Anchiornis huxleyi

Anchiornis huxleyi inhabited subtropical to temperate forests of northeastern China during the Late Jurassic, approximately 160 million years ago. The Tiaojishan Formation preserves a lacustrine and volcanic environment, with gymnosperm forests along the shores of lakes and rivers. The climate was warm and humid, favoring dense vegetation. The ecosystem included other paravians such as Xiaotingia and Aurornis, pterosaurs, salamanders, and insects.

The gastric pellets described by Zheng et al. (2018) revealed that Anchiornis was an opportunistic generalist predator. It consumed terrestrial lizards and freshwater fish (ptycholepid scales), and possibly insects and other small vertebrates. The presence of three lizard skeletons in a single pellet indicates the capacity for rapid ingestion of multiple prey items. Its small, numerous teeth were well-suited for capturing small to medium-sized live prey.

Anchiornis behavior is inferred from fossil evidence and comparison with modern relatives. The contrasting black and white wing feathers, plus the rufous crown, suggest a role in visual communication, possibly for territorial or reproductive display. The four-wing morphology combined with relatively long legs indicates a likely arboreal or semi-arboreal animal capable of climbing trunks and gliding between trees. The production of gastric pellets similar to modern owls suggests active hunting behavior.

As an advanced paravian, Anchiornis likely had endothermic (warm-blooded) metabolism, like modern birds. The abundance of high-quality feathers throughout the body indicates efficient thermoregulation. Accelerated growth documented by Prondvai et al. (2018) in subadult specimens suggests elevated metabolic rate. Kiat et al.'s (2025) molt analysis revealed an irregular molt pattern, similar to secondarily flightless birds, indicating Anchiornis may have lost flight capability from a flying ancestor.

Original description of Anchiornis huxleyi by Xu Xing and colleagues in Chinese Science Bulletin. The holotype IVPP V14378, from the Tiaojishan Formation of Liaoning, China, is an articulated skeleton of a small Late Jurassic feathered theropod. Xu et al. identified the animal as a feathered maniraptoran filling a critical morphological gap in avian origins. The initial phylogenetic analysis classified the specimen as a basal avialan, though later work revised this position to Anchiornithidae. The name huxleyi honors Thomas Henry Huxley, the Victorian biologist who first formally proposed the evolutionary connection between dinosaurs and birds.

Holotype of Anchiornis huxleyi (IVPP V14378) on display at the Shanghai Natural History Museum — the original specimen described by Xu et al. in 2009.

Skeletal reconstruction of Anchiornis huxleyi by Scott Hartman (2017), incorporating soft tissue outlines revealed by laser fluorescence — the most complete skeletal reference for the species described in 2009.

Second paper on Anchiornis published in Nature, based on a new specimen more complete than the holotype. Hu et al. reclassified the animal as a basal troodontid, not an avialan, resolving the temporal paradox by demonstrating that troodontids already existed before Archaeopteryx. The specimen revealed long feathers on the metatarsals, making Anchiornis a genuine four-winged dinosaur. This work established that all major groups of derived theropods had already originated in the early Late Jurassic. The presence of long hind limb feathers generated intense debate about their role in locomotion and flight.

Specimen YFGP-T5199 of Anchiornis huxleyi, showing the nearly complete skeleton with preserved feather impressions, including the long metatarsal feathers that defined the animal as a four-winged dinosaur.

Detail of feather impressions in an Anchiornis huxleyi fossil. The preservation of long feathers on the hindlimbs was central evidence in Hu et al. (2009) to classify the animal as four-winged.

Historic paper published in Science that revealed the complete coloration of Anchiornis huxleyi, the first determined for any Mesozoic dinosaur. The team led by Quanguo Li collected 29 samples from different parts of specimen BMNHC PH828 and compared the preserved melanosomes with those of modern bird feathers. The result showed dark gray body feathers, a rufous crown, rufous facial speckles, and white wing feathers with black tips. This work revolutionized paleontology by demonstrating that animal coloration can be preserved through fossilized melanosomes.

