An egg belonging to an extinct dwarf emu has been discovered on King Island in Australia. It’s the first time a complete egg of the species, which has been extinct for over 100 years, has been found and the researchers are hoping it might help shed some light on this mysterious animal.
Australia is currently home to just one species of emu, Dromaius novaehollandiae, but until relatively recently it was inhabited by a number of other species: the smaller Tasmanian emu and two dwarf emus: the Kangaroo Island emu and the smallest, the King Island emu. Unfortunately, these three smaller species fell into extinction during European colonization in the 18th and 19th centuries. As such, little is known about their behavior or lifestyle, which is why this new discovery is so exciting for researchers.
As reported in the journal Biology Letters, scientists at the Natural History Museum in the UK detail the discovery of the cracked egg laid by the southern Australian dwarf King Island emu. Only a few complete eggs of the Tasmanian emu and just one Kangaroo island emu egg exists. This is the first from the King Island emu.
"A carbon-14 date of approximately 5,500 years was retrieved from the dune where the egg was found, so it is likely that the egg is anything from 200 years to a few thousand years in age," Julian Hume, study author from the Natural History Museum, told IFLScience.
Although the newly found egg is about the same size as those laid by modern mainland emus, the King Island emu was almost half the size and weight of their living cousins today. The emu is the second-largest living bird by height after the ostrich, standing proud at around 1.75 meters (5.7 feet). By comparison, the King Island emu was the size of a large, overweight wild turkey, but still managed to pop out an egg the same size as a regular emu.
The researchers believe the surprisingly large egg is due to the harsh conditions on the island favoring hatchlings that were relatively mature, capable of foraging for food and maintaining body heat almost as soon as they left the egg. Other than size, the egg suggests that dwarf King Island emus had a very similar breeding strategy to the present-day emu.
“Our study has shown that dwarf emus had a comparable breeding strategy to mainland emu that included a large clutch size, synchronized hatching of young to counter predator effects, and thermos-regulation in hatchlings to provide warmth,” the study authors write.
The small stature of the King Island emu is no surprise. A phenomenon called island dwarfism explains how larger organisms often evolve to become smaller when their population's range is limited to a small environment, like islands, rather than the mainland. There are a few ideas why this occurs, but it’s generally considered a response to limited resources. There is also a concept of island gigantism, which explains the opposite effect, where smaller island animals increase dramatically in size compared to their mainland relatives.
Examples of animals that display island dwarfism include the island fox, the pygmy hippopotamus, and the extinct pygmy mammoth. It’s even happened to species of extinct hominin. There is also Homo floresiensis, a tiny archaic human species that inhabited the island of Flores in Indonesia until the arrival of modern humans about 50,000 years ago.