Rheiformes is an order that contains the family

Rheidae Rheidae is a family of flightless ratite birds which first appeared in the Paleocene. It is today represented by the sole living genus '' Rhea'', but also contains several extinct genera. Taxonomy Order Rheiformes (Forbes, 1884) Furbringer, 18 ...

(rheas). It is in the infraclass

Paleognathae Palaeognathae (; ) is a infraclass of birds, called paleognaths, within the class Aves of the clade Archosauria. It is one of the two extant infraclasses of birds, the other being Neognathae, both of which form Neornithes. Palaeognathae contain ...

, which contains all

ratite A ratite () is any of a diverse group of flightless, large, long-necked, and long-legged birds of the infraclass Palaeognathae. Kiwi, the exception, are much smaller and shorter-legged and are the only nocturnal extant ratites. The systematics ...

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 of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...

tinamous Tinamous () form an order of birds called Tinamiformes (), comprising a single family called Tinamidae (), divided into two distinct subfamilies, containing 46 species found in Mexico, Central America, and South America. The word "tinamou" comes ...

cassowaries Cassowaries ( tpi, muruk, id, kasuari) are flightless birds of the genus ''Casuarius'' in the order Casuariiformes. They are classified as ratites (flightless birds without a keel (bird anatomy), keel on their sternum bones) and are native t ...

emu The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus ''Dromaius''. The emu' ...

, 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, includ ...

. 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 the world's most comprehensive inventory of the global conservation status of biol ...

, , ''

Rhea americana The greater rhea (''Rhea americana'') is a species of flightless bird native to eastern South America. Other names for the greater rhea include the grey, common, or American rhea; ema (Portuguese); or ñandú (Guaraní and Spanish). One of two sp ...

'' is listed as near threatened, while ''

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

'' is listed as least concern. From 2014 to 2022, the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

recognised '' Rhea tarapacensis'' 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

{{Taxonbar, from=Q1113470 Bird orders Paleocene taxonomic orders Eocene taxonomic orders Oligocene taxonomic orders Miocene taxonomic orders Pliocene taxonomic orders Pleistocene taxonomic orders Holocene taxonomic orders Paleognathae