OF LOCOMOTORY ADAPTATIONS:
The Moree Thylacoleo
specimen was the first virtually complete specimen of Thylacoleo
to be found and provides the basis for limb comparisons with those of mammal
species whose locomotory habits are known.
(1944), and Hildebrand (1954, 1961), Smith and Savage (1956) and Savage
(1977) have discussed various indices of intra- and inter-limb lengths
which are distinctive of different mammalian locomotory methods.
The morphological trends which become evident include the retention of
the primitive attribute of a somewhat shorter fore- than hind limb in quadripedal
walking animals, the elongation of the distal limb structures in cursorial
forms (e.g. ungulates) and for the evolution of short yet strong legs in
fossorial and swimming species. However, one should bear in mind
that the forelimb may serve functions apart from locomotion, which may
modify the adaptation of the limb.
Moree Thylacoleo, discovered in 1966.
In this preparatory
examination, measurements were made of the length of the vertebral column
(taken as atlas - last lumbar vertebra), humerus, radius, metacarpal 3,
femur and tibia. Attention was only given to the Marsupialia although
the placental lion (Panthera leo) was included for comparison.
Skeletal elements from the collections of the Western Australian Museum
were made available by Dr. W.D. L. Ride. Figures in parentheses give
the number of specimens from which measurements were made, and where possible,
the measurements of both right and left limbs of each animal were procured.
(Antechinus flavipes (1), Dasyurus geoffroii ( I ), Sarcophilus
harrisii ( I ) )
and Peramelidae: (Macrotis lagotis (1), lsoodon obesulus
and Phalangeridae: (Pseudocheirus occidentalis
vulpecula (4) )
(Lasiorhinus lalifrons (2), Vombatus hirsutus (1) )
(Phascolarctos cinereus (2) )
and Potoroidae: (Macropus sp. (1), Bettongia lesuer
The most helpful comparisons
which can be performed in the instance of the Moree Thylacoleo are:
(a) humerus + radius + metacarpal 3 / length of vertebral column (atlas
to last lumbar) x 100; (b) length of forelimb / length of hind limb x 100;
(c) length of tibia / length of femur x 100; (d) length of radius / length
of humerus x 100. The frequently used ratio of hind limb to vertebral
column length could not be evaluated due to the fact that the pes was missing
from the Moree specimen.
Ratio (a), forelimb/vertebral
column, distinguishes cursorial and saltatorial forms. Animals belonging
to the first two groups have a tendency to exhibit comparatively long forelimbs
in relation to the length of the vertebral column. The forelimbs
of Thylacoleo are notably longer than those of such species as the
arboreal Pseudocheirus and Trichosurus and the smaller cursorial
The ratios for the fossorial wombats, Vombatus and Lasiorhinus
and the essentially saltatorial Bettongia,
Isoodon, and Antechinus
are low, ranging from 43 to 53.
Ratio (b), the intermembral
index, correspondingly allows the division of cursorial and arboreal from
saltatorial animals. It is notable, however, that wombats tend to
have limb ratios which are similar to those of climbing animals.
Again, Thylacoleo is grouped among the larger, carnivorous forms.
Within the hind limb,
the tibia/femur index (c) has been observed by Howell (1944) to be high
in saltatorial animals and in high-speed runners, but low in walking forms
such as cattle, lions, and hyenas. In this index, Thylacoleo
can be placed amongst the placental lion and wombats. Obviously,
could not have been a speedy, cursorial animal and its femoro-tibial index
of 82 does not approach that of the arboreal possums,
and Pseudocheirus (102-103). The distinction between Thylacoleo
and Sarcophilus is generally about 100 in unspecialised animals,
risapproximately equal length.
The final ratio, (d),
that of radius/humerus is usually 100 in unspecialised animals, moving
up to 140 in saltatorial types, to 120 in swift cursorial forms and dropping
down below 100 in fossorial and walking varieties. The placental
lion has a humero-radial index of merely 90 (Howell 1944) regardless of
its ability to make short bursts of speed. Among the marsupials Thylacoleo
displays a much higher index (115) than its placental counterpart and it
is therefore grouped with animals which are adapted to climbing rather
than running or walking.
How the koala (Phascolarctos)
is categorized among the four ratios presents something of a puzzle.
It appears close to Thylacoleo in each instance and there is reasonable
dissimilarity in its indices from those of the other arboreal marsupials,
the possums. Archer (1976) however, proposes that the Phascolarctidae
and their close relations the Vombatidae evolved directly from diprotodont
ancestors bearing selenodont teeth and that the Phalangerids are a completely
independent evolutionary lineage from the basic stock. This theory
has gained support from comparative serology studies performed by Kirsch
(1977). If this is the case, the divergence between the adaptations
of koalas and possums is not surprising.
Judging from the limb
proportions studied, Thylacoleo appears to have been a cursorial
marsupial which was not capable of rapid locomotion. It exhibited
no climbing adaptations although the relatively long radius places it among
the arboreal and saltatorial forms which have forelimbs that are commonly
used for manipulative and food gathering purposes as well as for locomotion.
carnifex composite skeleton from Victoria Fossil Cave, Naracoorte,
|| Based upon
present studies, the image that has been formed of Thylacoleo is
that of a robustly built animal which normally has a deliberate walk, but
that may have also been capable of short bursts of speed. The unusually
long forelimb with its enormous claw on the first digit was probably used
in manipulating food toward the mouth, and would indicate a predatory rather
than scavenging nature. The pseudo-opposability of Thylacoleo's
powerful first digit suggests a scansorial habit to Wells and Nichol (1977)
and, considering the phalangerid characteristics of the Thylacoleonidae,
this may have been the case. Thylacoleo, the 'pouched lion' may
have been more aptly named Thylacopardus or 'pouched leopard' if
the complete skeleton had been available for examination 100 years ago.