Table Of ContentThe Beagle, Records of the Northern Territory Museum of Arts and Sciences, 1992 9( I ):89-l 10
THE SMALLEST NEW GUINEA ZYGOMATURINES-
DERIVED DWARFS OR RELICT PLESIOMORPHS?
PETER F. MURRAY
Northern Territory Museum,
P.O. Box 2019, Alice Springs, NT 0871, Australia.
ABSTRACT
Three Pleistocene species of zygomaturine dipiotodontids are presently known from
New Guinea. Two of these distinctive marsupials are much smaller than any of the late
Tertiary zygomaturines that occurred in Australia, but are more similar in size to
certain mid to late Miocene genera. Stirton etal. (1967). Flannery and Plane (1986) and
Flannery (1988) have suggested that the late Tertiary New Guinea assemblages
represent relict species with closest affinities to the mid to late Miocene faunas of
Australia. A broad compitfison of the morphology of late Pleistocene New Guinea
zygomaturines indicates that they are derived species of the Australian Plio-Pleistocene
Zygomaturus clade. As the relict fauna hypothesis appears to stem primarily from a
"stage of evolution” interpretation of the New Guinea diprotodontids, this conclusion
has significant implications for the palaeozoogeographic interpretation of New
Guinea.
Keywords: Diprotodontidae, Zygomaturus, New Guinea, Tertiary biochronology,
palaeozoogeography, marsupial systematics and morphology.
INTRODUCTION new diprotodontid shows some close re.sem-
blances to Hulitherium. This paper provides an
Stirton (1967) and Plane (1967) originally alternative hypothesis of New Guinea
observed that the New Guinea zygomaturine zygomaturine phylogeny in which the available
diprotodontids Kolopsis rotundas Plane and evidence is found to agree with revised radio-
Kolopsoides cultridens Plane expressed closer metric dates and our current understanding of
affinities with the Australian Miocene species diprotodontid stage of evolution biochronology.
Kolopsis torus Woodbume than to any of the I intend to establish the following points in the
Plio-Pleistocene species o{Zygomaturus Mcleay. discussion: 1) that with the exception of
At the time it was thought that the Awe Local Kolopsoides cultridens, all known Pleistocene
Fauna (LF) was an early Pliocene-aged fauna. New Guinea zygomaturines are members of the
Moreover, it was generally held that the smaller Zygomaturus clade; 2) the character states of all
diprotodontids were more primitive and there¬ three New Guinea Pleistocene fonns are derived
fore older than the larger species. In the next relative to early to mid Pliocene Zygomaturus
decade, Flannery and Plane (1986) described a species known from mainland Australia; 3) there
small zygomaturine marsupial from the is sufficient biochronological and phylogenetic
Pleistocene of New Guinea as Hulitherium information to establish the most likely annectant
toma.<iettii Flannery and Plane. They conclude for the New Guinea Pleistocene species; 4) con¬
that the monotypic Hulitherium also represents a sequently, it is possible to give an estimation of
relict species, reminiscent of certain Miocene the time the genus Zygomaturus entered New
genera known from the mainland of Australia. Guinea; 5) that the size and morphology of the
Shortly after their 1986 publication, another two smallest species is best explained as habitat
New Guinea Pleistocene zygomaturine was dis¬ related size-reduction or insular dwarfing; and
covered in Irian Jaya. Though significantly finally 6) that the estimated time of arrival of
smaller and apparently more specialized, this zygomaturines in New Guinea does not support
89
P.F. Murray
Fig. 1. Lateral aspects of representative zygomaturine crania. A, Kolopsis torus, Alcoota LF. Late Miocene, an advanced
zygomaturine genus and likely structural precursor of Zygomalurus; B, HuUlherium tomasellii, Pureni LF, Late Pleistocene
(drawn from photograph in Flannery and Plane 1986); C, Zygomaturus Irilobus. Mowbray Swamp LF, Late Pleistocene (drawn
from a cast prepared by Queen Victoria Mu.seum, Launceston); I), N.G. Gen. nov. NTM P866()-1, P8660-2, P8668-3, Baliem
LF, Late Pleistocene. Labels ate defined in the key to anatomical abbreviations. Note deflected cranial bases, steep frontal
profiles, deep suborbital fossae, short, deep zygomatic arches with and strap-like zygomatic processes (missing on B), low
narial apertures and anteriorly situated orbits in B-D.
