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Alcheringa: An Australasian Journal of Palaeontology
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/talc20
A new species of Mukupirna (Diprotodontia,
Mukupirnidae) from the Oligocene of Central
Australia sheds light on basal vombatoid
interrelationships
Arthur I. Crichton, Trevor H. Worthy, Aaron B. Camens, Adam M. Yates, Aidan
M. C. Couzens & Gavin J. Prideaux
To cite this article: Arthur I. Crichton, Trevor H. Worthy, Aaron B. Camens, Adam M.
Yates, Aidan M. C. Couzens & Gavin J. Prideaux (2023): A new species of Mukupirna
(Diprotodontia, Mukupirnidae) from the Oligocene of Central Australia sheds light on basal
vombatoid interrelationships, Alcheringa: An Australasian Journal of Palaeontology, DOI:
10.1080/03115518.2023.2181397
To link to this article: https://doi.org/10.1080/03115518.2023.2181397
© 2023 The Author(s). Published by Informa
UK Limited, trading as Taylor & Francis
Group.
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A new species of Mukupirna (Diprotodontia, Mukupirnidae) from the Oligocene
of Central Australia sheds light on basal vombatoid interrelationships
Arthur I. Crichton, Trevor H. Worthy , Aaron B. Camens , Adam M. Yates, Aidan M. C. Couzens , and
Gavin J. Prideaux
ABSTRACT
The late Oligocene taxa Marada arcanum and Mukupirna nambensis (Diprotodontia,
Vombatiformes) are the only known representatives of the families Maradidae and Mukupirnidae,
respectively. Mukupirna nambensis was described from a partial skeleton, including a cranium but
no dentary, and reconstructed as the sister taxon to Vombatidae (wombats). By contrast, Ma.
arcanum is known only from a single dentary, preventing direct comparison between the two.
Here, we describe a new species, Mu. fortidentata sp. nov., based on craniodental and postcranial
specimens from the Oligocene Pwerte Marnte Marnte Local Fauna, Northern Territory, Australia.
Phylogenetic analysis of Vombatiformes, using 124 craniodental and 20 postcranial characters, pla-
ces these three species within Vombatoidea, wherein Marada arcanum is sister to species of
Mukupirna þVombatidae. Mukupirna fortidentata sp. nov. does not share any robust synapomor-
phies of the dentary with Ma. arcanum that would support placing them together in a clade to
the exclusion of Vombatidae. We therefore maintain separation of the families Mukupirnidae and
Maradidae. From a functional perspective, the craniodental specimens of Mu. fortidentata sp. nov.
reveal a suite of morphological traits that are unusual among vombatiforms, which we interpret
as adaptations for acquiring and processing hard plant material. These include: a short, broad ros-
trum; large, robust, steeply upturned incisors; and a steep, anteroposteriorly decreasing gradient
in cheek tooth size. The dental specimens of Mu. fortidentata sp. nov. also assist in the identifica-
tion of two further allied taxa: an early vombatid from the younger late Oligocene Tarkarooloo
Local Fauna, South Australia; and a possible vombatoid from the earliest Miocene Geilston Bay
Local Fauna, Tasmania. The Tarkarooloo Local Fauna taxon indicates that vombatids diverged from
other vombatoids prior to 24 million years ago.
ARTICLE HISTORY
Received 21 September 2022
Revised 13 February 2023
Accepted 13 February 2023
KEYWORDS
Mukupirnidae; Maradidae;
Vombatidae;
Vombatiformes; late
Oligocene; phylogenetic
analysis; Pwerte Marnte
Marnte
Arthur I. Crichton [arthur.crichton@flinders.edu.au], College of Science and Engineering, Flinders University, Bedford Park, Adelaide, 5042, South
Australia; Trevor H. Worthy [trevor.worthy@flinders.edu.au], Aaron B. Camens [aaron.camens@flinders.edu.au], Adam Yates
[Adamm.Yates@magnt.net.au] Museum and Art Gallery of the Northern Territory, Alice Springs 0870, Northern Territory, Alice Springs, 0870
Australia; Aidan M. C. Couzens [acouzens@ucla.edu], Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA
90095, USA; Gavin J. Prideaux [gavin.prideaux@flinders.edu.au], Flinders University School of Biological Sciences, Palaeontology, Adelaide, 5001
Australia.
THREE SPECIES of wombat (Vombatidae) and the koala
(Phascolarctidae) are the only extant representatives of a
once diverse radiation of vombatiform marsupials. This sub-
order included the largest Australian marsupial herbivores,
with six extinct families recognized, namely:
Diprotodontidae, Palorchestidae, Ilariidae, Wynyardiidae,
Maradidae and Mukupirnidae (e.g., Beck et al. 2022). Our
view of the divergences between these clades, and Australian
marsupial families more generally, has been concealed by
the temporal gap in the known fossil record from the early
Eocene (55 Ma) to late Oligocene (25 Ma) (e.g., Rich 1991,
Black et al. 2012b). By the late Oligocene, all eight vombati-
form families had already evolved uniquely specialized
dentitions, exacerbating the challenge of resolving their
interrelationships (e.g., Archer et al. 1999, Black 2007,
2012a,2012b, Brewer et al. 2015, Gillespie et al. 2016, Beck
et al. 2020,2022).
Maradidae is currently the most poorly understood of vom-
batiform families, being represented by only one species,
Marada arcanum Black, 2007, which was described and
remains known from just a single dentary from the late
Oligocene Hiatus Site, Faunal Zone A, of Riversleigh World
Heritage Area, northwest Queensland (Black 2007). When
described, Ma. arcanum was noted as expressing an unusual
mix of derived and ancestral traits, though sharing greatest
overall affinity to species of supposed wynyardiids within the
genera Namilamadeta and Muramura. More recently, the fam-
ily Mukupirnidae was erected to contain Mukupirna namben-
sis Beck,Louys,Brewer,Archer,Black&Tedford,2020,which
was described from a distorted cranium and partial postcranial
skeleton from the late Oligocene Pinpa Local Fauna (LF) of
Lake Pinpa, northeastern South Australia (Beck et al. 2020).
The phylogenetic position of Mu. nambensis within
Vombatiformes was assessed by Beck et al. (2020)usinga
ß2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis
Group.
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ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY
https://doi.org/10.1080/03115518.2023.2181397
Published online 19 Mar 2023
morphological character matrix, which resolved it as the sister
group to vombatids within Vombatoidea. Importantly, how-
ever, Ma. arcanum was not included in this analysis because it
is known only from the dentary, which is unknown for Mu.
nambensis. However, the similar size of Ma. arcanum and
Mu. nambensis (as indicated by molar row length), coupled
with similarities in molar morphology with species of
Namilamadeta and Muramura,ledBecket al. (2020)toflag
the possibility that they might belong within the same family,
genus or even species.
A further possibly allied taxon, reported as
Vombatomorphia? fam., gen. et sp. nov. by Murray &
Megirian (2006) prior to the erection of the families
Maradidae and Mukupirnidae, is represented by a lower m3
(NTM P2815-11) from the late Oligocene Pwerte Marnte
Marnte fossil locality. It was subsequently suggested by Black
et al. (2012b) that the tooth may belong to Marada arcanum.
Here we have described additional specimens referable to
this unnamed vombatomorphian from the Pwerte Marnte
Marnte LF, including its complete upper and lower cheek
dentition, as well as several postcranial specimens. This
material provides key information enabling appraisal of the
relative phylogenetic positions of Mukupirnidae and
Maradidae. Additionally, the functional morphology of the
craniodental material from the new Pwerte Marnte Marnte
taxon was examined to infer its dietary adaptations and, in
turn, to better understand the selective pressures faced by
early vombatoids prior to the evolution of hypselodonty. We
also use this opportunity to reassess undescribed molar frag-
ments from the late Oligocene Tarkarooloo LF, South
Australia, and have reinterpreted the taxonomic affinity of
an enigmatic partial dentary from the earliest Miocene
Geilston Bay, Tasmania.
Materials and methods
Terminology
Molar position homology follows Luckett (1993). Molar
cusp nomenclature follows Rich et al. (1978), with the
exception of the structure reported therein as the hypocone,
which is referred to as the metaconule following Tedford &
Woodburne (1987). Premolar cusp nomenclature follows
Pledge (2003). Mandibular terminology follows Stirton
(1967). Higher-level systematic nomenclature follows Aplin
& Archer (1987), with the exception of the use of the super-
family Vombatoidea for the clade that includes
Vombatidae þMukupirnidae following Beck et al. (2020),
and the subordinal placement of Thylacoleonidae as
Diprotodontia incertae sedis following Beck et al. (2022).
We also use ?Wynyardiidae to refer to species within the
genera Namilamadeta,Muramura and Ayekaye, because
their inclusion within the family Wynyardiidae has never
been robustly demonstrated, following Tedford et al. (1977),
Rich & Archer (1979), Pledge (1987), and Megirian et al.
(2004). Biostratigraphic nomenclature follows Woodburne
et al. (1994), Archer et al. (1997), Travouillon et al. (2006)
and Megirian et al. (2010). The age of vertebrate bearing-
localities from the Namba and Etadunna Formations follows
Woodburne et al. (1994) and Megirian et al. (2010), and
those of Riversleigh World Heritage Area follow Archer
et al. (1997) and Woodhead et al. (2016).
Specimen preparation and measurements
The specimens from the Pwerte Marnte Marnte fossil site
(Fig. 1) that are described herein were recovered from ca 2
tonnes of limestone that was quarried from a small (3 m by
2 m) area on expeditions in 2014 and 2020, led by Aidan
Couzens and Arthur Crichton, respectively.
The fossil locality preserves heavily fractured and distorted
partial skeletal elements in a 0.5–1 m thick calcareous lime-
stone conglomerate of densely concentrated non-diagnostic
bone fragments and well-rounded mainly quartz pebbles (see
Murray & Megirian 2006). Several poorly defined depositional
layers are evident, loosely delimited by changes in pebble and
bone fragment density. Within each depositional layer, the
fossiliferous material is heavily mixed, with no association
between elements. To the extent that it can currently be
assessed, there is overlap in faunal composition between the
layers, with little indication that the site preserves more than a
single local fauna (A. Crichton, pers. obs., January 2023). The
fossiliferous rock was processed during 2020 through 2022 at
Flinders University using a combination of etching with acetic
acid (5–10%) and mechanical approaches, e.g., rock saws and
pneumatic micro-jack tools. The only exceptions are NTM
P10438, collected by D. Megirian, P. Latz and H. Larson in
2005, and NTM P6371, collected by P. Murray, D. Megirian,
J. & I. Archibald in 2003. The Lake Tarkarooloo specimens
described herein were collected on an expedition led by
Thomas Rich in 1976.
Measurements were made using Mitutoyo digital callipers
(model No CD-8ʺC: Takatsu-ku, Kanagawa, Japan) and
rounded to 0.1 mm. Morphological comparisons were made
Figure 1. Map of Australia depicting the locations of late Oligocene and early
Miocene fossil sites from which vombatoids have been recovered.
Abbreviations: NSW, New South Wales; NT, Northern Territory; Qld, Queensland;
SA, South Australia; Tas, Tasmania; Vic, Victoria; WA, Western Australia; WHA,
World Heritage Area.
2 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
directly from the specimens or casts thereof using an
Olympus SZX12 microscope, with exceptions drawing upon
published descriptions and figures (Supplementary Data 1).
Phylogenetic analyses
Morphological matrix
A morphological dataset of 124 craniodental and 20 postcra-
nial characters (Supplementary Data 2, 3) was constructed
for representatives of the suborder Vombatiformes to assess
the relationships of the new Pwerte Marnte Marnte taxon,
and resolve interrelationships among other taxa, in particu-
lar between Mukupirna nambensis and Marada arcanum.
The matrix was built primarily upon that of Beck et al.
(2020), which, in turn, built on Brewer et al. (2015), Black
et al. (2012a) and previous works therein identified. Scoring
of cranial characters for Ramsayia magna (Owen 1872) fol-
lows Louys et al. (2022). To capture aspects of the dentary
morphology considered by Black (2007) in her family-level
distinction of Marada arcanum from other vombatiforms,
several further characters were here adopted from Black &
Archer (1997), Black (2007), Black et al. (2012a), and
Brewer et al. (2015). Where possible, the scoring of charac-
ters taken from the literature was reassessed to verify the
results of others and to ensure consistency. Forty-seven add-
itional craniodental characters were included. The descrip-
tion of all characters and assessed states can be found in
Supplementary Data 2 and 3, respectively. These were scored
for 46 taxa, with the following amendments to the matrix of
Beck et al. (2020): we excluded Wakaleo pitikantensis
(Rauscher, 1987) due to the paucity of represented material
(known from a damaged maxilla); we replaced ‘Ngapakaldia
spp.’with Ngapakaldia tedfordi Stirton, 1967, replaced
‘Muramura spp.’with Mur. pinpensis Pledge, 2003 and Mur.
williamsi Pledge, 1987; and included ‘Rhizophascolonus spp.’,
Mukupirna fortidentata sp. nov., and Marada arcanum. The
didelphimorphian Didelphis marsupialis Linnaeus, 1758 was
coded as the outgroup, alongside the peramelemorphians
Perameles bougainville Quoy & Gaimard, 1824 and Galadi
speciosus Travouillon, Gurovich, Beck & Muirhead, 2010
and the burramyid Cercartetus lepidus Thomas, 1888 (after
Beck et al. 2020). Multistate morphological characters per-
ceived as representing morphoclines were ordered.
Phylogenetic inference
Undated Bayesian analysis of the morphological dataset was
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. The Bayesian analyses were run for 15 million
generations, using four independent runs of four chains
(one cold and three heated chains, with the temperature of
the heated chains set to the default value of 0.2), sampling
trees every 1000 generations and a burn-in fraction of 25%.
The post-burn-in trees were summarized using a majority
rule consensus of all compatible groups, with Bayesian pos-
terior probabilities as support values.