Life restoration of Anchiornis huxleyi by Matt Martyniuk (2010), based directly on the coloration patterns determined by Li et al. (2010) — the first accurate chromatic reconstruction of a Mesozoic dinosaur.

Fossil of Anchiornis huxleyi exhibited at the Dinosaur Expo 2011 in Tokyo. The original caption highlights that melanin pigments in the feathers allowed scientists to determine the animal's coloration, confirming Li et al.'s (2010) results.

Longrich et al. analyzed the flight feather arrangement in Anchiornis and Archaeopteryx, revealing a primitive configuration shared by both. Anchiornis had 11 primary and 10 secondary feathers with rounded, symmetrical quills, unlike the asymmetric feathers of modern flying birds. This configuration indicates limited or absent aerodynamic capability. The work was fundamental in understanding how the feathered wing evolved: the primitive configuration likely served more for visual communication than for lift. It also established that the basic feathered wing pattern was already present before Archaeopteryx.

Wing fossil from Anchiornis huxleyi specimen STM-0-144. The flight feather configuration documented by Longrich et al. (2012) shows the primitive pattern of symmetrical quills, distinct from modern flying birds.

Simplified cladogram of Paraves showing phylogenetic relationships among the main paravian groups. Longrich et al. (2012) analyzed the primitive flight feather arrangement in Anchiornis and Archaeopteryx, two basal taxa in this phylogeny.

Lindgren et al. applied advanced molecular imaging techniques to Anchiornis specimen YFGP-T5199 to investigate the chemical composition of feathers. Using time-of-flight secondary ion mass spectrometry and infrared reflectance spectroscopy, they identified remnant eumelanosomes and fibril-like microstructures preserved as endogenous eumelanin and calcium phosphate. The study revealed that keratin, unlike melanin, is not preserved in Anchiornis feathers. An important finding: the analyzed specimen showed only gray-black melanosomes, unlike the rufous-colored specimen of Li et al. (2010), raising the possibility of intraspecific coloration variation.

Photographic and diagrammatic representation of specimen YFGP-T5199, with markers at feather sample collection points for molecular analysis. Circles indicate the exact positions of the samples studied by Lindgren et al. (2015).

Propatagium of Anchiornis huxleyi specimen STM-0-127 in laser fluorescence, compared with white light image. Wang et al. (2017) and Lindgren et al. (2015) contributed to understanding soft tissue structures in Anchiornis.

Dececchi et al. evaluated three hypotheses for flight evolution in bird antecedents: flap running, Wing Assisted Incline Running (WAIR), and wing-assisted leaping. Results showed that none of these behaviors met the required biomechanical thresholds before Paraves. For Anchiornis specifically, adults likely had no aerodynamic benefit from their wings, but juveniles may have been capable of WAIR and of increasing jump height and distance with wing flapping. The paper contributed decisively to the flight origin debate, suggesting Anchiornis occupies an intermediate stage before the full acquisition of powered flight.

Life reconstruction of Anchiornis huxleyi showing the four feathered wings and relatively long legs. Wing and leg morphology was central to Dececchi et al.'s (2016) biomechanical analysis of flight capability.

Size comparison of Anchiornis huxleyi with a human, based on the largest referred specimen (LPM-B00169). The animal's small stature was an important factor in Dececchi et al.'s (2016) biomechanical analyses.

Foth and Rauhut conducted a phylogenetic reevaluation of the Haarlem Archaeopteryx specimen, concluding it is not a true Archaeopteryx but an anchiornithid named Ostromia crassipes. As a result, they formalized Anchiornithidae as an independent family within Paraves, closer to avialans than to troodontids. This work is fundamental to the systematic position of Anchiornis huxleyi: by establishing Anchiornithidae as a valid and distinct family, it consolidated the classification of the genus outside Troodontidae, where it had initially been placed in 2009.

