Over millions of years, Australia's unique biodiversity has produced a large cabinet of curiosities. Among the weirder members of this group were the Mihirungs, members of the now extinct family Dromornithidae. Made up of several genera of flightless birds-among them one of the very largest birds that ever lived-the dromornithids ranged from 60-kilogram beasts, 1.5 meters tall, to giants twice that size, weighing nearly half a metric ton. They were, by orders of magnitude, the largest "geese" that ever lived. One species was comparable in size to the Ele-phantbird of Madagascar and the...