northern Territory
(Schwartz, 2006). The specimens were referred to Miralinidae
principally on the basis that they share an anteriorly projecting
sectorial parastyle on M1, and a nearly complete metaloph.
The specimens also have some similarity in loph structure to
that of macropodoids, which was regarded as convergent
(Schwartz, 2006). Here, we consider the similarities of these
teeth to the dP3 of balbarids and stem macropodids (see Black,
Travouillon, et al., 2014; Travouillon et al., 2014) to be strong
indicators of a macropodoid affinity for the species of Barguru.
Similarities include: an anteriorly projecting sectorial parastyle;
complete protoloph and metaloph; straight ectoloph; and
absence of a preprotocrista, premetaconulecrista, and central
cusp on the metaloph (“neometaconule”). Two macropodoid
families, Balbaridae and Macropodidae, are well represented in
the Bullock Creek and Kangaroo Well assemblages (Megirian
et al., 2004; Schwartz, 2016). The species of Barguru may rep-
resent as yet unnamed macropodoids, or may be synonymous
with one or more named macropodoid taxa, for which no defini-
tive deciduous premolars have hitherto been identified. As such,
we refer the specimens in question to Macropodoidea, but, at this
stage, cannot resolve whether the genus or species therein are
nomina dubia.
Functional Dental Morphology
Appraisal of the functional morphology of ektopodontid den-
tition has allowed for inferences to be drawn as to their possible
diet. It has variously been suggested that they may have eaten
leaves, flowers, fruit, seeds, grains, insects (particularly caterpil-
lars and grubs), and/or aquatic invertebrates (mollusks and crus-
taceans) (Pledge, 1982,1986,1991). It has also been speculated
that ektopodontids may have filled a rodent-type niche,
though, as noted by Pledge (1991), they differ functionally in
that the morphology of the lower incisors, and likely the upper
incisors, seems to have been unsuitable for gnawing. Here, we
re-examine the functional morphology of ektopodontid dentition
in light of the morphology presented by Chunia pledgei.
Ektopodontid molars are characterized by highly complex
enamel surface ornamentation involving transverse lophs that
are subdivided into cusps with anteroposteriorly elongate
cristae. High enamel complexity in molars can improve food pro-
cessing capability by increasing the number of food breakage
sites (e.g., Evans et al., 2007; Candela et al., 2013). Enamel com-
plexity can alternatively, or in conjunction, act to improve the
stability of the occlusal profile, allowing for greater masticatory
loads, and reduce the rate of occlusal wear by spreading the
punctual pressures over a larger number of contact sites (e.g.,
Gailer & Kaiser, 2014). Of additional note is that ektopodontid
molar cusps are composed almost entirely of enamel, with a
dentine core that is surprisingly small, exposed only at a late
stage of the life history (Koenigswald, 2019). Thick enamel is
generally an adaptation associated with resistance to fracturing
induced by hard food items (e.g., Vogel et al., 2008; Barani
et al., 2012).
Within modern phalangerid subfamilies, there is a trend of
increasing complexity in molar enamel ornamentation (e.g.,
Fig. 6C, D) from what molecular studies (Ruedas & Morales,
2005; Raterman et al., 2006; Meredith, Krajewski et al., 2009;
Kealy et al., 2019) reveal to be the basal Trichosurinae (Tricho-
surus +Wyulda) through Ailuropinae (Ailurops +Strigocuscus),
to the more derived Phalangerinae (Phalanger +Spilocuscus)
taxa. This trend is associated with a dietary shift from folivory
(Freeland & Winter, 1975; Dwiyahreni et al., 1999) to fruits of
notably high fiber content (Dwiyahreni et al., 1999; Saragih
et al., 2010; Farida & Dahrudin, 2017; Farida, 2020). Therefore,
with respect to members of Phalangeridae, increased enamel
ornamentation may aid in the processing of fibrous food items
by increasing the number of shearing contact sites during
mastication.
Most phalangeroids have a functional division in the cheek
teeth, wherein the m1 bears a laterally compressed trigonid
with a bladed anterior crest (paracristid) descending from a
raised protoconid (Fig. 6B–D), performing a cutting/cracking
function abetting a sectorial/plagiaulacoid premolar. Ektopo-
dontid molars differ notably in that the m1 trigonid, and to a
lesser degree the p3, have become molarized (Fig. 6A–D). This
indicates that whatever ektopodontids were eating required
greater mastication than that eaten by other possum taxa. For
much the same reason, similar changes in the m1 trigonid are
manifest in derived representatives of Diprotodontoidea and
Macropodoidea. It has been suggested that ektopodontids may
have used their premolars, abetted by the first molars, to break,
or puncture-crush, food items such as seed cuticles (Pledge,
1991). Similarly, in C. pledgei, the wide m1 with sub-pyramidal
rather than anteroposteriorly oriented cuspids on the protolo-
phid are interpreted to reflect a functional division along the
molar row, performing an initial puncture-crushing phase
during mastication. We consider this to be generally congruent
Crichton et al.—New ektopodontid possum from Australia (e2171299-13)

with the idea (Pledge, 1986,1991) that ektopodontids may have
occupied a granivorous and/or frugivorous niche.
