What were the dromornithids (“Demon Ducks of Doom”)?
The Mihirungs or dromornithids belong to a now extinct family of flightless anseriforms (Aves: Dromornithidae). Dromornithids lived in Australia from the Late Oligocene/Early Miocene to the Late Pleistocene (Murray and Vickers-Rich, 2004; Mayr, 2009) and became extinct towards the end of the Pleistocene along with the other members of the Australian megafauna. The dromornithids peaked in body size during the Middle and Late Miocene, when two Central Australian species (Figure) reached extraordinary stature and body weight (Dromornis or Bullockornis planei, Middle Miocene – 15-12 Ma, 2.5 m tall, 300 kg body weight; Dromornis stirtoni, Late Miocene – 9-7 Ma, 2.7 m tall, over 500 kg body weight based on femoral and tibiotarsal circumference; Murray and Vickers-Rich, 2004; Handley et al., 2016). Although the tallest giant moa (female Dinornis robustus) is believed to have reached an estimated height of 3.7 m (Feduccia, 1999) and the largest elephant-bird of Madagascar (Aepyornis maximus) may have reached a similar height (Figure), the bulky goose-like bodies of the Miocene dromornithids mean that they are arguably the heaviest birds ever to have lived (Murray and Vickers-Rich, 2004). Handley et al. (2016) have recently estimated mean body weight of male D. stirtoni based on tibiotarsi as 528 kg (range of 451 to 610 kg) and females as 451 kg (370 to 543 kg). The body weight of Dromornis stirtoni is certainly on a par with that of the largest ratites (Dinornis robustus and Aepyornis maximus; 230 to 300 kg, and up to 542 kg, respectively – Amadon, 1947; Campbell and Marcus, 1992; Deeming and Birchard, 2008) and certainly greater than the Eocene Diatryma/Gastornis gigantea (about 175 to 200 kg; Andors, 1992; Murray and Vickers-Rich, 2004; Deeming and Birchard, 2008) or the largest phororhacids of Tertiary South America (e.g. Brontornis burmeisteri – 350 to 400 kg; Alvarenga and Höfling, 2003; Deeming and Birchard, 2008; Handley et al., 2016). As such, the dromornithids represent an interesting case study in how the brain, sense organs and peripheral nervous system are modified in avian gigantism.
Reconstruction of Dromornis by Nobu Tamura
Apart from their enormous size, the dromornithids exhibited other structural and behavioural differences from their nearest living anseriform relatives, e.g. the magpie geese (Anseranas semipalmata) of Northern Australia or the South American screamers (Anhimidae)(Murray and Megirian, 1998). Central Australian folivore dromornithids inhabited a landscape dominated by fire-sensitive scleromorphic woodlands and fire-adapted sclerophyll vegetation and grasslands (Murray and Vickers-Rich, 2004), in contrast to the wetlands usually inhabited by modern aquatic macro- and filter feeder anseriforms. Dromornithids had powerful and laterally compressed beaks suitable for cracking hard seedpods, in contrast to the dorsoventrally flattened bills of aquatic anseriforms. Dromornithids probably browsed woody plants and fed on (and dispersed) the seeds of conifers such as Podocarpus, Dacrydium and Araucaria, all of which are present in the pollen profiles of Miocene Central Australia, as well as consuming tough cycad and palm seeds (Murray and Vickers-Rich, 2004).
References
Alvarenga, H.M.F., Höfling, E., 2003. Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Pap. Avulsos Zoologia. 43, 55-91.
Amadon, D., 1947. An estimated weight of the largest known bird. Condor 49, 159-164.
Andors, A., 1992. Reappraisal of the Eocene groundbird Diatryma (Aves: Anserimorphae), In: Campbell, K.E. (Ed) Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County. Los Angeles, Science Series, 36, 109-125.
Campbell, K.E. Jr, Marcus, L., 1992. The relationship of hindlimb bone dimensions to body weight in birds, In: Campbell, K.E. Jr (Ed.) Papers in Avian Paleontology Honouring Pierce Brodkorb. Natural History Museum of Los Angeles County, Los Angeles. Science series, 36, 395-411.
Deeming, D.C., Birchard, G.F., 2008. Why were extinct gigantic birds so small? Avian Biol. Res. 1, 187-194.
Feduccia, A., 1999. The Origin and Evolution of Birds. second ed. Yale University Press, New Haven.
Handley, W.D., Chinsamy, A., Yates, A.M., Worthy, T.H., 2016. Sexual dimorphism in the late Miocene Mihirung Dromornis stirtoni (Aves: Dromornithidae) from the Alcoota local fauna of Central Australia. J. Vert. Paleontol. e1180298.
Mayr, G., 2009. Paleogene Fossil Birds. Springer-Verlag. Berlin.
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 & Indianapolis.
Figure Legend
Fig. 1. This figure depicts silhouettes of the dromornithids alongside other large fossil birds and a human. Miocene dromornithids are arguably the largest birds ever to have lived, reaching body weights of 490 kg and heights of 2.7 m in the case of Dromornis stirtoni (Murray and Vickers-Rich, 2004). Their closest living relatives are the magpie geese, so the dromornithids are worthy of their nick-name – “The Demon Ducks of Doom”.
