Anchiornis

***Anchiornis*** ('near bird') is a genus of small, feathered, troodontid dinosaurs. _Anchiornis huxleyi_ is named in honour of Thomas Henry Huxley, the first to propose a close evolutionary relationship between birds and dinosaurs. A complete individual would be 34 cm (13 in) and weigh only 110 g (3.9 oz), making it the smallest known feathered dinosaur.

_Anchiornis_ fossils have been found in Liaoning, China, dating to the first part of the late Jurassic period, 160 to 161 million years ago.

## Description

_Anchiornis_ is a small, early troodontid dinosaur with a triangular skull like other troodontids. Also, _Anchiornis_ had long legs, usually an indication of a strong runner. However, the extensive leg feathers indicate that long legs may be an vestigial trait, because running animals tend to have reduced, not increased, hair or feathers on their legs. The forelimbs of _Anchiornis_ were also very long, unusual among troodontids (which tend to be short-armed) but similar to dromaeosaurids and early birds, emphasizing its basal ('primitive') position among dinobirds.

### Feathers

While the first specimen of _Anchiornis,_ found in the 2000s, preserved only faint traces of feathers around the preserved portion of the body, the well-preserved second specimen showed nearly complete feather preservation, allowing researchers to identify the structure of the feathers and how they were distributed.

As in other early birds, such as _Microraptor_, _Anchiornis_ had large wings, made up of flight feathers attached to the arm and hand (as in modern birds) as well as flight feathers on the hind legs, forming an arrangement of fore and hind wings. The forewing of _Anchiornis_ was composed of 11 primary feathers and 10 secondary feathers. Unlike _Microraptor_, the primary feathers in _Anchiornis_ were about as long as the secondaries and formed a more rounded wing, with curved but symmetrical central vanes, a small and thin relative size, and rounded tips, all indicating poorer aerodynamic ability compared to its later relative. In _Microraptor_ and _Archaeopteryx_, the longest forewing feathers were closest to the tip of the wing, making the wings appear long, narrow, and pointed. However, in _Anchiornis_, the longest wing feathers anchored near the wrist, making the wing broadest in the middle and tapering near the tip for a more rounded, less flight-adapted profile.

The hind wings of _Anchiornis_ were also shorter than those of _Microraptor_, and were made up of 12–13 flight feathers anchored to the tibia (lower leg) and 10–11 to the metatarsus (upper foot). Also unlike _Microraptor_, the hind wing feathers were longest closer to the body, with the foot feathers being short and directed downward, almost perpendicular to the foot bones. Unlike any other known Mesozoic dinosaur, the feet of _Anchiornis_ (except for the claws) were completely covered in feathers (much shorter than the ones making up the hind wing).

Two types of simpler, downy (plumaceous) feathers covered the rest of the body, as in _Sinornithosaurus_. Long downy feathers covered almost the entire head and neck, torso, upper legs,and the first half of the tail. The rest of the tail bore pennaceous tail feathers (rectrices).

### Colour

In 2010, a team examined numerous points among the feathers of an extremely well-preserved _Anchiornis_ specimen to survey the distribution of melanosomes, the pigment cells that give feathers their colour. By studying the melanosomes and comparing them with those of modern birds, the scientists were able to map the colours and patterning present on _Anchiornis_ when it was alive. Though this technique had been used before, _Anchiornis_ became the first Mesozoic dinosaur for which almost the entire life colouration was known.

Most of the body feathers of _Anchiornis_ were grey and black. The crown of head feathers was mainly reddish with a grey base and front, and the face had rufous speckles among predominantly black head feathers. The fore and hind wing feathers were white with black tips. The coverts (shorter feathers covering the bases of the long wing feathers) were grey, contrasting the mainly white main wings. The larger coverts of the wing were also white with grey or black tips, forming rows of darker dots along mid-wing. These took the form of dark stripes or even rows of dots on the outer wing (primary feather coverts) but a more uneven array of speckles on the inner wing (secondary coverts). The shanks of the legs were grey other than the long hind wing feathers, and the feet and toes were black.

Like many modern birds, _Anchiornis_ exhibited a complex pattern of coloration with different colours in speckled patterns across the body and wings, or "within- and among-feather plumage coloration". In modern birds, such colour patterning is used in communication and display, either to members of the same species (e.g. for mating or territorial threat display) or to threaten and warn off competing or predatory species.

## Palaeobiology

_Anchiornis_ is notable for its long forelimbs, which were 80% of the total length of the hind limbs. This is similar to _Archaeopteryx_; long forelimbs are necessary for flight. _Anchiornis_ also had a more avian wrist than other non-avialan theropods. The authors first thought that _Anchiornis_ could fly or glide. However, further finds showed that the wings of _Anchiornis_, while well-developed, were short when compared to later species like _Microraptor_, with relatively short primary feathers that had rounded, symmetrical tips, unlike the pointed, aerodynamically proportioned feathers of _Microraptor_. So the animal could glide, but probably not fly.

_Anchiornis_ has long hind legs, suggesting a fast-running lifestyle. However, the legs and even feet and toes of _Anchiornis_ were covered in feathers, making it unlikely that _Anchiornis_ was a capable ground runner. A tree-based glider is the probable life-style.

## Related pages

- Origin of birds