Common ostrich
Common ostriches usually weigh from , or as much as two adult humans. The Masai ostriches of East Africa ("S. c. massaicus") averaged in males and in females, while the nominate subspecies, the North African ostrich ("S. c. camelus"), was found to average in unsexed adults. Exceptional male ostriches (in the nominate subspecies) can weigh up to . At sexual maturity (two to four years), male common ostriches can be from in height, while female common ostriches range from tall. New chicks are fawn in colour, with dark brown spots. During the first year of life, chicks grow at about per month. At one year of age, common ostriches weigh approximately . Their lifespan is up to 40–45 years.
Ostrich
The earliest fossils of ostrich-like birds are Paleocene taxa from Europe. "Palaeotis" and "Remiornis" from the Middle Eocene and unspecified ratite remains are known from the Eocene and Oligocene of Europe and Africa. These may have been early relatives of the ostriches but their status is questionable, and they may in fact represent multiple lineages of flightless paleognaths. The African "Eremopezus", when not considered a basal secretarybird or shoebill, is sometimes considered an ostrich relative or an "aepyornithid-like" taxon. Apart from these enigmatic birds, the fossil record of the ostriches continues with several species of the modern genus "Struthio" which are known from the Early Miocene onwards. Several of these fossil forms are ichnotaxa (that is, classified according to the organism's footprints or other trace rather than its body) and their association with those described from distinctive bones is contentious and in need of revision pending more good material. While the relationship of the African fossil species is comparatively straightforward, a large number of Asian species of ostrich have been described from fragmentary remains, and their interrelationships and how they relate to the African ostriches are confusing. In China, ostriches are known to have become extinct only around or even after the end of the last ice age; images of ostriches have been found there on prehistoric pottery and petroglyphs.