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BIOLOGY:
- ANATOMY -
SKULL AND SKELETON: SKULL (page 2)
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relative skull lengths: Thylacinus, Dasyurus and Sarcophilus
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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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area of attachment and direction of pull 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. view the CT scan
Click the film icon above to view a CT (computerized tomography) scan of a thylacine skull from the Royal College of Surgeons (England) collection.

   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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comparison of thylacine and wolf skulls - image  C. Campbell
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A comparison of the thylacine and wolf skull structure in lateral view.  Side-by-side dorsal and palatal views of the skulls can be seen in A Comparison of the Thylacine and Wolf Skull.
Also, see anatomical diagrams of the thylacine skull.
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References
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back to: Skull (page 1) return to the subsection's introduction forward to: Skull (page 3)


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