Maximum parsimony analyses were performed on the
morphological dataset, in TNT version 1.5 (Goloboff et al.
2008), following the methods of Beck et al. (2020). 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 1000 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 calcu-
lated using 2000 standard bootstrap replicates, implemented
using a ‘traditional’search, which results in output as abso-
lute frequencies.
Estimating body mass
Body mass estimates for Mukupirna fortidentata sp. nov.
were calculated for the holotype NTM P11997 (rostral por-
tion of a skull), and the referred specimens NTM P13348
(distal half of left humerus) and NTM P13262 (left P3) (see
Table 4). The humeral estimate was derived from minimum
humeral circumference, using the regression equations of
Richards et al. (2019). Craniodental estimates were calcu-
lated using regression equations of Myers (2001) and incor-
porating the relevant smearing estimates therein recognized.
We used the three highest ranking equations from the
diprotodontian dataset in Myers (2001), namely: upper
molar row length, measured at the widest point of the
crown (UMORL); upper molar row length, measured at the
alveoli (UMRL); and upper third premolar maximum width
(3UPW).
Museum abbreviations
AMNH, Department of Vertebrate Paleontology, American
Museum of Natural History, New York, USA; NHMUK,
Natural History Museum, London, UK; NMV P,
Palaeontology section, Museums Victoria, Melbourne,
Victoria, Australia; NTM P, Museum of Central Australia,
Museum and Art Gallery of the Northern Territory, Alice
Springs, Northern Territory; QM F, Queensland Museum
Fossil Collection, Brisbane; SAMA P, Palaeontology section,
South Australian Museum, Adelaide, South Australia.
Systematic palaeontology
Order DIPROTODONTIA Owen, 1866
Suborder VOMBATIFORMES Woodburne, 1984; sensu
Beck et al. (2020)
Infraorder VOMBATOMORPHIA Aplin and Archer, 1987;
sensu Beck et al. (2020)
Superfamily VOMBATOIDEA Kirsch, 1968; sensu Beck
et al. (2020)
Family MUKUPIRNIDAE Beck, Louys, Brewer, Archer,
Black & Tedford, 2020
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 3
Genus Mukupirna Beck, Louys, Brewer, Archer, Black &
Tedford, 2020
Type species
Mukupirna nambensis Beck, Louys, Brewer, Archer, Black &
Tedford, 2020
Amended generic diagnosis
Species of Mukupirna are distinguished from other vombati-
forms, unless otherwise noted, by having: an i1 that is pro-
portionately larger and more steeply inclined; a horizontal
ramus markedly deeper below p3 than below m4; a strongly
bilobate P3 (except species of Muramura), with numerous
prominent crenulations descending the posterolingual and
posterobuccal faces; roots on upper cheek teeth that extend
out of the maxillae far beyond the alveolar rims; prominent
cristae on M1–2 that link stylar cusps C and D, effectively
closing off the transverse valley buccally (except early vom-
batids and Raemeotherium yatkolai); a conical metacone on
M1 lacking pre- or postmetacristae (except early vombatids);
a very short or absent diastema between I3 and C1 (except
Nimbavombatus boodjamullensis); molars with a medially
positioned cleft in the transverse lophs (except early vomba-
tids and Ma. arcanum); an anteroposteriorly straight post-
protocristid þcristid obliqua (except early vombatids,
species of Namilamadeta, and Ma. arcanum); and the proto-
conid and hypoconid on m2–m4 positioned at roughly one
third tooth-width from the buccal margin (except species of
Namilamadeta and Ma. arcanum).
Differs from species of Namilamadeta in having: bicuspid
rather than tricuspid p3/P3; proportionately shorter p3/P3;
and generally more bulbous molars. Differs from vombatids
in having: I1/i1 that that are not hypselodont; a bicuspid p3,
except Vombatus ursinus (Shaw 1800); a precingulid on the
anterobuccal face of protoconid on lower molars; and lack-
ing enamel tracts on cheek teeth. Differs from Marada
arcanum in having: an i1–p3 diastema two thirds shorter; a
mental foramen positioned directly ventral to the anterior
half of p3, rather than more anteroventrally; a posterior lobe
on p3 larger than the anterior lobe, rather than considerably
smaller; a p3 with lingual and buccal faces that are ridged
rather than smooth; a paracristid on m1 that forms a raised
crest as it projects lingually; an anteroposteriorly narrower
transverse valley that is V-shaped rather than U-shaped on
m1; lacking a cuspate lingual cingulid that closes off the
transverse valley on m1; a more buccally extensive precin-
gulid on the lower molars; an origin of the ascending ramus
that is proximate to m3 rather than posterior to m4; and
the posterior extent of mandibular symphysis is ventral to
p3 rather than anterior to p3.
Mukupirna fortidentata sp. nov.
Figs 2–9
Vombatomorphia? fam., gen. et sp. nov. Murray &
Megirian, 2006
Marada arcanum Black et al. 2012b (in part)
Diagnosis
The upper cheek teeth of Mukupirna fortidentata sp. nov. are
distinguished from those of Mukupirna nambensis in having
anterior molars that are proportionately wider, wherein M1
anterior width is subequal to length, as opposed to less than
length by 12%. Consequently, the anteroposteriorly decreasing
cheek tooth width gradient (M4 width/M1 width) of Mu. for-
tidentata sp. nov. is steeper than that of Mu. nambensis by
20%. The upper cheek teeth are also more strongly bilobed
than those of Mu. nambensis. In occlusal view, the longitu-
dinal axis of the P3 is aligned with the buccal cusps on M1,
whereas that of Mu. nambensis is aligned with the lingual
cusps. Mukupirna fortidentata sp. nov. lacks a diastema
between I3 and C1, whereas Mu. nambensis has a very short
(3.5 mm) diastema. The molar roots are also splayed outwards
from the crown towards the maxilla/dentary, and conse-
quently, total alveolar rim width is greater than molar crown
width by 10% on M1, as opposed to being subequal in Mu.
nambensis; furthermore, the lingual face of the molar roots
has a markedly deeper dorsoventral concavity at mid-length.
Etymology
Derived from the Latin fortis (strong) and dentata (toothed),
the name refers to the robustness of the incisors and anter-
ior cheek teeth. The gender of the genus Mukupirna was not
specified by Beck et al. (2020). Following article 30.2.4. of
ICZN (1999), the genus is to be treated as feminine because
the name ends in -a.
LSID of new species
http://zoobank.org/urn:lsid:zoobank.org:pub:2215F286-
BBD2-42E7-AF27-0326E251FE4B
Holotype
NTM P11997, a dorsoventrally crushed adult splanchnocra-
nium containing left P3–M3 and right C1–M4 (Figs 2,3).
Paratypes
NTM P11998, partial premaxilla preserving partial I1 and
I2; NTM P11999, partial left maxilla preserving posterior
extent of M1 and M2–M3; NTM P12000, left dentary pre-
serving i1–m4; NTM P12001, partial left dentary preserving
heavily worn p3–m3; NTM P10438, partial right dentary
preserving worn p3–m4; NTM P12002, right dentary pre-
serving p3; NTM P13257, partial left dentary preserving i1,
p3, m1 and lingual half of m2.
Referred material
NTM P12003, left maxilla fragment preserving half P3 and
half M1; NTM P2815–11, left m3; NTM P12004, left p3;
NTM P12005, right m1; NTM P12006, worn right m3;
NTM P12007, worn right? m2; NTM P12008, anterior half
P3; NTM P12009, posterior half P3; NTM P12010, posterior
half p3; NTM P12011, unworn anterior half m2; NTM
P13261, left I2; NTM P13262, left P3; NTM P13263, left I3;
NTM P13264, right I3; NTM P13348, distal half of a left
4 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
humerus; NTM P13347, right pisiform; NTM P13346, dam-
aged distal left tibia; NTM P13345, right talus; NTM
P13344, left talus; NTM P6371, damaged right calcaneus.
Comments
Several unassociated postcranial specimens recovered from
the Pwerte Marnte Marnte fossil site compare most closely
in general morphology (though up to 20% smaller) to the
equivalent elements of Mu. nambensis. It has not been pos-
sible to compare these elements to those of ilariids or
?wynyardiids. However, based on the relative size of the
known ilariid and ?wynyardiid material from the site, it is
expected that their postcranial skeletons would be markedly
larger and smaller, respectively, than the specimens in ques-
tion. In light of the strong possibility that these specimens
derive from Mu. fortidentata, we take this opportunity to
describe them.
Type locality, unit and age
Pwerte Marnte Marnte fossil locality (24210S 133430E), on
the southern flank of the James Range, Northern Territory,
Australia (Fig. 1), has produced the Pwerte Marnte Marnte
Local Fauna (Murray & Megirian 2006). Initial biochronologi-
cal assessment indicated a probable late Oligocene age for this
assemblage (Murray & Megirian 2006,Crichtonet al. 2023).
The stages of evolution expressed by several marsupial taxa
have been taken to suggest that it may predate those of the
Etadunna and Namba Formations of the southern Lake Eyre
Basin (Murray & Megirian 2006), and thus possibly corres-
pond to an as-yet-unnamed land mammal age immediately
preceding the Etadunnan (Megirian et al. 2010).
Descriptions and comparisons
Craniodental
Cranium
The specimen NTM P11997 is the rostral portion of a
dorsoventrally crushed adult cranium held together by
matrix (Fig. 2A–D). It includes the premaxillae, maxillae,
nasals, and partial lacrimals. The left P3–M3 and right P3–
M4 are preserved, as is the base of the right C1, and the
alveoli for the incisors and left C1. Damage to the posterior
end of the palate and left maxilla was caused by a rock-drill
while quarrying. Crushing of the specimen in the dorsoven-
tral plane has reduced the minimum distance between the
palate and nasal to 15 mm (Fig. 2D). The maxillae and pre-
maxillae are splayed laterally, with their dorsal extremities
crushed ventrally towards the nasals. The nasals remain
largely undistorted, though bearing some damage to their
posterior ends (Fig. 2C). The nasals are very robust (max-
imum observable thickness ¼8 mm), with an anteroposter-
ior length of at least 80 mm. The nasals terminate anteriorly
in a blunt point dorsal to the I1 alveolus. Abundant fora-
mina are present on the dorsolateral surfaces of the nasals.
In transverse section, the nasals arch ventrally towards their
lateral and medial margins. At the anterior-most point of
the naso–premaxillary suture, the nasals are relatively broad
(combined width of 35 mm), becoming laterally constricted
towards the suture with the maxillae (combined width of
28 mm), and, though damaged, appear to subsequently
expand laterally towards the nasofrontal suture (inferred
combined width of ca 37 mm) before tapering sharply.
What remains of the lacrimals is poorly preserved, with
the left side slightly more complete than the right (Fig. 2C).
On the left side, fragments of bone between the lacrimal
and nasal appear to derive from the premaxilla, suggesting a
probable sutural contact between the frontal and maxilla.
The lacrimal foramen (5 mm long and 4 mm wide) is pre-
served on the left side, anterior to the nasofrontal suture by
ca 7 mm and lateral to the suture by 8 mm.
Much of the anterolateral portion of the right premaxilla
is missing, while the left premaxilla has been distorted lat-
erally. The lateral surface of the premaxillae is densely pitted
with tiny foramina. The rostral rim of the premaxillae
curves dorsally towards its suture with the nasals. The
uncrushed right premaxilla bears a bulbous lateral expansion
that derives from a particularly large I1 alveolus. The inci-
sive foramen is situated in a deep, anteroposteriorly
extended palatal fossa (Fig. 2A). Intensive fracturing of the
palatal region of the premaxilla precludes measurement of
the incisive foramen, though the anterior edge is aligned
with the middle of the I3 alveolus, and the posterior edge
with the middle of the C1 alveolus (Fig. 2A). There is no
diastema between I3 and C1. The diastema separating C1
and P3 is quite short (7 mm).
The maxillae are relatively undistorted, with the left max-
illa being better preserved than the right. A large infraorbital
foramen (anteroposterior diameter of 5 mm, and dorsoven-
tral diameter of 8 mm) is situated dorsal to the P3 mid-
length by 13 mm. The region of the maxilla adjacent to the
infraorbital foramen is densely pitted by small foramina, as
is the lateral surface of diastema between the P3 and C1
alveoli. A weak sheath projects anteriorly from the posterior
rim of the infraorbital foramen. On the palatal region of the
maxilla, a prominent longitudinal ridge extends posteriorly
from the premaxillary–maxillary suture for 16 mm before
terminating in line with, though 11 mm medial to, the anter-
ior alveolus of P3 (Fig. 2A).
The rostral morphology of Mukupirna fortidentata
appears generally similar to that of Mu. nambensis, with the
former possibly somewhat broader than the latter, though
both NTM P11997 and AMNH FM 102646 are relatively
crushed. The nasals (unknown in Mu. nambensis) are pro-
portionately thicker than in any other vombatiform, as well
as thylacoleonids. Unlike Mukupirna fortidentata, in which
there is no diastema between I3 and C1, Mukupirna
nambensis has a short diastema between I3 and C1
(3.5 mm). The maxilla of N. boodjamullensis (QM F23774)
also seems to lack a diastema between C1 and the postero-
lingual remnant of the I3 alveolus. Mukupirna fortidentata
shares with Mu. nambensis and N. boodjamullensis a short
diastema between C1 and P3, being much shorter than that
of most ?wynyardiids and diprotodontoids. The ?wynyardiid
N. crassirostrum also has a short diastema between C1 and
P3, though it consequently has a much longer diastema
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 5
between I3 and C1. As in N. boodjamullensis and
Muramura williamsi, the infraorbital foramen is dorsal to
P3, while in species of Namilamadeta in it is positioned
slightly anterior to P3.
Upper dentition
The upper dental formula is I1–I3 C1 P3 M1–M4. The
alveoli of the left incisors, although damaged, are better pre-
served than those on the right (Fig. 2A–D). The alveoli for
the incisors and canines are oriented posteriorly at an angle
of ca 50from the dorsoventral axis. The alveolus for I1 is
very large and oblong from anterior view, wherein the anter-
ior rim is directly dorsal to the posterior rim (Fig. 2D).
