A feathered dinosaur is any species of dinosaur possessing

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...

s. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form. It has been suggested that feathers had originally functioned as thermal insulation, as it remains their function in the down feathers of infant birds today, prior to their eventual modification in birds into structures that support flight. Since scientific research began on dinosaurs in the early 1800s, they were generally believed to be closely related to modern

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

s, such as

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

s. The word ''dinosaur'' itself, coined in 1842 by paleontologist

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Owe ...

, comes from the Greek for 'terrible lizard'. This view began to shift during the so-called dinosaur renaissance in scientific research in the late 1960s, and by the mid-1990s significant evidence had emerged that dinosaurs were much more closely related to birds, which descended directly from the theropod group of dinosaurs. Knowledge of the origin of feathers developed as new fossils were discovered throughout the 2000s and 2010s and as technology enabled scientists to study fossils more closely. Among non-avian dinosaurs, feathers or feather-like integument have been discovered in dozens of

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

via direct and indirect fossil evidence. Although the vast majority of feather discoveries have been in coelurosaurian theropods, feather-like integument has also been discovered in at least three

ornithischia Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek s ...

ns, suggesting that feathers may have been present on the last common ancestor of the Ornithoscelida, a dinosaur group including both theropods and ornithischians. It is possible that feathers first developed in even earlier

archosaur Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...

s, in light of the discovery of vaned feathers in

pterosaurs Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...

. Crocodilians also possess beta keratin similar to those of birds, which suggests that they evolved from common ancestral genes.

History of research

Early

Archaeopteryx lithographica (Berlin specimen)

Shortly after the 1859 publication of Charles Darwin's '' On the Origin of Species'', British

biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual cell, a multicellular organism, or a community of interacting populations. They usually specialize in ...

Thomas Henry Huxley proposed that birds were descendants of dinosaurs. He compared the skeletal structure of '' Compsognathus'', a small theropod dinosaur, and the "first bird" '' Archaeopteryx lithographica'' (both of which were found in the

Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Bavarian limestone of

Solnhofen Solnhofen is a municipality in the district of Weißenburg-Gunzenhausen in the region of Middle Franconia in the ' of Bavaria in Germany. It is in the Altmühl valley. The local area is famous in geology and palaeontology for Solnhofen limest ...

). He showed that, apart from its hands and feathers, ''Archaeopteryx'' was quite similar to ''Compsognathus''. Thus ''Archaeopteryx'' represents a transitional fossil. In 1868 he published ''On the Animals which are most nearly intermediate between Birds and Reptiles'', making the case. The first restoration of a feathered dinosaur was Huxley's depiction in 1876 of a feathered ''Compsognathus'', made to accompany a bird evolution lecture he delivered in New York, in which he speculated that the aforementioned dinosaur might have had feathers.

'Dinosaur renaissance'

At the same time, paleoartists began to create modern restorations of highly active dinosaurs. In 1969,

Robert T. Bakker Robert Thomas Bakker (born March 24, 1945) is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor J ...

drew a running ''Deinonychus''. His student Gregory S. Paul depicted non-avian maniraptoran dinosaurs with feathers and protofeathers, starting in the late 1970s.

Fossil discoveries

The first known specimen of ''Archaeopteryx'', on the basis of which the genus was named, was an isolated feather, although whether or not it belongs to ''Archaeopteryx'' has been controversial. One of the earliest discoveries of possible feather impressions by non-avian dinosaurs is a trace fossil ('' Fulicopus lyellii'') of the 195-199 million year old

Portland Formation The Portland Formation is a geological formation in Connecticut and Massachusetts in the northeastern United States.dilophosaurid. Although some reviewers have raised questions about the naming and interpretation of this fossil, if correct, this early Jurassic fossil is the oldest known evidence of feathers, almost 30 million years older than the next-oldest-known evidence. Sinosauropteryxfossil

The most important discoveries at

Liaoning Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...

