Some seven years later Owen (1866) elaborated on his description after
receiving additional skull fragments from Darling Downs which were sent
to him by Edward Hill of Sydney. When pieced back together, these
fragments made a much more complete specimen than the skull from lake Colongulac.
The alveoli of the maxillary's pre-carnassial teeth were all present and
the canine itself was still in position. Owen then determined that
must have had an enormous tusk-like I1
and two smaller incisors on the premaxilla while the maxilla must have
carried the small, blunt canine followed by one or two small premolars
positioned medially to the anterior root of the carnassial. He also
made mention of the double wear facet on the medially-directed occlusal
surface of P3 which shows a slicing action
was had occurred against both P3 and M1.
Owen also pointed out the fact that the glenoid cavity was not semi-cylindrical
in design as in typical placental carnivores. Though it is transversely
elongate and bears processes limiting lateral excursion of the condyle,
its articulating surface is slightly convex ventrally and extends forward
for about 2 cm from the postglenoid process.
Information on the mandible was provided through a photo and a drawing
of Wellington Caves material sent by Mr. Gerard Krefft, Curator at the
Australian Museum, Sydney. From these, Owen demonstrated that there
was only one large tooth at the anterior perimeter of the dentary, though
its morphology could not be determined as the crown was no longer present.
Only two small alveoli lay between this tooth and the mandibular carnassial.
Based upon this pictorial information, Owen presumed that the thylacoleonid
taxonomic relationship lay with the diprotodontid marsupials as opposed
to the carnivorous dasyurids. Owen gave Thylacoleo's dental
formula as I 3/3 / ?, C 1/?,
P 2/2 / 2/2,
M 1/1 / 2/2
= 24, denoting his incertitude as to whether a second incisor or a canine
lay behind I1 and considering that the small anterior
premolar was double rooted. Owen restated his belief in the carnivorous
nature of Thylacoleo, and recorded that it "exemplifies the simplest
and most effective dental machinery for predatory life and carnivorous
diet known in the mammalian class, It is the extreme modification, to this
end, of the Diprotodont type of Marsupialia" (Owen, 1866: p. 81).
More fossil material from Darling Downs had reached Owen by 1871 and from
this he described I1, C1,
the two small premolars anterior to the maxillary carnassial and a mandibular
incisor in which the base of the crown was still present. However,
the premaxillary-maxillary suture was not well defined and appeared to
run through the alveolus of I3 which Owen
had therefore labeled as C1, while the
actual canine became P1. The photos
provided by Krefft had served as a basis for illustrations of isolated
teeth in this paper and, in the next year, Krefft (1872) cited that his
images of I2, I3,
and C1 had been labeled P1,
C1, and P3
respectively by Owen. This mistake was soon made clear.
In 1868, Flower had published a drawing of the skull in which the canine
was correctly labeled and in 1876 McCoy provided a comprehensive description
of the path of the premaxillary-maxillary suture in new fossil specimens
from Lake Colongulac. The suture was demonstrated to approach the
alveolus of I3 but then, at the periphery
of the jaw, it was redirected back to run through the alveolus of the canine.
The serrated enamel on the lateral margin of each I1
was noted by both Owen (1871) and Krefft (1872). Krefft also pointed
out that the enamel was restricted to the tips of the crowns on the interdental
surfaces of these particular teeth. He also noted wear facets in
this region which indicate that there was movement between the mandibular
incisors and that, thus, the mandibular symphysis could not have been fused.
Each of the large maxillary first incisors were shown to bear a wear facet
on its lingual surface illustrating that the mandibular incisors passed
behind the maxillary ones upon jaw closure. The crowns of I2
and I3 also exhibited evidence of abrasion
at their tips as a result of contact with I1.
The next notable breakthrough in the study of Thylacoleo carnifex
came about in 1883 when Owen (1883a) ardently acknowledged receipt of a
maxilla and a mandible from the Wellington Valley, both of which still
retained all of their teeth. The mandible possessed an intact, transversely-elongated
condyle and a deeply inflected mandibular angle but the coronoid process,
unfortunately, was broken. The broad, anteriorly-directed profile
of the latter was finally established in 1887 from a cast of a complete
dentary forwarded to Owen to G. P. Ramsay, successor to Krefft. In
this, Owen's final compendiary publication regarding
he reprised his conjecture that the animal was a diprotodontid which had
become adapted for a life of carnivory.
Of the skull anatomy discussed thus far, no mention has yet been made of
two nearly unique features of
Thylacoleo. The orbit of this
animal is delineated posteriorly by a slender bar that is missing from
most fossil specimens. This postorbital section of bone is also found
in the extinct Thylacosmilus of South America, but is not present
in other marsupials. It was illustrated without comment in a reconstruction
of the skull in Lydekker's catalouge (1887: fig. 28) but notice was drawn
to this peculiar characteristic by Anderson (1929) and by Gill (1954).
