|Skull of Bullockornis planei|
(P. Rich, 1979)
Dromornis planei, formerly placed in a separate genus Bullockornis, is an extinct flightless bird that lived in the Middle Miocene, approximately 15 million years ago. It is known from specimens of the Bullock Creek fauna, fossils found in the Northern Territory of Australia. As large as an ostrich or emu, the species possessed a stocky build. A proposed common name, referring to its discoverer and locality, is Plane's bull bird. The site of its discovery was once semi-arid site containing low vegetation around seasonal wetlands and rivers.
The species was first described by Patricia Vickers-Rich in 1979, assigning it to a new genus Bullockornis. The description's first generic epithet was derived by a partial reference to the Bullock Creek Site and the greek word for bird ornis, and the common name bull bird proposed by the author for genus. The type is a fossilised section of the right femur, with other material, vertebrae and a rib, also referred to the same species. The specific epithet honours the discoverer of the vertebrae fossils, Michael Plane, thus the proposed trivial name of "Plane's Bull Bird". Plane had been the first to investigate the Bullock Creek site, details of which were published in a 1968 paper.
It was one of several species of mihirungs, the dromornithids, that share ancestry with ducks and geese. The nickname "Demon Duck of Doom" is a reference to the large bill and body of the species. Fossil specimens of this species and other mihirungs are common, but the example of a near complete skull discovered in the 1980s was an unusual find. The direct evidence of the beak structure was evaluated in debate over the diet and habits of dromornithids. The bird's generic name is improperly translated as "ox-bird", but was named instead for the type locality for the genus at Bullock Creek, Australia. A taxonomic opinion in a revision of the family placed this species with the genus Dromornis in 2016.
Some paleontologists, including Peter Murray of the Central Australian Museum, believe that Bullockornis was related to geese and ducks. This, in addition to the bird's tremendous size and earlier misclassification as a carnivore, gave rise to its colourful nickname. It may be somewhat inaccurate, however, as other studies have recovered dromornithids as more closely related to Galliformes.
The existence of only this species at the Bullock Creek Site, as with the late Miocene Alcoota local fauna, correlates to the lack of diversity in large ratites, such as the evolution of the ostriches in the presence of a diversity of mammals.
Dromornis planei was a very large flightless bird, similar in height to an ostrich or emu but with a heavier build; the species is however exceeded in size by the largest of these "thunder birds" Dromornis stirtoni. Its bill was curved and deep, the overall size of the head and skull was remarkably large. 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.
A species known from the Bullock Creek fossil fauna in the Northern Territory, the habitat during the time of deposition was a seasonally wet floodplain and river. The flora was probably sedges and shrubs favouring a semi-arid climate. Dromornis planei remains are found with other large contemporaries, such as the diprotodont Neohelos, and the crocodiles Baru that preyed upon them as they came to the water's edge. The area was occupied by herbivores favoring shrubland, horned turtles, marsupial tapirs and diprotodontid species, but the fauna associated with this site were rarely the forest dwelling paleospecies of the period. Other mihirungs also occur in the Bullock Creek fauna, species of Ilbandornis.
The diet of these birds is uncertain, although it is determined that the bill was thin and had little bite force. Gastroliths are found with similar species of other regions, Genyornis, Ilbandornis and near relation Dromornis stirtoni, suggesting a herbivorous diet like the other species it is found alongside, yet suggestions have published that D. planei might have the carnivorous abilities attributed to the terror birds.
- Rich, P.V. 1979. The Dromornithidae, a family of large,extinct ground birds endemic to Australia: Systematic and phylogenetic considerations. Canberra Bureau of Mineral Resources, Geology and Geophysics Bulletin 184, 1–196.
- Murray, Peter; Vickers-Rich, Patricia (2004). Magnificent mihirungs : the colossal flightless birds of the Australian dreamtime. Bloomington: Indiana University Press. pp. 50–51. ISBN 978-0-253-34282-9.
- Nguyen, Jacqueline (7 November 2019). "Dromornis planei (Bullockornis planei)". The Australian Museum. Retrieved 4 May 2021.
- Ellis, R. (2004)
- Worthy, Trevor H.; Handley, Warren D.; Archer, Michael; Hand, Suzanne J. (3 May 2016). "The extinct flightless mihirungs (Aves, Dromornithidae): cranial anatomy, a new species, and assessment of Oligo-Miocene lineage diversity". Journal of Vertebrate Paleontology. 36 (3): e1031345. doi:10.1080/02724634.2015.1031345. ISSN 0272-4634. S2CID 87299428.
- Musser, Anne (22 July 2020). "Stirton's Thunder Bird". The Australian Museum. Retrieved 4 May 2021.
- Peter F. Murray, Patricia Vickers-Rich, Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime
- Ellis, R. (2004) No Turning Back: The Life and Death of Animal Species. New York: Harper Perennial. p. 102. ISBN 0-06-055804-0.
- Rich, P. (1979) "The Dromornithidae, an extinct family of large ground birds endemic to Australia". Bureau of National Resources, Geology and Geophysics Bulletin 184: 1–196.