have been a host of feathered dinosaur fossils, with a steady stream of new finds filling in the picture of the dinosaur–bird connection and adding more to theories of the evolutionary development of feathers and flight. Turner ''et al''. (2007) reported quill knobs from an ulna of '' Velociraptor mongoliensis'', and these are strongly correlated with large and well-developed secondary feathers. Citipati IGM 100 979

Behavioural evidence, in the form of an oviraptorosaur on its nest, showed another link with birds. Its forearms were folded, like those of a bird. Although no feathers were preserved, it is likely that these would have been present to insulate eggs and juveniles. Microraptor gui holotype

Not all of the Chinese fossil discoveries proved valid however. In 1999, a supposed fossil of an apparently feathered dinosaur named '' Archaeoraptor liaoningensis'', also found in Liaoning, turned out to be a forgery. Comparing the photograph of the specimen with another find, Chinese paleontologist Xu Xing came to the conclusion that it was composed of two portions of different fossil animals. His claim made ''

National Geographic ''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...

'' review their research and they too came to the same conclusion. In 2011, samples of amber were discovered to contain preserved feathers from 75 to 80 million years ago during the Cretaceous era, with evidence that they were from both dinosaurs and birds. Initial analysis suggests that some of the feathers were used for insulation, and not flight. More complex feathers were revealed to have variations in coloration similar to modern birds, while simpler protofeathers were predominantly dark. Only 11 specimens are currently known. The specimens are too rare to be broken open to study their melanosomes (pigment-bearing organelles), but there are plans for using non-destructive high-resolution X-ray imaging. Melanosomes produce colouration in feathers; as differently-shaped melanosomes produce different colours, subsequent research on melanosomes preserved in feathered dinosaur specimens has led to reconstructions of the life appearance of several dinosaur species. These include '' Anchiornis'', '' Sinosauropteryx'', ''Microraptor'', and ''Archaeopteryx''. In 2016, the discovery was announced of a feathered dinosaur tail preserved in amber that is estimated to be 99 million years old. Lida Xing, a researcher from the China University of Geosciences in Beijing, found the specimen at an amber market in

Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...

. It is the first definitive discovery of dinosaur material in amber.

Current knowledge

Non-avian dinosaur species preserved with evidence of feathers

Several non-avian dinosaurs are now known to have been feathered. Direct evidence of feathers exists for several species. In all examples, the evidence described consists of feather impressions, except those genera inferred to have had feathers based on skeletal or chemical evidence, such as the presence of quill knobs (the anchor points for wing feathers on the forelimb) or a pygostyle (the fused vertebrae at the tail tip which often supports large feathers).

Primitive feather types

Integumentary structures that gave rise to the feathers of birds are seen in the dorsal spines of reptiles and fish. A similar stage in their evolution to the complex coats of birds and mammals can be observed in living reptiles such as iguanas and ''

Gonocephalus :Gonocephalus ''is also a synonym of the catfish genus'' Clarotes. ''Gonocephalus'' is a genus of agamid lizards endemic to southeast Asia. Taxonomy Species from Melanesia and Australia which were formerly included in ''Gonocephalus'' are now ...

'' agamids. Feather structures are thought to have proceeded from simple hollow filaments through several stages of increasing complexity, ending with the large, deeply rooted feathers with strong pens ( rachis), barbs and barbules that birds display today. According to Prum's (1999) proposed model, at stage I, the follicle originates with a cylindrical epidermal depression around the base of the feather papilla. The first feather resulted when undifferentiated tubular follicle collar developed out of the old keratinocytes being pushed out. At stage II, the inner, basilar layer of the follicle collar differentiated into longitudinal barb ridges with unbranched keratin filaments, while the thin peripheral layer of the collar became the deciduous sheath, forming a tuft of unbranched barbs with a basal calamus. Stage III consists of two developmental novelties, IIIa and IIIb, as either could have occurred first. Stage IIIa involves helical displacement of barb ridges arising within the collar. The barb ridges on the anterior midline of the follicle fuse together, forming the rachis. The creation of a posterior barb locus follows, giving an indeterminate number of barbs. This resulted in a feather with a symmetrical, primarily branched structure with a rachis and unbranched barbs. In stage IIIb, barbules paired within the peripheral barbule plates of the barb ridges, create branched barbs with rami and barbules. This resulting feather is one with a tuft of branched barbs without a rachis. At stage IV, differentiated distal and proximal barbules produce a closed, pennaceous vane (a

contour feather The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs. Description A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the skin ...

