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The skull of the thylacine is variable with respect to both its absolute
size and the proportion of its separate parts, but to no greater extent
than that found in the placental wolf (Canis
lupus). The thylacine however,
exhibits a far greater degree of sexual
dimorphism in its cranial and dental characters than is the case in
any other marsupial species.
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There is a marked difference in the skull size between the sexes, the male
thylacine having a proportionally larger skull with a longer face.
The skull of the female is distinguishable from that of the male by its
smaller size, shorter muzzle, less expanded zygomata,
and with respect to its dentition, smaller but proportionally larger teeth.
It was Thomas Oldfield
(1888) who provided the earliest published range for both male and female
thylacine skulls.
Historically, Temminck
(1824, pp. 60-65) made the following remarks regarding the skull of the
thylacine: |
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Comparison of male and
female thylacine skulls.
* range from
205mm to 226, t range from 179mm. Oldfield (1888).
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| "By comparing the
cranium of this animal with those of dogs one must agree at first glance
the resemblance seems striking but is easy to see that on the whole they
are completely different in a way very marked by the form and the number
of teeth. It is true, that the lengthened shape of the muzzle and
strong conical curved canines give the head of this animal a resemblance
to that of dog's but one can still notice that independently of the disparity
of the teeth, the zygomatics are much more strongly arched than in any
species of dog. The thylacine also differs from the true
Dasyurids
with which it was joined not only by the number of true molars but by the
lower form of those on the jaw, size and force of the canines, the length
of the muzzle (and cranial changes) which results in forward placement
of the eyes whereas true Dasyurids have eyes on the sides of their head". |
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| In comparing the skull
of a thylacine with that of a placental carnivore, one of the most obvious
evolutionary similarities is in the carnassial (=sectorial) teeth.
Other features are the palatal
vacuities (holes in the palate) like those found
in the skulls of primitive mammals, posteriorly expanded nasal bones,
an alisphenoid tympanic wing flooring the middle ear, the involvement of
the jugal at the edge of the glenoid fossa for articulation of the lower
jaw, broad extension of the lachrymal bone onto the face of the skull and
mesially enlarged angular process of the dentary (lower jaw); features
the thylacine shares with most other marsupials. |
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The brain case is small
and narrow.
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The
lachrymal foramen is anterior to the orbit so that it opens onto
the surface of the face, rather than the inside of the orbital space.
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The jugal (also known
as the zygomatic or malar bone) is large. View a graph
demonstrating jugal width vs. skull length between T. cynocephalus
and C. lupus.
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The angular process
of the dentary is inflected medially in almost all marsupials.
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Flared (diamond-shaped)
nasal bones as opposed to the rectangular nasal bones of placental carnivores.
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Photos: International
Thylacine Specimen Database 5th Revision 2013.
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