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It is hypothesised that with the arrival of early Australian Aboriginals (around 48,000–60,000 years ago), hunting and the use of fire to manage their environment may have contributed to the extinction of the megafauna.Increased aridity during peak glaciation (about 18,000 years ago) may have also contributed.
— the period when the earliest humans first arrived in Australia.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 Australian Aborigines appear to have rapidly eliminated the megafauna of Tasmania about 41,000 years ago (following formation of a land bridge to Australia about 43,000 years ago as ice age sea levels declined) 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 indicate that fire increased in the local ecosystem about a century after the disappearance of megafaunal browsers, leading to a subsequent transition to fire-tolerant sclerophyll vegetation.
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.The term "megafauna" is usually applied to large animals (over 100 kg).In Australia, however, megafauna were never as large as those found on other continents, and so a more lenient criterion of over 40 kg is often applied The red kangaroo's legs work much like a rubber band. He grows up to 1.8 m tall and weighs up to 85 kg (187 lb).Females grow up to 1.1 m tall and weigh up to 35 kg (77 lb).Tails on both males and females can be up to 1 m long.The original describer of the emu Vieillot used two generic names: first Dromiceius, then Dromaius a few pages later.