Ratites
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Obsolete systematic group The taxon dealt with here is not part of the systematics presented in the German-language Wikipedia. More information can be found in the article text. |
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Cassowary ( Casuarius casuarius ) |
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The ratites are a group of flightless birds belonging to the ancient jawbirds . They represent the largest birds on earth today. Almost all species are ostrich-like, large and heavy; the kiwifruit alone are only a little bigger than a chicken. Although ratites have feathers and mostly rudimentary wings , they cannot fly due to their weight and poorly developed chest muscles.
According to more recent molecular genetic studies, ratites are paraphyletic without the cockles , so the cocktails are in a common group with the taxa referred to here as ratites .
distribution
Ratites live (or still lived in historical times) in the following regions of the world:
- in Africa the ostrich and in Madagascar the extinct elephant birds
- in Australia the emu , in New Guinea and Northern Australia the cassowaries
- in New Zealand the kiwifruit and the extinct moas
- in South America the rhea
features
The ratites lack the sternum crest . Because of this feature, they are also called flat-breasted birds or ratites . The latter name is derived from the Latin ratis "raft". Cockroaches, however, have a sternum crest.
The feathers of ratites and cockroaches have two shafts, a main shaft and an aft shaft, both of which are of equal length. The bow and hook rays are usually not effective enough to give the feather branches ( barbae ) the strength that characterizes other bird feathers. This makes the plumage appear loose and hanging.
All ratites are unable to fly. Ostriches and rheas still have large wings, which mainly fulfill ritual functions; in the other groups the wings are greatly reduced, in the moas they are even completely absent. While airworthy birds are not allowed to exceed a certain size in order to be able to rise further into the air, ratites are not restricted in size and weight. With the increase in size, a flightless bird gains better protection from predators. The extension of the legs allows a quick escape, the long neck allows it to feed from trees and high bushes. The body can store larger amounts of food because it is no longer necessary to maintain a low body weight for the purpose of flight. The digestive therefore goes more slowly and is more effective.
In contrast to other groups of birds, in which the males either have no or only a simply built penis , the copulatory organs are very well developed in ratites .
evolution
Many questions related to ratites remain unanswered. In particular, it was discussed whether this group was particularly "primitive" because of their inability to fly. The ratites' cerebellum hardly differs from that of birds capable of flying. The reduced wing skeleton also follows the same basic pattern as that of the flying species. However, ratites lack the air sacs in their long bones, which are typical for flight birds. Most experts now assume that ratites are descended from birds capable of flying.
Ratites go back to the Paleocene in the form of the Lithornithiformes , an order of cockroach-like birds. Rheas have been known since the Eocene , cassowaries since the Oligocene , ostriches, moas and cockroaches since the Miocene , and elephant birds and kiwis since the Pleistocene .
Systematics
The ratites include the following families :
- Ostriches (Struthionidae)
- Rheas (Rheidae)
- Cassowaries (Casuariidae)
- Emus (Dromaiidae)
- Kiwifruit (Apterygidae)
- † Moas (Dinornithidae)
- † elephant birds (Aepyornithidae)
- † Palaeotididae
There are now numerous contradicting systematics of ratites in which the families are grouped in different ways. In the following, the results of three relatively recent studies are presented in the form of cladograms . In all three cases, the cockles (Tinamiformes) are located within the ratites, which makes them paraphyletic , and the ostriches (Struthionidae) are a sister group of a clade formed by all other ratites and the cockles . Richard Prum and colleagues assume that they split off from the line leading to the other taxa 50 million years ago, while Haddrath and Baker assume that this occurred 100 million years ago in the Cretaceous period .
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Cladogram according to Mitchell et al .:
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Since ratites therefore do not form a monophylum , their scientific name, Struthioniformes, is only used today for ostriches, while the rheas are placed in the order Rheiformes and the kiwis in the Apterygiformes, while emus (Dromaiidae) and cassowaries (Casuariidae) the Forming order Casuariiformes.
Similar groups of birds
The ratites do not include the extinct Dromornithidae of Australia and Brontornithidae of South America. Quite similar in shape to ratites, according to more recent findings they are related to geese birds . The similarly extinct Gastornithidae from Laurasia and Sylviornithidae from New Caledonia , which are related to the aforementioned, and the unrelated Phorusrhacidae from South America, had a habitus similar to ratites.
literature
- Stephen J. Davies: Ratites and Tinamous . Oxford University Press, 2002 ISBN 0-19-854996-2 .
Individual evidence
- ↑ False Penis , in: Die Zeit No. 19 of May 9, 1999.
- ↑ a b Richard O. Prum et al. A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature, October 7, 2015; doi: 10.1038 / nature15697
- ↑ a b Oliver Haddrath, Allan J. Baker. 2012. Multiple nuclear genes and retroposons support vicariance and dispersal of the palaeognaths, and an Early Cretaceous origin of modern birds. Proceedings of the Royal Society . Series B 279: 4617-4625. DOI: 10.1098 / rspb.2012.1630
- ↑ Mitchell, Llamas, Soubrier, Rawlence, Worthy, Wood, Lee & Cooper. 2014. Ancient DNA reveals Elephant Birds and Kiwi are Sister Taxa and Clarifies Ratite Bird Evolution. Science . 344: 898-900. DOI: 10.1126 / science.1251981
- ^ IOC World Bird List: Ratites: tinamous to kiwis
