Australian megafauna


Australian megafauna comprises a number of large animal species in Australia, often defined as species with body mass estimates of greater than or equal to or greater than 130% of the body mass of their closest living relatives, that lived during the Pleistocene epoch. Most of these species became extinct during the latter half of the Pleistocene, and the roles of human and climatic factors in their extinction are contested.
There are similarities between prehistoric Australian megafauna and some mythical creatures from the Aboriginal dreamtime.

Causes of extinction

Many modern researchers, including Tim Flannery, think that with the arrival of early Aboriginal Australians, hunting and the use of fire to manage their environment may have contributed to the extinction of the megafauna. Increased aridity during peak glaciation may have also contributed, but most of the megafauna were already extinct by this time. Others, including Steve Wroe, note that records in the Australian Pleistocene are rare, and there is not enough data to definitively determine the time of extinction of many of the species, with many of the species having no confirmed record within the last 100,000 years. They suggest that many of the extinctions had been staggered over the course of the late Middle Pleistocene and early Late Pleistocene, prior to human arrival, due to climatic stress.
New evidence based on accurate optically stimulated luminescence and uranium-thorium dating of megafaunal remains suggests that humans were the ultimate cause of the extinction for some of the megafauna in Australia. The dates derived show that all forms of megafauna on the Australian mainland became extinct in the same rapid timeframe—approximately 46,000 years ago—the period when the earliest humans first arrived in Australia. However, these results were subsequently disputed, with another study showing that 50 of 88 megafaunal species have no dates postdating the penultimate glacial maxiumum around 130,000 years ago, and there was only firm evidence for overlap of 8-14 megafaunal species with people. Analysis of oxygen and carbon isotopes from teeth of megafauna indicate the regional climates at the time of extinction were similar to arid regional climates of today and that the megafauna were well adapted to arid climates. The dates derived have been interpreted as suggesting that the main mechanism for extinction was human burning of a landscape that was then much less fire-adapted; oxygen and carbon isotopes of teeth indicate sudden, drastic, non-climate-related changes in vegetation and in the diet of surviving marsupial species. However, early Aboriginal peoples appear to have rapidly eliminated the megafauna of Tasmania about 41,000 years ago without using fire to modify the environment there, implying that at least in this case hunting was the most important factor. It has also been suggested that the vegetational changes that occurred on the mainland were a consequence, rather than a cause, of the elimination of the megafauna. This idea is supported by sediment cores from Lynch's Crater in Queensland, which suggest that fire increased in the local ecosystem about a century after the disappearance of Sporormiella, leading to a subsequent transition to fire-tolerant sclerophyll vegetation. However, the use of Sporormiella as a megafaunal proxy has been criticised, noting that Sporormiella is found sporadically in the dung of various herbiviorous species, including extant emus and kangaroos, not just megafauna, that its presence depends on a variety of factors, often unrelated to megafaunal abundance, and that in Cuddie Springs, a well known megafaunal site, the densities of Sporormiella were consistently low. A study of extinct megafauna at the Walker Creek site in Queensland, found that their disappearance from the site after 40 kya came after an extended period of environmental deterioration.
Chemical analysis of fragments of eggshells of Genyornis newtoni, a flightless bird that became extinct in Australia, from over 200 sites, revealed scorch marks consistent with cooking in human-made fires, presumably the first direct evidence of human contribution to the extinction of a species of the Australian megafauna. This was later contested by another study that noted the too small dimensions for the Genyornis supposed eggs, and rather, attributed them to another extinct, but much smaller bird, the megapode Progura. The real time that saw Genyornis vanish is still an open question, but this was believed as one of the best documented megafauna extinction in Australia.
"Imperceptive overkill"; a scenario where anthropogenic pressures take place; slowly and gradually wiping the megafauna out; has been suggested.
On the other hand, there is also compelling evidence to suggest that the megafauna lived alongside humans for several thousand years. The question of; if the megafauna died before the arrival of humans is still debated; with some authors maintaining that only a minority of such fauna remained by the time the first humans settled on the mainland. One of the most important advocates of human role, Tim Flannery, author of the book Future Eaters, was also heavily criticised for his conclusions. A suprisingly late date of 33-37 kya is known for a Zygomaturus'' specimen from the Willandra Lakes Region in New South Wales, the latest known date for any Australian Megafauna. This is well after aboriginal arrival in Australia around 50 kya.

Living Australian megafauna

The term "megafauna" is usually applied to large animals. In Australia, however, megafauna were never as large as those found on other continents, and so a more lenient criterion of over is often applied

Mammals

The following is an incomplete list of extinct Australian megafauna in the format:
Monotremes are arranged by size with the largest at the top.
Marsupials are arranged by size, with the largest at the top.
was a hippopotamus-sized marsupial, most closely related to the wombat.

Monsters and large animals in Dreamtime stories have been associated with extinct megafauna.
The association was made at least as early as 1845, with colonists writing that Aboriginal people identified Diprotodon bones as belonging to bunyips, and Thomas Worsnop concluding that the fear of bunyip attacks at watering holes remembered a time when Diprotodon lived in marshes.
In the early 1900s, John Walter Gregory outlined the Kadimakara story of the Diyari, which describes the deserts of Central Australia as having once been "fertile, well-watered plains" with giant gum-trees, and almost solid cloud cover overhead. The trees created a roof of vegetation in which lived the strange monsters called Kadimakara—which sometimes came to the ground to eat. One time, the gum-trees were destroyed, forcing the Kadimakara to remain on the earth, particularly Lake Eyre and Kalamurina, until they died.
In times of drought and flood, the Diyari performed corroborees at the bones of the Kadimakara to appease them and request that they intercede with spirits of rain and cloud. Sites of Kadimakara bones identified by Aboriginal people corresponded with megafauna fossil sites, and an Aboriginal guide identified a Diprotodon jaw as belonging to the Kadimakara.
Gregory speculated that the story could be a remnant from when the Diyari lived elsewhere, or when the geographical conditions of Central Australia were different. The latter possibility would indicate Aboriginal coexistence with megafauna, with Gregory saying:
After examining fossils, Gregory concluded that the story was a combination of the two factors but that the environment of Lake Eyre had probably not changed much since Aboriginal habitation. He concluded that while some references to Kadimakara were probably memories of the crocodiles once found in Lake Eyre, others that describe a "big, heavy land animal, with a single horn on its forehead" were probably references to Diprotodon.
Geologist Michael Welland describes from across Australia Dreamtime "tales of giant creatures that roamed the lush landscape until aridity came and they finally perished in the desiccated marshes of Kati Thanda–Lake Eyre", giving as examples the Kadimakara of Lake Eye as well as continent-wide stories of the Rainbow Serpent, which he says corresponds with Wonambi naracoortensis.
Journalist Peter Hancock speculates in The Crococile That Wasn't that a Dreamtime story from the Perth area could be a memory of Megalania.
Rock art in the Kimberley appears to depict a marsupial lion and a marsupial tapir, as does Arnhem land art. Arnhem art also appears to depict Genyornis, a bird that is believed to have gone extinct 40,000 years ago.
An Early Triassic archosauromorph found in Queensland, Kadimakara australiensis, is named after the Kadimakara.