Consequently, the alveolus length for I1, as measured dorso-
ventrally, is 18 mm and the width is 9 mm. The alveolus for
the left I2 of NTM P11997 is also oblong, with a length of
5 mm and width of 9.5 mm, while that of the I3 is rounder
and measures 11.5 mm by 10.3 mm, respectively.
A partial left premaxilla (NTM P11999) preserves the I1
and I2 (Fig. 4A). The I1 is missing most of the crown,
retaining only a small section of the posterolingual surface.
Figure 2. Mukupirna fortidentata, sp. nov., partial skull (holotype, NTM P11997), in association with annotated line drawings. A, Occlusal view; B, lateral view; C,
dorsal view; D, anterior view. Scale bar equals 40 mm.
6 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
What remains of the I1 shows that it was relatively large
(labiolingual length ¼15 mm; mediolateral width ¼
11.5 mm) and crescent shaped, wherein the root is long
(40 mm) and curves posteriorly, dorsal to I2 and I3, while
the crown is oriented ventrally and may have recurved pos-
teriorly. On I1, enamel is restricted to the portion of the
tooth that projects outside of the alveolus. The dentine on
what remains of the lingual surface has occlusal wear, which
terminates 3 mm ventral to the rim of the alveolus.
The I2 preserved by NTM P11999 is relatively small
(anteroposterior length ¼5.4 mm; labiolingual width ¼
6.6 mm) and has an anteroposteriorly compressed root
(Fig. 4A). The occlusal surface of the I2 is worn flat and the
crown tapers posteriorly in width. Enamel extends down the
labial and lingual faces, but is absent from the anterior face.
An isolated I2 (NTM P13261) is very similar in morphology
to that preserved in NTM P11999 (Fig. 4B).
Two I3 specimens (NTM P13263; NTM P13264) are
referred to the taxon based on: their relative size as com-
pared to the alveoli for the I3 preserved in NTM P11997
and NTM P11999; high crown height on the posterolabial
face, consistent with being oriented anteriorly at a relatively
steep angle from the dorsoventral axis; and their relative
abundance in the assemblage, consistent with Mu. fortiden-
tata as the most common large mammal otherwise repre-
sented (Fig. 4C). The specimens of I3 are considerably
larger than those of the I2 (NTM P13263, anteroposterior
length ¼6.5 mm, labiolingual width ¼7.7 mm; NTM
P13264, anteroposterior length ¼6.1 mm, labiolingual width
¼7.4 mm), with a long root (24 mm: NTM P13264) that is
Figure 3. Occlusal view of the upper cheek teeth of species of mukupirnid. A,Mukupirna nambensis right cheek tooth row (cast of holotype, AMNH FM102646),
with M4 digitally repositioned. B,Mukupirna fortidentata right cheek tooth row (holotype, NTM P11997), with an annotated line drawing; and C, the associated left
cheek tooth row. Scale bar equals 10 mm. Abbreviations: hy, hypocone; mcl, metaconule; me, metacone; pa, paracone; pas, parastyle; pr, protocone; stB, stylar cusp
B; stC, stylar cusp C; stD, stylar cusp D.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 7
round in cross section. They are high crowned, wherein the
enamel extends 14 mm down the labial surface and 7 mm
down the lingual face (Fig. 4C). Enamel is absent from the
anterior surface. The occlusal surface is worn flat. The
crown tapers posteriorly in width. An enamel fold is present
on the posterolingual surface.
On NTM P11997, the root of the right C1 is preserved
and projects anteroventrally 7 mm from the rim of the
alveolus (Fig. 2A). There is no enamel remaining, wherein
the lingual face of the crown is broken off and the labial
occlusal face is worn down to 3 mm from the rim of the
alveolus. At the alveolus, the anteroposterior width of the
C1 is 6.4 mm and the labiolingual width is 7.4 mm.
The axis of the P3 to M4 is relatively straight, with a
moderate helical trend in the occlusal plane from lingually
inclined (P3) to buccally inclined (M4) (Fig. 2A). The tooth
row (P3–M4) measures 55 mm at the base of the crown and
61 mm at the alveoli, deriving from an anteriorly projected
anterior root on the P3 and a posteriorly projected posterior
root on the M4 (also in paratype P11999). The molar roots
also splay outwards dorsally from the crown, and conse-
quently alveolar width is greater than molar width at the
crown by up to 10% (also in paratype P11999: Fig. 4D). The
molar size gradient decreases steeply posteriorly (M4/M1
length ¼0.70; M4/M1 anterior width ¼0.56). Relative
crown height also decreases posteriorly (Figs 2B,4D). The
occlusal surface is relatively worn, wherein the four primary
cusps, and the transverse links between them, have dentine
exposed. A slight anteroposteriorly decreasing tooth wear
gradient is evident along the cheek tooth row.
The alveoli for the C1 and I3 are wider than those of
Mu. nambensis by approximately 20%, while those of I1 and
I2 cannot be reliably compared. Both Mu. fortidentata and
Mu. nambensis have a relative posterior to anterior molar
length ratio (M4/M1 length) close to 0.70, while the molar
width ratio (M4/M1 anterior width) in Mu. fortidentata is
considerably lower (0.56) than Mu. nambensis (>0.68)
mainly due to the wider anterior molars of Mu. fortidentata
(Table 1;Fig. 3). This represents the steepest molar width
gradient among all vombatiforms. Thylacoleonids
(Diprotodontia incertae sedis) have a markedly steeper
molar size gradient, wherein the posterior molars are
strongly atrophied or completely lost. In absolute terms, the
cheek tooth row length (measured at the base of the crown)
Figure 4. Mukupirna fortidentata, sp. nov., referred upper dentition specimens. A, Left premaxilla (NTM P11998), depicted from left right in mesial, occlusal and lat-
eral views. B, Left I2 (NTM P13261), depicted from left right in lingual, occlusal, buccal and posterior views. C, Left I3 (NTM P13264) depicted from left right in lin-
gual, occlusal, buccal and posterior views. D, partial left maxilla preserving M1–M4 (NTM P11999), depicted from left right in mesial, occlusal and lateral views.
Scale bar equals 20 mm.
8 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
of Mu. fortidentata (55.0 mm) is 8% longer than that of Mu.
nambensis (51.4 mm), after digitally repositioning the M4 of
AMNH FM 102646 (see Fig. 3). The molar roots are also
not splayed outwards towards the alveoli in Mu. nambensis,
with alveoli being subequal to molar width at the crown, as
opposed to up to 10% wider in Mu. fortidentata.
The crown of the P3 is bulbous and has an outline in
occlusal view that is bilobed (Fig. 3B), with the posterior
lobe 23% wider than the anterior lobe (Table 1). The apices
of the cusps on the longitudinal crest spanning between the
lobes have been obliterated by wear, forming a deep occlusal
facet that slopes lingually. Nonetheless, the bilobed morph-
ology is consistent with a bicuspate crown, wherein the
anterior and posterior lobes likely supported the parastyle
and paracone respectively. The tooth crown is robustly sup-
ported by two large roots that extend ventrally far beyond
the alveoli, wherein the base of the crown is 12 mm ventral
to the rim of the alveolus on the anterior lobe, and 7 mm
ventral on the posterior lobe (Fig. 2B). The anterior root is
slanted anteriorly at an angle of 20from the dorsoventral
axis. Enamel does not extend down the roots.
A small and relatively worn posterolingual cusp (hypo-
cone) is present, with a smaller similarly worn cusp directly
anterior (protocone) (Fig. 3B). Worn cristae ascend up the
lingual face from the hypocone and protocone. From
the apex of the parastyle, a crista descends anteriorly to near
the base of the crown before bifurcating, with one arm (buc-
cal precingulum) continuing buccally and quickly terminat-
ing, and the other arm (lingual precingulum) continuing
posterolingually around the base of the anterior lobe. From
the apex of the parastyle, a prominent crista also descends
each of the lingual and buccal faces, terminating near the
base of the crown. Numerous fine ridges characterize the
buccal face and, to a lesser degree, the posterolingual face,
of the paracone (Fig. 3). The P3 specimens NTM P12003
and NTM P13262 differ from those of NTM P11997 in hav-
ing ridges that are less prominent on the posterolingual face,
and in being approximately 9% larger.
The P3 differs from that of Mu. nambensis in being pro-
portionately wider relative to M1 length, and more strongly
bilobed (Fig. 3). The main cusps of the P3 are also aligned
with the buccal cusps on M1, rather than the lingual cusps
in Mu. nambensis (Fig. 3). We considered the possibility
that the alignment of cusps on the P3 relative to the M1 in
Mu. nambensis may be an artefact of the fragmented and
partially deformed nature of the holotype AMNH FM
102646, but discounted its likelihood on grounds that the
posterior end of the P3 crest is fitted into a shallow depres-
sion on the anterior face of M1, likely representing the
P3–M1 facet. In ?wynyardiids and N. boodjamullensis, the
main cusps on the P3 are also aligned with the buccal cusps
on the M1. Unlike Mu. fortidentata, the posterolingual cusp
on the P3 is reportedly absent in Mu. nambensis (Beck et al.
2020); however, a thin section is missing from the postero-
lingual face of the crown of the right P3 on the holotype of
the latter. Enamel does not extend as far down the root on
the anterobuccal face as it does in Mu. nambensis; though
this is demonstrably intraspecifically variable in the p3 of
Mu. fortidentata (see below). Though similar in relative
length, the absolute lengths of P3 specimens from Mu.
fortidentata are 9–19% larger than those of Mu. nambensis
(Table 1).
Among ?wynyardiids, the P3 is most similar to that of
species of Muramura, differing in its markedly greater abso-
lute size, and better-developed ridges on the paracone. The
P3 differs from those of the species of Namilamadeta by
being more strongly bilobed. ?Wynyardiids all bear three
cusps on the P3 in unworn specimens, with the posterior
two being weakly differentiated. It is possible that the P3 of
Mu. fortidentata also possessed three apices in its unworn
state.
The upper molars have bunolophodont crown morph-
ology (Fig. 3B). Anterior width is greater than posterior
width. The crown is divisible into four quadrants, each of
which has a bulbous outline in occlusal view. The occlusal
surface is relatively worn, wherein the four primary cusps,
and the transverse links between them, have dentine
exposed. The lingual cusps have the greatest wear, being
worn flat, with each exposing a C-shaped lingual rim of
thick enamel from occlusal view. The buccal margins of the
occlusal surfaces of the crowns on the right M1 and M2 of
NTM P11997 (Fig. 3B), and the metacone of the left M1 on
NTM P11999 (Fig. 4D), have chips of enamel missing either
due to post-depositional damage or lifetime wear. The den-
tine exposed by at least some of these chips is worn, indicat-
ing that they occurred during life. The left M1 and M2 of
NTM P11997 are more complete and will therefore form the
point of reference for the morphological description of these
tooth positions, with any differences between the left and
right molars identified therein. The anterior two cusps rep-
resent the protocone (lingual) and paracone (buccal); and
the posterior two cusps represent the metaconule (lingual)
and metacone (buccal) (Fig. 3B). Though thoroughly worn,
the primary cusps are transversely linked by cristae, which
Table 1. Measurements (in mm) of the upper cheek teeth from Mukupirna fortidentata and Mukupirna nambensis.
Specimen
P3 M1 M2 M3 M4
L AW PW L AW PW L AW PW L AW PW L AW PW
Mukupirna fortidentata
NTM P11997 L 14.0 8.6 11.3 11.9 12.3 11.6 11.0 11.5 10.3 –9.6 –– – –
NTM P11997 R 14.0 8.7 11.2 11.512.2 11.8 11.3 11.6 10.3 10.4 9.6 7.8 8.7 7.0 5.1
NTM P11999 L ––– – –11.4 10.6 11.1 9.5 9.9 9.0 7.0 8.4 6.8 5.6
NTM P12003 L >14.8 ––>13.4 –––––––––––
NTM P13262 L 15.3 9.3 12.3 – –––––––––––
Mukupirna nambensis
AMNH FM 102646 R 12.8 7.4 >9.2 >11.5 10.2 10.3 11.1 9.8 9.3 9.6 8.6 7.3 8.0 >6.9 5.6
Measurements of Mu. nambensis taken from a cast of the right maxilla from AMNH FM 102646. Abbreviations: L, length; AW, anterior width; PW, posterior width.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 9
descend lingually from the buccal cusps and buccally from
the lingual cusps. The juncture between the cristae is
demarked by a medially positioned cleft in the transverse
lophs. The stylar cusps C and D, positioned posterobuccally
and anterobuccally relative to the paracone and metacone
respectively, are integrated into the transverse lophs
(Fig. 3B).
The M1 is slightly wider (3%) than it is long and has a
slightly greater anterior than posterior width (4%) (Table 1).
Though well-worn, the metacone appears larger than the
paracone, and the protocone larger than the metaconule.
Anterobuccal to the protocone, what remains of the prepro-
tocrista continues buccally along the anterior margin to
meet a worn preparacrista that links posteriorly to the meta-
cone. The worn preparacrista is bulbous, seeming to form a
cuspate structure in the stylar cusp B position (Fig. 3B). The
paracone is lingually displaced, positioned at one third
tooth-width from the buccal margin. The paracone is linked
posterobuccally to a worn stylar cusp C.
Though relatively worn, the metacone appears to have
been conical, wherein the anterior and posterior occlusal
margins are rounded with no discernible pre- or postmeta-
crista. The occlusal outline of the metacone is positioned
slightly posterolingual to the outline of stylar cusp D
(Fig. 3B). Prominent cristae link between stylar cusp C and
D, effectively closing off the transverse valley on the buccal
face. A crista also descends posteriorly from stylar cusp D,
meeting the postmetaconulecrista.
