Rheiformes
Order of birds
From Wikipedia, the free encyclopedia
Rheiformes is an order that contains the family Rheidae (rheas).[3] It is in the infraclass Paleognathae, which contains all ratites. Extant members are found in South America. While the IOC World Bird List and the Clements Checklist categorise Rheiformes as its own order,[3][4] the BirdLife Data Zone includes rheas, along with ostriches, tinamous, cassowaries, emu, and kiwis, in the order Struthioniformes.[5] Of the two extant species of rheas recognized by the IUCN Red List, as of 2022[update], Rhea americana is listed as near threatened,[6] while Rhea pennata is listed as least concern.[7] From 2014 to 2022, the IUCN recognised Rhea tarapacensis as a separate species, and listed it as near threatened in its last assessment in 2020;[8] in 2022, it was again recognised as a subspecies of R. pennata.[7]: Taxonomy
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| Rheiformes | |
|---|---|
| |
| Greater rhea (Rhea americana) | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Infraclass: | Palaeognathae |
| Clade: | Notopalaeognathae |
| Order: | Rheiformes Forbes, 1884 |
| Subgroups[2] | |
| |
Today, the order is represented by the sole living genus Rhea, though it contains 4-5 genera in total depending on the affiliation of the extinct genus Diogenornis. The taxonomy of the order is as follows:[9]
Order Rheiformes (Forbes, 1884) Furbringer, 1888 [Rheimorphae Bonaparte, 1849; Rheae Forbes 1884][10][11][12][13][14]
- Family Rheidae (Bonaparte 1849) Bonaparte, 1853
- ? Genus †Diogenornis de Alvarenga 1983 (Late Paleocene) – possibly a member of Casuariiformes instead.[2][9]
- Genus †Heterorhea Rovereto 1914 (Pliocene)
- Genus †Hinasuri Tambussi 1995 (Miocene-Pliocene)
- Genus †Opisthodactylus Ameghino 1895 (Miocene)
- Genus Rhea Brisson 1760 (Miocene-Recent)
Extant species summary
The IOC World Bird List (version 15.1) recognizes 2 species of Rheiformes.[15] As of January 2026, IUCN/BirdLife International have assessed both species within the order, but neither have a global population estimate.
| Common name | Binomial name | Population | Status | Trend | Notes | Image |
|---|---|---|---|---|---|---|
| Greater rhea | Rhea americana | unknown[6] | NT[6] |  [6] |
 | |
| Lesser rhea
(Darwin's rhea) |
Rhea pennata | unknown[7] | LC[7] | [7] |
The populations of subspecies R. p. tarapacensis and R. p. garleppi are estimated to total 1,000-2,499 mature individuals. The population of the nominate subspecies, R. p. pennata, is expected to be much larger but has not been quantified.[7] | .JPG) |