Is the “Genyornis” egg of a mihirung or another extinct bird from the Australian dreamtime?

The iconic Australian Genyornis newtoni (Dromornithidae, Aves) is the sole Pleistocene member of an avian clade now hypothesized to be alternatively in Anseriformes or the sister group of crown Galloanseres. A distinctive type of fossil eggshell commonly found in eroding sand dunes, has been referred to Genyornis newtoni since the 1980s. The 126 by 97 mm Spooner Egg, dated at 54.7 ± 3.1 ka by optical dating of its enclosing sediments, is a...