the hypothesi.s of an early Miocene faunal dis¬ At present, the majority of Australian Tertiarv
junction (Flannery 1988) from Australia. age estimations of Local Faunas are based on
Three Late Pleistocene New Guinea faunal correlations, primarily involving a suc¬
zygomaturines have each been assigned to dif¬ cession of diprotodonlid marsupials (Stirton et
ferent genera; Hiiliiherium (Flannery and Plane al. 1967, Archer et al. 1989). In light of receiu
1986), Zygomalurus (Hardjasasmita 1985); and revisions of the age of the Awe Fauna (Hoch and
a new genus, as yet undescribed (Flannery, pers. Holm 1986, Page and McDougal 1972), the
comm.) (Figs 1-2). I refer to T. Flannery’s pro¬ systematic conclusions in Stirton ei al. (1967)
posed new genus as “N.G. Gen. nov." in order to and Flannery and Plane (1986) imply that
avoid a nomen nudum. My observations on tliis biostratigraphic age determinations for New
new New Guinea species are based on another Guinea are inherently unreliable. In re-examin¬
specimen (NTM P8660-1, P8660-2, P8660-3) ing .some of the morphological evidence relating
that may differ somewhat from Flannery’s pro¬ to the apparent di,screpancy in stage of evolution
posed type, which I have not had the opportunity correlations with radiometric age determinations
to examine first hand. However, the points 1 for New Guinea, 1 found that a relatively minor
made at the CAVEPS symposium (Murray and re-interpretation of the data places the
Walker 1991) did not entail a formal description biochronological evidence in accordance with
of the species, and it was only after 1 received a the radiometric dates.
prepublication copy of Flannery’s manuscript The genus Zygomalurus, which first appeared
that I realized that there might be a potential in the late Miocene Sandringham Sands at
problem. Beaumaris, Victoria, had differentiated into three
90
New Guinea Zygomaturines
C
Fig. 2. Cranium of Baliem LF zygomaturine NTM P8660-1 (N.G. Gen. nov.), A, lateral aspect; B, ventral aspect; C, dorsal
aspect; showing many similarities to the Australian Pleistocene species Zygomaturus trilobus. Labels are defined in key to
abbreviations.
91
P.F. Murray
or perhaps four Australian species by the late Woodburne et al. 1985). Evidence presented in
Pleistocene (Stirton et cil. 1967, Woodburne et this paper indicates that Kolopsis rotundas is a
al. 1985). There is no evidence for the existence member of the Zygomatums clade. The New
of the genus before the late Miocene or early Guinea zygomaturine genus Kolopsoides Plane,
Pliocene (Woodburne et al. 1985). 1967, is considered here to represent a distinct
The morphological succession toward derived lineage external to the Kolopsis-
Zygomatums is based upon the addition of cusps Zygomatums ingroup.
and proportional changes in the permanent upper
premolar crown; initially, the hypocone becomes
a consistent feature in the mid Miocene genus ANATOMICAL ABBREVIATIONS
Neohelo.s Stirton. followed by the division of the
para-metacone into two distinct cusps in the late APF Anterior palatal fenestra/incisive
foramen
Miocene genus Kolopsis Woodburne (Stirton et
BC Buccal cingulum
al. (1967) (Fig. 3). Present in the mid to late
DIF Digastric fossa
Miocene were two basic zygomattirine clades: 1)
DIE Digastric eminence
plesiomorphous 3-and 4-cusped forms retaining
ENA External nares
an elongated, undifferentiated para-metaconal
FAC Facial crest
crest {Neohelos, Plai.siodon Woodburne,
FOL Forelink
Alkwertatheriiim Murray) and 2) apomorphous
FRC Frontal crest
5-cuspcd forms with fully differentiated para-
FRO Foramen rotundum
cone and metacone {Kolopsis and Zygoinaturus)
HYC Hypocone
(Murray 1990) (Figs 3-4).
