Right femur of Bullockornis, a Dromornithid (Bird)

This right femur is the holotype (the first recognition of a new species) of an enormous Australian megafauna called Dromornis (formerly Bullockornis) planei. Dromornis is a flightless bird that reached a height of 2.5m and weighed in at approximately 300kg, making it much heavier than the largest flightless bird of today, the ostrich. It lived during the Miocene (24 Ma to 5 Ma) (Ma = Millions of years ago) of Australia, with remains only been found in the Northern Territory, near Bullock Creek. Hence, where it got its initial name.
Dromornis belongs to an extinct group of flightless birds, only found in Australia called Dromornithidae, Greek for dromaios (swift-running) and ornis (bird). Despite the strong resemblance to modern day ratites (large flightless-birds such as Emus, Cassowary and Ostrich), these guys are closely related to modern day ducks and geese. This relationship and the bird's intimidating morphology is how it got its nickname the "Demon Duck of Doom".
Interestingly, the diet of these guys are still debated among palaeontologists. Since Dromornis planei had a large beak and skull, palaeontologists suggested that it herbivorous and used for breaking and tearing apart tough plant material. This is supported by the presence of Gastroliths (gizzard stones), which are consumed by the animal to help break down plant material, which is seen in modern day birds. However, other palaeontologists have suggested that Dromornis was more carnivorous, making it similar to the flightless birds from Africa and Europe. More fossil discoveries of Dromornis will help palaeontologists better understand the diet of these giant flightless birds.