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The External Anatomy
of the Thylacine
Facial features
(continued):
The rhinarium (Latin
= "of the nose") is the moist, fleshy tissue surrounding the nostrils.
Its function is believed to be olfactory; detecting smells and ascertaining
the direction of their source.
.
Rhinarium
of Thylacinus from the front (A) and from above (B).
Pocock
- Proceedings of the Zoological Society (1926) (Fig. 27 p. 1041).
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| Pocock states:
"The rhinarium in
Thylacinus is large, coriaceous, entirely naked, and sometimes projects
prominently beyond the edge of the upper lip, towards which its anterior
surface then recedes downwards and backwards.
Viewed from the front
(A),
it is about as wide as high, but the inferior third of it is constricted
to form a very definite philtrum about as wide as high with nearly vertical
sides defined by the hair of the upper lip. The philtrum is marked
by a pair of vertical parallel grooves, one on each side of the middle
line, which do not ascend as high as the nostrils. The upper edge
is strongly convex, from side to side, and the internarial space is wide
and marked by a median vertical groove, which does not reach the summit
of the upper surface above and ceases below on a level with the upper ends
of the grooves of the philtrum. There is a tolerably deep infranarial
area on each side.
Viewed from above
(B),
its upper surface is about one fourth wider than long, its anterior edge
is slightly emarginated, its posterior edge ill defined from the integument
behind it, its lateral edges behind the nostrils are convex, and only a
small area of the nostril is exposed.
In profile view the
nostrils are large and open outwards and forwards".
The ears of the thylacine
are erect, forward-facing, rounded and covered with short fur. The
external opening is shielded by a line of longer golden-coloured hairs.
Pocock provides a comprehensive description of the structure of the external
ear. He opens by stating:
"The ear in Thylacinus
is moderately large; its height exceeds its antero-posterior width and
it is attached to the head by a broad base. Its anterior edge is
lightly convex up to the somewhat narrowed apex, and from the apex to its
inferior point of attachment the margin is more strongly but less regularly
convex". |
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Ear
of Thylacinus expanded, with the supratragus raised. Pocock
- Proceedings of the Zoological Society (1926)
(Fig.
29 p. 1044). Anatomical features (A-D) described below.
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Ear of Thylacinus
(Specimen OUM 7942).
Courtesy: Oxford University
Museum of Natural History.
Photo: Dr. Stephen Sleightholme.
International Thylacine Specimen Database, 5th Revision 2013.
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(A)
anterior ridge; (B) anterior passage, which can be closed by raising ridge
C against A;
(D)
ridge reinforcing border of inferior passage in front of ear canal.
|
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| Pocock concludes with
a detailed description of the cartilaginous structure of the external ear,
and notes that the "cavity of the external ear is capable of being closed".
Little is noted in the
literature regarding the thylacine's eyes. George Harris (1808) states:
"Eyes
large and full, black, with a nictitant
membrane, which gives the animal a savage and malicious appearance".
William Patterson, in a letter to Sir Joseph Banks (1805), gives the measurements
of the eye of his specimen: "length of the eye, which is remarkably
large and black, 1 ¾ inches (4.45cm); breadth of the eye
¾ inch (1.91cm)". |
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Close-up view of the
thylacine's eyes - Beaumaris Zoo (QD), Hobart (1933).
Photo courtesy: David Fleay
Trustees.
|
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| Hans
Naarding, a field ranger with the Tasmanian Parks and Wildlife
Department, sighted what he believed to be a thylacine at Togari in 1982.
In his report, he made comment on the eye reflection: "Eye reflection
was pale yellow".
The Hamilton Spectator
of the 20th June 1896 (p. 2) states with reference to the thylacine's eyes:
"The eyes, which
are large, are furnished with a membrane, like the eyes of owls; and this
is called the nictitating membrane. This is almost continually moving
in the daytime, as the eyes are exposed to more or less of sun-shine".
The
thylacine is unique in having the largest gape of any mammal. The
gape
angle is often quoted to be in the order of 120°. This however,
is a gross exaggeration, as opening the jaw more than 80° would violate
the integrity of the joint. |
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Motion
picture still of the last
captive thylacine at the
Beaumaris Zoo (QD), Hobart
(1933), displaying the species's "threat-yawn" response.
Image courtesy: David Fleay
Trustees.
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Thylacine skull (Specimen
OUM 7937).
Courtesy: Oxford University
Museum of Natural History.
Photo: Dr. Stephen Sleightholme.
International Thylacine Specimen Database, 5th Revision 2013.
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The wide gape may well
be advantageous in stalking fast-moving prey such as wallabies. In
theory, the greater the gape, the greater the grasp, and this would vastly
increase the chance of a capture and consequent kill. The gape yawn
was a threat warning to indicate that an individual's presence was not
wanted, and may also be related to sexual display in the male thylacine.
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Thylacine
yawn sequence created by Arnfinn Holderer (2016), with technical contributions
from C. Campbell and Dr. S. Sleightholme. Click gear button in lower
right corner and select "?" to view control options for changing viewing
angle and distance. This animation is copyright and unauthorized
use strictly prohibited.
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