Ratite
Ratites | |
---|---|
Members of the four genera of large extant ratites. Clockwise from top left: greater rhea, common ostrich, southern cassowary and emu | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Infraclass: | Palaeognathae |
Groups included | |
| |
Cladistically included but traditionally excluded taxa | |
| |
Synonyms | |
A ratite (
Our understanding of relationships within the paleognath clade has been in flux. Previously, all the flightless members had been assigned to the order
Most parts of the former
Species
Living forms
The African ostrich is the largest living ratite. A large member of this species can be nearly 2.8 metres (9.2 ft) tall, weigh as much as 156 kilograms (344 lb),[18] and can outrun a horse.
Of the living species, the Australian emu is next in height, reaching up to 1.9 metres (6.2 ft) tall and about 50 kilograms (110 lb).[18] Like the ostrich, it is a fast-running, powerful bird of the open plains and woodlands.
Also native to Australia and the islands to the north are the three species of
The smallest ratites are the five species of
Holocene extinct forms
At least nine species of
Classification
There are two taxonomic approaches to ratite classification: one combines the groups as families in the order Struthioniformes, while the other supposes that the lineages evolved mostly independently and thus elevates the families to order rank (Rheiformes, Casuariformes etc.).
Evolution
The longstanding story of ratite evolution was that they share a common flightless ancestor that lived in
Recent analyses of genetic variation between the ratites do not support this simple picture. The ratites may have diverged from one another too recently to share a common Gondwanan ancestor. Also, the Middle Eocene ratites such as Palaeotis and Remiornis from Central Europe may imply that the "out-of-Gondwana" hypothesis is oversimplified.
Molecular phylogenies of the ratites have generally placed ostriches in the basal position and among extant ratites, placed rheas in the second most basal position, with Australo-Pacific ratites splitting up last; they have also shown that both the latter groups are monophyletic.[23][9][10] Early mitochondrial genetic studies that failed to make ostriches basal[12][13] were apparently compromised by the combination of rapid early radiation of the group and long terminal branches.[10] A morphological analysis that created a basal New Zealand clade[24] has not been corroborated by molecular studies. A 2008 study of nuclear genes shows ostriches branching first, followed by rheas and tinamous, then kiwi splitting from emus and cassowaries.[23] In more recent studies, moas and tinamous were shown to be sister groups,[6][8][10] and elephant birds were shown to be most closely related to the New Zealand kiwi.[9] Additional support for the latter relationship was obtained from morphological analysis.[9]
The finding that tinamous nest within this group, originally based on twenty nuclear genes[23] and corroborated by a study using forty novel nuclear loci[25] makes 'ratites' polyphyletic rather than monophyletic, if we exclude the tinamous.[26][11] Since tinamous are weak fliers, this raises interesting questions about the evolution of flightlessness in this group. The branching of the tinamous within the ratite radiation suggests flightlessness evolved independently among ratites at least three times.[23][27][11] More recent evidence suggests this happened at least six times, or once in each major ratite lineage.[9][11] Re-evolution of flight in the tinamous would be an alternative explanation, but such a development is without precedent in avian history, while loss of flight is commonplace.[23][11]
Cladogram based on Mitchell et al. (2014)[9] and Yonezawa et al. (2016)[16] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
By 2014, a mitochondrial DNA phylogeny including fossil members placed ostriches on the basal branch, followed by rheas, then a clade consisting of moas and tinamous, followed by the final two branches: a clade of emus plus cassowaries and one of elephant birds plus kiwis.[9]
Kiwi and tinamous are the only palaeognath lineages not to evolve gigantism, perhaps because of competitive exclusion by giant ratites already present on New Zealand and South America when they arrived or arose.[9] The fact that New Zealand has been the only land mass to recently support two major lineages of flightless ratites may reflect the near total absence of native mammals, which allowed kiwi to occupy a mammal-like nocturnal niche.[29] However, various other landmasses such as South America and Europe have supported multiple lineages of flightless ratites that evolved independently, undermining this competitive exclusion hypothesis.[30]
Most recently, studies on genetic and morphological divergence and fossil distribution show that paleognaths as a whole probably had an origin in the northern hemisphere. Early Cenozoic northern hemisphere paleognaths such as Lithornis, Pseudocrypturus, Paracathartes and Palaeotis appear to be the most basal members of the clade.[16] The various ratite lineages were probably descended from flying ancestors that independently colonised South America and Africa from the north, probably initially in South America. From South America they could have traveled overland to Australia via Antarctica,[31] (by the same route marsupials are thought to have used to reach Australia[32]) and then reached New Zealand and Madagascar via "sweepstakes" dispersals (rare low probability dispersal methods, such as long distance rafting) across the oceans. Gigantism would have evolved subsequent to trans-oceanic dispersals.[16]
Loss of flight
Loss of flight allows birds to eliminate the costs of maintaining various flight-enabling adaptations like high pectoral muscle mass, hollow bones and a light build, et cetera.[33] The basal metabolic rate of flighted species is much higher than that of flightless terrestrial birds.[34] But energetic efficiency can only help explain the loss of flight when the benefits of flying are not critical to survival.
Research on flightless rails indicates the flightless condition evolved in the absence of predators.
