The Dromornithids: An Introduction

Australia has been separated from the rest of the world for the majority of the last 65 million years, with complete separation occurring around 30 million years ago. This has given the various forms of life on the continent plenty of time to evolve into their own unique groups. One particularly fascinating and enigmatic group is the family of extinct, giant flightless birds known as the dromornithids.

Australia today is famous for a group of flightless birds known as the emus; and for a long time the dromornithids were believed to be members of the same group of birds (the ratites). However, in 1998 a study by Murray and Megirian demonstrated that dromornithids are in fact neognathous birds in the Anseriformes. Nonetheless, it remains debatable as to which anseriform group is sister to the dromornithids (Murray & Vickers-Rich 2004, Olson 2005, Agnolin 2007). With a fossil record spanning around 25 million years, dromornithids are known from the late Oligocene through to the late Pleistocene (Field & Boles 1998, Nguyen et al. 2010). An ancient origin for the group is implied by a possible dromornithid foot impression from the early Eocene (approx. 50 million years ago) of Queensland (Vickers-Rich and Molnar 1996). Following an overdue taxonomic revision of the Dromornithidae (Nguyen et al. 2010), the family includes seven accepted species in four genera, with a geographic distribution including every state in Australia. The largest species, Dromornis stirtoni, is estimated to have stood at 3 m tall and weighed up to 500 kg, potentially even larger than the famous elephant bird of Madagascar.

There has been some debate as to whether the dromornithids were herbivorous or carnivorous, with features of the skull hinting at the potential for either way of life. Skull material is not known from every species however, and all members of the group may not have shared the same feeding ecology. Gizzard stones have been found in association with dromornithid remains, suggesting they needed the stones to help process plant material, although carnivores such as crocodiles are also known to possess them.

The dromornithids went extinct in the late Pleistocene and it is still unclear what combination of human hunting, landscape changing or climate change was the ultimate cause of their demise.

I have also had a personal interest in the dromornithids as myself and Dr. Erich Fitzgerald published a short paper on the Dromornithids last year (Park and Fitzgerald, 2012). In it we detailed the oldest known occurrence of the dromornithids in Victoria, a poorly preserved partial tarsometatarsus (one of the bones in the legs of birds). This bone appeared to represent a new species as it could not be referred to any of the known taxa elsewhere in Australia. Previously, the earliest known dromornithids in Victoria were from the late Pleistocene ( approx. 30,000 years ago) Lancefield Swamp locality, so this find pushes their presence in Victoria back in time considerably. It also cautions against deriving evolutionary patterns solely on the basis of fossils from northern Australia.

The dromornithids as a group still retain a lot of mystery and unanswered questions, and are long overdue for a thorough reanalysis. In fact, one of my colleagues plans to do exactly that over the next few years and I for one look forward to seeing what new details he can reveal about these ‘magnificent Mihirungs’.

References

AGNOLIN, F.L., 2007. Brontornis burmeisteri Moreno & Mercerat, un Anseriformes (Aves) gigante del Mioceno medio de
Patagonia, Argentina. Revista del Museo Argentino de Ciencias Naturales 9, 15–25.

FIELD, J.H. & BOLES, W.E., 1998. Genyornis newtoni and Dromaius novaehollandiae at 30,000 b.p. in central northern New South Wales. Alcheringa 22, 177–188.

MURRAY, P.F. & MEGIRIAN, D., 1998. The skull of dromornithid birds: anatomical evidence for their relationship to Anseriformes. Records of the South Australian Museum 31, 51–97.

MURRAY, P.F. & VICKERS-RICH, P., 2004. Magnificent Mihirungs: the Colossal Flightless Birds of the Australian Dreamtime. Indiana University Press, Bloomington, 410 pp.

NGUYEN, J.M.T., BOLES, W.E. & HAND, S.J., 2010. New material of Barawertornis tedfordi, a dromornithid bird from the Oligo- Miocene of Australia, and its phylogenetic implications. Records of the Australian Museum 62, 45–60.

OLSON, S.L., 2005. Review of Magnificent Mihirungs: the Colossal Flightless Birds of the Australian Dreamtime. The Auk 122, 367–371.

Travis Park & Erich M. G. Fitzgerald (2012): A late Miocene–early Pliocene Mihirung bird (Aves: Dromornithidae) from Victoria, southeast Australia, Alcheringa: An Australasian Journal of Palaeontology, 36:3, 419-422.

VICKERS-RICH, P. & MOLNAR, R.E., 1996. The foot of a bird from the Eocene Redbank Plains Formation of Queensland, Australia. Alcheringa 20, 21–29.