From what can be ascertained of the relatively worn M1
crown, the morphology is generally similar to that of Mu.
nambensis. The M1 differs from that of Mu. nambensis in
being approximately 3% wider than it is long, rather than
11% narrower than long. The buccal face is more lingually
sloped, such that the stylar cusps and the paracone and
metacone are comparatively displaced. The crown is more
strongly bilobed from occlusal view. The molar roots are
splayed from the crown towards the alveoli, such that tooth
width at the alveoli is 10% greater than that at the crown, as
opposed to being subequal in Mu. nambensis. The lingual
molar root also has a markedly deeper dorsoventral concav-
ity at mid-length on the lingual surface, which may reflect
incipient partitioning of the root in Mu. fortidentata.
The M2 is similar in overall morphology to the M1 but is
8% shorter and 6% narrower (Table 1) and the preparacrista
is markedly more buccally positioned. The paratype NTM
P11999 differs from the holotype in that there is no discern-
ible cusp in the stylar cusp C position (Fig. 3B,4D). The
M2 differs from that of Mu. nambensis in the same attrib-
utes as that of the M1.
The M3 is similar in overall morphology to the M2, but
is 8% shorter and 17% narrower (Table 1); more strongly
bilophodont, wherein the stylar cusp C is atrophied; and sty-
lar cusp D is more transversely in line with the principal
cusps (metacone and metaconule) on the metaloph. The
buccal face also bears noticeably less lingual sloping. The
lingual molar roots splay anteroposteriorly into the alveoli
and are strongly partitioned by the palate at mid-length as it
rises up the lingual face of the dorsoventral concavity
towards the crown. The M3 differs from that of Mu. nam-
bensis in the same attributes as that of the M2, with excep-
tion of relative length vs width, wherein both taxa bear an
M3 that is longer than wide.
The M4 is similar in overall morphology to M3 but is
16% shorter and 27% narrower. Additionally, the talonid is
markedly reduced and, as a result of surface wear, has no
clearly discernible metaconule or metacone. It differs from
Mu. nambensis in the same attributes as that of the M3,
with the exception of the relative proportions as both are
subequal in size.
Dentary
This description is primarily based on the most complete
dentary specimen (NTM P12000), which preserves the i1, p3
and m1–4, but is missing much of the ascending ramus,
including the coronoid, condylar and angular processes
(Fig. 5).
The dentary is relatively short and deep, with greatest
dorsoventral depth of the horizontal ramus below the p3
(>35 mm), and lowest below the posterior root of m4
(26 mm). Specimens NTM P10438, NTM P12001 and NTM
P12002 are slightly deeper posteriorly, though still have
greatest depth below p3 (Fig. 6). The diastema between the
i1 and p3 is short (14 mm), and is bound by a distinct dor-
sal ridge along its lateral margin. Four roughly evenly spaced
foramina are situated directly buccal to the diastemal ridge,
in association with rugose pitting.
Mesial to the diastema, the unfused mandibular symphy-
sis has a smooth though uneven surface (Fig. 5B). The pos-
terior edge of the symphysis is damaged, but it appears to
terminate ventral to the posterior root of p3. A large mental
foramen (anteroposterior length, 2 mm; dorsoventral height,
3 mm) is situated 11 mm ventral to the middle of the anter-
ior root of p3. One smaller nutrient foramen (diameter,
1 mm) is positioned 16 mm ventral to the mid-length of the
posterior alveolus of m1. The digastric sulcus is relatively
well developed, extending along the lower third of the
mesial side of the horizontal ramus, from ventral to the m2
trigonid to ventral to the posterior margin of the m4 at the
anterior end of the pterygoid fossa. The pterygoid fossa is
deep, with a maximum depth of 10 mm. A small and dam-
aged foramen is present dorsal to the pterygoid fossa,
approximately 18 mm posterior to, and 12 mm ventral to,
the posterior border of the m4. This likely represents the
pterygoid foramen. The ascending ramus is relatively thick
(greatest thickness, 4 mm) with a slightly rugose anterolin-
gual surface. The anterior edge of the ascending ramus is
inclined posteriorly at a relatively shallow angle of 60rela-
tive to the horizontal ramus, and originates at a point
opposite the mid-length of m3 (Fig. 5C). Posterior to the
m4, there is a small postalveolar shelf. The masseteric fossa
is deep, though with a poorly defined anterior rim. Possibly
owing to distortion, there is no discernible masseteric for-
amen, though there is an artificial inclusion filled with cal-
cite crystals at the anteroventral border to the masseteric
fossa. We believe that this inclusion does not derive from
the masseteric foramen, on the basis that the edges are
10 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
broken and the structure is absent on specimens NTM
P12001 and NTM P12002. Remnants of the posterior shelf
of the masseteric fossa project laterally from the posteroven-
tral margin of the masseteric fossa (Fig. 5C).
The horizontal ramus of Mu. fortidentata differs from
that of Ma. arcanum and ?wynyardiids in a having markedly
greater dorsoventral depth below the p3 compared to below
the m4. This shape resembles that of thylacoleonids. The
Figure 5. Mukupirna fortidentata, sp. nov., left dentary (paratype, NTM P12000), with annotated line drawings. Depicted from top to bottom in mesial, occlusal and
lateral views. Scale bar equals 20 mm.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 11
relative length of the diastema between the i1 and p3 (dia-
stema length/cheek tooth row length) is much shorter in
Mu. fortidentata (0.28) than in Ma. arcanum (0.73) and
Warendja wakefieldi Hope & Wilkinson, 1982 (0.50), and
slightly shorter than in the ?wynyardiids Na. albivenator
Pledge, 2005 (0.35) and Muramura pinpensis (0.31), as well
as Raemeotherium yatkolai Rich, Archer & Tedford, 1978
(0.35). In Mu. fortidentata, the anterior mental foramen is
positioned ventral to the anterior root of the p3, while in
Ma. arcanum, species of ?wynyardiid, and R. yatkolai,itis
positioned anteroventral to the p3. In Warendja wakefieldi,
the anterior mental foramen is anteroventral to the p3 in
NMV P48980 and ventral to it in NMV P48982. The pres-
ence of a shallow angle of the anterior border of the ascend-
ing ramus relative to the horizontal ramus in Mu.
fortidentata (60) is similar to that of Ma. arcanum (55),
Warendja wakefieldi (56–59), and, to a lesser degree, spe-
cies of Namilamadeta (65–70), Muramura (65–70) and
Raemeotherium yatkolai (70). The anterior edge of the
ascending ramus rises from buccal to the m3 mid-length in
Mu. fortidentata and vombatids, buccal to the m4 in
?wynyardiids, and posterior to the m4 in Ma. arcanum and
R. yatkolai. Both Mu. fortidentata and ?wynyardiids share a
deep pterygoid fossa. Marada arcanum appears to bear a
very shallow pterygoid fossa, though much of the posterior
extremity of the only known dentary (QMF42738) is miss-
ing. The digastric sulcus is deeper and longer than in most
vombatiforms, being flat in Marada arcanum and
vombatids, and very shallow and posteriorly restricted in
?wynyardiids. The digastric sulcus morphology is most simi-
lar to that of the late Oligocene thylacoleonid Wakaleo
schouteni Gillespie, Archer & Hand, 2019 (see Gillespie et al.
2019).
Lower dentition
The lower dental formula is i1, p3, m1–m4. The cheek tooth
row (p3–m4) measures 53.7 mm, with a steeply posteriorly
decreasing molar size gradient (m4/m1 length ¼0.79;
m4/m1 anterior width ¼0.77) (Figs 5–7;Table 2). Relative
crown height also decreases posteriorly. Greatest tooth wear
is present on the apices of the cusps, particularly on the p3
and m1. On NTM P10438, the cusps on p3–m4 are worn
down to roughly half crown height (Fig. 6). The cheek teeth
on NTM P12001 are more heavily worn, such that only a
sliver of enamel remains on the lingual and buccal faces of
p3 and m1, and the crown is worn down to the base of the
transverse valley on the m2 and m3 (Fig. 6).
Tooth row length is similar in Mu. fortidentata and Ma.
arcanum at 53.7 mm and 51.8 mm, respectively, though the
posteriorly decreasing molar size gradient is considerably
weaker in the latter (m4/m1 length ¼0.88; m4/m1 anterior
width ¼0.97) (Fig. 7;Table 2). As for the upper molar
width gradient, the lower molar width gradient in
Mukupirna fortidentata is the steepest of all vombatiforms.
Figure 6. Mukupirna fortidentata, sp. nov., dentary specimens, depicted from top to bottom: in mesial, occlusal and lateral views. A, right dentary (paratype, NTM
P10438). B, left dentary (paratype, NTM P12001). Scale bar equals 20 mm.
12 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
The i1 is long (crown height ¼37 mm) and deep (labio-
lingual length ¼14 mm; mesolateral width ¼8 mm). The
crown is projected anteriorly at a steep angle of 50from
the plane of the horizontal diastema (Fig. 5). The labial face
curves dorsally such that it is almost vertical near the apex.
The enamel surface is punctate and has a thickness of
0.5 mm, restricted to the labial and mediolateral surfaces.
Tooth wear is restricted to the lingual surface, decreasing
Figure 7. Occlusal view of the lower cheek teeth of species of maradid and mukupirnid. A,Marada arcanum left dentary (holotype, QM F42738: image flipped),
modified from Black (2007). B,Mukupirna fortidentata right dentary (Paratype, NTM P12000), with annotated line drawings. Scale bar equals 10 mm. Abbreviations:
end, entoconid; hyd, hypoconid; lcd, lingual cingulid; med, metaconid; pacd, paracristid; pcd, precingulid; prd, protoconid.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 13
posteriorly in extent from the apex. The mediolateral width
of the crown tapers slightly towards the somewhat pointed
apex, wherein the lateral margin curves mesially along the
occluding edge. The tooth is not hypselodont, wherein the
enamel does not extend down the root into the alveolus.
The root is long (>35 mm) and curves posteriorly, ventral
to the p3.
The i1 is proportionately larger than that of contempor-
ary vombatiform taxa. The angulation at which the i1 proj-
ects relative to the plane of the horizontal ramus (50)is
similar to that of species of Ilaria and Phascolarctos cinereus
(Goldfuss, 1817), and steeper than in the species of
Muramura (20), Namilamadeta (30), and Ma. arcanum
(ca 30). The relative size and angulation of the i1 is similar
to that of thylacoleonids, though differing in that enamel
does not encapsulate the crown, in common with most
other vombatomorphians.
Similar to the P3, the crown of the p3 is bulbous and
slightly two-lobed, with posterior width 17% greater than
anterior width. These lobes abut one another anteroposter-
iorly, forming a crest that is aligned slightly anterobuccal to
posterolingual, meeting the m1 buccal to paracristid
(Fig. 6A). The apices of the lobes have been obliterated by
wear, forming an occlusal facet that slopes buccally.
Nonetheless, the two-lobed morphology is consistent with a
bicuspate crown, wherein the anterior and posterior lobes
likely supported a protoconid and metaconid, respectively.
The enamel is moderately wrinkled, with weak ridges
descending from the crest. Particularly well-developed ridges
descend the lingual and buccal faces from the apex of each
of the protoconid and metaconid. A prominent ridge also
continues anteriorly and posteriorly down the crown from
the protoconid and metaconid, respectively. The posterior
ridge from the metaconid bifurcates into two ridges,
descending each of the posterolingual and posterobuccal
faces before sweeping anteriorly. The p3 is supported by two
large roots that extend dorsally beyond the rim of the alveoli
by 4 mm. Thinning enamel extends a moderate length down
the roots on the buccal face, and to a lesser degree on the
lingual face. The extent to which enamel extends down the
roots on the p3 varies noticeably between specimens NTM
P12000, P12004 and P12002, but in no specimen does it
extend down the root into the alveolus.
In common with Ma. arcanum, the p3 in Mu. fortiden-
tata appears to be bicuspid (Fig. 7), while that of ?wynyar-
diids is tricuspid. Enamel extends slightly down the
anterobuccal face of the anterior root of the p3 in Mu. forti-
dentata,Ma. arcanum and species of Ilaria. The p3 differs
from that of Ma. arcanum in being proportionately longer
relative to m1 by 16%; having moderately wrinkled rather
than smooth enamel; and a protoconid smaller than the
metaconid rather than the former being several times larger
than the latter (Fig. 7).
The lower molars have a sub-rectangular outline in occlu-
sal view, with a bunolophodont crown morphology that is
composed of four bulbous principal cuspids with rounded
outer faces (Fig. 7B). The cuspids are transversely linked by
cristids, which together form lophids. Owing to the juncture
between the transverse cristids, each lophid is partitioned at
mid-width by a cleft. Weak crenulations descend the anter-
ior and posterior face of the lophids, indicative of prominent
ridges in their unworn condition.
In occlusal view, the m1 has corners that are rounded,
and lingual and buccal margins that are concave at mid-
length (Fig. 7B). The trigonid is noticeably taller than the
talonid. The tooth is high-crowned. The buccal face is par-
ticularly high-crowned, such that the juncture between the
postprotocristid and cristid obliqua occurs at two-thirds of
the crown height. A precingulid is present anterobuccal to
the protoconid. Though the apices of all cusps are somewhat
worn, the protoconid is clearly the tallest cusp. The protoco-
nid is positioned centrally, slightly buccal to tooth mid-
width, and consequently the buccal face of the trigonid has
a gentle slope towards the base of the crown. The paracristid
is directed anterolingually from the protoconid to the anter-
ior margin of the tooth, where it then continues lingually to
the paraconid position, forming a prominent raised crest. A
distinct valley separates the paracristid from the metaconid,
with no premetacristid linking them. The metaconid, posi-
tioned posterolingual to the protoconid, is the smallest cusp.
A worn posterolingually oriented cristid links the protoconid
to the metaconid, which together form the protolophid. The
postmetacristid descends the posterolingual face of the meta-
conid to the transverse valley.
