Current evolutionary consensus, based on both molecular and morphological data, suggests that there are two broad subdivisions at the base of living birds (Neornithes), the neognaths (Neognathae) and palaeognathous birds (Palaeognathae). Palaeognaths are characterised by their primitive skull morphology and a secondarily acquired characteristic – flightlessness. The group, as traditionally defined and still recognised by phylogenetic analyses, includes flightless birds (ostrich, rhea, emu, cassowaries and kiwis) and flighted tinamous. Flightless forms are found today on the former landmasses of Gondwana, Africa, South America and Australia, whereas tinamous are restricted to South America. Traditionally, palaeognaths have been subdivided into ratites (all the large flightless groundbirds) and tinamous, although some data sets suggest that this classification might be overly simplistic: Recent molecular studies have concluded that the South American flighted taxa are nested within the traditional ratite grouping. This is interesting because it means that ratite flightlessness has evolved convergently at least four times.

Key Concepts:

  • The evolutionary relationships of living birds (clade Neornithes) remain poorly resolved despite more than a century and a half of investigation.

  • Palaeognaths (Palaeognathae) comprise the large, flightless living ratites (emu, ostrich, cassowary and rhea) and their smaller, flying cousins; tinamou.

  • The fossil record of palaeognaths shows that this group was once made up of medium‐sized flying birds, the oldest currently known from the Paleocene (ca. 60 million years ago (Ma)).

  • Palaeognaths are widely considered by biologists and palaeontologists to be the sister‐group of Neognaths, the clade that includes all other living birds.

Keywords: palaeognath; ratite; ostrich; emu; tinamou; cassowary; rhea; kiwi; flightless; bird; systematics; evolution; flight

Figure 1.

The broad subdivision within living birds into the Palaeognathae and Neognathae.

Figure 2.

Consensus regarding the evolutionary relationships of the Palaeognathae (including the fossil lithornithids).


Further Reading

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How to Cite close
Dyke, Gareth J, and Leonard, Leona M(Nov 2012) Palaeognathae. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0001550.pub3]