The morphological variance presented between ektopodontid
species and genera also alludes to a degree of niche differen-
tiation within the family. This would be consistent with the occur-
rence of several possibly sympatric ektopodontid taxon pairs
including: C. omega and E. tommosi from the upper Oligocene
Tarkarooloo LF, Namba Formation; as well as E. serratus and
E. litolophus from the Kutjamarpu LF, Wipajiri Formation
(Pledge et al., 1999), currently considered Lower Miocene
(Megirian et al., 2004,2010; Travouillon et al., 2006; Woodhead
et al., 2016) or possibly lower Middle Miocene (Black et al.,
2013; Gurovich et al., 2014).
It is also worthy of note that species of the diminutive phasco-
larctid genus Nimiokoala Black and Archer, 1997, as well as Lito-
koala garyjohnstoni Louys, Black, Archer, Hand and Godthelp,
2007, present some parallels in cheek tooth morphology to
those of Ektopodontidae alluding to the possibility that these dis-
tantly related marsupial groups may have had similar diets
(Black & Archer, 1997; Black, Price, et al., 2014). Similarities
in the cheek tooth morphology between these taxa include: pro-
minent cusps with longitudinal cristae positioned between the
principal buccal and lingual cusps, which together form trans-
verse lophs on the lower molars; a large cuspate parastyle on
M1; and a reduced p3 that is tricuspid with posterobuccal
cuspid. The skull of Nimiokoala is also reportedly—in some
ways—intermediary between phalangerids and other phascolarc-
tids (Louys et al., 2009).
Stage-of-Evolution and the Pwerte Marnte Marnte Local Fauna
On the basis of stage-of-evolution comparisons of several
described but unnamed taxa, including an undescribed genus
and species of ilariid (Murray & Megirian, 2006), the Pwerte
Marnte Marnte LF was considered to pre-date the basal local
faunas of the Etadunna and Namba formations of the southern
Lake Eyre Basin (Murray & Megirian, 2006; Megirian et al.,
2010). The recovery of an ektopodontid taxon from the assem-
blage is useful in this regard because this group has often been
viewed as one of the most biochronologically informative for
the Australian Oligocene through Miocene (Woodburne et al.,
1985; Pledge, 1986; Woodburne & Clemens, 1986a; Pledge
et al., 1999; Megirian et al., 2004). Within Chunia, Woodburne
and Clemens (1986a) considered the poorly represented
Chunia sp. cf. C. illuminata from the Pinpa LF of the Namba For-
mation to exhibit a more plesiomorphic stage-of-evolution than
C. illuminata of the Ditjimanka LF, Etadunna Formation (c.
24.9 Ma: Woodburne et al., 1994; Megirian et al., 2010). The
Pinpa form, Chunia sp. cf. C. illuminata, was considered to be
possibly distinct from C. illuminata, but insufficiently represented
to merit referral to a new species (Woodburne & Clemens,
1986a). Chunia illuminata is itself considered to represent a
more plesiomorphic stage-of-evolution than C. omega of the Tar-
karooloo LF, Namba Formation (≥24.1 Ma: Woodburne et al.,
1994; Megirian et al., 2010).
Chunia pledgei has greatest overall similarity in lower molar
morphology to that of Chunia sp. cf. C. illuminata (Fig. 5A–D).
Similarities include the number of cuspids comprising lophids
and relative crown height. Based on biocorrelative and stage-
of-evolution comparisons, the Pinpa LF is thought to be the
oldest assemblage of the Namba Formation, similar in age or
slightly older than Faunal Zone A of the Etadunna Formation
(Woodburne et al., 1994). Faunal Zone A itself, represented by
the “Wynyardiid”interval (Minkina LF sensu Megirian et al.,
2010), is the oldest faunal zone of the Etadunna Formation, con-
strained by Woodburne et al. (1994) to 25.5–25.7 Ma using radio-
metry, magnetostratigraphy, and biocorrelation of forams
(Woodburne et al., 1985; Lindsay, 1987). A late Oligocene–
Early Miocene age for the lowest members of the Namba For-
mation was also concluded by Martin (1990) through examin-
ation of the palynology record recovered from the Wooltana-1
bore, representing an independent proxy for the validity of infer-
ences by Woodburne et al. (1994). More recently, the age of the
Etadunna Faunal Zones has been re-examined, with the Zone A
adjusted to 25.2 Ma in accordance with a recalibrated polarity
timescale (Megirian et al., 2010), and 26.1 Ma following reassess-
ment of the magnetostratigraphic data using a best-fit age-model
(Metzger & Retallack, 2010).
