Palaeognathae , or paleognaths (from Ancient Greek "palaió-" "old" + "gnáthos" "jaw") is one of 2 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 ("Rhea") and 2 of ostrich ("Struthio"). Recent research has indicated that paleognaths are monophyletic but the traditional taxonomic split between flightless and flighted forms is incorrect; tinamous are within the ratite radiation, meaning flightlessness arose independently multiple times via parallel evolution.