Dinosauria cladogram showing the type of integument (scales, feathers, etc.) preserved in different groups, per Benton et al. (2019). Foth and Rauhut (2017) formalized Anchiornithidae as an independent family within Paraves, positioned between avialans and dromaeosaurids.

Distribution map of paravians in the Late Jurassic with paleogeographic context. Foth and Rauhut (2017) demonstrated that Anchiornis and the Haarlem specimen (Ostromia) are part of the same anchiornithid radiation recorded in China and possibly Europe.

Wang et al. used laser-stimulated fluorescence (LSF) imaging on Anchiornis specimen STM 0-144 to reveal the complete soft tissue body outline. The method illuminated anatomical details invisible under normal light: patagia-bearing arms, drumstick-shaped legs, and a slender tail. Structures such as the propatagium and foot pads, previously known only in modern birds, were documented in the Late Jurassic for the first time. The work also revealed the foot profile, showing that the toes were covered with soft tissue similar to flying birds. This paper transformed the understanding of basal paravian functional anatomy.

Plantar footpads of Anchiornis huxleyi specimen STM-0-147, revealed by laser fluorescence. Wang et al. (2017) documented these soft tissue structures that were previously known only in modern birds.

Tail outline and leg and pubic boot outline of Anchiornis huxleyi from Wang et al. (2017). Laser fluorescence analysis revealed the tail was slender — different from earlier interpretations.

Pei et al. described four new nearly complete specimens of Anchiornis huxleyi from the Tiaojishan Formation. The study extensively revised the genus's diagnostic character list and the refined phylogenetic analysis updated Anchiornis's position in the paravian tree. This 67-page monograph became the definitive anatomical reference for the genus, serving as the basis for all subsequent biomechanical and phylogenetic studies.

Paleogeographic and paleoclimatic map of the Late Jurassic (150 Ma) with dinosaur fossil localities. Pei et al. (2017) described four new Anchiornis specimens from the Tiaojishan Formation in northeastern China, one of the regions with the highest concentration of Jurassic paravians.

Three-dimensional model of Anchiornis huxleyi on display at the National Museum of Natural History in Luxembourg. Modern reconstructions of the animal were refined by the detailed anatomical data of Pei et al. (2017).

Guo, Xu, and Jia described new specimens of Anchiornis huxleyi from Jianchang, western Liaoning, which showed slightly different morphological characters from previously reported specimens. The study revised the genus diagnosis and concluded that these characters indicate a different phylogenetic position from prior analyses. The work is important for demonstrating morphological variability within the species and for contributing high-quality anatomical data, especially regarding cranial and limb anatomy.

View of the holotype of Anchiornis huxleyi (partially preserved specimen). The new Jianchang specimens described by Guo et al. (2018) showed slightly different morphology compared to the holotype.

Size comparison of Anchiornis huxleyi with a human, based on the largest referred specimen (LPM-B00169). Guo et al. (2018) described new Jianchang specimens with slightly different morphology, relevant for assessing size variability within the species.

Zheng et al. documented six gastric pellets from Anchiornis huxleyi specimens, containing lightly acid-etched lizard bones and ptycholepid fish scales, some preserved within the oesophagus. This study demonstrated that a digestive system similar to modern birds, including the production of regurgitated pellets as owls do, was already present in basal Paraves during the Late Jurassic. Anchiornis is thus the oldest and most basal theropod known to have produced gastric pellets. Its diet included terrestrial lizards and aquatic fish, suggesting an opportunistic generalist hunter.

Gastric pellets produced by the troodontid Anchiornis, containing fish scales and bones, published by Zheng et al. (2018) in Scientific Reports. Panels show specimens STMA0-4, STM0-224, and STM0-227.

Cranial and cervical region of Anchiornis huxleyi specimen STM0-179, showing the preserved gastric pellet contents. Zheng et al. (2018) identified lizard bones within this pellet.

