Origins

Tinamous and ratites: Superorder Paleognathae; Struthioniformes

The ratites are flightless birds with reduced wing bones and a sternum that lacks a keel—the bony plate that serves as an anchor for flight muscles in most birds. Tinamous have a reduced sternal keel.

The ostriches are the largest living birds; some individuals are 2.75 meters tall and 150 kilograms in weight. The ostriches and the other large ratites—rheas, emus, and cassowaries—are long-necked birds with strong, muscular legs adapted for running. All are terrestrial, and the number of toes is reduced to two in the ostriches and to three in the rheas, emus, and cassowaries. The smaller kiwis and most tinamous retain four toes.

Most members of the Paleognathae have distinct feather tracts, but the ostriches have feathers distributed continuously over the body. The plumage is loose in all groups except the tinamous; it is hair-like in the kiwis. An aftershaft is strongly developed in the emus and cassowaries, absent in the ostriches, rheas, and kiwis, and small to well developed in tinamous. Kiwis lay enormous eggs, and tinamous lay glossy, heavily pigmented, often brightly colored eggs. Males incubate the eggs and care for the young in unusual mating systems. The precocial chicks of both ratites and tinamous are clad in down at hatching.

Figure A–1 Ratites and tinamous: (1) Elegant Crested Tinamou (Tinamidae); (2) Southern Cassowary (Casuariidae); (3) Southern Brown Kiwi (Apterygidae); (4) Greater Rhea (Rheidae); (5) Common Ostrich (Struthionidae).

Order/Family	Members	Distribution	Genera	Species
Tinamidae	Tinamous	Neotropics	9	47
Rheidae	Rheas	Neotropics	1	2
Struthionidae	Ostrich	Africa	1	2
Dromaiidae	Emu	Australia	1	1
Casuariidae	Cassowaries	Australia, New Guinea	1	3
Apterygidae	Kiwis	New Zealand	1	5

Relationships

•	Monophyletic
	o	Morphological, biochemical, and chromosomal evidence supports the monophyly of the ratites with caveats.
	o	Tinamous and ratites share a unique configuration of bones between the nasal passages (the paleognathous palate).
•	Relationships among orders:
	o	Sister group to the Neognathae
	o	Some classifications, including IOC World List, treat the ratites in separate orders
•	Relationships among families
	o	Ostriches are treated by some as the basal ratite clade
	o	Tinamous are sister to the Moas
	o	Kiwis may not be surviving moas as once thought.

References

Cooper, A., C. Lalueza-Fox, S. Anderson, A. Rambaut, J. Austin, and R. Ward. 2001. Complete mitochondrial genome sequences of two extinct moas clarify ratite evolution. Nature 409: 704-707.

Härlid, A., and U. Arnason. 1999. Analyses of mitochondrial DNA nest ratite birds within the Neognathae: Supporting a neotenous origin of ratite morphological characters. Proc. Roy. Soc. London 266B: 305-309.

Harrath, O., and A. J. Baker. 2001. Complete mitochondrial genome sequences of extinct birds: Ratite phylogenetics and the vicariance biogeography hypothesis. Proc. Roy. Soc. London 268B: 939-945.

Haddrath, O., and A.J. Baker 2012, Multiple nuclear genes and retroposons support vicariance and dispersal of the palaeognaths, and an Early Cretaceous origin of modern birds, Proc. Royal Soc. B 279, 4617-4625.

Harshman, John and Joseph W. Brown. 2008. Palaeognathae. Version 01 September 2008 (under construction). http://tolweb.org/Palaeognathae/15837/2008.09.01 in The Tree of Life Web Project, http://tolweb.org

Lee, K., J. Feinstein, and J. Cracraft. 1997. Phylogenetic relationships of the ratite birds: Resolving conflicts between molecular and morphological data sets. Pp. 173-211 in Avian Molecular Evolution and Systematics (D. P. Mindell, ed.). New York, Academic Press.

Smith, J.V., E.L. Braun, and R.T. Kimball (2013), Ratite Non-Monophyly: Independent Evidence From 40 Novel Loci, Syst. Biol. 62, 35-49.

van Tuinen, M., C. G. Sibley, S. B. Hedges. 1998. Phylogeny and biogeography of ratite birds inferred from DNA sequences of the mitochondrial ribosomal genes. Mol. Biol. Evol. 15: 370-376.