The transverse valley separating the protolophid and
hypolophid is closed off buccally by the worn
Table 2. Measurements (in mm) of the lower cheek teeth of Mukupirna fortidentata and Marada arcanum.
Specimen
P3 M1 M2 M3 M4
L W L AW PW L AW PW L AW PW L AW PW
Mukupirna fortidentata
NTM P12000 L 11.3 8.9 12.2 9.1 9.4 11.7 8.8 8.5 10.5––9.6 7.0 6.3
NTM P10438 R 12.9>8.8 12.1 9.7 9.5 >12.1 9.3 9.2 11.3 –8.2 9.5 7.2 6.4
NTM P13257 L 10.5 8.5 10.5 8.3 8.8 –––––––––
NTM P12001 L 11.18.4––– 11.38.9 –– 8.5––––
NTM P12004 L 11.3 8.3––– – –– – – – ––
NTM P12002 R 12.08.6––– – –– – – – –––
NTM P12007 R –––––>10.4 8.77.8 –––
NTM P12006 R –––––– ––10.5>7.8 7.5–––
NTM P2815-11 L ––––––––10.9 8.9 7.7 –––
Marada arcanum
QMF42738 R 8.7 5.2 11.4 7.4 7.3 10.9 8.0 7.5 10.8 8.4 7.3 10.0 7.2 6.3
Measurements of Ma. arcanum were taken from Black (2007). Abbreviations: L, length; AW, anterior width; PW, posterior width.
14 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
postprotocristid þcristid obliqua. The preentocristid is weak
and does not meet the posterior terminus of the similarly
weak postmetacrista. A small pocket is present at the lingual
end of the transverse valley, lingual to the posterior ter-
minus of the postmetacrista and the anterior terminus of
the preentocristid. This pocket derives from a weak, and
partitioned, lingual cingulid.
Unlike the protolophid, the hypolophid is partitioned at
mid-width by a cleft. The hypolophid is oriented anterolin-
gually, reflecting the posterior position of the hypoconid
relative to the entoconid (Fig. 7B). The hypolophid is a third
wider than the protolophid, reflecting the more lingual pos-
ition of the protoconid relative to the hypoconid and the
more buccal position of the metaconid relative to the ento-
conid. The posthypocristid descends posterolingually from
the hypoconid to near the base of the crown, and then
curves and continues lingually to meet the postentocristid at
an almost 90angle.
In common with Ma. arcanum and vombatids, but unlike
?wynyardiids and ilariids, on m1: the four principal cuspids
are bulbous and somewhat conical, wherein the buccal faces
of the protoconid and hypoconid are rounded rather than
anteroposteriorly compressed (also in species of
Namilamadeta); the juncture between the postprotocrista
and cristid obliqua is more buccally positioned, rather than
more centrally positioned; the postprotocristid þcristid obli-
qua is anteroposteriorly straight; and the lingual face of the
hypoconid is expanded such that the cleft in the hypolophid
defining the point of contact between the hypoconid and
entoconid occurs midway between their apices, rather than
much closer to the apex of the hypoconid. The m1 differs
from that of Ma. arcanum by having: a proportionally
greater maximum width by 12%; a paracristid that forms a
raised crest as it projects lingually; thick crenulations that
descend the anterior and posterior faces of the hypolophid;
a postprotocristid longer than the cristid obliqua; an antero-
posteriorly narrower transverse valley that is V-shaped
rather than U-shaped; lacking a cuspate lingual cingulid that
closes off the transverse valley; and lacking a transverse val-
ley incised into the anterobuccal face of the hypoconid (Fig.
7). It differs from vombatids in having a precingulid on the
anterobuccal face of protoconid, and lacking enamel tracts
that extend down the roots on the buccal face of the proto-
conid and hypoconid.
The m2 is similar to the m1, with the exception of being
smaller, lower crowned and having subtle differences in
the arrangement of structures on the trigonid (Fig. 7).
The precingulid anterobuccal to the protoconid is deeper
and more buccally extensive, forming a pocket that contin-
ues anterolingually to meet the paracristid. The lingual end
of the paracristid forms a relatively flat shelf that is closed
off lingually by a weak premetacristid. On the m2, the pro-
tolophid more closely parallels the orientation, length and
general morphology of the hypolophid than does that on the
m1. In particular, the protoconid is more buccally posi-
tioned, while the metaconid is larger and more anterolin-
gually positioned. The protoconid and hypoconid are also
positioned slightly more posteriorly than the metaconid and
entoconid, respectively. In turn, the protolophid and hypolo-
phid are both oriented slightly anterolingually to
posterobuccally.
Mukupirna fortidentata and Ma. arcanum are more simi-
lar in the morphology of the m2 than the m1. The m2 dif-
fers from that of Ma. arcanum in having: a transverse valley
that is V-shaped rather than U-shaped; a precingulid that is
more buccally extensive; and lacking a pocket buccal to the
transverse valley (Fig. 7). The m2 differs from that of vom-
batids, ilariids and ?wynyardiids in the same attributes as
does that of the m1. In common with Ma. arcanum, vomba-
tids and ?wynyardiids, the protolophid and hypolophid are
each oriented slightly anterolingually to posterobuccally,
rather than traversing directly buccolingually as in
diprotodontoids.
The m3 on NTM P12000 was broken and distorted by
taphonomic processes, with fragments scattered as pre-
served. These were repositioned during preparation (Fig. 7).
From what remains of the tooth, it is evident that consider-
able natural wear occurred during life, extending almost to
the base of the enamel on the buccal face. This likely reflects
that, during life, the occluding upper molar was malformed
and positioned ventrally far below the other cheek teeth.
The comparatively little-worn molar specimen NTM P2815-
11, reported by Murray & Megirian (2006), is also consid-
ered to represent an m3. The specimen, NTM P2815-11, is
generally similar to the m2 preserved in P12000, except in:
being smaller, lower crowned, and trapezoidal in occlusal
outline owing to a proportionately narrower talonid. As in
the m2, the m3 is generally similar in morphology to that of
Ma. arcanum. In addition to the differences discussed with
respect to the m2, the m3 differs from that of Ma. arcanum
in being proportionately smaller, and the talonid is smaller
relative to the trigonid (Fig. 7;Table 2).
The m4 is similar to the m3, except in: being smaller;
lower crowned; having an even talonid; a hypolophid that
traverses buccolingually rather than posterobuccally to ante-
rolingually; and a prominent cristid descending anterobuc-
cally from the apex of the hypoconid to the transverse valley
(Fig. 7). The m4 is also less worn than the other molars,
with more clearly defined ridges or crenulations on the
anterior and posterior faces of the lophids. In addition to
the differences discussed with respect to the m3, the m4 dif-
fers from that of Ma. arcanum in that the hypolophid tra-
verses buccolingually rather than posterobuccally to
anterolingually. The m4 shares with that of Ma. arcanum a
cristid descending the anterobuccal face of the hypoconid,
which is also present in Muramura pinpensis.
Forelimb
Humerus
The distal half of a left humerus (NTM P13348) is preserved
from just proximal to the termination of the deltopectoral
crest (Fig. 8A, B, E, F, I). The lateral supracondylar ridge is
abraded, and the medial condyle is missing. The fragment of
the crest preserved suggests that it was thick, but the degree
to which it protruded from the shaft is unknown. The lateral
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 15
supracondylar ridge is well developed, and extends proxim-
ally along the diaphysis to just below the termination of the
deltopectoral crest. The medial supracondyloid foramen is
large, and the supracondylar bridge is oriented at 55rela-
tive to the diaphysis. This indicates that the distal humerus
was markedly wide relative to the diaphysis. The capitulum
is hemispherical, with an interruption on the lateral border,
and the lateral epicondyle projects a distance approximately
equal to the width of the capitulum. The trochlea is gently
concave, and the medial extent of the ulnar facet is not pre-
served but the capitulum and ulnar facets are level. Both the
radial and olecranon fossae are extremely deep.
The radial and olecranon fossae are deeper than in any of
the compared species. The humerus is similar in morphology
to those of early diprotodontoids such as Ngapakaldia tedfordi
and Nimbadon lavarackorum Hand, Archer, Godthelp, Rich
and Pledge, 1993, though with a better-developed lateral con-
dyle. The diaphysis below the deltopectoral crest is also more
slender than in N. tedfordi, and the deltopectoral crest is more
laterally deflected than in Ni. lavarackorum. The trochlea is
deeper than in the arboreal taxa studied, but not as deep as in
extant vombatids. The crushed and distorted nature of the
Mukupirna nambensis humerus (AMNH 102646) described by
Beck et al. (2020) makes comparison difficult, but it appears
similar to the humerus described here except that it is about
20% smaller and the lateral supracondylar ridge extends more
proximally in M. nambensis.
Pisiform
The right pisiform (NTM P13347) is robust, with a distinct
but thick waist and a bulbous distal end (Fig. 9D, H, L, P,
T, X). The tuber is about 40% wider (mediolaterally) than it
is deep (craniocaudally). The triquetral facet is somewhat
damaged but appears to be flat, triangular, and restricted to
the craniomedial portion of the proximal end. The facet for
the styloid process of the ulna is large (ca twice the size of
the triquetral facet), oval, deeply mediolaterally convex, and
near-perpendicular to the triquetral facet. The distal end is
enlarged to accommodate attachment of a well-developed m.
flexor carpi ulnaris tendon.
Overall, the pisiform is most similar in shape to that of
Lasiorhinus latifrons Owen, 1845 (and most unlike those of
extant arboreal taxa such as Phascolarctos cinereus,
Trichosurus vulpecula Kerr, 1792 and Pseudocheirus peregri-
nus Boddaert, 1785), but is more robust, with the proximal
end being more like that seen in Zygomaturus trilobus
Macleay, 1858. It does not display the triangular proximal
end seen in Nimbadon lavarackorum,Ngapakaldia tedfordi
and extant wombats (e.g., see Munson 1992, Black et al.
2012c). The specimen is similar to that of Mukupirna nam-
bensis, but is slightly smaller, with a more pronounced waist
and a rounder distal end (see Beck et al. 2020).
Hind limb
Tibia
A distal left tibia (NTM P13346), consisting of the distal
third of the diaphysis and damaged distal epiphysis, is
preserved (Fig. 8C, D, G, H, J). The specimen is of the right
size and morphology to fit with the left talus (NTM
P13345). It is a robust bone, and the shaft shows a degree of
mediolateral compression, even after allowing for compac-
tion of the fossil. The cranial and caudal borders of the lat-
eral talar facet are damaged, and the preserved portion is
flat and slopes downwards cranially. The medial talar facet
is small and occupies the cranial part of the lateral face of
the medial malleolus. The malleolus is prominent and forms
an angle of 130with the lateral talar facet. Its medial edge
is interrupted by a deep groove, possibly for the tendon of
the m. tibialis cranialis.
The distal tibia of Mukupirna nambensis is not known,
precluding comparisons. The distal tibia is most similar to
that seen in vombatids, but the medial malleolus is cranio-
caudally shorter and mediolaterally wider relative to the lat-
eral talar facet; the medial talar facet is closer to horizontal
and more continuous with the lateral facet; and the groove
on the medial malleolus is larger in the former. The frag-
ment preserved suggests that the medial talar facet may con-
tinue onto the malleolus in a fashion similar to that seen in
the extant arboreal taxa studied, but this cannot be con-
firmed. The tibial fragment differs from Ngapakaldia and
Nimbadon in that the medial malleolus is restricted to the
cranial part of the medial border, rather extending along the
whole of the medial border.
Talus
Two near-perfect tali are known, one right (NTM P13345:
Fig. 9A, E, I, M, Q, U) and one left (NTM P13344: Fig. 9B,
F, J, N, R, V). The tibial facets occupy approximately half of
the dorsal surface, and the components corresponding to the
lateral and malleolar facets form a continuous surface, the
shared border being represented by a slight, gently convex
ridge. The lateral tibial facet is about three times as large as
the malleolar facet, and twice as large as the fibular facet; it
is rectangular, and the trochlea is shallow. The malleolar
facet occupies the middle third of the medial border of the
talus, and is roughly triangular and almost flat. The fibular
facet is triangular and flat, occupying the caudal half of the
lateral edge of the talus. It is angled at 140(in NTM
P13345) or 120(in NTM P13344) relative to the main tibial
facet, and the two facets are separated by a low, straight
ridge. A large ligamental pit at the cranial border of the lat-
eral tibial facet separates it from the navicular facet, but the
navicular and malleolar facets are joined for ca 5mmon
the medial edge. The calcaneal facet is mediolaterally con-
cave caudally and convex cranially and is restricted to the
lateral half of the plantar talus. The medial plantar tuberos-
ity is large and dome shaped, and forms the medial edge of
a deep groove on the caudal border of the talus through
which the flexor tendons pass. A large, deep, lozenge-
shaped, ligamental pit runs from the medial plantar tuberos-
ity to the medial edge of the cuboid facet, separating the
navicular and calcaneal facets. The cuboid facet is continu-
ous with the calcaneal facet and is large, being approxi-
mately half the size of the latter facet. The navicular facet
16 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
Figure 8. Limb elements referred to Mukupirna fortidentata, sp. nov. Distal left humerus (NTM P13347) in A, cranial, B, lateral, E, caudal, F, medial and I, distal views.
Distal left tibia (NTM P13346) in C, cranial, D, lateral, G, caudal, H, medial and J, distal views. Scale bar equals 30 mm. Abbreviations: ca, capitulum; dpc, deltopec-
toral crest; gtc, groove for the tendon of the m. tibialis cranialis; le, lateral epicondyle; lsr, lateral supracondylar ridge; ltf, lateral talar facet; mm, medial malleolus;
msb, medial supracondylar bridge; msf, medial supracondylar foramen; mtf, medial talar facet; of, olecranon fossa; rf, radial fossa; tr, trochlea.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 17
occupies the medial half of the cranial face and cranial half
of the medial face and is broadly U-shaped.