Prondvai et al. integrated qualitative and quantitative osteohistological approaches to examine intraskeletal growth dynamics in five paravian taxa: Anchiornis, Aurornis, Eosinopteryx, Serikornis, and Jeholornis. For Anchiornis, the subadult specimen exhibited moderately allometric intraskeletal growth patterns. Extensive bone remodeling indicated earlier functional maturation of the femur, which reached its subadult dimensions growing faster than most other elements. The study provided essential data on the growth biology and life history of Anchiornis huxleyi.

Size comparison between Epidexipteryx hui and Anchiornis huxleyi alongside a human figure. Prondvai et al.'s (2018) bone histology study analyzed subadult Anchiornis specimens, indicating the animal was still growing.

Type locality of the Tiaojishan Formation at Nanshimenzi Village, Qinglong County, Hebei. The formation is the source of all known Anchiornis specimens, including those analyzed by Prondvai et al. (2018).

Cincotta et al. investigated the taphonomic preservation of tail feathers from Anchiornis huxleyi (specimen YFGP-T5199) using a suite of geochemical techniques. Results confirmed that melanin is preserved in Anchiornis fossil feathers, but keratin is not, contradicting previous hypotheses. The feathers underwent calcium phosphate mineralization. The work demonstrated that the distribution of melanosomes along the tail feathers was uniform, consistent with a dark coloration. This study is important for understanding fossilization mechanisms of soft structures in feathered dinosaurs.

Measurement landmarks in Anchiornis propatagia preserved at different degrees of elbow extension (Wang et al. 2017). Soft tissue analysis techniques developed for Anchiornis paved the way for Cincotta et al.'s (2020) chemical feather composition studies.

Near-complete, articulated right foot of Anchiornis huxleyi specimen STM 0-147 in laser fluorescence. The exceptional preservation of Anchiornis enabled in-depth soft tissue studies such as Cincotta et al.'s (2020).

Wang et al. (2025) presented a detailed digital reconstitution of the skull of Anchiornis huxleyi (specimen STM 0-47) from Jianchang, Liaoning, based on computed tomography. The study revealed a diapsid akinetic skull retaining the plesiomorphic dinosaurian condition, lacking the cranial kinesis adaptations of modern birds. The mixture of cranial characters shared with dromaeosaurids, troodontids, and stemward avialans demonstrated that the evolutionary history of the bird skull is more complex than previously believed.

Skeletal reconstruction of Anchiornis huxleyi by Jaime A. Headden (2010). Wang et al.'s (2025) cranial study provided the most accurate skull reconstruction of this species to date, using computed tomography.

Mounted Archaeopteryx skeleton at the Royal Belgian Institute of Natural Sciences, Brussels. Wang et al. (2025) compared the cranial anatomy of Anchiornis with that of Archaeopteryx and other paravians to elucidate the evolution of the avian skull.

Kiat et al. (2025) examined nine Anchiornis huxleyi specimens with retained feather coloration, revealing for the first time evidence of irregular molt in a non-avian pennaraptoran. The irregular molt strategy, combined with the unique wing structure, indicates the plumage of an animal incapable of flight, similar to secondarily flightless birds today. The most surprising implication: molt strategy responds rapidly to secondary loss of flight, suggesting Anchiornis may have lost flight capability from a flying ancestor, making the evolution of flight in dinosaurs far more complex and iterative than previously thought.

Digitized pencil drawing of Anchiornis huxleyi by Nobu Tamura (2009), showing the general wing morphology. Kiat et al. (2025) analyzed wing feather structure in multiple specimens to determine the molt pattern.

Paraves diversity panel showing six representatives of the group, including Anchiornis (third from top). Kiat et al. (2025) analyzed feather molt patterns in Anchiornis and other paravians to infer flight capability.

Full-size T-rex animatronic from the Jurassic Park franchise, with the iconic red Jeep — Amaury Laporte · CC BY 2.0