Struthioniformes, also known as ratites, are the order for flightless birds. They are believed to have evolved from a common ancestor. There are 14 different species in this order:
Ostrich (Struthio Camelus)
Emu (Dromaius novaehollandiae)
Greater Rhea (Rhea Americana)
Little Spotted Kiwi (Apteryx Owienii)
Northern Cassowary (Casuarius unappendiculatus)
Southern Cassowary (Casuarius Casuarius)
Great Spotted Kiwi (Apteryx haastu)
Southern Brown Kiwi (Apteryx australis)
North Island Brown Kiwi (Apteryx mantelli)
Okarito Kiwi (Apteryx rowi)
King Island Emu (Dromaius ater)
Dwarf Cassowary (Casuarius bennetti)
Kangaroo Island Emu (Dromaius baudinianus)
Darwin’s Rhea (Rhea pennata)
All of these organisms share a lot of things in common that got them characterized in the same group. For example, they lack a keel on their sternum or breastbone. The keel is the part of the bird where the wing muscles are attached, so therefore, they are flightless. This is the main characteristic that these organisms share with only each other and no other species. They also have no feather vanes, which makes it unnecessary to oil their feathers. Since they don't have the need to oil their feathers, they don't have a preen gland which would contain the preening oil. Struthioniformes also have extremely strong and long legs but they lack an air chamber. This causes the bloodflow to their legs to be a little different than most organisms.