The Latin name Anchiornis derives from a Greek word meaning "near bird", and huxleyi refers to Thomas Henry Huxley, a contemporary of Charles Darwin.

Anchiornis fossils have been found only in the Tiaojishan Formation of Liaoning, China, in rocks dated to the Late Jurassic, about 160 million years ago.

It is known from hundreds of specimens, and given the exquisite preservation of some of these fossils, it became the first Mesozoic dinosaur species for which almost the entire life appearance could be determined, and an important source of information on the early evolution of birds.

The name Anchiornis huxleyi was chosen by Xu and colleagues in honor of Thomas Henry Huxley, an early proponent of biological evolution, and one of the first to propose a close evolutionary relationship between birds and dinosaurs.

[5] A second specimen came to light around the same time, and was given to a team of scientists from Shenyang Normal University by a local farmer when they were excavating at the Yaolugou dig site.

Two scientists visited the site in order to compare the new fossil with the rock types found there, and were able to confirm that the new specimen probably did come from the area the farmer described.

It is larger and much more complete than the first specimen, and preserved long wing feathers on the hands, arms, legs and feet, showing that it was a four-winged dinosaur similar to Microraptor.

[7] The Shandong Tianyu Museum of Nature in Pingyi County, China, for example, was reported to hold 255 specimens of Anchiornis in its collections in 2010.

While this specimen has yet to be fully described, it was photographed for a 2011 article in National Geographic and was used in a study of Anchiornis covert feathers and wing anatomy the following year.

[9] Anchiornis huxleyi was a small, bipedal theropod dinosaur with a triangular skull bearing several details in common with dromaeosaurids, troodontids, and primitive avialans.

Additional studies indicate that Anchiornis had body plumage that consisted of short quills with long and independent, flexible barbs.

This also gave each feather an overall forked shape and resulted in the theropod possessing a softer textured and "shaggier" appearing plumage than is seen in modern birds.

[11][12] The holotype, belonging to a subadult or young adult individual, measured 34 centimetres (1.12 ft) long and weighed 110 grams (3.9 oz).

The wing feathers had curved but symmetrical central quills, with small and thin relative size, and rounded tips, all indicating poor aerodynamic ability.

[3] Like other maniraptorans, Anchiornis had a propatagium, a flap of skin connecting the wrist to the shoulder and rounding out the front edge of the wing.

[6] These bound fingers were incorporated into a post-patagium, or flap of skin and other tissues that helped support the bases of the main wing feathers.

[3] The hindwings of Anchiornis were also shorter than those of Microraptor, and were made up of 12 to 13 flight feathers anchored to the tibia (lower leg) and 10 to 11 to the tarsus (upper foot).

[3] Unlike many other paravians, the feet of Anchiornis (except for the claws) were completely covered in feathers, though these were much shorter than the ones making up the hindwing.

By studying the types of melanosomes and comparing them with those of modern birds, the scientists were able to map the specific colors and patterning present on this Anchiornis when it was alive.

In 2015, Sankar Chatterjee placed Anchiornis along with Microraptor and other four-winged paravians in a group he called "Tetrapterygidae", just outside the Avialae, though this was not supported with a phylogenetic analysis.

[18] In a 2017 re-evaluation of the Haarlem Archaeopteryx specimen, Anchiornis was found to be in a group with other genera, like Eosinopteryx, Xiaotingia, and was placed in the family Anchiornithidae along with other relatives.

[23][24] Anchiornis has hindleg proportions more like those of more primitive theropod dinosaurs than avialans, with long legs indicating a fast-running lifestyle.

[3] The hind wings of Anchiornis were smaller and made of more curved, symmetrical feathers than those of Microraptor, suggesting that they were used mainly for display rather than flight.

[10][25] The skeletal structure of Anchiornis is similar to Eosinopteryx, which appears to have been a capable runner due to its uncurved rear claws and absence of flight feathers on its tail or lower legs.

Anchiornis shared a similar body plan and the same ecosystem as Eosinopteryx, suggesting different niches and a complex picture for the origin of flight.