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Australia
and the Marsupials - A Historical and Modern Perspective
"It is
not possible that there is not in such a vast sea, some immense continent
of solid land
capable of keeping
the globe in equilibrium in its rotation, and of serving as a counterweight
to the mass of northern Asia".
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Charles
de Brosses
"Histoire
des navigations aux terres australes" (1756)
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Around the beginning of the Eocene Epoch, some 55 million years ago, the
land that would become Australia broke away from Antarctica. It began
drifting northward, and was completely separated from the rest of the Earth's
major land masses. Through this isolation, the marsupials that were
living there became largely free from competition with the placental mammals
which were rapidly diversifying in most other regions of the world.
Ever since Australia began its long northward journey, the marsupials have
been its dominant mammal group. |
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Early European cartographers (map makers) had long speculated about the
possible existence of a mysterious, unknown southern land, which they called
"Terra
Australis Incognita". During the Age of Exploration, when the
first European voyagers reached the shores of the legendary continent,
they were amazed to find that the mammals living there were quite different
from any that they had seen previously. These newly discovered creatures
were marsupials. The existence of this group of mammals was known
to the Europeans long before their encounter with Australia however, as
opossums had already been found in North and South America.
However, Captain
James Cook's kangaroo was the first marsupial to become widely known.
Cook's own description reads: |
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A
map of Terra Australis produced in 1531 by the French mathematician and
cartographer Oronce Finé (1494-1555).
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| "In
form, it is most like the Jerboa, which it also resembles in its motion,
...; but it greatly differs in size, the Jerboa not being larger than a
common rat, and this animal, when full grown, being as big as a sheep:
... The head, neck and shoulders are very small in proportion to
the other parts of the body; the tail is nearly as long as the body, thick
near the rump, and tapering towards the end: the fore-legs of this individual
were only eight inches long, and the hind legs two-and-twenty: its |
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An
illustration by George Stubbs, which was featured in John Hawkesworth's
"An
Account of the Voyages ... in the Southern Hemisphere" (1773).
Stubbs was commissioned by Joseph Banks (the naturalist who traveled with
Capt. James Cook on his Pacific voyage of 1768-71) to paint the portrait
using kangaroo specimens brought back from the voyage.
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progress
is by successive leaps or hops, of a great length, in an erect posture;
the fore-legs are kept bent close to the breast, and seemed to be of use
only for digging..."
Cook also reported bats, a "kind of pole-cat", "wolves" and:
"an animal of the Opossum tribe: it was a female, and with it he' (Joseph
Banks) 'took two young ones: it was found to resemble the remarkable
animal which Mons.
de Buffon has described in his Natural History
by the name of Phalanger, but it was not the same. Mons. Buffon supposes
this tribe to be peculiar to America, but in this he is certainly mistaken." |
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Through such records, we can see that although the marsupials were not
officially classified by zoologists as a unique group separate from the
placental mammals until the nineteenth century, the similarities between
the American and Australian marsupials were already starting to be noticed
before the end of the 1700s. |
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Being an enormous island surrounded by deep water, Australia has been isolated
from the rest of the world's faunal realms for many millions of years.
Thus, mammalian exchanges to and from other land masses (other than by
flying or swimming species of placentals) have been quite rare, except
within comparatively recent times with the assistance of man.
The discovery of the mammals of Australia had a strong impact on scientific
ideas about the magnitude of the animal kingdom. Back in Europe,
explorers' reports of the new animals were at first ridiculed by a number
of |
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The
platypus (Ornithorhynchus anatinus), one of only three species of
living monotreme mammals.
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| zoologists of the
time. Preserved specimens of creatures as bizarre as the platypus
(Ornithorhynchus anatinus), which seemed to be a taxidermist's
handiwork of piecing together parts of completely different animals, were
often thought of as hoaxes until scientific examination proved otherwise. |
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Eastern
grey kangaroos (Macropus giganteus).
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To begin forming an understanding of Australia's mammalian fauna, let us
first consider the taxonomic relationships of the groups which exist there.
All living species of mammals are classified into three main sub-divisions;
the placentals, marsupials, and monotremes.
The main characteristic of the placentals is that the young are retained
in the uterus, where they are nourished for an extended length of time
by a placenta. Placentals do not have a marsupium
(pouch). The young are fed with milk, as in the other mammal groups.
Placentals also possess certain structural features of the skull which
are unique. This group is worldwide in |
distribution and is
the division to which the vast majority of living mammal orders belong
(e.g. carnivores, cetaceans, artiodactyls, bats, rodents, primates, etc.). |
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