Anchiornis: a feathered paravian near the origin of birds

Anchiornis huxleyi was a small feathered paravian from the Late Jurassic of northeastern China, about 161–160 million years ago. Hundreds of flattened fossils preserve a combination rarely available for early theropods: bones, feather impressions, stomach residues and, in one specimen, pigment patterns. Long vaned feathers extended along both the forelimbs and hind limbs, giving the animal a four-winged outline.

Its position close to birds makes Anchiornis important for understanding early paravian evolution, but the details of its family placement and its ability to fly remain disputed. The fossil supports an extensively feathered, bipedal animal; it does not prove sustained powered flight or make it an uncontested “first bird”. The species is included in the dinosaur catalogue as a non-avian theropod close to the origin of birds.

Quick facts

Name, discovery and the type specimen

The name Anchiornis combines Greek-derived words meaning “near” and “bird”, reflecting its position close to early birds. The species name huxleyi honours Thomas Henry Huxley, whose nineteenth-century comparisons helped establish the close relationship between birds and dinosaurs.

Xing Xu and colleagues named the genus in 2009. The holotype, IVPP V14378, was found near Yaolugou in Jianchang County, Liaoning. It is an articulated skeleton without the skull, part of the neck and the rear of the tail, and it preserves faint feather traces. Its length was estimated at about 34 centimetres and its mass at roughly 110 grams. Bone structure indicates a growing but not fully mature individual.

A more complete specimen described the same year preserved long feathers on both the forelimbs and hind limbs, revealing four prominent feathered surfaces. Hundreds of comparable fossils later entered collections. Near-complete examples have allowed researchers to examine skull anatomy, teeth, limbs and variation between individuals rather than relying on the type slab alone.

Where it sits among early birds and theropods

Anchiornis belongs among theropods, coelurosaurs, maniraptorans and Paraves. Paraves includes birds and several nearby branches of small feathered dinosaurs. The Jurassic Archaeopteryx is a useful comparison because both animals had extensive feathers and a mosaic of bird-like and dinosaur-like features. Their wing anatomy and positions in phylogenetic trees are not identical.

The exact branch occupied by Anchiornis has shifted between analyses. The original description placed it within Avialae, on the bird side of the paravian tree. A more complete specimen soon yielded a position inside Troodontidae. Other studies recovered a distinct Anchiornithidae near birds, troodontids and dromaeosaurids. A combination of traits found across these branches makes the result sensitive to which fossils and characters are included in a comparison.

The robust conclusion is that Anchiornis was an early paravian close to the evolutionary radiation from which birds emerged. Its exact position is not universally agreed. That uncertainty does not conflict with evidence that birds evolved from feathered dinosaurs; it reflects rapid branching and overlapping combinations of anatomy among early paravians. Calling it either a definite bird or an unequivocal troodontid goes beyond the current agreement.

Species and related names

Only the type species, Anchiornis huxleyi, is securely recognised in the genus. Individuals vary in size and some proportions, but no reliable second species has been established. Differences can result from growth, individual variation, compression during burial or preparation of the slabs.

In 2017, Aurornis xui, another small paravian from the same broad region, was proposed as a possible junior synonym of A. huxleyi. That interpretation did not become final; later datasets often continue to score Aurornis separately. The related genera Eosinopteryx and Serikornis are close in some analyses, but automatically merging them into Anchiornis is not a stable consensus.

Hundreds of compressed fossils

The fossil record is unusually rich for a Jurassic paravian. It includes nearly complete skulls and skeletons, individuals of different sizes, feather impressions and patches of other soft tissue. Four almost complete fossils described in 2017, PKUP V1068 and BMNHC PH804, PH822 and PH823, added detail about the skull and the rest of the skeleton. The series also let researchers test whether an apparent diagnostic feature was shared or varied between animals.

Most skeletons were flattened on fine-grained slabs. That preservation reveals body outlines and plumage, but bones can overlap and become difficult to separate. The collecting locality and geological horizon are not documented equally well for every specimen. Anatomical claims are therefore strongest when they recur across several fossils, rather than when they depend on one spectacular but incomplete slab.

Some fossils preserve food residues. Pellets were found with several skeletons, and material near the oesophagus in some individuals includes bones of small lizards and fish scales. These are direct signs that such animals were eaten. They do not show that Anchiornis specialised in fish or hunted in water; prey could have been caught at a shore, scavenged or obtained in another way.

Size and the four-winged covering

Known individuals were approximately 35 to more than 60 centimetres long. Part of this range reflects growth stage. The holotype's estimated mass is about 110 grams, but that value should not be transferred to every individual. Estimates for larger animals depend on how missing body regions and soft tissues are reconstructed.

