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Relative skull lengths:
Thylacinus,
Dasyurus
and Sarcophilus.
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| The jaw of the thylacine
is considerably longer than that of its dasyurid cousins, and has
a simple hinge joint lying in the same plane as the teeth. The joint
is inherently stable and acts as a pivot for the lower and upper jaws.
The mandible of the thylacine, as is true for all carnivores, cannot be
moved forward, and it also has restricted side-to-side motion. The
small brain case of the thylacine, when compared to that of the placental
wolf, together with the large zygomatic arches of the cranium, have facilitated
strong development of the temporalis and masseter muscles. |
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Thylacine skull showing
the area of attachment and direction of pull of the temporalis and masseter
muscles.
Skull photo: International
Thylacine Specimen Database 5th Revision 2013.
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The principal muscle
utilised for operating the jaw in all carnivores is the temporalis or temporal
muscle. The temporalis is an extensive, fan shaped muscle that covers
the temporal region. It is a powerful masticatory muscle that can
easily be seen and felt during closure of the mandible. The temporalis
is extremely well developed in the thylacine and accounts for most of the
muscle mass on the sides of the head. The muscle originates on the
floor of the temporal fossa and deep surface of the temporal fascia, and
is inserted on the tip and medial surface of the coronoid process and anterior
border of ramus of the mandible. The temporalis muscle delivers fast
and forceful jaw closure. In all carnivores, the temporalis is well
developed because they must drive the canine teeth forcefully into the
prey.
| The masseter
muscle is a quadrangular-shaped muscle that covers the lateral aspect of
the ramus and the coronoid process of the mandible. It originates
on the inferior border and medial surface of the zygomatic arch and is
inserted into the lateral surface of the ramus of the mandible and its
coronoid process. The masseter muscle, in contrast to the temporalis,
provides slow, powerful jaw closure. In the thylacine, the facial
musculature is greatly reduced, as is the case with all carnivores.
Heavy facial musculature, would by virtue of its mass, hinder the thylacine's
wide gape.
It would also play virtually no part in the preparation of food for swallowing. |
| Click
the film icon above to view a CT (computerized tomography) scan of a thylacine
skull from the Royal College of Surgeons (England) collection. |
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These major skull modifications
have improved the biomechanical compression forces through the elongated
snout of the thylacine, and have compensated for what would have otherwise
been a soft bite due to the distance from the mandibular articulation to
the canines. They have endowed the thylacine with a similar bite
force to that of an equivalent-sized placental carnivore. |
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