| Pedopenna | |
|---|---|
 | |
| Skeletal of all known material | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Paraves |
| Family: | †Anchiornithidae |
| Genus: | †Pedopenna Xu &Zhang, 2005 |
| Species: | †P. daohugouensis |
| Binomial name | |
| †Pedopenna daohugouensis Xu & Zhang, 2005 | |
Pedopenna (/ˌpɛdoʊˈpɛnə/) (meaning "foot feather") is agenus of small, feathered,maniraptorandinosaur from theDaohugou Beds inChina. It is possibly older thanArchaeopteryx, though the age of theDaohugou Beds where it was found is debated. A majority of studies suggest that beds probably date from between the lateMiddle Jurassic (168 million years ago) and earlyLate Jurassic Period (164-152 million years ago).[1]
The namePedopenna refers to the longpennaceous feathers on the metatarsus;daohugouensis refers to the locality of Daohugou, where theholotype was found.[2]Pedopenna daohugouensis probably measured 1 meter (3 ft) or less in length, but since this species is only known from the hind legs, the actual length is difficult to estimate.Pedopenna was originally classified as aparavian, the group ofmaniraptoran dinosaurs that includes bothdeinonychosaurs andavialans (the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.[3] More recently, it has been recovered as ascansoriopterygid.[4] The most recent study recovered it within the familyAnchiornithidae.[5]
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The feet ofPedopenna resembled those of the relatedtroodontids anddromaeosaurids (which together form the groupDeinonychosauria), though were overall more primitive. In particular, the second toe ofPedopenna was not as specialized as in deinonychosaurs. WhilePedopenna did have an enlarged claw and slightly shortened second toe, it was not as highly developed as the strongly curved, sickle-like claws of its relatives.[2]
Xu Xing andZhang Fucheng, who interpreted theDaohugou fossil beds wherePedopenna was found as mid to lateJurassic in age, used the presence of such a primitive member of the avian lineage, in combination with many primitive members of closely related lineages there, to support the idea that Avialae originated inAsia.[2]
The bird-like characteristics ofPedopenna are further evidence of the dinosaur-bird evolutionary relationship. Apart from having a very bird-like skeletal structure in its legs,Pedopenna was remarkable due to the presence of longpennaceous feathers on themetatarsus (foot). Somedeinonychosaurs are also known to have these 'hind wings', but those ofPedopenna differ from those of deinonychosaurs likeMicroraptor.Pedopenna hind wings were smaller and more rounded in shape. The longestfeathers were slightly shorter than the metatarsus, at about 55 mm (2 in) long. Additionally, the feathers ofPedopenna were symmetrical, unlike the asymmetrical feathers of some deinonychosaurs and birds. Since asymmetrical feathers are typical of animals adapted to flying, it is likely thatPedopenna represents an early stage in the development of these structures. While many of the feather impressions in the fossil are weak, it is clear that each possessed arachis andbarbs, and while the exact number of foot feathers is uncertain, they are more numerous than in the hind-wings ofMicroraptor.Pedopenna also shows evidence of shorter feathers overlying the long foot feathers, evidence for the presence ofcoverts as seen in modern birds. Since the feathers show fewer aerodynamic adaptations than the similar hind wings ofMicroraptor, and appear to be less stiff, suggests that if they did have some kind of aerodynamic function, it was much weaker than in deinonychosaurs and birds.[citation needed]
Xu and Zhang, in their 2005 description ofPedopenna, suggested that the feathers could be ornamental, or even vestigial. It is possible that a hind wing was present in the ancestors of deinonychosaurs and birds, and later lost in the bird lineage, withPedopenna representing an intermediate stage where the hind wings are being reduced from a functional gliding apparatus to a display or insulatory function.[2] This theory may be corroborated by the discovery ofSerikornis in 2017, an anchiornithid with soft, symmetrical feathers and filaments on parts of the body that were similar toPedopenna's.
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