Last updated April 11, 2018 at 11:13 am
The size of extinct emus that lived on Australian islands was dependent on the size of their island homes.
“Black Emus of Kangaroo Island”: the large bird is thought to be based on a Kangaroo Island emu, and the small one on the King Island emu. Credit: Charles-Alexandre Lesueur, F. Lambert
Australia’s largest native bird, the emu, is known for its impressive size. Its iconic status has seen it adorn our coat of arms and our 50c coins. However, smaller, emus used to exist on offshore islands up until the 19th century, before going extinct due to British colonisation and subsequent hunting to extinction.
Through studying the DNA and bone measurements from emu fossils, researchers have found that smaller extinct emus are actually sub-populations of the regular modern-day emu. The evolution of these smaller emus that lived on islands, including Kangaroo Island, King Island and Tasmania, was a relatively quick occurrence.
Further to that, it appears that the dwarfism trait happened independently on each island.
The emu, which can grow up to 1.9 metres in height, is the only living representative of its genus. Very little is known about related and extinct forms of non-mainland emus. In 2011, research was published which found that the King Island and modern emu shared a common ancestor.
“Our results have shown that all the island emus are genetically closely related to the much larger mainland emu,” says lead author Dr Vicki Thomson, from the University of Adelaide.
“The smallest, the King Island emus, are typically two-thirds of the size of our mainland emus, with others ranging upwards according to the size of their island.”
Tasmanian Emu. Credit: Artwork by John Gerrard Keulemans
Since the time since geographical isolation was not correlated with the size of island emus, co-author Dr Kieren Mitchell, from the Australian Centre for Ancient DNA, says, “This suggests that island size, and presumably the associated reduced food resources available, may have been important in causing smaller body size in island emus.”
In other words – the size of the emu was related to the size of the island they lived on.
Dr Thomson says, however, that more work needs to be done to confirm the role island size plays in the smaller stature of the extinct island emus.
“We do know that prior to European arrival, Kangaroo Island, King Island and Tasmania had these smaller bodied emus and they would have been isolated from the mainland after sea-levels rose around 10-15,000 years ago.
The authors wrote about the potential of this research for understanding evolutionary biology in the paper, “These recently extinct island emu populations may represent an important natural laboratory for studying rapid and extreme adaptation to changing environments, as large flightless birds provide a unique contrast to island endemic mammals and reptiles.”
The research is published in Biology Letters.
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