A ratite is any of a diverse group of large, flightless birds of Gondwanan origin, most of them now extinct. Unlike other flightless birds, the ratites have no keel on their sternum —hence the name from the Latin ratis (for raft). Without this to anchor their wing muscles, they could not fly even if they were to develop suitable wings.
Most parts of the former Gondwana have ratites, or did have until the fairly recent past.
Some taxonomical systems consider the various families of ratites to be orders, but the system used here uses the order "Struthioniformes" to refer to all ratites.

Living forms
The African Ostrich is the largest living ratite. A large member of this species can be nearly 3 meters (9.8 ft) tall, weigh as much as 159 kilograms (350 lb), and can outrun a horse.
Of the living species, the Australian
emu is next in height, reaching up to 2 meters (6.6 ft) tall and about 60 kilograms (130 lb). Like the ostrich, it is a fast-running, powerful bird of the open plains and woodlands.
Also native to Australia and the islands to the north are the three species of cassowary. Shorter than an emu, but heavier and solidly built,
cassowaries prefer thickly vegetated tropical forest. They can be very dangerous when surprised or cornered because of their razor sharp talons. In New Guinea cassowary eggs are brought back to villages and the chicks raised for eating as a much-prized delicacy, despite (or perhaps because of) the risk they pose to life and limb.
South America has two species of
rhea, mid-sized, fast-running birds of the Pampas. The larger American rhea grows to about 1.5 meters (4.9 ft) tall and usually weighs 20 to 25 kilograms (44–55 lb). (South America also has 47 species of the small and ground-dwelling but not flightless tinamou family, which is closely related to the ratite group.)
The smallest ratites are the five species of kiwi from New Zealand. (see Kiwis).

Extinct forms
At least 11 species of moa lived in New Zealand before the arrival of humans, ranging from turkey-sized to the Giant Moa Dinornis giganteus with a height of 3.3 metres (11 ft) and weighing about 250 kilograms (550 lb). They went extinct by A.D. 1500 due to hunting by Maori settlers, who arrived by A.D. 1300.
Aepyornis, the "elephant bird" of Madagascar, was the heaviest bird ever known. Although shorter than the tallest moa, a large
Aepyornis could weigh over 450 kilograms (990 lb) and stand up to 3 meters (9.8 ft) tall.

Order Struthioniformes
Family Casuariidae
Genus Casuarius (see Cassowarys)
Southern Cassowary, Casuarius casuarius located in the humid forests of northeastern Australia, New Guinea, and the Aru Islands.
Dwarf Cassowary, Casuarius bennetti located in New Guinea, New Britain, and Yapen Island.
Northern Cassowary, Casuarius unappendiculatus located in the lowlands of Yapen Island and New Guinea.
Genus Dromaius
Emu, Dromaius novaehollandiae located in Australia.

Family Struthionidae
Genus Struthio
Common Ostrich Struthio carmelus,
Somali Ostrich Struthio molybdophanes,