The second feature of note, one which is totally unique to Thylacoleo,
was also remarked upon by Anderson. Thylacoleo's sphenopalatine
foramen, through which the orbit and nasal cavity are in contact, is significantly
larger, relatively, than that seen in any other land mammal. No explanation
for why this should be has been put forward. In 1956, Woods produced
an in depth description of the skull of Thylacoleo based upon the
Darling Downs specimens held at the Queensland Museum. From one skull
he was able to create an endocranial cast which he compared with the one
described by Gervais as far back as 1869.
Among the marsupials, the brain of Thylacoleo would appear to most
closely resemble that of the phascolomids (wombats). The ear region
(including the stapes) as well as the temporomandibular joint, however,
show affinities to those of the phascolarctids (koalas). Woods also
pointed out the fact that no deciduous teeth had been found in any specimen.
Presently, skull and dental material of Thylacoleo carnifex have
been found in every state in Australia. The Western Australian and
Tasmanian specimens are few in number as compared to those discovered in
the other states, but it would seem that they belonged to animals that
were of smaller build than those hailing from the eastern states.
This discrepancy in size has been examined by Finch and Freedman (1982).
A metacarpal was described by Owen (1859), a radius, ulna and terminal
phalanx (1883a) and a pelvic girdle (1883b), while De Vis made a description
of a femur (1887) and a radius (1900), and Longman (1925) classified a
Thylacoleo. Ungual phalanges were discovered
by Krefft, one of which he described (1870) as Mylodon australis
although Owen (1871, 1877) was inclined to consider them as being Thylacoleonine.
Although many of these specimens had been recovered from the same localities
as Thylacoleo skulls, however, there was no solid evidence that
they were genuinely parts of a Thylacoleo.
The sole published record of postcranial material which was undoubtedly
referable to Thylacoleo was that of Wells and Nichol (1977).
They described the Thylacoleo manus in both articulated and disassembled
manner and were of the belief that the forelimb stance was digitigrade.
According to these authors considerable mobility would have been exhibited
by the pollex and appeared to be pseudo-opposable to the pisiform.
The pes was not complete but its structure inferred a plantigrade posture
and a hallux that was divergent from the other digits.
A nearly complete skeleton of Thylacoleo was discovered in a loam
pit in 1966 near Moree in northern New South Wales. The right scapula
and right ilium were still in association with the vertebrae and the vertebral
groups articulated together to form a complete column apart from the terminal
caudal units. The limb bones were broken but could be pieced back
together to make a complete forelimb and hindlimb which were missing only
the pes. The adult specimen was in association with a juvenile, represented
only by a large skull fragment and a section of the lower jaw. Found
with these was the crushed skull of a Thylacoleo pouch-young.
This material has been used in examinations of mastication, feeding habits
and locomotion (Finch and Freedman 1982, Finch 1982).
Moree Thylacoleo skeleton. Unearthed at a loam pit in New
South Wales in 1966, it offered the first solid glimpse of Thylacoleo's
postcranial anatomy. Source: Archer et al. 1984.
In 2002 came the discovery of the first virtually complete Thylacoleo
skeleton ever found, from Fightstar Cave on Western Australia's Nullarbor
Plain. The skeleton, which had the appearance of being remarkably
recent, had lain undisturbed for hundreds of thousands of years, and its
discovery astonished and excited palaeontologists around the world.
Nullarbor Thylacoleo skeleton, lying as it was discovered in Fightstar
Cave in 2002.
Western Australian Museum.
A careful excavation of the specimen was undertaken with the hope of obtaining
preserved genetic material, but the skeleton was too old to yield any DNA,
and extremely fragile. When samples were dated, they revealed
the skeleton to be far older than its appearance would suggest. After
a thorough investigation, researchers concluded that the skeleton had not
mineralised, remaining preserved in its original state since its death
between 780,000 to 500,000 years ago. This amazing level of preservation
is due to the low humidity, cool temperature and continuously stable environment
within the cave. The skeleton is now on display in the Western Australian
Museum in Perth. Covering some 200,000 sq. km, the Nullarbor Plain
is the world's largest limestone karst landscape, and is tens of millions
of years old. There are many as of yet unexplored caves on the Nullarbor
which undoubtedly contain more fossil Pleistocene marsupial remains, some
of which may be of species new to science.
Nullarbor Thylacoleo skeleton in its display case at the Western
Australian Museum in Perth.
Western Australian Museum.