). A closed vane develops when pennulae on the distal barbules form a hooked shape to attach to the simpler proximal barbules of the adjacent barb. Stage V developmental novelties gave rise to additional structural diversity in the closed pennaceous feather. Here, asymmetrical flight feathers, bipinnate plumulaceous feathers, filoplumes, powder down, and bristles evolved. Some evidence suggests that the original function of simple feathers was insulation. In particular, preserved patches of skin in large, derived,

tyrannosauroids Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent be ...

show scutes, while those in smaller, more primitive, forms show feathers. This may indicate that the larger forms had complex skins, with both scutes and filaments, or that tyrannosauroids may be like

rhinos A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species o ...

and elephants, having filaments at birth and then losing them as they developed to maturity. An adult '' Tyrannosaurus rex'' weighed about as much as an African elephant. If large tyrannosauroids were endotherms, they would have needed to radiate heat efficiently.Norell, M. Xu, X. (2005
"The Varieties of Tyrannosaurs"
Natural History Magazine, May 2005. This is due to the different structural properties of feathers compared to fur. Some evidence also suggests that more derived feather types may have served as insulation. For instance, a study of oviraptor pennaceous wing feathers and nesting posture suggests that elongated wing feathers evidently may have served to fill gaps between brooding individuals' insulatory body chamber and the outside environment. This "wall" of wing feathers could have shielded eggs from temperature extremes. There is an increasing body of evidence that supports the display hypothesis, which states that early feathers were colored and increased reproductive success. Coloration could have provided the original adaptation of feathers, implying that all later functions of feathers, such as thermoregulation and flight, were

co-opt Co-option (also co-optation, sometimes spelt coöption or coöptation) has two common meanings. It may refer to the process of adding members to an elite group at the discretion of members of the body, usually to manage opposition and so maintai ...

ed. This hypothesis has been supported by the discovery of pigmented feathers in multiple species. Supporting the display hypothesis is the fact that fossil feathers have been observed in a ground-dwelling herbivorous dinosaur clade, making it unlikely that feathers functioned as predatory tools or as a means of flight. Additionally, some specimens have iridescent feathers. Pigmented and iridescent feathers may have provided greater attractiveness to mates, providing enhanced reproductive success when compared to non-colored feathers. Current research shows that it is plausible that theropods would have had the visual acuity necessary to see the displays. In a study by Stevens (2006), the binocular field of view for '' Velociraptor'' has been estimated to be 55 to 60 degrees, which is about that of modern owls. Visual acuity for '' Tyrannosaurus'' has been predicted to be anywhere from about that of humans to 13 times that of humans. Paleontological and evolutionary developmental studies show that feathers or feather-like structures were converting back to scales. The idea that precursors of feathers appeared before they were co-opted for insulation is already stated in Gould and Vrba (1982). The original benefit might have been metabolic. Feathers are largely made of the keratin protein complex, which has disulfide bonds between amino acids that give it stability and elasticity. The metabolism of amino acids containing sulfur can be toxic; however, if the sulfur amino acids are not catabolized as the final products of urea or uric acid but used for the synthesis of keratin instead, the release of hydrogen sulfide is extremely reduced or avoided. For an organism whose metabolism works at high internal temperatures of or greater, it can be extremely important to prevent the excess production of hydrogen sulfide. This hypothesis could be consistent with the need for high metabolic rate of theropod dinosaurs. It is not known with certainty at what point in

phylogeny the earliest simple "protofeathers" arose, or whether they arose once or independently multiple times. Filamentous structures are clearly present in

, and long, hollow quills have been reported in specimens of the ornithischian dinosaurs '' Psittacosaurus'' and ''

Tianyulong ''Tianyulong'' (Chinese: 天宇龍; Pinyin: ''tiānyǔlóng''; named for the Shandong Tianyu Museum of Nature where the holotype fossil is housed) is an extinct genus of heterodontosaurid ornithischian dinosaur. The only species is ''T. confuc ...

