Giant kangaroos and enormous crocodiles that lived 40,000 years ago in tropical northern Australia died out because of climate change, a study has found.
As the rest of the world was running from giant man-eating carnivores, Australia was home to a kangaroo that stood 2.5 metres tall and weighed a massive 274kg.
It fought for its place in the food chain alongside a marsupial "lion" and the world's largest wombats.
They were hunted by giant reptiles, from an extinct freshwater croc around seven metres long to huge lizards, including one called Megalania that was six metres long.
The discoveries come out of an area near Mackay called South Walker Creek, which is the youngest megafauna site in northern Australia and once home to at least 16 species of giant animals.
Extreme environmental change and not humans was the most likely cause of their extinction, according to the study published in Nature Communications.
The loss of water flow, intensified drying, increased burning and vegetation change created the conditions to drive the extinction of at least 13 species of super-sized megafauna species, the study led by Queensland Museum found.
"The megafauna at South Walker Creek were uniquely tropical, dominated by huge reptilian carnivores and mega-herbivores that went extinct around 40,000 years ago, well after humans arrived on to mainland Australia," said palaeontologist Scott Hocknull.
"Their extinction is coincident with major climatic and environmental deterioration both locally and regionally, including increased fire, reduction in grasslands and loss of fresh water.
"Together, these sustained changes were simply too much for the largest of Australia's animals to cope with."
The South Walker Creek site was the stomping ground of several new species, which are yet to be formally described.
Never-before-seen megafauna fossils ranging from minute fish scales to colossal limb bones have been discovered at the site.
The fossils were discovered in 2008 by the Barada Barna people during a cultural heritage clearance at the South Walker Creek mine site which is operated by BHP Billiton Mitsui Coal.
State Minister for Science Leeanne Enoch said the research highlights the historical effects of climate change not only on our environment, but native species.
"After more than a decade, Queensland Museum's research into megafauna and fossil collections continues to lead the way in uncovering more about our planet.
"We can learn so much from our prehistoric past through valuable research such as the work performed by scientists like Dr Hocknull," Ms Enoch said.
Australian Associated Press