The Struthionidae family consists of the flightless birds known as ostriches, including the common ostrich and Somali ostrich, which are the only extant (living) species, along with their extinct relatives. These birds, belonging to the genus Struthio, are part of the larger group of paleognath birds called ratites, which also includes kiwis, emus, and rheas. Ostriches have been around since the Miocene epoch, with the possibility that related fossils date back to the Paleocene, Eocene, and Oligocene periods. Remarkably, the common ostrich is the largest bird species alive today, while the extinct Pachystruthio genus contained some of the heaviest birds to have ever existed. Ostriches were once widespread across Eurasia, and the closest relatives of ostriches are thought to be the Ergilornithidae of Asia. Today, ostriches are native to various open and semi-arid habitats in Africa, but the once-native Arabian ostrich has been hunted to extinction, and attempts to reintroduce ostriches in the wild have not been successful in regions like Israel. There have been cases of feral populations of common ostriches arising from escaped individuals in places like Australia.