Summary

In past 20 years volume of the data on earliest fossil birds promptly has grown. Simultaneously knowledge of theropods has essentially extended. Among them most sensational became finds of fine plumaged dinosaurs from the Early Cretaceous of China. The wide recognition was received with a hypothesis about an origin of birds from theropod dinosaurs. As a result of the birds have disappeared as a class and have come in structure clade of the Theropod. Feathered Chinese coelurosaurs nobody considers for ancestors of birds. But the development at them feather structures is accepted for the proof of an origin of birds from the Theropod. Between that, except for feathers, in various evolutionary lines of the Theropod such now are open typically "bird's" derived characters like the furcula, uncinate processes, pygostyle, and a two-headed quadrate. Such prevalence of these characters testifies, faster, about parallel or even convergent their origin, instead of about homologies in connection with a common origin, as it cladistics treats.

Modern evoluthionary morphology has proved, that parallelisms are a rather characteristic phenomenon in evolution of various groups of vertebrates. Most clearly parallelisms are shown in evolution of crossopterygians at transition to terrestrial tetrapods and among therapsid reptiles at transition to mammals. Obviously, the evolution of birds was not exception.

In morphology of theropod dinosaurs it is possible to note some features, which categorically do not allow to consider as their ancestors of true fan-tailed birds. They are the paired oviducts, the presence of diaphragm, arctometatarsal pes, the opistocoelous cervical vertebrae, and 1-2-3 digit formula in the forelimb.

At the same time at Archaeopteryx and his Cretaceous relatives Enantiornithes a sufficient number of synapomorphies is marked which specify an origin of this line of evolution from Coelurosaurs. Among these synapomorphies the preservation in the forelimb of the first, second and third digits serves so unconditional proof of relationship of these groups, that does not require presentation of other synapomorphies, though they are available. The same feature completely rejects an opportunity of relationship of fan-tailed birds (Ornithurae) with Archaeopteryx and the Enantiornithes. Last two taxa form the clade of the Sauriurae.

In the forelimb of the Ornithurae second, third and fourth digits are preserved. This character and sufficient number others synapomorphies approve monophyly of the evolutionary lineage of fan-tailed birds. Fan-tailed birds are known now from the very beginning of the Cretaceous period. Late Cretaceous hesperornises and ichthyornises concern to separate deadlock evolution lineages of fan-tailed birds. A little orders of modern birds it is known from the Late Cretaceous. But the data of molecular phylogenetics testify about radiation of fan-tailed birds on modern orders still in the Early Cretaceous or on the border of the Early Cretaceous and Late Cretaceous. Obviously, we while simply have no actual paleontological finds for acknowledgement of such hypothesis.

At a level of today's knowledge it is possible only to tell, that ancestors of the Ornithurae could be any Triassic thecodonts. However, one form is known which stands very close to the basis ornithurine lineage of evolution. It is Late Triassic Protoavis from Texas. There is a long number of synapomorphies, connecting Protoavis with ornithurine birds. First of all, among them it is necessary to name a voluminous braincase, a well developed cerebellum, fusion of third and fourth metacarpals, the deep kidney fossae in pelvis. The truth, Protoavis it is impossible to name as a bird and direct ancestor of ornithurine birds.

Thus, the Ornithurae and Archaeopteryx (together with the Enantiornithes) concern to various evolutionary lineages of feathered creatures, arisen from different groups of reptiles. Besides, the origin them is moved apart in time on tens millions years.

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