Microraptor

Microraptor (Greek, μικρός, mīkros: "small"; Latin, raptor: "one who seizes") is a genus of small, four-winged paravian dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation (Aptian stage), 120 million years ago. Three species have been named (M. zhaoianus, M. gui, and M. hanqingi), though further study has suggested that all of them represent variation in a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dinosaur, is usually considered to be a synonym of Microraptor.[1]

Like Archaeopteryx, well-preserved fossils of Microraptor provide important evidence about the evolutionary relationship between birds and dinosaurs. Microraptor had long pennaceous feathers that formed aerodynamic surfaces on the arms and tail but also on the legs. This led paleontologist Xu Xing in 2003 to describe the first specimen to preserve this feature as a "four-winged dinosaur" and to speculate that it may have glided using all four limbs for lift. Subsequent studies have suggested that Microraptor was capable of powered flight as well.

Microraptor was among the most abundant non-avialan dinosaurs in its ecosystem, and the genus is represented by more fossils than any other dromaeosaurid, with possibly over 300 fossil specimens represented across various museum collections.[2]

Microraptor
Temporal range: Early Cretaceous, 120 Ma
Microraptor gui holotype
Fossil specimen, with white arrows pointing at preserved feathers
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Dromaeosauridae
Clade: Microraptoria
Genus: Microraptor
Xu et al., 2000
Type species
Microraptor zhaoianus
Xu et al., 2000
Species
  • M. zhaoianus Xu et al., 2000
  • M. gui Xu et al., 2003
  • M. hanqingi Gong et al., 2012
Synonyms
  • Cryptovolans Czerkas et al., 2002

Description

Microraptor scale
Wingspan and body size compared with a human

With adult specimens estimated up to 77 centimetres long (2.53 ft) and with a weight estimated up to 1 kilogram (2.2 lb), Microraptor was among the smallest-known non-avian dinosaurs.[3] Holtz estimated it at 90 centimetres (3.0 ft).[4] An estimate by Benson et al. in 2012 was that Microraptor had a maximum length of 1.2 m (3.9 ft).[5] Aside from their extremely small size, Microraptor were among the first non-avialan dinosaurs discovered with the impressions of feathers and wings. Seven specimens of M. zhaoianus have been described in detail, from which most feather impressions are known. Unusual even among early birds and feathered dinosaurs, Microraptor is one of the few known bird precursors to sport long flight feathers on the legs as well as the wings. Their bodies had a thick covering of feathers, with a diamond-shaped fan on the end of the tail (possibly for added stability during flight). Xu et al. (2003) compared the longer plumes on Microraptor's head to those of the Philippine eagle. Bands of dark and light present on some specimens may indicate color patterns present in life,[6] though at least some individuals almost certainly possessed an iridescent black coloration.[7] Several anatomical features found in Microraptor, such as a combination of unserrated and partially serrated teeth with constricted 'waists', and unusually long upper arm bones, are shared with both primitive avians and primitive troodontids. Microraptor is particularly similar to the basal troodontid Sinovenator; in their 2002 description of two M. zhaoianus specimens, Hwang et al. note that this is not particularly surprising, given that both Microraptor and Sinovenator are very primitive members of two closely related groups, and both are close to the deinonychosaurian split between dromaeosaurids and troodontids.[6]

Coloration

Microraptor Restoration
Restoration of M. gui with coloration based on fossilized melanosomes

In March 2012, Quanguo Li et al. determined the plumage coloration of Microraptor based on the new specimen BMNHC PH881, which also showed several other features previously unknown in Microraptor. By analyzing the fossilized melanosomes (pigment cells) in the fossil with scanning electron microscope techniques, the researchers compared their arrangements to those of modern birds. In Microraptor, these cells were shaped in a manner consistent with black, glossy coloration in modern birds. These rod-shaped, narrow melanosomes were arranged in stacked layers, much like those of a modern starling, and indicated iridescence in the plumage of Microraptor. Though the researchers state that the true function of the iridescence is yet unknown, it has been suggested that the tiny dromaeosaur was using its glossy coat as a form of communication or sexual display, much as in modern iridescent birds.[7][8]

