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A ratite is any of a diverse group of large, flightless birds of
Gondwanian origin, most of them now extinct. All belong to the order Struthioniformes. Unlike other flightless
birds, the ratites have no keel on their breastbone and, lacking a strong anchor for their wing muscles, could not fly even were
they to develop suitable wings.
Most parts of the former Gondwana have ratites, or have had until the fairly
recent past.
- The African Ostrich is the largest living ratite. A large specimen can be 3
metres tall, weigh 135 kilograms, and out-run a horse.
- Aepyornis, the 'elephant bird' of Madagascar was the largest bird ever known. Although shorter than the
tallest moa, a large one could weigh 450 kilograms. There were two species when humans arrived from Borneo and Africa, probably in the 1st Century CE. Both seem to have
survived for a time: the smaller Aepyornis mullerornis probably disappearing first, the giant Aepyornis maximus
may have existed until as late as 1600.
- Of the living species, the Australian Emu is next in size, reaching two metres and about
60 kilograms. 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 extensive moa family of New
Zealand had 11 different species until humans began arriving in numbers at about 1300AD. 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. However, some believe small populations may have survived in isolated regions until more recent times.
- The smallest ratites are the four species of kiwi from New Zealand. Kiwi are chicken-sized, shy, and almost blind. 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 the largest eggs in relation to body-size
of any bird.
- South America has two species of rhea, mid-sized, fast-running birds
of the pampas. The larger American
Rhea grows to about 1.5 metres tall and weighs 20 to 25 kilograms. (South America also has 73 species of the small,
ground-dwelling but not flightless tinamou family, which is distantly related to the
ratite group.)
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.
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