I" Upper inci.sor
A species of Kolopsis (Figs 1, 3-4) is the most
INA Internal nares
likely structural precursor for Zygomatums
lOF Infraorbital foramen
(Stirton et al. 1967, Woodburne et al. 1985,
JUG Jugal
Murray 1990). Accordingly, the genus Kolop.sis
JUZ Jugal portion of zygomatic arch
is the designated sister taxon of the genus
LAC Lacrimal
Zygomatums, constituting the plesiomorphic
LC Lingual cingulum
outgroup for phylogenetic analysis below the
LNC Lamina of neurocranium
generic level. The genus Kolopsis, which appar¬
MAJ Jugal portion of masseteric or
ently became extinct in Australia in the late
zygomatic process
Miocene, was thought to have persisted in New
MAM Maxillary portion of masseteric
Guinea until the late Pliocene (Plane 1967,
'4.5
4,5
Fig. 3. Occlusal aspects of P’ and of A, Neohelos sp. Bullock Creek LF, mid Miocene; B, Kolopsis torus, Alcoota LF. late
Miocene; C. Kolopsis sp. now Ongeva LF, late Miocene; Zvfioinoturus trilobus, Victoria Cave LF, Late Pleistocene; E, N.G.
Gen. now NTM P8660-1,, Baliem LF, Late Pleistocene. The morphological succession in dentition from Neohelos to
Zygomaturus is gradual and continuous. Zygomiiturus P' morphology is dislingushed by a trend towards molarization.
broadening of the crown and reduction of crown length relative to M*. The four principle cusps become arranged in a square
and the parastyle becomes more confluent with the outline of the crown. Large numerals refer to Zygomiiturus synapomorphies
given in Tables I -2; labels on structures are defined in the key to abbreviations.
92
New Guinea Zygomaturines
or zygomatic process PAC Paracone
MAP Masseteric/zygomatic process PAL Palatine
MCN Median cleft between nasals PCR Postpara-metacrista
MEC Metacone PEF Postorbital eminence of frontal crest
MEL Metaloph PLF Posterolateral palatine foramen
MES Metastyle P-MC Para-metacone
MFS Median frontal sulcus PME Premaxillary eminence
MIL Midlink PMS Premaxillary-maxillary suture
MLF Maxillo-labial fossa PMX Premaxilla
MPF Posteromedian palatine foramen PPC Postparacrista
MX Maxilla PRC Protocone
MXO Ossicle of maxilla PRL Protoloph
NPE Naso-premaxillary eminence PST/PAS Parastyle
NMS Naso-maxillary suture PTF Pterygoid fossa
OLF Internal cavity of olfactory bulb SAC Sagittal crest
OPF Optic foramen SQZ Squamosal process of zygomatic
ORB/ORF Orbit/orbilal fossa arch
P’ Permanent upper premolar SUF Suborbital fossa
Fig. 4. Diagram depicting the broader cladislic units of the Zygomaturinae ba-sed on upper third prcmolar and second molar
morphology; species are ordered stratigraphically according to the estimated age of respective local faunas; A, N.G. Gen. nov.
Balicm LF. New Guinea, late Pleistocene; H, Zygomalurus irilobus, Victoria Cave LF, Naracoorte, S.A., late Pleistocene;
C, Kolopsis rotundas. Awe LF, New Guinea, late Pliocene; D, Z cf. Irilobus, Chinchilla LF, QLD., late Pliocene; E, Z. keanei.
Woodward Quarry, Palankarinna LF, S.A., late Pliocene; F, Z gilli, Beaumaris LF, Vic., late Miocene-early Pliocene;
G, Kolopsis sp., Ongeva LF, N.T., late Miocene; H. Kolopsis torus Alcoola LF, N.T., late Miocene; I, Neohelos sp., Bullock
Creek LF, N.T., mid Miocene; drawn to scale. Abbreviations: H=addition of hypocone; M=differentiation of metacone from
unitary para-mctaconal cusp; S=increased separation of paracone and metacone accompanied by broadening of cusps;
R=reduction of styles on M^; P=closer approximation and broadening of parastyle; B=paracone and metacone situated closer
to the buccal margin of the crown.
