If the humans at that time had gattline guns and AK 47’s maybe they could have made a dent in the wildlife population but only someone entirely stupid would say humans with spears caused their extintion...Its amazing how stupid some people are...
Yes, it's amazing.
By the way: What's a "gattline gun?"
Regards,
If humans considered the last remaining ones a threat (or were hungry as hell) they might be able to finish off the last of a species, and that may have happened — but I agree with ya, Australia, like the Americas, was devoid of a small band of super-hunters that swept the continents clean of megafauna.