The two tali (NTM P13345 & NTM P13344) are most
similar in overall shape to those of extant vombatids
(Lasiorhinus spp., and Vombatus ursinus) but the malleolar
facet is closer to horizontal in the former (as is seen in extant
arboreal taxa). The tali are less craniocaudally elongate than
those of the extant arboreal taxa examined, and the medial
plantar tuberosity is larger and rounder than in all other spe-
cies examined; a feature noted in Mukupirna nambensis by
Beck et al. (2020). The Continuous Lower Ankle Joint Pattern
(including the sustentacular and ectal facets) of Szalay (1994)
is most like that of Ngapakaldia tedfordi, excepting that it
extends toward the plantar tuberosity in the latter.
Calcaneus
The right calcaneus (NTM P6371: Fig. 9C, G, K, O, S, W)
articulates very closely with one of the tali (NTM P13345).
The distal half of the tuber, the accessory sustentacula (viz.
Szalay 1994), and the area for attachment of the calcaneofibular
ligament are all missing. The proximal part of the tuber pre-
served is mediolaterally compressed and slants dorsolaterally to
plantomedially. The talar facet is oriented near to the transverse
plane and mirrors the corresponding facet on the talus with a
Figure 9. Podial elements referred to Mukupirna fortidentata, sp. nov. A, E, I, M, Q, U, left talus (NTM P13344); B, F, J, N, R, V, right talus (NTM P13345); C, G, K, O,
S, W, partial right calcaneus (NTM P6371); and D, H, L, P, T, X, right pisiform (NTM P13347). Scale bar equals 20 mm. Abbreviations: cf, cuboid facet; CLAJP, continu-
ous lower ankle joint pattern; ct, calcaneal tuber; cut, tuberosity for attachment of the m. flexor carpi ulnaris tendon; ectf, ectal facet; ff, fibular facet; fg, flexor
groove; ltf, lateral tibial facet; mtf, medial tibial facet; nf, navicular facet; nn, navicular notch; pit, pisiform tuber; pt, plantar tuberosity; sf, styloid facet; suf, sustentac-
ular facet; trf, triquetral facet.
18 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
concave sustentacular component and convex ectal component.
The cuboid facet is L-shaped in dorsal view with a strong lateral
component. The navicular facet is a deep, V-shaped notch on
the medial border of the cuboid facet.
The fragmentary nature of the calcaneus makes it difficult
to make comparisons to other taxa. The tuber appears to be
relatively slender in cross section and in this sense, it is
similar to that of P. cinereus, T. vulpecula and Nimbadon
lavarackorum and unlike Ngapakaldia tedfordi. The cubona-
vicular joint is also most similar in morphology to that seen
in T. vulpecula and N. lavarackorum. It also matches the
descriptions of the calcaneus of Mukupirna nambensis pro-
vided by Beck et al. (2020).
Vombatidae gen. et. sp. indet.
Fig. 10
Referred material
NMV P157575, worn trigonid of left m2 or m3.
Type locality, unit and age
Tarkarooloo Local Fauna from Tom O’s Quarry, west side
of Lake Tarkarooloo (Fig. 1:31
080S 140060E), Namba
Formation, in the Callabonna Sub-basin, South Australia
(Rich et al. 1991, Woodburne et al. 1994). Based on biocor-
relative and stage-of-evolution comparisons, it is thought
that the Tarkarooloo Local Fauna is of late Oligocene age,
correlating with the Ngama Local Fauna (Zone D of the
Etadunna Formation: ca 24.1 Ma), or is slightly older
(Woodburne et al. 1994, Megirian et al. 2010).
Description and comparisons
The partial lower molar NMV P157575 is identified as pre-
serving the trigonid, rather than the talonid, on the basis
that: a weak precingulid is present; and the lingual cuspid
(metaconid) is positioned more anteriorly than the buccal
cusp (protoconid) (Fig. 10A). The specimen compares best
in size and general morphology to those of species of vom-
batid (Figs 6,10). It shares with those of species of basal
vombatids, as well as Mukupirna and Marada: a generally
simple and bulbous profile of the primary cusps; enamel
that is noticeably thicker on the buccal face than lingual face
of lower molars; and relatively large size as compared to
species of ?wynyardiid. In addition—though quite worn—the
posterior terminus of the postprotocrista is close to the buccal
margin; and therefore, the postprotocristid and cristid obliqua
were likely quite anteroposteriorly straight, rather than
descending posterolingually and anterolingually, respectively.
Figure 10. Vombatomorph molar fragments from the Tarkarooloo Local Fauna, with annotated line drawings in occlusal view. A, Vombatidae gen. et. sp. indet.,
trigonid of left m2 or m3 (NMV P.157575), photographed from left to right in occlusal, buccal and anterior views. B, Fam., gen. et. sp. indet., partial right ?m4 (NMV
P.157576), photographed from left to right in occlusal, lingual, and anterior views. C, Fam., gen. et. sp. indet., partial ?posterior moiety of right ?upper molar (NMV
P.157536), photographed from left to right in occlusal, lingual and posterior views. Scale bar equals 4 mm. Abbreviations: co, cristid obliqua; hyd, hypoconid; me,
metacone; med, metaconid; pa, paracone; pacd, paracristid; pcd, precingulid; pomed, postmetacristid; poprd, postprotocristid; prd, protocone.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 19
In common with early vombatids, but unlike species of
Mukupirna and Marada, the trigonid of NMV P157575 has:
enamel that extends much further down the buccal face of
the roots than the lingual face; the apex of the protoconid
positioned very close to the buccal margin; and what
remains of the crown attests to a strongly bilobed outline
from occlusal view. Additionally, NMV P157575 lacks a true
precingulid, instead retaining only a slight swelling on the
anterior face, buccal to the paracristid. A similar swelling is
present on the heavily worn Nimbavombatus boodjamullensis
lower molar specimen QM F23773 (Brewer et al. 2015, fig.
5), and to a lesser degree on the Rhizophascolonus ngangaba
specimens QM F23768 and QM F23769 (Brewer et al. 2018:
fig. 12). The enamel tracts are much shorter than those of
Rhizophascolonus spp., and of similar length, or slightly
shorter than, those of N. boodjamullensis. To the extent
NMV P157575 can be compared to the lower molars of N.
boodjamullensis, it differs in its larger size by 20%.
Three further molar fragments (NMV P48996, NMV
P157576 and NMV P157563) recovered from Tom O’s
Quarry, Lake Tarkarooloo, are worthy of brief discussion.
The partial molar NMV P48996 (fig. 5, Rich & Archer
1979), was referred to Vombatidae by Rich and Archer
(1979) on the basis that it is bilobed and hypsodont with
closed roots. It may derive from the same taxon as the
referred vombatid specimen NMV P157575. The where-
abouts of NMV P48996 is currently unknown, and conse-
quently, direct comparison could not be made.
The molar fragments NMV P157576 and NMV P157563
may also derive from the same taxon as NMV P157575,
though they do not preserve any attributes that would
definitively unite them (Fig. 10), and consequently are
referred to Vombatomorphia fam., gen. et. sp. indetermin-
ate. On NMV P157576, crown height increases towards the
damaged face, indicating that if it is a lower molar, then it
is a right molar, and if it is an upper, then it is a left molar.
Additionally, one of the lophs is markedly narrower, indicat-
ing that the tooth is likely an M4 or m4. The protolophid is
also markedly narrower than the hypolophid on m1 in basal
vombatids (e.g., Rhizophascolonus ngangaba: see Brewer
et al. 2018). We consider it less likely that NMV P157576
represents an m1 on the basis that: the cusps on the wider
loph are considerably taller than those on the narrower
loph; and the tooth is very low crowned. The specimen
NMV P157563 would seem likely to be the lingual side from
an upper molar given that the loph transverses buccolin-
gually, rather than posterolingually to anterobuccally, as is
typically the case in lower molars (Fig. 10C).
Results of phylogenetic analyses
Parsimony analyses with all taxa included, and ordering of
states where morphoclines were inferred, generated a strict
consensus of 120 most parsimonious trees, each of 420 steps
(Fig. 11A). The strict consensus tree had a consistency index
of 0.45 and a retention index of 0.79.
The Bayesian results, presented as a 50% majority rule
consensus topology of the post-burnin trees, were for the
most part consistent with that under maximum parsimony,
though with higher support values for most nodes (Fig. 11).
Marada,Mukupirna and vombatids were moderately
strongly supported as a clade (BPP ¼0.83 under Bayesian
inference, Fig. 11B;BS¼69% in parsimony, Fig. 11A).
Monophyly of Vombatidae was strongly supported (BPP ¼
1.0; BS ¼78%) to the exclusion of Marada and Mukupirna.
Under Bayesian inference, Mukupirna fortidentata and Mu.
nambensis formed a moderately strongly supported clade
(BPP ¼0.91) sister to Vombatidae (BPP ¼0.63), to which
Ma. arcanum was basal. This maradid–mukupirnid–vomba-
tid group formed the strongly supported sister clade to
Diprotodontoidea under Bayesian inference (BPP ¼0.88; BS
¼27%), together sister to a paraphyletic ?Wynyardiidae.
Ilariidae was supported as the most basally diverging family
within Vombatomorphia (BPP ¼0.78, BS ¼94%).
Monophyly of Vombatomorphia þPhascolarctidae was
strongly supported (BPP ¼1.0, BS ¼90%), with low sup-
port for Thylacoleonidae sister to this clade (BPP ¼0.56).
Results of body mass estimates
Body mass of Mukupirna fortidentata was estimated at 48 kg
using minimum humeral circumference of NTM P13348
(see Table 4). The estimates that derive from dental meas-
urements (NTM P11997) were quite varied, at 26, 36 and
84 kg for UMORL, UMRL and 3UPW, respectively (see
Table 4). The largest dental specimen from Mu. fortidentata
(the left P3, NTM P13262), yielded a body mass estimate
31% higher than the corresponding estimate for the holotype
NTM P11997.
Table 3. Measurements (in mm) of the molar specimens from the Tarkarooloo
LF vombatoid, the Geilston Bay LF ?vombatoid, as well as the basal vombatids
Nimbavombatus boodjamullensis,Rhizophascolonus ngangaba and R. crowcrofti.
Specimen Tooth position L AW Pw
Tarkarooloo LF, Vombatidae gen. et. sp. indet.
MV P157575 L m2 or m3 >5.7 7.1
Tarkarooloo LF, Vombatomorphia fam., gen. et sp. indet.
MN P157576 R m4? >10 >7.2 >6.7
MV P157563 Upper molar? >6.3 >7.3
Geilston Bay LF ?vombatoid
NHM UK PV OR 40157 R m1 9.96.36.9
m2 8.4 7.0 6.7
m3 8.06.9 6.3
m4 7.9 5.8 5.6
Nimbavombatus boodjamullensis
QM F51404 m1 7.1 4.2 5.5
QM F23773 m2 or m3 8.0 5.8 6.0
Rhizophascolonus ngangaba
QM F23764 m1 11.5 4.9 6.6
QM F57967 m1 10.8 4.8 6.2
QM F57968 m2 13.0 6.7 7.9
QM F23768 mx 11.9 7.2 7.3
Rhizophascolonus crowcrofti
QM F52745 mx 13.3 10.4 10.4
QM F52746 mx 15.5 10.3 10.1
QM F57960 mx? 14.5 9.5 9.1
QM F57961 mx 14.0 10.7 10.6
QM F57962 mx 13.4 10.0 10.1
Measurements of NHM UK PV OR 40157 taken were from a cast (SAMA
P.21377) and those of the vombatids are from Appendix 3 of Brewer et al.
(2018). Abbreviations: L, length; AW, anterior width; PW, posterior width.
20 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
Discussion
We have described Mukupirna fortidentata sp. nov., based
on a partial skull, and isolated partial maxillae and dentaries,
from the Pwerte Marnte Marnte site in the Northern
Territory, Australia. The taxon differs from Mu. nambensis
principally in having: the longitudinal axis of the P3 aligned
with the buccal molar cusps; a proportionally steeper antero-
posteriorly decreasing molar width gradient; upper molars
Figure 11. Phylogeny of vombatiforms based on: A, maximum parsimony analysis with numbers at nodes representing bootstrap support values; B, undated
Bayesian analysis, presented as a majority rule consensus with numbers at nodes representing Bayesian posterior probabilities.
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 21
that are more strongly bilobed; and no diastema between
the I3 and C1.
Implications for Mukupirnidae and Maradidae
The complete upper and lower dentition of Mukupirna forti-
dentata sp. nov. allows for assessment of the relationship
between species of Mukupirna and Marada, and therefore,
the families Mukupirnidae and Maradidae, respectively.
Phylogenetic analyses in this study support Marada,
Mukupirna and vombatids as forming a monophyletic
Vombatoidea sensu Beck et al. (2020) (BS ¼69%, BPP ¼
0.83: Fig. 11). Vombatidae is strongly supported (BS ¼78%,
BPP ¼1.0) as monophyletic; the species of Mukupirna form
the immediate sister clade (BPP ¼0.63), with Ma. arcanum
the next most basally diverging taxon. The dentary and asso-
ciated lower dentition of Mu. fortidentata reveal several
morphological differences from Ma. arcanum that we con-
sider to be compelling evidence in support of their generic
distinction. In particular, the dentary of Mu. fortidentata is
overall more robust than that of Ma. arcanum, wherein it is
markedly shorter and deeper, with a shorter diastema.
Moreover, the lower dentition of Mu. fortidentata differs
most notably from that of Ma. arcanum in: having an i1
that is proportionately larger, projecting at a steeper angle
relative to the plane of the horizontal ramus of 50com-
pared to ca 30; a p3 with a larger posterior than anterior
lobe, rather than a markedly smaller posterior lobe; an m1
with a paracristid that forms a prominent shelf as it projects
anterolingually; a more buccally extensive precingulid on the
lower molars; and a markedly steeper anteroposterior gradi-
ent in molar length and width (Table 2). It could be argued
that the lower dentitions of Ma. arcanum and species of
Mukupirna are not sufficiently dissimilar from one another
to merit family level distinction. However, it also cannot be
demonstrated that these taxa form a clade, as they do not
share any obvious synapomorphies to the exclusion of
Vombatidae.
