The Common ostrich (Struthio camelus), or simply ostrich, is a species of flightless bird native to certain large areas of Africa and is the largest living bird species. It is one of two extant species of ostriches, the only living members of the genus Struthio in the ratite order of birds. The other is the Somali ostrich (Struthio molybdophanes), which was recognized as a distinct species. The ostrich is distinctive in its appearance and can run for a long time at a speed of 55 km/h (34 mph) with short bursts up to about 70 km/h (40 mph), the fastest land speed of any bird. It is the largest living species of bird and the largest living dinosaur. It lays the largest eggs of any living bird (the extinct elephant birds of Madagascar and the giant moa of New Zealand laid larger eggs).
The feathers of adult males are mostly black, with white primaries and a white tail. However, the tail of one subspecies is buff. Females and young males are grayish-brown and white. The head and neck of both male and female ostriches are nearly bare, with a thin layer of down. The skin of the female's neck and thighs is pinkish gray, while the male's is gray or pink dependent on the subspecies. The long neck and legs keep the head of these birds up to 2.8 m (9 ft 2 in) above the ground, and their eyes are said to be the largest of any land vertebrate - 50 mm (2 in) in diameter - helping them to see predators at a great distance. The eyes are shaded from sunlight from above. Their skin varies in color depending on the subspecies, with some having light or dark gray skin and others having pinkish or even reddish skin. The strong legs of the common ostrich are unfeathered and show bare skin, with the tarsus (the lowest upright part of the leg) being covered in scales: red in the male, black in the female. The tarsus of the common ostrich is the largest of any living bird, measuring 39 to 53 cm (15+1⁄2 to 21 in) in length. The bird is didactyl, having just two toes on each foot (most birds have four), with the nail on the larger, inner toe resembling a hoof. The outer toe has no nail. The reduced number of toes is an adaptation that appears to aid in running, useful for getting away from predators. New chicks are fawn in color, with dark brown spots. After three months they start to gain their juvenile plumage, which is steadily replaced by adult-like plumage during their second year. At four or five months old, they are already about half the size of an adult bird, and after a year they reach adult height, but not till they are 18 months old will they be fully as heavy as their parents.
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