Chunia pledgei also seems to be precluded from being directly
antecedent to any other species of Chunia on the basis of derived
dental attributes including: a postcingulum on the buccal face of
the metaconule on ?M2; and a lingual kink of the cristid obliqua
on m2 that is merged with the principal pre-cuspid2-cristid and par-
titioned into smaller cristids, as opposed to remaining largely dis-
tinct from cuspid 2 in C. illuminata. Therefore, while congruent
with a late Oligocene age, the molar morphology of C. pledgei
does not, in and of itself, support or refute the hypothesis that
the Pwerte Marnte Marnte LF is the oldest Australian Oligocene
assemblage. Comprehensive sampling of the fauna is needed to
more precisely constrain the relative age of the Pwerte Marnte
Marnte LF, ideally coupled with additional age constraints.
CONCLUSIONS
Chunia pledgei sp. nov. is a new plesiomorphic ektopodontid
(Diprotodontia, Phalangeroidea), representing the first named
taxon from the Pwerte Marnte Marnte Local Fauna, Northern
Territory. Phylogenetic analyses recovered generic relationships
within Ektopodontidae that are consistent with those of previous
authors, though they remain poorly resolved. The analyses failed
to recover species of the genus Durudawiri in a monophyletic
Miralinidae, indicating that they require systematic review. We
also transfer the purported basal phalangerid Eocuscus saras-
tamppi to Miralinidae (Miralina sarastamppi comb. nov.). The
M1 specimens used to describe the Early to Middle Miocene mir-
alinid genus Barguru, and three species therein, are identified as
deciduous third premolars from early macropodoids. These find-
ings imply that the Miralinidae are known only from the late Oli-
gocene, and, conversely, the oldest named phalangerids are from
the Early Miocene. More generally, the high morphological
diversity of phalangeroids by the late Oligocene implies that
the families had an extensive evolutionary history prior to the
late Oligocene. Support for a late Oligocene age for the Pwerte
Marnte Marnte LF is inferred from the stage-of-evolution of
C. pledgei, though confirmation that this assemblage is the
oldest of Oligocene age in Australia requires further evidence.
ACKNOWLEDGMENTS
We thank M.-A. Binnie and D. Stemmer, respectively, for pro-
viding access to South Australian Museum Palaeontology and
Mammal Collections. We are grateful to W. Klein from Orange
Creek Station for allowing access to the Pwerte Marnte Marnte
fossil site. AIC was supported by The Australian Government
Research Training Program Scholarship. Support for the 2014
field trip to the site has come from the Society of Vertebrate
Paleontology (Patterson Memorial Grant) to A. Couzens. We
thank A. Couzens, C. Burke, S. Arman, W. Handley, and
G. Gully for organizing and/or assistance with the 2014 and
2020 field trips to the site. We also thank C. Burke for prepara-
tory guidance, J. Blokland for support relating to the phyloge-
netic component, and A. Yates for his ongoing assistance of
research on the Pwerte Marnte Marnte assemblage. We also
acknowledge the Southern Arrernte People, known as the
Pwerte Marnte Marnte Aboriginal Corporation, for their
Crichton et al.—New ektopodontid possum from Australia (e2171299-14)

custodianship of the lands on which the fossil locality is situated.
We thank reviewers R. Beck and K. Travouillon for thoughtful
comments that improved the work.
LIST OF SUPPLEMENTARY FILES
Supplementary_File_1.R2.docx
Supplementary_File_2_morph_matrix_tnt.R2.nex
Supplementary_File_3_morph_matrix_mrbayes.R2.nex
Supplementary_File_4.R2.nex
Supplementary_File_5_tnt_all_included.R2.tnt
Supplementary_File_6_thylacoleonid_outgroup.R2.nex
Supplementary_File_7_macropodoid_outgroup.R2.nex
Supplementary_File_8_petauroid_outgroup.R2.nex
Supplementary_File_9_all_included.R2.nex
Supplementary_File_10_TNT_MPTs.R2.tre
Supplementary_File_11_consensus_tree_thylacoleonid_
outgroup.R2.tre
Supplementary_File_12_consensus_tree_macropodoid_
outgroup.R2.tre
Supplementary_File_13_consensus_tree_
petauroid_outgroup.R2.tre
Supplementary_File_14_consensus_tree_all_included.R2.tre
ORCID
Aaron B. Camens http://orcid.org/0000-0003-0464-0665
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