Ratite

A ratite is any of a diverse group of flightless and mostly large and long-legged birds of the infraclass Palaeognathae. Kiwi, however, are relatively much smaller and shorter-legged, as well as being the only nocturnal ratites. The systematics of and relationships within the paleognath clade have been in flux. Previously, all the flightless members had been assigned to the order Struthioniformes, which is more recently regarded as containing only the ostrich. The modern bird superorder Palaeognathae consists of ratites and flighted Neotropic tinamous (compare to Neognathae). Unlike other flightless birds, the ratites have no keel on their sternum – hence the name from the Latin ratis (raft, a vessel which has no keel). Without this to anchor their wing muscles, they could not fly even if they were to develop suitable wings. Recent research has indicated that ratites are a paraphyletic group; tinamous fall within them, and are the sister group of the extinct moa. This implies that flightlessness is a trait that evolved independently multiple times in different ratite lineages. Most parts of the former supercontinent Gondwana have ratites, or did have until the fairly recent past. So did Europe in the Paleocene and Eocene, from where the first flightless paleognaths are known. Ostriches were present in Asia as recently as the Holocene, although the genus is thought to have originated in Africa. However, the ostrich order may have evolved in Eurasia. A recent study posits a Laurasian origin for the clade. The African ostrich is the largest living ratite. A large member of this species can be nearly 2.8 metres (9.2 ft) tall, weigh as much as 156 kilograms (344 lb), and can outrun a horse. Of the living species, the Australian emu is next in height, reaching up to 1.9 metres (6.2 ft) tall and about 50 kilograms (110 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. They reach up to 1.7 metres (5.6 ft) tall and weigh as much as 59 kilograms (130 lb) South America has two species of rhea, large fast-running birds of the Pampas. The larger American rhea grows to about 1.4 metres (4.6 ft) tall and usually weighs 15 to 40 kilograms (33–88 lb). The smallest ratites are the five 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. The smallest species of kiwi is the little spotted kiwi, at 0.9 to 1.9 kilograms (2.0–4.2 lb) and 35 to 45 centimetres (14–18 in).