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The Internal Anatomy
of the Thylacine - A Historical Perspective
Bernard William Tucker
(1901-1950), was demonstrator in Zoology and Comparative Anatomy at Oxford
University. He performed a detailed dissection and study of the head
of the London Zoo's last female thylacine, which was on display at the
zoo from 26th January 1926 until her death on 9th August 1931. |
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London Zoo's last thylacine,
1926. Courtesy: Zoological Society of London.
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| Surprisingly, in his
report of 1882, Cunningham did not make any comment on the anatomy of the
head of either of his specimens. Tucker was somewhat astonished when
asked to undertake the study that virtually nothing had previously been
written on the subject. Tucker states:
"Considerable attention
has been paid to the head and neck musculature of marsupials and naturally
a certain amount of information on the cranial nerves and blood vessels
is scattered throughout the literature, but nowhere could I find the kind
of coherent and comprehensive account of these portions of the anatomy
of a marsupial type which I had expected would afford a basis of comparison
with Thylacinus. No doubt a partial explanation of this astonishing
state of affairs is that morphologists have found the cranial anatomy of
the marsupials so closely similar to that of the placentals. This
similarity, indeed, is well known. Yet it seems very strange and
highly unsatisfactory that there should be any part of the anatomy of a
whole sub-class of mammals of which a full and connected account is not
available. This consideration, together with the fact that the extreme
rarity of Thylacinus seemed to render it almost a duty to make the fullest
possible use of the material, convinced me of the need to make a more detailed
study than I had first visualised".
Tucker examined both
the arterial and venous flow, and the deep and superficial nerve supply
to the head, and produced comprehensive notes and working drawings of his
findings. His study of the cranial anatomy is still the most detailed
ever produced. He also wrote a full account of the musculature of
the neck and shoulder. Tucker's unpublished notes and drawings are
now held in the collection of the Oxford University Museum, together with
the remains of the dissected head (Specimen OUM 7942) (Source: ITSD 5th
Revision 2013). |
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Dissection of the neck
musculature of the thylacine. Drawing: Dr. Stephen Sleightholme (after
Tucker).
Courtesy: Oxford Museum
of Natural History.
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| Professor Dr. Heinz
Friedrich Moeller (1936-2009), was the Director
of the Zoological Museum and the Department of Comparative Morphology of
Vertebrates at the University of Heidelberg. He was internationally
regarded as a leading authority on the zoology of the thylacine, publishing
a series of papers and a book, "Der Beutelwolf",
on the subject (view details on "Der
Beutelwolf").
In 1968, Moeller published
a paper, "Zur Frage der Parallelerscheinungen bei Metatheria und Eutheria.
Vergleichende
Untersuchungen an Beutelwolf und Wolf", in which he noted that
the brain of the thylacine is considerably smaller in relation to body
size than that of the placental wolf. The average capacity of the
braincase was 53.5 cc as measured by Moeller on a series of 30 thylacine
skulls. In an equal number of wolf skulls, the braincase capacity
was 134.4 cc. The average length of the thylacine skulls was 207.1
mm, compared to an average length of 213.4 for the wolf skulls. |
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| Comparative
brain studies of the quoll (Dasyurus), Tasmanian devil (Sarcophilus)
and thylacine (Thylacinus) in lateral, dorsal and ventral view. |
In 1970, Moeller published
the most detailed account to date on the comparative studies of the brain
of the greater dasyurids (Thylacinus, Sarcophilus and Dasyurus)
with respect to their evolutionary status in a paper entitled "Vergleichende
untersuchungen zum evolutionsgrad der gehirne groBer Raubbeutler (Thylacinus,
Sarcophilus und Dasyurus. I. Hirngewicht. II. Hirnform und Furchenbild".
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the microscope icon for a magnified view of: lissencephalic
brain. |
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| Click
the microscope icon for a magnified view of: gyrencephalic
brain. |
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Moeller notes that the brain of Dasyurus is lissencephalic
from the Greek "Lissos" = smooth, hence, a smooth-surfaced or non-convoluted
brain. The brain of Sarcophilus shows only a few furrow-like
impressions. The brain of Thylacinus is gyrencephalic
from the Greek "Gyros" = ring (gyrus), and "Enkaphale" =
brain. Gyrencephalics have folded or convoluted brains.
Moeller observed that
when comparing the outward appearance of the brains, and the casts of the
braincases, that the neocortex of Sarcophilus, and to a higher degree
that of Thylacinus, is enlarged. This enlargement in Thylacinus
goes hand in hand with diminishing of the olfactory parts of the brain.
The surface expansion of cerebral cortex is one of the most distinguishing
evolutionary features of the mammalian brain. The cerebral cortex is responsible
for higher cognitive functions and is thought to underlie the concomitant
growth in intellectual capacity.
Note: The marsupial
brain is smaller than that of a placental mammal of similar size and lacks
a corpus callosum, a structure that permits nerve communication between
the right and left cerebral hemispheres. Marsupials however, have
an enlarged anterior commissure that serves a similar purpose. |
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| Lateral
views of the thylacine brain (endocranial
cast) from the right, front, left and back. A 360°
rotational view of this cast can be seen here. |
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