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 requirement for flightlessness. The kiwi does not exhibit gigantism, along with tinamous, even though they coexisted with the moa and rhea that both exhibit gigantism. This could be the result of different ancestral flighted birds arrival or because of competitive exclusion. The first flightless bird to arrive in each environment utilized the large flightless herbivore or omnivore niche, forcing the later arrivals to remain smaller. In environments where flightless birds are not present, it is possible that after the K/T Boundary there were no niches for them to fill. They were pushed out by other herbivorous mammals. New Zealand had