Casuariiformes Casuariiformes The Casuariiformes is an order of large flightless bird that has four surviving members: the three species of cassowary, and the only remaining species of emu. They are divided into either a single family, Casuariidae, or more typically two, with the emu splitting off into its own family, Dromaiidae. All four living members are native to Australia-New Guinea, but some possible extinct taxa occurred in other landmasses. The emus form a distinct family, characterized by legs adapted for running. As with all ratites, there are several contested theories concerning their evolution and relationships. As regards this order, it is
Flightless bird oceanic islands. Incongruences between ratite phylogeny and Gondwana geological history indicate the presence of ratites in their current locations is the result of a secondary invasion by flying birds. It remains possible that the most recent common ancestor of ratites was flightless and the tinamou regained the ability to fly However, it is believed that the loss of flight is an easier transition for birds rather than the loss and regain of flight, which has never been documented in avian history. Moreover, tinamou nesting within flightless ratites indicates ancestral ratites were volant and multiple losses of flight occurred independently throughout