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18.12.2015 19:58 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part2 Birds Ch.1 The bigest bird of all time - Vorombe Titan
Автор: valentint Категория: Забавление   
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Последна промяна: 01.07.2019 13:41

Birds (Aves)

Birds, also known as Aves, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide.They rank as the world"s most numerically-successful class of tetrapods, with approximately ten thousand living species, more than half of these being passerines, sometimes known as perching birds. Birds have wings which are more or less developed depending on the species; the only known groups without wings are the extinct moa and elephant birds. Wings, which evolved from forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in flightless birds, including ratites, penguins, and diverse endemic island species of birds. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.
A consensus of paleontologists agrees that Avialae ("bird wings") is a clade of flying dinosaurs containing their only living representatives, the birds. It is usually defined as all theropod dinosaurs more closely related to modern birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used.

An alternate theory to the dinosaurian origin of birds, espoused by a few scientists, notably Larry Martin and Alan Feduccia, states that birds (including maniraptoran "dinosaurs") evolved from early archosaurs like Longisquama.This theory is contested by most other paleontologists and experts in feather development and evolution.

A close relationship between birds and dinosaurs was first proposed in the nineteenth century after the discovery of the primitive bird Archaeopteryx in Germany. Birds and extinct non-avian dinosaurs share many unique skeletal traits.Moreover, fossils of more than thirty species of non-avian dinosaur have been collected with preserved feathers. There are even very small dinosaurs, such as Microraptor and Anchiornis, which have long, vaned, arm and leg feathers forming wings. The Jurassic basal avialan Pedopenna also shows these long foot feathers. Witmer in 2009 concluded that this evidence is sufficient to demonstrate that avian evolution went through a four-winged stage.Fossil evidence also demonstrates that birds and dinosaurs shared features such as hollow, pneumatized bones, gastroliths in the digestive system, nest-building and brooding behaviors.
The consensus view is that birds evolved from dinosaurs, but the most bird-like dinosaurs, including almost all of the feathered dinosaurs and those believed to be most closely related to birds are known mostly from the Cretaceous, by which time birds had already evolved and diversified. If bird-like dinosaurs are the ancestors of birds they should, then, be older than birds, but Archaeopteryx is 155 million years old, while the very bird-like Deinonychus is 35 million years younger. This idea is sometimes summarized as "you can"t be your own grandmother".
The early 1990s saw the discovery of spectacularly preserved bird fossils in several Early Cretaceous geological formations in the northeastern Chinese province of Liaoning.In 1996, Chinese paleontologists described Sinosauropteryx as a new genus of bird from the Yixian Formation,but this animal was quickly recognized as a theropod dinosaur closely related to Compsognathus. Surprisingly, its body was covered by long filamentous structures. These were dubbed "protofeathers" and considered homologous with the more advanced feathers of birds,although some scientists disagree with this assessment.Chinese and North American scientists described Caudipteryx and Protarchaeopteryx soon after. Based on skeletal features, these animals were non-avian dinosaurs, but their remains bore fully formed feathers closely resembling those of birds."Archaeoraptor", described without peer review in a 1999 issue of National Geographic,turned out to be a smuggled forgery,but legitimate remains continue to pour out of the Yixian, both legally and illegally. Feathers or "protofeathers" have been found on a wide variety of theropods in the Yixian,and the discoveries of extremely bird-like dinosaurs,as well as dinosaur-like primitive birds,have almost entirely closed the morphological gap between theropods and birds.
Avialans diversified into a wide variety of forms during the Cretaceous Period.Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves).While the earliest forms, such as Archaeopteryx and Jeholornis, retained the long bony tails of their ancestors,the tails of more advanced avialans were shortened with the advent of the pygostyle bone in the group Pygostylia. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size.Around 95 million years ago, they evolved a better sense of smell.
The first large, diverse lineage of short-tailed avialans to evolve were the enantiornithes, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of ecological niches, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the Mesozoic era.
All modern birds lie within the crown group Aves (alternately Neornithes), which has two subdivisions: the Palaeognathae, which includes the flightless ratites (such as the ostriches) and the weak-flying tinamous, and the extremely diverse Neognathae, containing all other birds.These two subdivisions are often given the rank of superorder, although Livezey and Zusi assigned them "cohort" rank.Depending on the taxonomic viewpoint, the number of known living bird species varies anywhere from 9,800 to 10,050.
The discovery of Vegavis, a late Cretaceous member of the Anatidae, proved that the diversification of modern birds started before the Cenozoic.The affinities of an earlier fossil, the possible galliform Austinornis lentus, dated to about 85 million years ago, are still too controversial to provide a fossil evidence of modern bird diversification.

The bigest birds of all time

The largest bird of all time might have been Vorombe titan weighing up to 860 kg (1,900 lb)
The debate over ‘world’s largest bird’ has been put to rest as British scientists have discovered that a three-metre-tall ostrich-like creature – Vorombe Titan, weighed almost a tonne and is the world’s largest bird.
Elephant birds are members of the extinct family Aepyornithidae, with two genera — Aepyornis and Mullerornis — previously recognized by scientists.
They lived on the island of Madagascar during the Late Quaternary and went extinct somewhere around the 13th to 17th centuries.
The first species of elephant bird to be described, Aepyornis maximus, has often been considered to be the world’s largest bird.
In 1894, British scientist C.W. Andrews described an even larger species, Aepyornis titan, which has usually been dismissed as an unusually large specimen of Aepyornis maximus.
In 2018, James Hansford and Samuel Turvey, two researchers from the Zoological Society of London, found that it was sufficiently distinct from Aepyornis and allocated it in the new genus Vorombe. They also recognized Aepyornis ingens as a synonym of V. titan.The study by Hansford and Turvey is the first taxonomic reassessment of elephant birds in over 50 years.
Vorombe stood 3 m (9.8 ft) tall and weighed 536 to 732 kg (1,182 to 1,614 lb), with a mean of 642.9 kg (1,417 lb). This is greater than the mass estimates of other extinct Quaternary giant birds such as Dinornis, which was between 61 and 275 kg (134 and 606 lb), and Dromornis, between 316.6 and 727.8 kg (698 and 1,605 lb), making it the largest known bird.

The largest femur (MNHN MAD 368) measured by Hansford and Turvey could not be formally assigned to a cluster (group) as it was incomplete. The specimen is thought to belong to Vorombe on the basis of its size. It had a least-shaft circumference of 308 mm (12.1 in), which gives a weight estimate of 860 kg (1,900 lb), making it the largest known bird individual ever recorded. This is comparable to or greater than the mass estimates of the smallest (insular dwarf) sauropod dinosaurs: Europasaurus, at 690 kg (1,520 lb); and Magyarosaurus, between 700 and 1,000 kg (1,500 and 2,200 lb)
.Vorombe titan, Aepyornis maximus and Mullerornis modestus were found across much of Madagascar, and were sympatric in the arid spiny forests in the south, succulent woodlands in the southwest and grassland/subhumid forest mosaic in the Central Highlands. The significant size differences between the three taxa indicates that they exploited different dietary niches and plant interactions. Elephant birds shared the Quaternary ecosystems of Madagascar with hippos, giant lemurs and giant tortoises.




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Автор: valentint
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