of Feeding Habits:
The strange features of the skull and dentition of Thylacoleo, along
with the scarcity of postcranial material, brought about a fervid and prolonged
debate regarding its feeding habits.
In all of his works, Owen fostered no possibility other than that of a
carnivorous lifestyle for Thylacoleo and interpreted the animal
as "one of the fellest and most destructive of predatory beasts"
(1859). Broom (1898) and Woods (1956) concurred with Owen, while
Glauert (1912) was more of the opinion that Thylacoleo was a scavenger.
The discovery of fractured and incised bones led De Vis (1883), Anderson
(1889), Zeitz (1907) and Spencer and Walcott (1911) to assert that the
carnassial teeth of Thylacoleo functioned as bone crushers.
However, Cope (1882) suggested crocodile eggs or carrion as having been
its staple diet. Bensley (1903) made note that the phalangerid stock
had been of an omnivorous-herbivorous nature in which there was an orientation
towards the reduction in size of the canine teeth. He postulated
that Thylacoleo had evolved from such ancestors towards a carnivorous
diet, which would account for many of the curious features of its dentition.
However, a number of palaeontologists suggested that Thylacoleo
may have been a herbivore. Flower (1868), Dawkins (1864), Krefft
(1866) and Lydekker (1894) all wrote of plant food but, baffled by the
down-sizing of the molars, added that fruits or perhaps an occasional bird
or mammal may have been eaten. Anderson (1929) put forward the idea
that cycad pith or fruits of the family Curcubitaceae might have formed
the diet of Thylacoleo, while Gill (1954) provided a discerning
deliberation of the mystery but put forth no suggestion for what the animal's
food source may have been.
Because of the bewildering group of arguments surrounding the nature of
diet, a reassessment is necessary of the morphological characteristics
which give evidence for its feeding habits and masticatory functions.
A more in depth presentation of Thylacoleo morphology is provided
in Finch (1981).
possesses a brachycephalic skull, such as is seen in many other carnivorous
mammals. Its jaws are shortened, bringing the canine teeth closer
to the condyle and thus allowing greater force to be applied upon them
by the adductor muscles. Also, the reduction of the rostrum has allowed
the eyes to be directed anteriorly, providing binocular vision and thus
giving a greater degree of visual acuity which is of assistance in hunting
skull (replica), at the American Museum of Natural History.
Thylacoleo's zygomatic arch is deep and widely divergent from the
cranium, supplying an expansive area for muscle attachment and also providing
space for a large temporalis muscle. The size of the latter is also
evidenced by the well-developed sagittal and lambdoidal crests from which
a section of the temporalis originates. The postorbital bar, a rare
structure in carnivores, is also found in Thylacosmilus,
the "marsupial saber-tooth" of South America, and may have served as an
area of attachment for temporalis fibres and the aponeurosis which overlays
the entire muscle. It also shields and secures the eyes from pressure
by the contracting jaw muscles. This bar also acts as a supporting
structure for the anterior section of the jugal bone which is subjected
to compression and tension at the maxillo-jugal suture through piercing
by the incisors and slicing by the carnassials respectively (Buckland-Wright,
1978). No clear boss or bony projection from the anteroventral margin
of the zygomatic arch is to be seen, suggesting that the superficial masseter
muscle was relatively weak.
The condyle is a laterally-elongated bar some 45 mm in width. Its
dorsal surface is somewhat flattened and it rests in a glenoid fossa, its
articulating surface being rather convex ventrally. A well defined
postglenoid process prevents backward movement of the condyle, however,
there is no preglenoid barrier. This condition is comparable to that
of the phalangers, particularly that seen in the omnivorous Phalanger
maculatus and is not analogous with the typical placental carnivore
condition in which only orthal
movement is possible.
mandible of T. carnifex from the Wellington Caves, New South Wales.
The condyle is low on the dentary, and on a level with the tooth row.
The condylar neck is robust and short while the coronoid process is wide
and high. This suggests that the animal had a powerful, scissors-like
jaw closure. The thick condylar neck is resistant to force, and the
low articulation lengthens the effort lever arm of the temporalis muscle
by amplifying the distance between the fulcrum and the centre of the insertion
area of the muscle (Scapino, 1972).