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As Williams et al. (
1998
) also noted in their earlier discussion of prehistoric extinc-
tions, unicausal explanations are seldom persuasive.
Some workers have pointed out that much of the evidence for faunal extinctions
come from the better-watered south-western and south-eastern periphery of the con-
tinent and not from the more arid interior, although this stricture does not apply to the
extinction of the giant flightless bird
Genyornis
in and around the Lake Eyre Basin
that was so well-documented by Miller and his co-workers (Miller et al.,
1999
). In
response to this criticism, Prideaux et al. (
2009
) completed a detailed investigation
of what the largest-ever kangaroo,
Procoptodon goliah
, was actually eating in the
arid zone of south-east Australia. From the carbon isotopic composition of the tooth
enamel, combined with tooth microwear patterns, they concluded that
P. goliah
was
a specialist chenopod browser, most likely of the saltbush genus
Atriplex
,andthat
it drank more water in the arid zone than its grazing contemporaries did, much like
sheep that eat saltbush today. Because saltbushes and chenopod shrublands do not
burn easily, they discounted fire as a major cause of the demise of
P. goliah
, concluding
that it had survived many previous climatic cycles from more to less arid conditions,
so hunting of this tall, conspicuous animal by the first Australians remained the most
plausible cause. However, this is an inference by default, because no positive evidence
of actual hunting is forthcoming.
It is useful to recall that most of the larger marsupials that became extinct in the
late Quaternary were primarily browsers (eaters of shrubs and leaves from trees)
rather than grazers (grass-eaters). The long-term change in the Australian flora took
place against a backdrop of rapid climatic fluctuations superimposed on long-term
desiccation (Martin,
2006
). The result as far as the browsers were concerned would
have been a progressive impoverishment of their habitat during the Quaternary, with
grassland expanding at the expense of forest and woodland. The arrival of humans,
allied with their initial ignorance of how best to control the destructive impact of fire,
would have aggravated the pressure on the large browsers with their slow breeding
cycles. As the large marsupials declined in number, so too did their large carnivorous
predators, such as
Thylacoleo
and
Megalania
. In the words of John Calaby, the late
Pleistocene arrival of humans on the Australian landscape was simply the last nail in
the coffin for a group of animals already on the way to extinction (Calaby,
1976
), a
view accepted by Williams et al. (
1993
;
1998
).
Another approach to this problem is to investigate the possible consequences (as
opposed to the causes) of late Quaternary extinctions of the larger herbivores on local
and regional habitats. Flannery (
1994
) suggested that the late Quaternary extinction
of the large marsupials in Australia would have altered the vegetation, effecting a
change in fire regime and causing a major ecosystem change. Miller et al. (
2005
)also
argued for Australian 'ecosystem collapse' shortly after the demise of the Pleistocene
megafauna, which according to their work on the now extinct, giant flightless bird
Genyornis
, vanished soon after the arrival of humans (and humanly lit bushfires) on
