Ratite

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A ratite is any of a diverse group of large, flightless birds of Gondwanian origin, most of them now extinct. Unlike other flightless birds, the ratites have no keel on their sternum and, lacking a strong anchor for their wing muscles, could not fly even were they to develop suitable wings. The ratite comes from the Greek word for raft, because their breastbone looks like a raft.

Most parts of the former Gondwana have ratites, or have had until the fairly recent past.

Living species

• The African Ostrich is the largest living ratite. A large member of this species can be 3 m tall, weigh 135 kg, and outrun a horse.
• Of the living species, the Australian emu is next in size, reaching up to 2 m tall and about 60 kg. 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 and very solidly built, cassowaries prefer thickly vegetated tropical forest. They can be very dangerous when surprised or cornered. 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.
• The smallest ratites are the six species of kiwi from New Zealand. Kiwi are chicken-sized, shy, and nocturnal. They nest in deep burrows and use a highly developed sense of smell to find small insects and grubs in the soil. Kiwi are notable for laying eggs that are very large in relation to their body size. A Kiwi egg may equal 15 to 20 percent of the body mass of a female kiwi.
• South America has two species of rhea, mid-sized, fast-running birds of the pampas. The larger American rhea grows to about 1.5 m tall and weighs 20 to 25 kg. (South America also has 73 species of the small and ground-dwelling but not flightless tinamou family, which is distantly related to the ratite group.)

Extinct species

• Aepyornis, the "elephant bird" of Madagascar, was the largest bird ever known. Although shorter than the tallest moa, a large aepyornis could weigh 450 kg.
• The extensive moa family of New Zealand had ten to 15 different species until humans began arriving in numbers in the 13th century or earlier. Like the cassowaries, moa were mostly forest-dwellers without any mammalian predators. They are believed to have been brought to extinction by hunting within a few hundred years of human settlement (i.e., before 1500). However, some^{[[Citing sources citation needed]]} believe small populations may have survived in isolated regions until more recent times.

Evolution

The traditional account of ratite evolution has the order emerging in Gondwana in cretaceous times, then evolving in their separate directions as the continents drifted apart. Cladistic evidence for this is strong: ratites share too many features for their current forms to be easily explained by convergent evolution. However, recent analysis of genetic variations between the ratites conflict with this: DNA analysis appears to show that the ratites diverged from one another too recently to share a common Gondwanian ancestor, and suggest that the kiwis are more closely related to the cassowaries than the moa. At present there is no generally accepted explanation. Research continues.

Fictional species

The Chocobo from the Final Fantasy series of video games is a fictional bird that resembles a ratite. Chocobos are a popular form of transportation, and are ridden and pull carts in a manner similar to horses.

Also notable is the mythical Medieval Arabian Roc, which was a large raptorous bird capable of carrying off an elephant. The ostrich is the presumed chick according to several sources.

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