Palaeognathae, or paleognaths, is one of the two living clades of birds – the other being Neognathae. Together, these two clades form the clade Neornithes. Palaeognathae contains five extant branches of flightless lineages (plus two extinct clades), termed ratites, and one flying lineage, the Neotropic tinamous. There are 47 species of tinamous, 5 of kiwis (Apteryx), 3 of cassowaries (Casuarius), 1 of emus (Dromaius) (another became extinct in historic times), 2 of rheas and 2 of ostrich.