Pedopenna is a
genusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of small, feathered,
maniraptoraManiraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n
dinosaurDinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the
Daohugou BedsThe Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones...
in
ChinaChinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. It is possibly older than
ArchaeopteryxArchaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, though the age of the
Daohugou BedsThe Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones...
where it was found is debated. A majority of studies suggest that beds probably date from between the late
Middle JurassicThe Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
(168 million years ago) and early
Late JurassicThe Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
Period (164-152 million years ago).
The name
Pedopenna refers to the long pennaceous feathers on the metatarsus;
daohugouensis refers to the locality of Daohugou, where the
holotypeA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
was found.
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 a
paravianParaves is a branch-based clade containing birds and other closely related dinosaurs. The paravians include the Avialae, including Archaeopteryx and modern birds, and the Deinonychosauria, which includes the dromaeosaurids and troodontids....
, the group of
maniraptoraManiraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n dinosaurs that includes both
deinonychosaursThe Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
and
avialansAvialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
(the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.
Description
The feet of
Pedopenna resembled those of the related troodontids and dromaeosaurids (which together form the group
DeinonychosauriaThe Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
), though were overall more primitive. In particular, the second toe of
Pedopenna was not as specialized as in deinonychosaurs. While
Pedopenna 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.
Xu Xing and Zhang Fucheng, who interpreted the
DaohugouThe Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones...
fossil beds where
Pedopenna was found as mid to late
JurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
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 birds originated in
AsiaAsia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.
Feathers
The bird-like characteristics of
Pedopenna 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 long pennaceous
featherFeathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s on the
metatarsusThe metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
(foot). Some deinonychosaurs are also known to have these 'hind wings', but those of
Pedopenna differ from those of animals like
MicroraptorMicroraptor is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China...
.
Pedopenna hind wings were smaller and more rounded in shape. The longest feathers were slightly shorter than the metatarsus, at about 55 mm (2 in) long. Additionally, the feathers of
Pedopenna were symmetrical, unlike the asymmetrical feathers of some deinonychosaurs and birds. Since asymmetrical feathers are typical of animals adapted to flying, it is likely that
Pedopenna 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 a rachis and barbs, and while the exact number of foot feathers is uncertain, they are more numerous than in the hind-wings of
Microraptor.
Pedopenna also shows evidence of shorter feathers overlying the long foot feathers, evidence for the presence of
covertA covert feather on a bird is one of a set of feathers, called coverts, which as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.- Wing-coverts :...
s as seen in modern birds. Since the feathers show fewer aerodynamic adaptations than the similar hind wings of
Microraptor, 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. Xu and Zhang, in their 2005 description of
Pedopenna, 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, with
Pedopenna representing an intermediate stage where the hind wings are being reduced from a functional gliding apparatus to a display or insulatory function.