Travel Reference
In-Depth Information
Figure 42 A wallaroo, Macropus robustus , leaps up a slope on Uluru (Ayers Rock) in cen-
tral Australia. The ancestors of these pouched animals migrated early to the part of Gondwana
that would become Australia and New Guinea.
Unfortunately, the fossil record tells us distressingly little about how
mammals sorted themselves out in South America, Antarctica, and Austra-
lia during the critical period when these plates began to move apart. South
America was home to thriving and diverse populations of marsupial and
placental mammals, but Australia somehow ended up only with marsupi-
als. Marsupials comprise most of Australia's mammal fossil record as well
(though argument continues about some possible placental mammal fi nds
in Queensland). Did the marsupials simply get to Oz fi rst, and did Antarc-
tica, growing as dark and dreary as Mordor as it continued to move south,
act as a barrier to subsequent placental mammal invasions? Or did placen-
tal mammals lose out to better-adapted marsupials in Australia's tough
environment?
My guess is that the marsupials were simply lucky enough to get to
Australia fi rst. They may have had a tough time doing so, because Australia
shows signs of having been isolated even before the Age of Mammals. This,
 
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