A Miocene giant
In the subtropical woodlands of Australia, around eight million years ago, lived the colossal bird Dromornis stirtoni. Standing up to 3 meters tall and weighing as much as 650 kilograms, it is one of the heaviest bird known to have ever existed. Its fossils are found almost exclusively at the Alcoota Fossil Beds in the Northern Territory, a site that represents an ancient waterhole. The dense collection of bones suggests that large groups of animals, including Dromornis, congregated there during periods of drought and died together.
Despite its emu-like posture, Dromornis stirtoni was not a ratite. Its evolutionary lineage places it closer to modern waterfowl, like ducks and geese, earning it nicknames such as "Stirton's thunder bird" and "demon duck". The family to which it belongs, Dromornithidae, are often called mihirungs. The name comes from Aboriginal oral traditions which describe giant emu-like birds. Dromornis had a long neck, powerful legs, and hoof-like toes. Its wings were mere stubs, making it completely flightless.
The diet debate
The diet of Dromornis stirtoni is a subject of scientific debate. The bird's massive skull, comparable in size to that of a horse, held an immense and powerful beak. Some researchers argue this powerful beak was for shearing through tough plant matter, like seed pods and stems. Evidence for herbivory includes the beak's blunt, unhooked tip—unlike that of predatory birds—and its hoof-like feet, which were ill-suited for grasping prey. Amino acid analysis of eggshells from a related, younger species, Genyornis, also points towards a plant-based diet.
However, the sheer size and power of the skull and beak have led other paleontologists to suggest it may have been carnivorous or at least an omnivorous scavenger. The skull's structure indicates it could deliver a very strong bite. Studies of its brain case suggest it had well-developed stereoscopic vision, or depth perception, a feature common in predators. Whether it was a hunter, a scavenger, or a browser of tough vegetation, its diet remains unknown for this Australian giant.