Description
Ratites in general have many physical characteristics in common, although many are not shared by the family
Ostriches have the greatest dimorphism, rheas show some dichromatism during the breeding season. Emus, cassowaries, and kiwis show some dimorphism, predominantly in size.
While the ratites share a lot of similarities, they also have major differences. Ostriches have only two toes, with one being much larger than the other. Cassowaries have developed long inner toenails, used defensively. Ostriches and rheas have prominent wings; although they do not use them to fly, they do use them in courtship and predator distraction.[39]
Without exception, ratite chicks are capable of swimming and even diving.[citation needed]
On an
Gallery of living species
-
Ostrich herd (S. camelus massaicus)
-
American rhea
Behavior and ecology
Feeding and diet
Ratite chicks tend to be more
Some extinct ratites might have had odder lifestyles, such as the narrow-billed
Reproduction
Ratites are different from the flying birds in that they needed to adapt or evolve certain features to protect their young. First and foremost is the thickness of the shells of their eggs. Their young are hatched more developed than most and they can run or walk soon thereafter. Also, most ratites have communal nests, where they share the incubating duties with others. Ostriches, and great spotted kiwis, are the only ratites where the female incubates; they share the duties, with the males incubating at night. Cassowaries and emu are polyandrous, with males incubating eggs and rearing chicks with no obvious contribution from females. Ostriches and rheas are polygynous with each male courting several females. Male rheas are responsible for building nests and incubating while ostrich males incubate only at night. Kiwis stand out as the exception with extended monogamous reproductive strategies where either the male alone or both sexes incubate a single egg.[39] Unlike most birds, male ratites have a phallus that is inserted into the female's cloaca during copulation.[43]
Ratites and humans
Ratites and humans have had a long relationship starting with the use of the egg for water containers, jewelry, or other art medium. Male ostrich feathers were popular for hats during the 18th century, which led to hunting and sharp declines in populations. Ostrich farming grew out of this need, and humans harvested feathers, hides, eggs, and meat from the ostrich. Emu farming also became popular for similar reasons and for their emu oil. Rhea feathers are popular for dusters, and eggs and meat are used for chicken and pet feed in South America. Ratite hides are popular for leather products like shoes.[39]
United States regulation
The USDA's
See also
References
- ^ OCLC 427298119.
- ^ a b c d e f Salvadori, Tomasso; Sharpe, R. Bowdler (1895). Catalogue of the Birds in the British Museum. Vol. XXVII. Red Lion Court Fleet Street, London UK: Taylor and Francis. p. 570.
- ^ ITIS (2007). "Struthioniformes". Integrated Taxonomic Information System. Retrieved 13 Jun 2012.
- ^ Brands, Sheila J., ed. (2020). "Systema Naturae 2000 / Taxon: Order Struthioniformes". The Taxonomicon. Zwaag, The Netherlands: Universal Taxonomic Services. Retrieved 14 November 2020.
- ^ Harshman, John; Brown, Joseph W. (13 May 2010). "Palaeognathae". The Tree of Life Web Project.
- ^ PMID 20525622.
- JSTOR 20095143.
- ^ PMID 21596537.
- ^ S2CID 206555952.
- ^ PMID 24825849.
- ^ PMID 30948549.
- ^ PMID 11370967.
- ^ S2CID 4430050.
- ^ .
- ^ S2CID 129449364.)
{{cite journal}}
: CS1 maint: DOI inactive as of January 2024 (link - ^ PMID 27989673.
- .
- ^ ISBN 978-0787657840.
- S2CID 13524994.
- .
- S2CID 22483929.
- S2CID 55323962.
- ^ PMID 18765814.
- .
- PMID 22831877.
- S2CID 6472805.
- ^ Holmes, Bob (2008-06-26). "Bird evolutionary tree given a shake by DNA study". New Scientist. Retrieved 2009-02-04.
- ^ Zimmer, C. (2014-05-22). "A Theory on How Flightless Birds Spread Across the World: They Flew There". The New York Times. Archived from the original on 2014-05-23. Retrieved 2014-05-24.
- PMID 26201466.
- S2CID 132516050.
- ^ Tambussi, C.P.; Noriega, J.I.; Gazdzicki, A.; Tatur, A.; Reguero, M.A.; Vizcaino, S.F. (1994). "Ratite bird from the Paleogene La Meseta Formation, Seymour Island, Antarctica" (PDF). Polish Polar Research. 15 (1–2): 15–20. Retrieved 28 December 2019.
- PMID 20668664.
- S2CID 86511951.
- S2CID 951896.
- PMID 16632395.
- JSTOR 4088088.
- PMID 27071105.
- ^ http://www.freedictionary.com for definitions of the two latin words
- ^ ISBN 978-0-7876-5784-0.
- S2CID 31628714.
- ^ Alvarenga, H. M. F. (1983). "Uma ave ratitae do Paleoceno Brasileiro: bacia calcária de Itaboraí, Estado do Rio de Janeiro, Brasil". Boletim do Museu Nacional (Rio de Janeiro), Geologia. Nova Série. 41: 1–8.
- ISBN 978-3-540-89628-9.[page needed]
- ISBN 978-1-4832-6943-6.
- ^ Womach, Jasper (2005). Agriculture: A Glossary of Terms, Programs, and Laws (PDF) (Report). 2005. Archived from the original (PDF) on 2011-08-10. Retrieved 15 Jul 2009.