Paleobiology

Wings and flight

Microraptor had four wings, one on each of its forelimbs and hindlimbs, somewhat resembling one possible arrangement of the quartet of flight surfaces on a tandem wing aircraft of today. It had long pennaceous feathers on arms and hands 10–20 cm long (3.9–7.9 in) with legs and feet 11–15 cm long (4.3–5.9 in). The long feathers on the legs of Microraptor were true flight feathers as seen in modern birds, with asymmetrical vanes on the arm, leg, and tail feathers. As in modern bird wings, Microraptor had both primary (anchored to the hand) and secondary (anchored to the arm) flight feathers. This standard wing pattern was mirrored on the hindlegs, with flight feathers anchored to the upper foot bones as well as the upper and lower leg. Though not apparent in most fossils under natural light, due to obstruction from decayed soft tissue, the feather bases extended close to or in contact with the bones, as in modern birds, providing strong anchor points.[9]

It was originally thought that Microraptor was a glider, and probably lived mainly in trees, because the hindwings anchored to the feet of Microraptor would have hindered their ability to run on the ground.[10] Some paleontologists have suggested that feathered dinosaurs used their wings to parachute from trees, possibly to attack or ambush prey on the ground, as a precursor to gliding or true flight.[5] In their 2007 study, Chatterjee and Templin tested this hypothesis as well, and found that the combined wing surface of Microraptor was too narrow to successfully parachute to the ground without injury from any significant height. However, the authors did leave open the possibility that Microraptor could have parachuted short distances, as between closely spaced tree branches.[3][5] Wind tunnel experiments have demonstrated that sustaining a high-lift coefficient at the expense of high drag was likely the most efficient strategy for Microraptor when gliding between low elevations. Microraptor did not require a sophisticated, 'modern' wing morphology to be an effective glider.[11] However, the idea that Microraptor was an arboreal glider relies on it to have regularly climbed or even lived in trees, when study of its anatomy have shown that its limb proportions fall in line with modern ground birds rather than climbers, and its skeleton shows none of the expected adaptations in animals specialized for climbing trees.[12]

Microraptor gui holotype under UV light
M. gui holotype under two different UV light filters, revealing extent of preserved feathers and soft tissue

Describing specimens originally referenced as a distinctive species (Cryptovolans pauli), paleontologist Stephen Czerkas argued Microraptor may have been a powered flier, and indeed possibly a better flyer than Archaeopteryx. He noted that the Microraptor's fused sternum, asymmetrical feathers, and features of the shoulder girdle indicated that it could fly under its own power, rather than merely gliding. Today, most scientists agree that Microraptor had the anatomical features expected of a flying animal, though it would have been a less advanced form of flight compared to birds. For example, some studies suggest the shoulder joint was too primitive to allow a full flapping flight stroke. In the ancestral anatomy of theropod dinosaurs, the shoulder socket faced downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the vertebral column until relatively advanced avialans like the enantiornithes appeared.[13] However, other scientists have argued that the shoulder girdle in some paravian theropods, including Microraptor, is curved in such a way that the shoulder joint could only have been positioned high on the back, allowing for a nearly vertical upstroke of the wing. This possibly advanced shoulder anatomy, combined with the presence of a propatagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an alula, much like a "thumb-like" form of leading edge slot, may indicate that Microraptor was capable of true, powered flight.[14]

Other studies have demonstrated that the wings of Microraptor were large enough to generate the lift necessary for powered launching into flight even without a fully vertical flight stroke. A 2016 study of incipient flight ability in paravians demonstrated that Microraptor was capable of wing-assisted incline running, as well as wing-assisted leaping and even ground-based launching.[12]

