Bullockornis planei, nicknamed the Demon-Duck of Doom or Thunderbird, is an extinct flightless bird that lived in the Middle Miocene, approximately 15 million years ago, in what is now Australia. Bullockornis stood approximately 2.5 metres (8 ft 2 in) tall. It may have weighed up to 250 kg (550 lb). Features of Bullockornis's skull, including a very large beak suited to shearing, have made some researchers consider that the bird may have been carnivorous, but most currently agree that it was a herbivore. The bird's skull is larger than that of many small horses.