古颚总目，又名平胸总目(Ratitae)，是鸟纲今鸟亚纲的一个总目。这个总目底下还可以分成以列五个目：

此外，本总目尚包括两个已经灭绝的目：

虽然本总目的鸟类都有较大的体型，但亦有小体型的品种。但这些鸟类品种都有一个特性，就是翼很短，所以都不能飞翔。胸骨无龙骨突起，雄鸟有交接器。这一总目的鸟几乎都是分布在南半球。

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. 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.