We note that, contrary to the results of our phylogenetic
analysis, Ma. arcanum shows several attributes in cheek
teeth morphology that are suggestive of a somewhat inter-
mediate stage of evolution between the species of
Mukupirna and vombatids. These include: p3 size reduced
relative to the m1, with a posterior lobe reduced relative to
anterior lobe (see QM F57966 in Brewer et al. 2018, fig. 14);
a cuspate lingual cingulid (metastylid) on the m1 (see QM
F57967 & QM F23764 in Brewer et al. 2018, fig. 11); enamel
that extends slightly down the root on the buccal face of
m1; loss of the precingulid on the m1, and a reduced
precingulid on the m2–m4; lower molars with a juncture
between the postprotocristid and cristid obliqua that is
closer to the buccal margin; and lower molars that are pro-
portionately narrower with a more equal anteroposterior
size gradient along the molar row. In this study, the recov-
ered phylogenetic placement of Ma. arcanum as more basal
within Vombatoidea, rather than sister to Vombatidae, may
reflect in part that the taxon also shares some attributes of
dentary morphology (unknown in basal vombatids) with the
plesiomorphic diprotodontoid Raemeotherium yatkolai (see
Black 2007).
Lake Tarkarooloo vombatid
The vombatid taxon from the Tarkarooloo LF is insuffi-
ciently known to formally name. It is tentatively referred to
Vombatidae, rather than Maradidae or Mukupirnidae,
because the lower molar specimen NMV P157575 has:
enamel that extends much further down the buccal face of
the roots than on the lingual face; a more strongly bilobed
outline from occlusal view; and only a faint remnant of the
precingulid (Fig. 10). In particular, the presence of enamel
extending down the buccal surface of the roots on the lower
molars (and the lingual surface of the roots on upper
molars) is thought to represent a stage towards the develop-
ment of hypselodont cheek teeth, which characterizes the
dentitions of later vombatids (Brewer et al. 2015, Brewer
et al. 2018, Beck et al. 2020).
The oldest named vombatids (see Stirton et al. 1967,
Brewer et al. 2008, Brewer et al. 2015, Brewer et al. 2018),
date to 18.5 Ma in the early Miocene (ages given follow
Woodburne et al. 1994, Megirian et al. 2010, Woodhead
et al. 2016). A partial dentary referred to an indeterminate
species of Rhizophascolonus is known from Bone Reef Site,
Riversleigh, which was initially considered Faunal Zone A
(late Oligocene) on the basis of biocorrelation (Archer et al.
1989,1997, Travouillon et al. 2006), though more recently
stage-of-evolution comparisons seem to place it within
Faunal Zone B (Arena et al. 2016), as noted by Brewer et al.
(2018). In this study, the referral of the partial lower molar
NMV P157575 to Vombatidae would seem to corroborate
Rich & Archer (1979) in their familial referral of the (?lost)
molar fragment, NMV P48996, which was also recovered
from Tom O’s Quarry, Lake Tarkarooloo. Together, these
specimens provide support that early vombatids were pre-
sent by at least 24.1 Ma in the late Oligocene.
Table 4. Body mass estimates (in kg) for Mukupirna fortidentata, based on measurements taken from craniodental (following Myers 2001) and
postcranial (following Richards et al. 2019) material.
Specimen Variable x (mm) Regression equation Smearing estimate (%) Body mass (kg)
NTM P13348 L MHC (63) logBM ¼2.671(log )0.128 –48
NTM P11997 R UMRL (44.3) logBM ¼–0.418 þ3.011(log x) 4.4 36
NTM P11997 R UMORL (41.3) logBM ¼–0.567 þ3.072(log x) 4.7 26
NTM P11997 R þL/2 3UPW (11.25) logBM ¼1.775 þ2.991(log x) 1.3 84
NTM P13262 L 3UPW (12.3) logBM ¼1.775 þ2.991(log x) 1.3 110
Abbreviations: logBM, log body mass; MHC, minimum humeral circumference; 3UPW, upper third premolar maximum width; UMORL, upper
molar row length at the crown; UMRL, upper molar row length at the alveoli.
22 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
Geilston Bay dentary
The taxonomic affinity of a dentary (NHM UK PV OR
40157) preserving the worn m1–m4 from the purportedly
very early Miocene Geilston Bay Local Fauna, Tasmania, has
been the subject of some uncertainty since it was initially
reported by Tedford et al. (1975). The specimen was first
considered to be a partial maxilla with affinities to the
diprotodontid genus Ngapakaldia, though considerably
smaller (Tedford et al. 1975). It was subsequently reinter-
preted as the dentary of a large petauroid by Tedford &
Kemp (1998) based on an anteroposteriorly decreasing
molar length gradient (considered a shared primitive state),
increasing crown height anteriorly, a linear and peripheral
cristid obliqua, and an entoconid as the largest talonid cusp
(considered shared derived states). Crosby et al. (2001) sub-
sequently suggested that isolated teeth from Geilston Bay,
attributed by Tedford & Kemp (1998), to Petauroidea, were
more congruent with phalangerid affinities given their well-
defined lophids, though they did not specifically make refer-
ence to the dentary in question. We agree with Tedford &
Kemp (1998) that the markedly peripheral cristid obliqua
and postprotocristid preclude the taxon from being a mem-
ber of Phalangeroidea, sensu Aplin & Archer (1987).
We propose instead that NHM UK PV OR 40157 may
belong to an early vombatoid. The morphological attributes
used to refer the specimen to Petauroidea by Tedford &
Kemp (1998) are all shared by early vombatoids. The relative
height of the entoconid as the tallest talonid cusp on NHM
UK PV OR 40157 appears to be a product of greater wear to
the buccal than lingual cusps, as occurs in early vombatoids.
Further attributes of molar morphology that are shared with
vombatoids include: a bilobed outline from occlusal view; a
generally simple and bulbous profile of the primary cusps;
transverse lophs that are constricted at roughly mid-width;
and enamel that is thicker on the buccal rather than lingual
face of the lower molars; as well as being roughly intermediate
in size between those of Nimbavombatus boodjamullensis and
species of Rhizophascolonus (Table 3). The juncture between
the postprotocristid and cristid obliqua is also very close to
the buccal margin, indicating that, in their unworn condition,
these cristids were likely quite anteroposteriorly straight, rather
than descending posterolingually and anterolingually, respect-
ively. As is characteristic of early vombatids, but not species of
Mukupirna and Marada, the protoconid and hypoconid are
positioned very close to the buccal margin, and the molars
lack a distinct precingulid. The taxon also shares with
Rhizophascolonus ngangaba Brewer, Archer, Hand & Price,
2018, a cuspate lingual cingulid forming a metastylid on m1
(also present in Ma. arcanum). The molars on NHM UK PV
OR 40157 nonetheless differ notably from all referred vomba-
tids in that enamel does not extend down the roots on the
buccal face of m2–m4. Taken together, a vombatoid affinity
for the specimen would seem plausible, though this cannot be
confirmed owing to the high degree of wear to the molars.
Comments on vombatiform interrelationships
Within Vombatiformes, the family Phascolarctidae (koalas),
often placed within the infraorder Phascolarctomorphia
following Aplin & Archer (1987), have long been considered
sister to Vombatomorphia þThylacoleonidae (e.g., Marshall
et al. 1990, Myers & Archer 1997, Myers et al. 1999, Black
2008, Black et al. 2012b, Black et al. 2014, Brewer et al.
2015). More recently, Thylacoleonidae has instead been
recovered as the most basal diverging clade in
Vombatiformes (Gillespie et al. 2016, Beck et al. 2020), or
outside Vombatiformes altogether and classified as
Diprotodontia incertae sedis (Beck et al. 2022). We find
strong support for monophyly of Vombatomorphia and
Phascolarctidae (BPP ¼1.00, BS ¼90%: Fig. 11) to the
exclusion of Thylacoleonidae. Following the phylogenetic
definition of Vombatiformes proposed by Beck et al. (2020),
Thylacoleonidae was weakly supported within the suborder
under Bayesian inference (BBP ¼0.56), while unresolved
under parsimony. We tentatively uphold the subordinal
nomination of Thylacoleonidae as Diprotodontia incertae
sedis by Beck et al. (2022), because the analyses in the pre-
sent study included only a single representative diprotodon-
tian from outside of these clades; namely, the burramyid
Cercartetus lepidus.
Among vombatomorphians, Ilariidae was strongly sup-
ported under Bayesian inferences (BPP ¼0.94; BS ¼78%)
as basally diverging to a paraphyletic Wynyardiidae, with
species of Muramura sister to a clade comprising
Namilamadeta snideri þVombatoidea þDiprotodontoidea
(BPP ¼1.0). Paraphyly of ?Wynyardiidae, as represented by
species of Muramura and Namilamadeta, was also found by
Beck et al. (2022). Although long tentatively referred to
Wynyardiidae, the monophyly of the one known species of
Wynyardia,W. bassiana Spencer, 1901, with those of
Muramura,Namilamadeta and Ayekaye has never been
robustly demonstrated. In part, this reflects the overwhelm-
ing systematic focus that mammalian palaeontologists have
historically put on the cheek dentition: W. bassiana was
described from a partial skeleton lacking the dentition
(Spencer 1901). Referral of further species to Wynyardiidae
was initially based on similarities in post-cranial material
and non-dental cranial characters (Rich & Archer 1979),
and later on the basis of a conceptual ‘?wynyardiid’denti-
tion after Tedford et al. (1977), Rich & Archer (1979), and
Pledge (1987). To more robustly assesses whether the
referred ?wynyardiid taxa form a monophyletic group would
require a phylogenetic analysis that more comprehensively
samples non-dental characters, enabling inclusion of
Wynyardia bassiana.
Diprotodontoid interrelationships also remain equivocal
owing to their highly autapomorphic cheek tooth
morphology, making identification of key dental homologies
problematic. In this study, strong support was found
under Bayesian inference for a monophyletic
vombatoid–diprotodontoid clade (BPP ¼0.88: Fig. 11). This
clade received low support (0.16 BPP) in Beck et al. (2020),
while Beck et al. (2022) instead recovered diprotodontoids
forming a polytomy with ilariids and a wynyardiid–
vombatid clade. Within Diprotodontoidea, earlier interpreta-
tions of palorchestid molar homologies, in particular those
of the stylar cusps, have been used to polarize them as the
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 23
sister group to diprotodontids (Murray 1990, Black 2006).
Here, interpretations of stylar cusp homologies in diproto-
dontids (see char. 40, Supplementary data 2), as polarized by
the upper molars of Raemeotherium yatkolai Rich, Archer
and Tedford, 1978 (SAMA P43060), have contributed to a
nested placement for palorchestids within Diprotodontoidea,
sister to Ngapakaldia tedfordi. A sister relationship between
palorchestids and species of Ngapakaldia is consistent with
the original hypothesis of Stirton (1967), which was based
largely by P3 morphology coupled with several basicranial
attributes, though the latter have since been held as symple-
siomorphies within Diprotodontoidea, after Archer (1984),
and Murray (1986). In this study, only a representative sam-
ple of taxa from this clade were included in the analyses,
and very few were scored for their postcranial skeletons.
Comprehensive phylogenetic assessment targeted at diproto-
dontoids, including their cranial and postcranial skeleton as
well as review of their dental homologies, is needed to more
robustly resolve the interrelationships therein.
Comments on the diet and palaeoecology of Mukupirna
fortidentata
The species of Mukupirna possess a unique suite of cranio-
dental adaptations compared to other vombatiforms. It has
been suggested that both Mu. nambensis and species of early
vombatids may have eaten subterranean food items, such as
roots and tubers, obtained via scratch-digging (Brewer et al.
2008, Brewer et al. 2018, Beck et al. 2020). Additional
insights into the functional morphology of the group are
provided by the complete upper and lower dentition of
Mukupirna fortidentata sp. nov., as well as referred postcra-
nial specimens.
Craniodental
One of the striking features of the upper and lower first
incisors of Mu. fortidentata is their considerable labiolingual
width. In anterior mammalian teeth (incisors and canines),
their cross-sectional area is correlated to resistance to bend-
ing (Biknevicius et al. 1996, Bacigalupe et al. 2002, Freeman
& Lemen 2008). With respect to Mu. fortidentata, the con-
siderable labiolingual width of the first incisors suggests that
they might have been able to resist high bending stresses
associated with the exertion of high bite forces. Conversely,
the mediolateral width of the first incisors is markedly nar-
rower, tapering anteriorly towards a slightly pointed apex.
This likely focused the bite force on a smaller area, improv-
ing their effectiveness at puncturing or fracturing food items
(Samuels 2009, Martin et al. 2016).
Angulation of the incisors is also often related to the
amount of pressure required for initial food processing (e.g.,
Martin et al. 2016). Steeply inclined lower incisors, such as
those of Mu. fortidentata, have a bite point that is closer to
the jaw adductor muscles, which effectively increases bite
strength for a fixed gape by reducing the length of the out-
lever (Samuels 2009, Druzinsky 2010). Steeply inclined lower
incisors also provide the structural strength to receive high
stress loads by distributing force down the longitudinal axis
of the tooth, rather than oblique to it.
The lower incisor morphology of Mu. fortidentata bears
some general similarity to that of species in the extinct
eutherian suborder Tillodontia (e.g., see Gazin 1953), such
as Tillodon fodiens (Marsh 1875). The diet of tillodonts has
been interpreted to comprise a high proportion of tough
vegetation, including roots and tubers (e.g., Schoch 1986,
MacFadden 2000, Rose 2006). Compared to rodents, the
lower incisor morphology of Mu. fortidentata bears notable
resemblance to those with nut- and fruit-dominated diets,
such as tree squirrels and the tree rat Mesembriomys gouldii
(Gray 1843): e.g., in terms of labiolingual length, mesolateral
width, inclination, and tapering of width towards the apex.
