A long, long time ago, marsupials the size of small trucks, 2-meter-tall "thunder birds" and 5-meter-long venomous lizards roamed Australia. These animals—and more—were Australia's megafauna.

After the extinction of the dinosaurs during the Cretaceous mass extinction (the fifth mass extinction) about 66 million years ago, a new era of “megafauna” emerged. These were large animals ...