THE BIG DEAD BIRDS OF AUSTRALIA
by Matt Fielding, 6th August at 10:44 AM
When we think of fossils, we typically think of dinosaurs and giant mammals. However, Australia was also home to more than 90 known extinct bird species. These include some of the largest and weirdest birds to roam the Earth, such as the massive Mihirungs (which include the demon duck of doom), the egg-burying megapodes and the dwarf emus of the Bass Strait islands.
One of the oldest bird families that we know of are the Mihirungs (also known as the Dromornithids or Thunderbirds) (Murray & Vickers Rich 2004). These birds were huge! One species, Dromornis stirtoni, was possibly the largest bird to walk the Earth standing at 3 metres tall and weighing up to 650 kilograms (Handley et al. 2016). These generously sized birds were once considered to be relatives of the emu and cassowary due to their similar appearance and inability to fly. However, recent work suggests they were actually more closely related to chickens and ducks (Worthy et al. 2017) – they’re basically enormous chooks! While fossils of Mihirungs have been found from as far back as 24 million years ago, some remains have been dated to as recently as 50 thousand years ago (Murray & Vickers Rich 2004).
These recent fossils belong to the species Genyornis newtoni, the last surviving member of the Mihirungs and possibly the most well-known extinct bird from Australia. The Genyornis is included in a group of animals we call the ‘megafauna’, a range of larger-than-expected animals, which include king-sized kangaroos, whopping wombats, enormous echidnas and gigantic goannas. It is suggested that most megafauna, including the Genyornis, went extinct around 45,000 years ago following the arrival of humans in Australia (Johnson et al. 2016). The Genyornis’ fame stems from its contribution to understanding the extinction of Australia’s megafauna. Their eggshells have provided scientists with possible evidence of predation by humans, through burnt fragments of eggshells, and shifts in vegetation types, through nutrient changes in the eggshells of the Genyornis and emu over time (Miller et al. 2016).
However, recent work has suggested that these eggshells may not even belong to the Genyornis and the eggs may actually belong of a group of birds called the megapodes (Grellet-Tinner, Spooner & Worthy 2016). These birds are relatives of the extant malleefowl but were a little larger and included groups unofficially known as the “tall turkeys” and the “nuggety chickens” (Shute, Prideaux & Worthy 2017). Megapodes use heat from the environment to incubate their eggs. Therefore, it is suggested these ancient birds used sand dunes (which is where most eggshells were found) for incubation (Grellet-Tinner, Lindsay & Thompson 2017). Despite egg ownership being unclear, the eggshells still improve our understanding of the past Australian environment and extinctions.
There have been a number of extinctions more recently too, occurring after the landing of Europeans in Australia. Found on King Island, Kangaroo Island and Tasmania, three subspecies of emu went extinct around 200 years ago (Thomson et al. 2018). Their extinction was probably the result of predation by humans and the introduction of non-native species, such as rats and dogs. These extinct emus were quite different from extant emus, with the King and Kangaroo Island emus being dwarf in size, standing at less than half the size of current emus (Heupink, Huynen & Lambert 2011). The dumpy birds likely evolved their short statue due to their isolation from the mainland (the result of sea level rise about 10,000 years ago at the end of the last Ice Age) and adaptation to the low scrubby vegetation found on the islands (Thomson et al. 2018).
So what’s the point in studying these dead birds? They’re certainly cool but it’s a little late to save them and we don’t have the technology for de-extinction just yet. However, these extinct birds can tell us something about the threatened birds we have now and how best to protect them. Understanding the processes that led to the extinctions of these ancient birds improves our understanding of extinction in general and can inform conservation decisions to reduce future loss of our wonderful avian fauna, keeping our bird buddies around to sing for future generations.
Grellet-Tinner, G., Lindsay, S. & Thompson, M.B. (2017) The biomechanical, chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs. Journal of Microscopy, 267, 237-249.
Grellet-Tinner, G., Spooner, N.A. & Worthy, T.H. (2016) Is the “Genyornis” egg of a mihirung or another extinct bird from the Australian dreamtime? Quaternary Science Reviews, 133, 147-164.
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. Journal of Vertebrate Paleontology, 36.
Heupink, T.H., Huynen, L. & Lambert, D.M. (2011) Ancient DNA suggests Dwarf and ‘Giant’ Emu are conspecific. PLOS ONE, 6.
Johnson, C.N., Alroy, J., Beeton, N.J., Bird, M.I., Brook, B.W., Cooper, A., Gillespie, R., Herrando-Pérez, S., Jacobs, Z., Miller, G.H., Prideaux, G.J., Roberts, R.G., Rodríguez-Rey, M., Saltré, F., Turney, C.S.M. & Bradshaw, C.J.A. (2016) What caused extinction of the Pleistocene megafauna of Sahul? Proceedings of the Royal Society B: Biological Sciences, 283, 20152399.
Miller, G., Magee, J., Smith, M., Spooner, N., Baynes, A., Lehman, S., Fogel, M., Johnston, H., Williams, D., Clark, P., Florian, C., Holst, R. & DeVogel, S. (2016) Human predation contributed to the extinction of the Australian megafaunal bird Genyornis newtoni ∼47 ka. Nature Communications, 7.
Murray, P.F. & Vickers Rich, P. (2004) Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime. Indiana University Press, Bloomington, IN.
Shute, E., Prideaux, G.J. & Worthy, T.H. (2017) Taxonomic review of the late Cenozoic megapodes (Galliformes: Megapodiidae) of Australia. Royal Society Open Science, 4.
Thomson, V.A., Mitchell, K.J., Eberhard, R., Dortch, J., Austin, J.J. & Cooper, A. (2018) Genetic diversity and drivers of dwarfism in extinct island emu populations. Biology Letters, 14.
Worthy, T.H., Degrange, F.J., Handley, W.D. & Lee, M.S.Y. (2017) The evolution of giant flightless birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres). Royal Society Open Science, 4.
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