93
P.F. Murray
Fig. 5. Outlines of skulls of Australian Miocene zygomaturine genera representing plesiomorphic sister taxa of the genus
Zygomalurus. scaled to equivalent check tooth row length for comparison; A, Kolopsis torus, Alcoota LF, late Miocene (XI/
3) ; B, K. torus, Alcoota LF (showing typical size variation, possibly dimorphic), (XI/3); C, Neohelos sp., Bullock Creek LF,
mid Miocene, (Xl/3); D, Plaisiodon centralis, Alcoota LF (compare with type, Woodburne 1967: Fig. 32), late Miocene (XI/
4) . Small, narrow numerals depict symplesiomorphic states described in Table 1.
94
New Guinea Zygomaturines
Fig. 6. Lateral aspects of crania of A. Zygomaturus trilobiis (after Owen 1877); B, Htililherium tomaseltii (after Flannery and
Plane 1986); C, N.G. Gen. nov. NTMP8660-1 showing Zv.gomamrM.5 synapomorphies (large numerals. Tables 1-2); compare
with previous figure (Fig. 5), the shape of the premaxillary-maxillary suture, position of orbit, profile of frontal, profile of narial
aperture, proportions of cheek tooth row relative to rostrum.
95
P.F. Murray
MATERIALS
Northern Territory Museum (NTM) collec¬
tion of Alcoota and Bullock Creek Local Fauna
Diprotodontidae (Kolopsis, Plaisiodon,
Alkwertatherium, Pyramios Woodburne,
Neohetos)', cranium and dentitions of Z. trilobus,
Mcleay, Victoria Cave, South Australia; Z.
trilobus, Mowbray Swamp, Tasmania (casts);
cranium and two dentaries of Zygomatiirus sp.
nov.. University of California. Santa Barbara,
Department of Anthropology (original and NTM
casts, P8660-1, P8660-2, P8660-3) Late
Pleistocene, Baliem Valley, New Guinea.
RESULTS
Characteristics of Zygomaturus. Kolopsis
is the plesiomorphic sister taxon of Zygomaturus
on the basis of its synapomorphic possession of
a divided para-metacone on the P’ which, how¬
ever, is plesiomorphic with regard to Zygomaturus
in that the paracone and metacone are closer
together, and the postmetacrista remains com¬
paratively long. Zygomaturus apomorphies of
the P' include closer approximation of the
parastyle to the paracone and greater separation
of the paracone from the metacone. The differ¬
ence can be readily determined by noting the
transverse alignment of the metacone with the
hypocone in all known species of Zygomaturus,
whereas in Kolopsis species the metacone is
transversely aligned with the sulcus between the
protocone and the hypocone (Figs 3-4).
Some other proportional differences are also
apparent. For example, the para-metaconal crest
in Kolopsis spp. is situated near the longitudinal
midline of the crown whereas in Zygomaturus
spp. it lies closer to the buccal margin (Fig. 3). In
Kolopsis spp. the melastyle and parastyle of M*
Fig. 7. Frontal aspecl.s of crania of A, Kolopsis loruS\
are large, flange-like crests. These structures are
B, Zygomaturusirilobus(aflerOwen 1877, note absence
comparatively small in Zygomaturus spp. In
sagittal crest in Owen’s specimen in contrast to the wcl'
Zygomaturus spp. the P’ length is considerably developed sagittal crest in the Tasmanian specimen):
less than the M' length. In Kolopsis spp. the M' C, N.G. Gen. nov. NTM P8660-1 (tracing of a computer
is nearly equal in length or only slightly longer, generated mirror-image restoration). Small numerals ref'
resent the plesiomorphic state of the morphocline, larf^
than the P\
numerals indicate Zygomaturus synapomorphies (Tablt:*
Zygomaturus possesses many other striking 1-2). Note the following strong contrasts in B and C wilh
apomorphic contrasts with Kolopsis (Figs 5-10, Kolopsis torus (A): transversely wide, low narial apertuf®
Tables 1 -2). Among the more obvious characters with thickend dorsal margins compared to transversely
are the markedly reduced incisive foramina, narrow narial aperture with thin dorsal margins (11):
frontally directed orbits compared to laterally directed
anteriorly situated orbital margins, deep, bowed
orbits (13); laterally directed flange-like zygomatic proc¬
zygomatic arches and long transversely flat¬ esses compared to straight, conical processes (15); anterior
tened zygomatic processes, pre.sence of a flange- convergence of cheek teeth (23).
