D. australis Dromornis australis fossils are found in
Pliocene deposits of
Australia. They were once considered the smallest species of the genus
Dromornis, around three quarters the size of
Dromornis stirtoni, until the discovery of
Dromornis planei specimens were described in 2016. Mass estimates range from 133 to 208 kg.
Discovery The fossil remains of a large femur were discovered at
Peak Downs in Queensland, at a depth of around in a well shaft. This type of locality was described as an assemblage of boulders and pebbles beneath around thirty feet of alluvial soil; the femur was located over a boulder in the rock beds. The description of
Dromornis australis by Richard Owen, best known for extensive work on the paleontology of Australian mammals, was the first of an extinct Australian avian species. Owen had previously sought evidence of
Dinornis in the palaeontological collections of early Australian excavations. A femur that he had noted in the appendix of
Thomas Mitchell's explorations, found in a cave, did not allow him to confirm an alliance with any previously described species of large flightless birds. The new material had been found while digging a well at Peak Downs and forwarded to Owen via
W. B. Clarke, a geologist employed by the state of New South Wales, with a remark by
Gerard Krefft that placed it with the New Zealand
moas of
Dinornis. Richard Owen found affinities and distinctions in an osteological comparison to species of the extinct
Dinornis and the extant
Dromaius (the emu) and proposed that it represented a new genus. The femur is similar in size to
Ilbandornis woodburnei, another dromornithid species. Other osteological features of the specimens have been compared to
Dromornis stirtoni, the gigantic "Stirton's thunderbird". The specimens were discovered by two of the collaborating authors,
Michael Archer and
Suzanne J. Hand, the head researchers of taxa at the celebrated Riversleigh site and its associated fauna.
Description This species stood around high and weighed up to , a considerable size but smaller than its congeners; the later species
Dromornis stirtoni is determined to have been up to . The fossil specimens used to describe
Dromornis murrayi have been dated to 26 million years ago, being discovered at a 'shelf', a rich layer of fossilised bones, that included leg and cranial remains of the unknown species. Subsequent studies also agreed upon placing this species within the genus
Dromornis. The species stood approximately 2.5 metres (8 ft 2 in) tall. It may have weighed up to 250 kg (550 lb). Features of 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 small horses. The species is presumed to have had greatly reduced wing structures, as with other flightless birds the
sternum was not keeled. The exceptionally large legs of
D. planei enabled it to move its great mass relatively quickly. The disparity in robustness was interpreted by the researchers as evidence of the biology of the species, behaviours such as incubation by the female, pair bonding, parental care and aggression while nesting, and courtship or display habits exhibited by extant waterfowl, the
anseriforms. Comparison of two partial crania with the near complete cranium of
Dromornis planei (
Bullockornis) shows the head of this species to be about 25% larger . Reconstruction of overlapping remains of the rostrum have revealed its form and size, the lower mandible would have been around 0.5 metres. The size and proportions of the head and its bill are comparable to that of mammals such as camels or horses The large bird had "stubby", reduced wings, which ultimately deemed it flightless. However, whilst the bird was flightless, a strong development between the bony crests and tuberosities, where the wings were attached, allowed them to flap their wings. This histological technique has been applied to other large and extinct avian species, including investigation into the paleobiology of the elephant birds Aepyornithidae.
Habitat At present the only recorded fossil discoveries of
Dromornis stirtoni have been from the
Alcoota Fossil Beds. The vegetation type of the region in that period was open woodland favouring its semi-arid climate, within which seasonal rainfall occurs.
D. stirtoni probably existed in an assemblage of fauna that included other dromornithids and browsing marsupials as the apex herbivores. The Alcoota Local Fauna were deposited at the only known upper Miocene fossil beds of Central Australia. The early conceptions of a fearsome bird receives some support from the proposed behaviour of the larger males aggressively defending a preferred range against competitors, other males or herbivores, and predators. Lastly, analysis of the amino acids within the egg shells of
D. stirtoni suggest that the species was herbivorous. Despite this however, there are various indicators that suggest the bird may have been carnivorous or omnivorous (Murray, 2004). The size and muscularity of the birds skull and beak would also suggest that they may not have been herbivores, as no source of vegetable food in their environment would have required such a powerful beak (Vickers-Rich, 1979). In recognition of the varying opinions, it is widely accepted that whilst the large bird may have occasionally scavenged or eaten smaller prey, they were mostly herbivorous. == Extinction ==