'' although there has been disagreement. In 2009, Xu et al. noted that the hollow, unbranched, stiff integumentary structures found on a specimen of ''

Beipiaosaurus ''Beipiaosaurus'' is a genus of therizinosauroid theropod dinosaurs that lived in Asia during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the discovery of ''Yutyrannus ...

'' were strikingly similar to the integumentary structures of ''Psittacosaurus'' and pterosaurs. They suggested that all of these structures may have been inherited from a common ancestor much earlier in the evolution of archosaurs, possibly in an

ornithodire Avemetatarsalia (meaning "bird metatarsals") is a clade of diapsid Reptile, reptiles containing all archosaurs more closely related to birds than to crocodilians. The two most successful groups of avemetatarsalians were the dinosaurs and pterosau ...

from the Middle Triassic or earlier. More recently, findings in Russia of the basal

neornithischia Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. It is the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside ...

n '' Kulindadromeus'' report that although the lower leg and tail seemed to be scaled, "varied integumentary structures were found directly associated with skeletal elements, supporting the hypothesis that simple filamentous feathers, as well as compound feather-like structures comparable to those in theropods, were widespread amongst the whole dinosaur clade." The 2016 publication in the Journal of Geology in contrast finds that the integumentary structures found on ''Kulindadromeus'' and ''Psittacosaurus'' are highly deformed scales and not feather-like structures. Display feathers are also known from dinosaurs that are very primitive members of the bird lineage, or Avialae. The most primitive example is '' Epidexipteryx'', which had a short tail with extremely long, ribbon-like feathers. Oddly enough, the fossil does not preserve wing feathers, suggesting that ''Epidexipteryx'' was either secondarily flightless, or that display feathers evolved before flight feathers in the bird lineage. Plumaceous feathers are found in nearly all lineages of Theropoda common in the northern hemisphere, and pennaceous feathers are attested as far down the tree as the

Ornithomimosauria Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period (geology), Period of Laurasia (now Asia ...

. The fact that only adult ''

Ornithomimus ''Ornithomimus'' (; "bird mimic") is a genus of ornithomimid dinosaurs from the Late Cretaceous Period of what is now North America. ''Ornithomimus'' was a swift bipedal theropod which fossil evidence indicates was covered in feathers, equipped w ...

'' had wing-like structures suggests that pennaceous feathers evolved for mating displays.

Phylogeny and the inference of feathers in other dinosaurs

This technique, called phylogenetic bracketing, can also be used to infer the type of feathers a species may have had, since the developmental history of feathers is now reasonably well-known. All feathered species had filamentaceous or plumaceous (downy) feathers, with pennaceous feathers found among the more bird-like groups. The following cladogram is adapted from Godefroit ''et al.'', 2013. Grey denotes a clade that is not known to contain any feathered specimen at the time of writing, some of which have fossil evidence of scales. The presence or lack of feathered specimens in a given clade does not confirm that all members in a clade have the specified integument, unless corroborated with representative fossil evidence within clade members. The following cladogram is from Xu (2020). # Slender monofilamentous integument # Broad monofilamentous integument # Basally joining filamentous feather # Basally joining shafter filamentous feather # Radially branched shafted filamentous feather # Bilaterally branched filamentous feather # Basally joining branched filamentous feather # Basally joining membranous-based filamentous feather # Symmetrical open-vaned feather # Symmetrical close-vaned feather # Asymmetrical close-vaned feather # Proximally ribbon-like close-vaned feather # Rachis-dominant close-vaned feather

References

External links

Dinosaur colour and feathers
''University of Bristol'', 12 February 2019

DinoBuzz, UC Berkeley. * {{Portal bar, Evolutionary biology, Dinosaurs, Paleontology, Science Cenozoic dinosaurs Evolution of tetrapods Mesozoic dinosaurs