The skull was small and triangular, with numerous fine pointed teeth. These could grip small prey but did not form the slicing apparatus of a large predator. The forelimbs were long, and each hand carried three clawed digits. A furcula is preserved, but a bony sternum has not been found even in the large sample. That absence does not prove the living animal lacked a sternum: cartilage would be less likely to fossilise.

The hind limbs were long and slender. The second toe did not carry the exaggerated killing-claw complex seen in many dromaeosaurids. Long pennaceous feathers extended along the arms and hands as well as the lower legs, feet and toes. These surfaces created a four-winged silhouette. Microraptor provides a later comparison, but it lived at a different time and had different limb proportions and feather geometry.

Shorter contour feathers covered the torso, and the head carried a small crest. The long bony tail was also feathered. Limb feathers were relatively narrow and mostly symmetrical. These details establish extensive plumage but do not alone show how much lift the surfaces could create during a jump, glide or flapping stroke.

What the colour study found

In 2010, researchers mapped pigment-related structures in one well-preserved specimen assigned to A. huxleyi. The pattern suggested grey and dark areas on the body, pale long feathers with darker tips, and a reddish-brown patch on the crown. It was among the earliest near-complete attempts to reconstruct a dinosaur's plumage pattern from fossil pigment evidence.

This is not a photographic record of every Anchiornis. The method is most informative about colours associated with melanin and less decisive for tones produced by other pigments or by feather microstructure. It examined one animal; differences by age, sex or individual are unknown. New observations of several wings confirm regular dark bars on feather tips, but they do not remove all limits on the colour reconstruction.

Food, habitat and possible behaviour

Anchiornis lived around the lakes and volcanic deposits of the Tiaojishan Formation. Vegetation grew near water, and the wider fauna included insects, fish, amphibians, lizards, early mammals, pterosaurs and small dinosaurs. These communities belong to the later part of the Jurassic Period.

Pellets support a diet that included small lizards and fish. Invertebrates or other small animals may also have been eaten, but they are not equally well represented in direct stomach evidence. Fish scales do not turn the dinosaur into a water specialist. A meal could have been collected near shallow water or obtained in some other way.

The skeletons support bipedal movement. Claws and feathers have prompted suggestions of climbing, but Anchiornis did not have the specialised grasping foot of a modern tree-climbing bird. Feathers may have contributed to display, insulation, stability during a jump or braking during a descent. Specific display poses, calls, group living and parental care remain unknown.

Could Anchiornis fly?

Early reconstructions proposed gliding or a basic form of flapping because the animal had long arms and feather surfaces on four limbs. Later work focused on mostly symmetrical, narrow flight feathers, a rounded wing outline, the absence of a preserved bony sternum and an unusual arrangement in which long coverts overlapped the main feathers.

A 2025 study considered 226 museum specimens, but suitable feather preservation for the relevant comparison was available in only nine. Most showed about 20–25 primary feathers; one individual had 28. Three long rows of coverts lay over the primaries. The authors interpreted mismatched feather-growth stages as irregular moulting and argued that Anchiornis was flightless. They also proposed a secondary loss of flight, but that conclusion depends on the disputed position of the genus in the evolutionary tree and on a limited fossil sample.

What can be said securely is narrower: sustained active flight has not been demonstrated, and the feathered limbs were not exact replicas of a modern bird's wings. Some models allow modest aerodynamic assistance during a jump or descent. That possibility is different from powered flight and should not be presented as settled behaviour.

Common errors in popular accounts

Anchiornis is sometimes called a “missing link”. That phrase suggests a straight ladder between dinosaurs and birds, whereas evolution branches. The genus is valuable because its fossils preserve a mosaic of traits and unusually rich plumage evidence, not because one animal completes a linear chain.

Four feathered limbs also do not automatically mean four working wings. The surfaces are real, but their aerodynamic function must be tested. Current evidence does not establish full powered flight, though small contributions to jumping or descent remain possible under some models.

One colour pattern should not be imposed on every individual. The pigment study concerns one specimen and is limited by which pigments can be detected. Likewise, fish scales in a pellet do not show that the animal lived in water, and hundreds of skeletons from a fossil-rich deposit do not prove that they lived in flocks or nested together.

What the fossils establish

Anchiornis huxleyi is one of the best-represented early paravians. Hundreds of Late Jurassic fossils from China reveal a small biped with feathered arms, legs, torso and tail, and some specimens record small vertebrate meals. The fossils preserve part of one individual's colour pattern. They do not settle the genus's exact place among early paravians, demonstrate sustained flight or reveal a complete social life. Those limits make Anchiornis more useful, not less: separate claims can be matched to the particular fossils that support them.