Pedopenna (from Latin pes - “leg” and penna - “feather, wing”) is a genus of small feathered dinosaur dinosaurs from the Daohugou deposits in China . It cannot be ruled out that it is older than Archeopteryx , although the dating of the Daohugou deposits remains controversial. Some estimates give the Early Cretaceous age ( barrem , about 140.2-145.5 million years ago), but recent radiometric dates indicate the middle of the Jurassic (Upper Callovian , about 164.7-161.2 million years ago). Currently, the dating of the formation is controversial and is determined between 168 and 140 million years ago [1] .
| † Pedopenna |
| Scientific classification |
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| No rank : | Bilateral symmetrical |
| Infraclass : | Archosauromorphs |
| No rank : | Archosauriformes |
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| International scientific name |
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Pedopenna Xu & Zhang, 2005 |
| Single view |
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† Pedopenna daohugouensis
Xu & Zhang, 2005 |
Geochronology164.7—161.2 Ma | million years | Period | Era | Aeon |
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| 2,588 | Even | | | Ka | F
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e
R
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s
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th | | 23.03 | Neogene | | 66.0 | Paleogen | | 145.5 | a piece of chalk | M
e
s
about
s
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th | | 199.6 | Yura | | 251 | Triassic | | 299 | Permian | P
but
l
e
about
s
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th | | 359.2 | Carbon | | 416 | Devonian | | 443.7 | Silur | | 488.3 | Ordovician | | 542 | Cambrian | | 4570 | Precambrian |
◄ Nowadays◄ Cretaceous-Paleogene extinction◄ Triassic extinction◄ Mass Permian Extinction◄ Devonian extinction◄ Ordovician-Silurian extinction◄ Cambrian explosion |
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Pedopenna received its generic name because of the long contour feathers on the metatarsus ; the species name daohugouensis is associated with the name of the location where the holotype was discovered [2] . The possible intravital size of Pedopenna daohugouensis is about 1 m or less in length, but since this species is known only by its hind limbs, the actual length is difficult to determine. Pedopenna is considered as a dinosaur from the Paraves group, which is close to birds, including birds and their closest relatives among the maniraptors , but some researchers classify the animal as a real representative of the Avialae clade, closer to modern birds than deinonychosaurs [3] .
The hind limbs of Pedopenna resemble those of the related troodontids and dromaeosaurids (which together form a group of deinonychosaurs), but are generally more primitive. In particular, the second finger of Pedopenna is not as specialized as that of deinonychosaurs. Although it is slightly shortened and has an enlarged claw , it is not as strongly developed and curved as the crescent claws of its relatives [2] .
The authors of the description, who hold the opinion of the Middle or Upper Jurassic age of the Daohugou deposits, believe that the discovery in the territory of modern China of a primitive relative of birds along with finds of other bird-like dinosaurs may indicate that the ancestors of the birds lived in Asia [2] .
The similarity of Pedopenna with birds is another proof of the proximity of dinosaurs and birds. Besides the fact that the skeleton of the hind limbs is very similar to that of birds, Pedopenna is remarkable for the presence of long contour feathers on the metatarsus. In some deinonychosaurs, “leg wings” were also found, but in Pedopenna they differ from similar structures in the microraptor and the like. The “foot wings” of Pedopenna are smaller and rounded. The longest feathers are slightly shorter than the metatarsus and do not exceed 5.5 cm in length. In addition, Pedopenna feathers were symmetrical, in contrast to the asymmetric feathers of some deinonychosaurs and birds. Since asymmetric feathers are typical of flight-adapted animals, it is very likely that Pedopenna feathers represent an early stage in the evolution of these structures. Despite the fact that many of the prints of the feathers are rather faint, it is clearly seen that each had foci and beards. Although the exact number of leg feathers is not known, there were more of them than on the “hind” wings of the microraptor.
In Pedopenna , shorter feathers are also visible, overlapping the bases of longer leg feathers, which proves the existence of covering feathers, as in modern birds. The fact that the feathers of Pedopenna have fewer aerodynamic adaptations than the feathers of the hind wings of the micro-praptor and, apparently, were less dense, suggests that if they performed an aerodynamic function, it is significantly less successful than that of deinonychosaurs and birds. Xu Xing and Zhang Fucheng in the description of Pedopenna suggested that her feathers could only serve as decoration or even be in the process of reduction. Perhaps the hind wings were found in the ancestors of deinonychosaurs and birds, and were later lost in the line leading to the birds. In this case, Pedopenna can be an intermediate stage when the hind wings are in the process of reduction from a fully functional apparatus for planning to a purely demonstrative or isolating function [2] .