The Origins of the Thunderbird

Paleontologist Trevor Worthy says the Thunderbird's vegetarian diet might partly explain their size. They got up to a whopping great 1,300 pounds, which has been a lot 10 times a human. After 8 million years ago, Australia became more arid and that's when the giant Thunderbird disappears. We can find growth cycles in the bones that suggest they took about 15 years to reach an adult body size. And this is really a long time compared to modern birds that grow up very quickly.