Rheiformes is an order that contains the family Rheidae (rheas). It is in the infraclass Paleognathae, which contains all

ratite Ratites () are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal ...

s. Extant members are found in South America. While the IOC World Bird List and the Clements Checklist categorise Rheiformes as its own order, the BirdLife Data Zone includes rheas, along with

ostriches Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...

tinamous Tinamous () are members of the order Tinamiformes (), and family Tinamidae (), divided into two distinct subfamily, subfamilies, containing 46 species found in Mexico, Central America, and South America. The word "tinamou" comes from the Carib la ...

cassowaries Cassowaries (; Biak language, Biak: ''man suar'' ; ; Papuan_languages, Papuan: ''kasu weri'' ) are flightless birds of the genus ''Casuarius'', in the order Casuariiformes. They are classified as ratites, flightless birds without a keel (bird a ...

emu The emu (; ''Dromaius novaehollandiae'') is a species of flightless bird endemism, endemic to Australia, where it is the Tallest extant birds, tallest native bird. It is the only extant taxon, extant member of the genus ''Dromaius'' and the ...

, and kiwis, in the order

Struthioniformes Struthioniformes is an order of birds with only a single extant family, Struthionidae, containing the ostriches. Several other extinct families are known, spanning across the Northern Hemisphere, from the Early Eocene to the early Pliocene, incl ...

. Of the two extant species of rheas recognized by the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

, , '' Rhea americana'' is listed as near threatened, while '' Rhea pennata'' is listed as least concern. From 2014 to 2022, the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

recognised ''

Rhea tarapacensis Darwin's rhea or the lesser rhea (''Rhea pennata'') is a large flightless bird, the smaller of the two Extant taxon, extant species of rhea (bird), rheas. It is found in the Altiplano and Patagonia in South America. Description The lesser rh ...

'' as a separate species, and listed it as near threatened in its last assessment in 2020; in 2022, it was again recognised as a subspecies of ''R. pennata''.

References

{{Authority control Bird orders Paleocene taxonomic orders Eocene taxonomic orders Oligocene taxonomic orders Miocene taxonomic orders Pliocene taxonomic orders Pleistocene taxonomic orders Holocene taxonomic orders Notopalaeognathae