Below is Rachel’s follow-up guest post answer to last Friday’s challenging mystery object. Many thanks Rachel – it was a good one!
Well, I seem to have led you all a merry dance this week! Admittedly, it was sneaky to not include a scale bar or provide you with another view of the skull, but if I’d put the top view in I think it would have been game over in about five minutes…
As cromercrox so rightly pointed out, it is a bird skull. Many of the guesses tended towards water birds, with suggestions including goose, gull, and rail.
Manabu Sakamoto was the first to suggest a ratite, and later tentatively guessed ostrich, while Matt King went for a rhea.
Paolo and I actually thought it might be a rhea to start with, but after comparing it to an identified rhea skull in the collections and the ratite images on Skullsite, we decided that it is in fact an Emu, Dromaius novaehollandiae (Latham, 1790).
(Photo taken by me at the Healesville Sanctuary near Melbourne, Australia)
The emu is a member of the group of (mostly) large, flightless birds known as ratites, along with the cassowary, ostrich, rhea, kiwi and extinct moa. It is an Australian ground-dwelling bird with tiny vestigial wings and very powerful running legs.
It has no flight feathers at all, and instead is covered in downy feathers with a double rachis emerging from a single shaft. This heavy coat insulates the bird very effectively, preventing heat reaching the skin and allowing them to be active in the hot Australian sun.
There are some wonderful aboriginal folk tales about how the Emu became flightless. Here is just one version of the story.
In evolutionary terms, flightlessness appears to have evolved several times in the ratites, counter to the long-held theory that they developed from a single flightless common ancestor and were then dispersed as the supercontinent Gondwana split apart.
It seems that flightlessness evolved separately at least three times, after the split-up of Gondwana, in the African, South American and Australian ratites. It has been suggested that ratites were able to develop flightlessness due to a reduction in predation pressures after the extinction of the dinosaurs 65 million years ago, which made it safer to forage on the ground.