96
New Guinea Zygomaturines
Fig. 8. Palatal aspects of crania of A, Kolopsis torus\ B, Zygomaturus trilobiis\ C, Hulithenum lomaseiui (after Flannery and
plane 1986); D, N.G. Gen. nov. NTM P8660-I. Small numerals indicate plesiomorphous states, large numerals indicate
apomorphous states (Tables 1,2); note synapomorphous reduction of incisive foramina (20), robust premaxillary eminence
between widely separated central incisors (16-17), markedly constricted diastema! palate (21), position of premaxillary suture
immediately behind the I' alveolus (27) and convergent cheek tooth rows (23).
97
P.F. Murray
like premaxillary crest between and above the
central incisors, I' crowns widely separated and
often divergent at the tips, chevron-shaped
premaxillo-maxillary suture commencing im¬
mediately posterior to 1’, steep frontal profile and
strongly deflected basicranial axis. These fea¬
tures are apparently interrelated in a functional
complex that serves to place the bite force of the
molars and the incisors closer to the fulcrum of
the jaw.
Two primary modifications from the
plesiomorphic state (Kolopsis) have occurred in
Zygomaliirus: 1) the ascending ramus of the
dentary is reflected anteriorly, reducing the an¬
gle between the tips of the incisors and the
digastric process and from the digastric process
to the dentary condyle; 2) the width between the
dentary condyles and the glenoid fossae is in¬
creased in relation to the distance from the
condyles and glenoid fossae to the upper and
lower inci.sor tips (Figs 11-12).
These modifications result in a relative length¬
ening of the lever arm for the m. masseter while
reducing the length of the load arm of the dentary.
As the ascending ramus has become more verti¬
cal, the maxillary alveolus has deepened in order
to retain its occlusal relationship. On the inside
of the jaw, the digastric fossa, due to its eleva¬
tion, has become separated from the pterygoid
fossa. In the more obtusely angled jaws of
Kolopsis and Neohelos, the fossae are confluent
(Fig. 9).
The position of the glenoid fossa is corre¬
spondingly elevated in relation to the occlusal
line, resulting in a marked degree of upward
flexion of the neurocranium. Because the linear
dimension of the dorsal surface of the neurocra¬
nium is considerably shortened, the naso-frontal
angle becomes less obtuse. The dorsiflexion of
the neurocranium is also responsible for the
anterodorsal rotatation of the jugal, which re¬
sults in a distinctive lateral emargination of the
orbit.
The splanchnocranium retains its upper inci¬
sive occlusal relationship with the increased
recumbency of the lowers by a reduction of the
length of the ventral premaxillary portion of the
diastema. The complex shape of the premaxillo-
maxillary suture in Zygomaliirus is directly re¬ Fig. 9. Internal surfaces of dcnlary ascending rami
lated to the overthrust of the fronto-naso-maxil- A,Z irilohus. Mowbray Swamp LF, Tasmania; 1$, N.G. Cen.
nov. Baliem LF; C. Kolopsis torus. Alcoota LF, Note conflu¬
lary relationships dorsally, in reponse to
ent digastric and pterygoid fossa in K. torus. Apomorphous
neurocranial elevation and the ventral reduction states in A and B include erect or anteriorly inclined coronoid
of the length of the premaxilla. process (33); elevated angular process (30); separation of
The widening of the base of the triangle pterygoid and digastric fossae (32); posteriorly situated di¬
formed by the condyles and incisor tips reduces gastric eminence (31). Not to scale.
98
