Paleontologists Find First Complete Egg of Extinct King Island Dwarf Emu
While the egg was about the same size as those laid by mainland emus, a duo of avian paleontologists from Australia and the United Kingdom used it to calculate the King Island emu (Dromaius novaehollandiae minor) was about 44% smaller than the living species.
Islands off the southern coast of Australia once harbored three subspecies of the mainland emu (Dromaius novaehollandiae): the smaller Tasmanian emu (D. n. diemenensis) and two dwarf emus — the King Island emu and the Kangaroo Island emu (D. n. baudinianus).
Due to limited distribution and small population size, they all became extinct rapidly after discovery by human settlers due to over-hunting.
They disappeared from King Island by 1805, with a captive pair surviving in Paris until 1822; from Kangaroo Island by 1830; and from Tasmania by 1850.
Little was recorded about their life histories and only a few historical museum specimens exist, including a number of complete eggs from Tasmania and one egg from Kangaroo Island.
In new research, avian paleontologists Julian Hume and Christian Robertson performed a detailed analysis of eggs of dwarf emus.
They examined 38 intact eggs of the mainland emu, 6 eggs of the Tasmanian subspecies, and the first known complete egg of the King Island subspecies.
The unique egg was found at Yellow Rock River on King Island in association with a skeleton of the King Island emu, other individual emu bones and eggshell.
The results show that despite the reduction in size of all island emus, especially the King Island emu that averaged 44% smaller than mainland birds, the egg remained similar sized in linear measurements, but less in volume and mass, and seemingly had a slightly thinner eggshell.
“This was a response to reduced resources and harsh environmental conditions on their respective island homes, where evolution likely favored larger emu chicks that were relatively mature and mobile at hatching, and could immediately forage for food and maintain body heat to combat cold,” the researchers said.
“This scenario provides an interesting evolutionary response to insular environmental conditions in dwarf emu breeding strategy, but due to their complete and rapid extinction, the true extent of these adaptations is now impossible to determine.”
A paper on the findings was published in the journal Biology Letters.
Julian P. Hume & Christian Robertson. 2021. Eggs of extinct dwarf island emus retained large size. Biol. Lett 17 (5): 20210012; doi: 10.1098/rsbl.2021.0012