Reduction of the number of toes (the fifth shows no traces whatever, not even in Archaeopteryx) begins with the hallux, which is completely or partly absent in many birds; the second toe is absent in Struthio only.
Ostriches, undistinguishable from Struthio, have been found in Samos and in the Sivalik Hills.
All the existing Ratitae (with the exception of the ostriches of Africa and South America, belonging to the genera Struthio and Rhea, and comprising at most but five species) are found in Austrogaea and nowhere else.
Struthio in Africa and Arabia, fossil also in the Sivalik Hills, and Aepyornithidae in Madagascar; Pittzdae, Bucerotinae and Upupinae, of which Upupa itself in India, Madagascar and Africa; Coraciidae; Pycnonotidae or bulbuls; Trogonidae, of which the Asiatic genera are the less specialized in opposition to the Neotropical forms; Vulturidae; Leptoptilus, Anastomus and Ciconia among the storks; Pteroclidae; Treroninae among pigeons.
Between fifty and sixty so-called families of land birds alone are found within its limits, and of them at least nine are peculiar; the typical genera of which are Buphaga, Euryceros, Philepitta, Musophaga, Irrisor, Leptosoma, Colius, Serpentarius, Struthio, Aepyornis.