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.
Australian megafauna are a number of large animal species in Australia, often defined as species with body mass estimates of greater than 30 kilograms, or equal to or greater than 30% greater body mass than their closest living relatives. Many of these species became extinct, it is thought by many scientists, that with the arrival of humans (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 to the extinction of the megafauna.
Australia has a few remaining native megafauna, such as the Red Kangaroo, Emu and Estuarine Crocodile, whilst the oceans that surround our continent are home to the largest living marine megafauna, like the Blue Whale, Giant Squid, Whale Shark and Leather-back turtle. However, Australia didn’t always have so few native megafauna, instead our island continent was once home to the largest ever monotremes (egg-laying mammals), marsupials (pouched mammals), lizards and birds. Evidence of these extinct megafauna can be found across Australia as fossilised remains found in deep dark caves, eroding from river and creek banks, in ancient swampy peat bogs and dried-up salt lakes, and even eroding from old beach dunes.
Thylacoleo ("pouch lion") is an extinct carnivorous marsupial that lived in Australia 2 million to 46 thousand years ago. Some of these "marsupial lions" were the largest mammalian predators in Australia of that time, with Thylacoleo carnifex approaching the weight of a small lion.
Procoptodon (Giant Short-faced Kangaroo) was the largest kangaroo to ever live, standing 8 feet tall and possessing a truly bizarre body-shape. Unlike modern day kangaroos Procoptodon had an extremely short face, almost human-like, enormously long and strong forearms, robust and muscular legs and a short thick tail. Procoptodon was not built for excessive hopping, in fact, it would have used its long arms, strong legs and thick tail to balance itself whilst it pulled down large branches from trees, stripping them of their new leaves to feed such a bulky body. Fossils of this giant have been found in the Winton district, preserved as fragmentary teeth and a possible pelvis.