In taxa with first incisors that are mesolaterally broad, a
more transversely oriented blade is often formed, which
functions as a wider cutting surface, representing a better
structure for acquiring vegetation (Samuels 2009). This
morphology is exemplified by specialist herbivores that
engage habitually in gnawing/cropping woody/fibrous plant
material, such as beavers, tuco-tucos and the lesser bam-
boo rat.
In Mu. fortidentata, the considerable depth of the dentary
below p3 and m1 is expected to represent a further adapta-
tion for resisting high stress loads associated with the inci-
sors. Bite force potential is also likely increased by the
relatively short and broad rostrum, reducing the out-lever
and increasing the temporalis moment arm (Greaves 2000,
Santana et al. 2012), with its generally robust morphology
also providing the structural strength to receive high stress
loads. Despite their markedly different diet, thylacoleonids
have a broadly similar jaw morphology for much the same
reason, with steeply inclined lower incisors, greatest depth
of the dentary below p3, as well as a short and broad
rostrum.
Several aspects of the cheek tooth morphology of Mu.
fortidentata are also congruent with the processing of rela-
tively hard food items. The large, splayed roots extending
ventrally far beyond the alveoli most likely represent an
adaptation to accommodate relatively high stress loads dur-
ing mastication. The enamel on the cheek teeth is fairly
thick (0.7 mm at the buccal margin of the upper molars),
which can be an adaptation for resistance to tooth fracture
induced by hard object feeding (e.g., Lucas et al. 2008,
Vogel et al. 2008, Barani et al. 2012). The high crown height
on the anterior molars (e.g., the juncture between the post-
protocristid and cristid obliqua occurs at two-thirds of the
crown-height on m1) may be an adaptation for the process-
ing of food items high in abrasives (e.g., Janis 1988, Jardine
et al. 2012, Damuth & Janis 2014), though less so than their
hypselodont relatives.
The steep gradient in molar dimensions suggests that the
neutral point, where the maximum bite force can be
achieved without accompanying secondary rotational forces
(Bramble 1978), is near the front of the cheek tooth row.
Larger bite forces could be generated with more posterior
biting, but the risk of condyle disarticulation is higher. This
steep anteroposteriorly decreasing gradient in molar
24 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
dimensions is not particularly suitable for thorough mastica-
tory grinding by the posterior molars.
Among diprotodontians, the cheek tooth morphology of
Mukupirna species have some similarity to those of the musky
rat-kangaroo, Hypsiprymnodon moschatus Ramsay, 1876,and
species of bettong, particularly Bettongia penicillata Gray,
1837. These taxa share molars with bulbous cusps linked by
weak crests in a bunolophodont configuration, and third pre-
molars with prominent ridges that descend the buccal and lin-
gual faces. Hypsiprymnodon moschatus is frugivorous,
primarily consuming the flesh of fruits and less commonly the
seeds (Dennis 2002). By comparison, the diet of Bettongia pen-
icillata is dominated by underground fungal fruiting bodies
(truffles), though also includes invertebrates, seeds and other
plant material (Zosky et al. 2017). The function of the more
distinctly plagiaulacoid premolars in these macropodoids is to
initiate and propagate cracks in hard food materials via a scis-
sor-like puncture crushing or shearing action (e.g., McNamara
2014). In species of Mukupirna, the apices of the primary
cusps appear to occlude more directly, as might be suitable
for crushing or shearing by via transverse movement. As
noted by Beck et al. (2020), the ridges on the premolar in
Mukupirna may function to strengthen the enamel.
The molar morphology in Mukupirna species is also
strongly reminiscent of that in species of the Old World
monkey subfamily Cercopithecinae, such as macaques, gue-
nons, and vervet monkeys. In cercopithecines, fruit is the
most common dietary component, though many are quite
opportunistic and also consume seeds, nuts, leaves, rhi-
zomes, grasses, bark, insects and small vertebrates (e.g., Kay
1978, Harding 1981, Ungar 2019). The proportion of each
food group taken varies between species, with these differen-
ces generally manifested in the prominence of molar struc-
tures; wherein more folivorous cercopithecines tend to have
relatively higher cusps, longer shearing blades and larger
crushing basins for a given tooth length than frugivorous
relatives (Kay 1978). In primates, dietary composition is also
influenced by the physical properties of food items in the
context of seasonal fluctuations in their availability (van
Schaik et al. 1993). Foods that are nutritious and relatively
easy to process, such as fruits, are prioritized. During peri-
ods when these preferred foods are scarce, primates must
switch to foods that are harder to process, of lower nutri-
tional quality, or both (Marshall & Wrangham 2007,
Rosenberger 2013, Berkovitz & Shellis 2018). One might
expect dietary composition in species of Mukupirna to fol-
low to similar patterns.
Postcranial skeleton
The postcranial specimens attributed to Mu. fortidentata are
generally similar to the equivalent elements of Mu. namben-
sis, attesting to comparable functional morphology. In par-
ticular, with respect to the distal right humerus (NTM
P13348), there are large attachment areas for the flexors and
extensors of the elbow, wrist and manus, suggesting signifi-
cant strength in these movements. Moreover, the depth of
the radial and olecranon fossae, coupled with the range of
movement indicated by the extent of the trochlea, suggest
that the elbow was well braced against lateral stresses whilst
still capable of being fully extended or fully flexed.
The shape and development of the styloid facet on the
pisiform (NTM P13347) suggests moderate stress was placed
on the pisiform–ulna joint. This differs from extant arboreal
taxa, and reflects that comparatively more weight rested on
the back of the manus. The enlarged attachment for the m.
carpi ulnaris suggests significant strength in flexion of the
wrist, perhaps associated with scratch-digging, consistent
with suggestions by Beck et al. (2020).
With respect to the distal left tibia (NTM P13346), the
orientation of the medial talar facet suggests that a greater
degree of inversion of the pes was possible than in the vom-
batids and diprotodontids studied. This is supported by the
deep groove for the tendon of the m. tibialis cranialis, which
is one of the main muscles responsible for inversion of
the pes.
The relatively shallow trochlea and near-horizontal mal-
leolar facets of the talus indicate a mobile tibio-talar joint
with little bracing against lateral stresses. The extensive
navicular facet suggests a prominent, functional first digit.
The narrow flexor groove and the caudoplantar edge of the
talus suggests a proportionately smaller flexor tendon mass
than in most other taxa studied.
The CLAJP of the calcaneus indicates a significant degree
of movement/rotatory capability in the talocalcaneal joint.
The orientation of the tuber is more like that seen in climb-
ing and digging marsupials, and the tuber does not display
the thickening typical of terrestrial diprotodontids (or
Ngapakaldia). The cubonavicular facet also displays a degree
of interlocking to help brace against lateral stresses that is
more common amongst the climbing taxa studied.
Body mass
Mukupirna nambensis is among the largest marsupials
known from the Etadunnan land mammal age (after
Megirian et al. 2010), second only to species in the ilariid
genus Ilaria (Beck et al. 2020). The largest craniodental
specimens (e.g., NTM P13262: Table 1) referred to Mu. for-
tidentata are almost 20% larger than their equivalents on the
Mu. nambensis holotype (AMNH FM 102646), while the
smallest specimens (e.g., NTM P11999 Table 1) have over-
lapping dimensions. The referred postcranial specimens are,
conversely, smaller than those of Mu. nambensis by up to
20%, with exception of the right pisiform, NTM P13347.
The body mass estimates for Mu. fortidentata are quite
varied (Table 4), and as such, should be treated tentatively.
That based on minimum humeral circumference (NTM
P13348) yielded an estimate of 48 kg, whereas the dental-
based estimates from the holotype (NTM P11997) ranged
from 26 to 84 kg, reflecting the unequal cheek tooth propor-
tions in the taxon. The largest dental specimen referred to
the taxon (left P3, NTM P13262) yielded a body mass esti-
mate 31% higher than the corresponding value derived from
the holotype (Table 4). These body mass estimates for Mu.
fortidentata overlap with that for Mu. nambensis derived
from total skull length (46 kg) in Beck et al. (2020), but differ
markedly from those based on femoral (143 kg) and humeral
ALCHERINGA: AN AUSTRALASIAN JOURNAL OF PALAEONTOLOGY 25
(171 kg) circumference. We regard the most parsimonious
explanations for this discrepancy to be that either: some of
the postcranial specimens are incorrectly referred to Mu.
fortidentata; or the postcranial skeleton of Mu. fortidentata
was proportionately smaller than that of Mu. nambensis.
Palaeoecological conclusions
Mukupirna fortidentata shows several craniodental adapta-
tions for the processing of hard plant material under rela-
tively high stress loads. In particular, the robust and steeply
inclined lower incisors with somewhat pointed apices likely
played a role in piercing, fracturing and/or gnawing solid
food items prior to mastication. We expect that Mu.
fortidentata was something of a generalist, with a diet that
may have included fruits, seeds, nuts, bulbs, tubers, rhi-
zomes, and, to a lesser degree, shoots and leaves. The post-
cranial material of Mu. fortidentata shows several
characteristics, broadly consistent with those of Mu. nam-
bensis, that suggest the elbow, proximal carpus and tarsus
had a high range and strength of movement, as well as
being generally well braced against lateral stress.
Later vombatoids, in comparison, have craniodental
adaptations (including hypselodonty) for the mastication of
more abrasive plant material. Therefore, it is possible that in
Vombatoidea the specialization for processing hard food
items preceded that for the consumption of more abrasive
plant material. Alternatively, and perhaps more likely, by the
late Oligocene, prior to the evolution of hypselodonty, early
vombatoids may have already radiated to fill a variety of
niches for the processing of hard, tough and/or abrasive
plant material.
Biochronological significance
By resolving that Vombatomorphia? fam., gen. et sp. nov. of
Murray and Megirian (2006) represents a species of
Mukupirna, we provide additional support for the relative
temporal proximity of the Pwerte Marnte Marnte Local
Fauna and the basal local faunas of the Namba Formation
as well as, by implication, their Etadunna correlates (see
Murray & Megirian 2006, Crichton et al. 2023), which
together form the Etadunnan land mammal age (Megirian
et al. 2010). With respect to stage-of-evolution, Mu.
fortidentata has several craniodental attributes that appear
more derived than in Mu. nambensis, as polarized by the
morphologies presented by species of Muramura and
Namilamadeta, which could be interpreted as support that
the Pinpa LF is in fact older than the Pwerte Marnte Marnte
LF. These attributes include: a proportionally steeper antero-
posteriorly decreasing molar width gradient; splaying of the
molar roots outwards from the crown towards the maxilla/-
dentary; and lacking a diastema between the I3 and C1.
That being said, it could also be interpreted that Mu. forti-
dentata presents the more plesiomorphic condition with
respect to the alignment pf P3 relative to M1 and, possibly,
the relative size of the postcranial skeleton. Comprehensive
sampling of the fauna is needed to more precisely constrain
the relative age of the Pwerte Marnte Marnte Local Fauna,
ideally coupled with additional age constraints.
Conclusion
Mukupirna fortidentata sp. nov. from the late Oligocene
Pwerte Marnte Marnte Local Fauna, Northern Territory, is
an early vombatoid, closely related to Mu. nambensis from
the late Oligocene Pinpa Local Fauna of the Namba
Formation. The phylogenetic placement of the maradid
Marada arcanum is resolved to lie within Vombatoidea, as
sister to species of Mukupirna þVombatidae. Mukupirna
fortidentata and Ma. arcanum appear to lack any synapo-
morphies in the dentary or lower dentition that would sup-
port their forming a clade to the exclusion of Vombatidae.
Craniodental attributes of Mu. fortidentata suggest that this
species was well adapted to processing hard plant material
under relatively high stress loads. The dental material from
Mu. fortidentata also assists in the identification of two fur-
ther allied taxa: a vombatid from the younger late Oligocene
Tarkarooloo Local Fauna, South Australia; and a ?vombatoid
from the earliest Miocene Geilston Bay Local Fauna,
Tasmania. The Lake Tarkarooloo taxon, in particular, pro-
vides support that early vombatids were present by at least
24.1 Ma in the late Oligocene. This would imply that repre-
sentatives from all three referred vombatoid families had
originated by the late Oligocene.
Acknowledgements
We thank M.-A. Binnie and D. Stemmer, respectively, for providing
access to South Australian Museum Palaeontology and Mammal
Collections, as well as T. Ziegler and R. Schmidt for providing access
to the Museums Victoria Palaeontology Collections. We are grateful to
W. Klein from Orange Creek Station for allowing access to the Pwerte
Marnte Marnte fossil site. We thank C. Burke, S. Arman, W. Handley
and G. Gully for organizing and/or assistance with the 2014, 2020 and
2022 field trips to the site. We also thank C. Burke for preparatory
guidance, and J. Blokland for support relating to the phylogenetic com-
ponent. We acknowledge the Southern Arrernte People, known as the
Pwerte Marnte Marnte Aboriginal Corporation, for their custodianship
of the lands on which the fossil locality is situated. We thank reviewers
K. Black, P. Brewer and J. Louys, and editor Robin Beck, for their
thoughtful comments and suggestions.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
AIC was supported by The Australian Government Research Training
Program Scholarship. Support for the 2014 field trip to the site was
provided by a Patterson Memorial Grant from the Society of
Vertebrate Palaeontology to AMCC.
Supplementary material
Supplementary research materials for this article can be accessed at
https://doi.org/10.1080/03115518.2023.2181397.
26 ARTHUR I. CRICHTON ET AL. OLIGOCENE AUSTRALIA VOMBATOIDS
ORCID
Trevor H. Worthy http://orcid.org/0000-0001-7047-4680
Aaron B. Camens http://orcid.org/0000-0003-0464-0665
Aidan M. C. Couzens http://orcid.org/0000-0001-5840-5412
Gavin J. Prideaux http://orcid.org/0000-0002-9958-0265
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