Ostrich

Struthionidae is a family of flightless ratite birds which first appeared during the Eocene epoch. It is today represented by the sole living genus Struthio, but also contains several extinct genera. Traditionally the order Struthioniformes contain the world's ratites, but recent genetic analysis has found that the group is not monophletyic, as it paraphyletic in respect to the tinamous.

Species
There are nine known species from this genus, of which eight are extinct. There are five more possible species of which trace fossils have been found. They are:
 * †Struthio coppensi (Early Miocene of Elizabethfeld, Namibia)
 * †Struthio linxiaensis (Liushu Late Miocene of Yangwapuzijifang, China)
 * †Struthio orlovi (Late Miocene of Moldavia)
 * †Struthio karingarabensis (Late Miocene - Early Pliocene of SW and CE Africa) - oospecies(?)
 * †Struthio kakesiensis (Laetolil Early Pliocene of Laetoli, Tanzania) - oospecies
 * †Struthio wimani (Early Pliocene of China and Mongolia)
 * †Struthio daberasensis (Early - Middle Pliocene of Namibia) - oospecies
 * †Struthio brachydactylus (Pliocene of Ukraine)
 * †Struthio chersonensis (Pliocene of SE Europe to WC Asia) - oospecies
 * †Struthio asiaticus, Asian Ostrich (Early Pliocene - Late Pleistocene of Central Asia to China ?and Morocco)
 * †Struthio dmanisensis, Giant Ostrich (Late Pliocene/Early Pleistocene of Dmanisi, Georgia)
 * †Struthio oldawayi (Early Pleistocene of Tanzania) - probably subspecies of S. camelus
 * †Struthio anderssoni - oospecies(?)
 * Struthio camelus, Ostrich extant
 * Struthio molybdophanes, Somali Ostrich

Fossil records and egg shell fragments show that the ancestors of this genus originated about 40-58 million years ago (mya) in the Asiatic steppes as small flightless birds. By about 12 mya they had evolved into the larger size of which we are familiar. By this time they had spread to Mongolia and, later, South Africa.

Evolution
The genus Struthio used to include the Emu, Rhea, and also the Cassowary, until they each were placed in their own genera.