The humble Ostrich belongs to the ratite family Struthioniformes, other members are rheas, emus, cassowaries, moa, kiwi and the largest known bird, extinct Elephant Bird.
Ostriches inhabited Gondwana land which split apart in the early Jurassic Period 184 million years ago.
Therefore the humble Ostrich has for over about 184 million odd years evolved from the Dinosaurs. With many examples of what they may have evolved from, depending on the area inhabited.
From records and research it would appear that there were as many as 14 Dinosaur – Ostrich predecessors. The relationship of the African Species is straightforward, however a large number of Asian Species can only be described from fragmentary remains and the relationship between them and the African Species are unclear. In China the ostrich is believed to have become extinct around the last ice age.
The Arabian ostriches in the Middle East were hunted to extinction by the middle of the 20th century. (Source Wikipedia)
Traces of Ostriches were found all over the various continents, from egg shell remains in caves in China, to pictures of Ostriches in the Egyptian tombs and on prehistoric pottery.