The researchers argue that newly arrived humans hunted the animals to extinction, with the reduced grazing pressure causing an increase in the fuel load and fire intensity. This prompted the disappearance of rainforests and the expansion of eucalypt-dominated forests.
Still, several scientists challenged the findings and the debate, which is more than a century old, appears likely to continue.
Some disputed whether the presence of the ancient spores reflected the abundance of the giant animals.
"The only evidence we have from Queensland for megafauna indicates that they were gone before humans arrived," said Judith Field, from the University of NSW.
"The results of this paper are interesting. The interpretations drawn from it are unsubstantiated and can be explained by other mechanisms."