Stephen Czerkas, Gregory S. Paul, and others have argued that the fact Microraptor could fly and yet is also very clearly a dromaeosaurid suggests that the Dromaeosauridae, including later and larger species such as Deinonychus, were secondarily flightless. The work of Xu and colleagues also suggested that the ancestors of dromaeosaurids were probably small, arboreal, and capable of gliding, although later discoveries of more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view.[10][15] Work done on the question of flight ability in other paravians, however, showed that most of them probably would not have been able to achieve enough lift for powered flight, given their limited flight strokes and relatively smaller wings. These studies concluded that Microraptor probably evolved flight and its associated features (fused sternum, alula, etc.) independently of the ancestors of birds.[12]

Hindwing posture

Microraptor models
Wind tunnel experiments with different wing configurations

Sankar Chatterjee suggested in 2005 that, in order for Microraptor to glide or fly, the forewings and hindwings must have been on different levels (as on a biplane) and not overlaid (as on a dragonfly), and that the latter posture would have been anatomically impossible. Using this biplane model, Chatterjee was able to calculate possible methods of gliding, and determined that Microraptor most likely employed a phugoid style of gliding: launching itself from a perch, the animal would have swooped downward in a deep U-shaped curve and then lifted again to land on another tree. The feathers not directly employed in the biplane wing structure, like those on the tibia and the tail, could have been used to control drag and alter the flight path, trajectory, etc. The orientation of the hindwings would also have helped the animal control its gliding flight. Chatterjee also used computer algorithms that test animal flight capacity to test whether or not Microraptor was capable of true, powered flight, as opposed to or in addition to passive gliding. The resulting data showed that Microraptor did have the requirements to sustain level powered flight, so it is theoretically possible that the animal flew, as opposed to gliding.[3]

Some paleontologists have doubted the biplane hypothesis, and have proposed other configurations. A 2010 study by Alexander et al. described the construction of a lightweight three-dimensional physical model used to perform glide tests. Using several hindleg configurations for the model, they found that the biplane model, while not unreasonable, was structurally deficient and needed a heavy-headed weight distribution for stable gliding, which they deemed unlikely. The study indicated that a laterally abducted hindwing structure represented the most biologically and aerodynamically consistent configuration for Microraptor.[2] A further analysis by Brougham and Brusatte, however, concluded that Alexander's model reconstruction was not consistent with all of the available data on Microraptor and argued that the study was insufficient for determining a likely flight pattern for Microraptor. Brougham and Brusatte criticized the anatomy of the model used by Alexander and his team, noting that the hip anatomy was not consistent with other dromaeosaurs. In most dromaeosaurids, features of the hip bone prevent the legs from splaying horizontally; instead, they are locked in a vertical position below the body. Alexander's team used a specimen of Microraptor which was crushed flat to make their model, which Brougham and Brusatte argued did not reflect its actual anatomy.[16] Later in 2010, Alexander's team responded to these criticisms, noting that the related dromaeosaur Hesperonychus, which is known from complete hip bones preserved in three dimensions, also shows hip sockets directed partially upward, possibly allowing the legs to splay more than in other dromaeosaurs.[17]

Ground movement

Microraptor by durbed
Restoration of two individuals by the ground

Due to the extent of the hindwings onto most of the animal's foot, many scientists have suggested that Microraptor would have been awkward during normal ground movement or running. The front wing feathers would also have hindered Microraptor when on the ground, due to the limited range of motion in the wrist and the extreme length of the wing feathers. A 2010 study by Corwin Sullivan and colleagues showed that, even with the wing folded as far as possible, the feathers would still have dragged along the ground if the arms were held in a neutral position, or extended forward as in a predatory strike. Only by keeping the wings elevated, or the upper arm extended fully backward, could Microraptor have avoided damaging the wing feathers. Therefore, it may have been anatomically impossible for Microraptor to have used its clawed forelimbs in capturing prey or manipulating objects.[18]

Implications

Tetrapteryx
William Beebe's hypothetical "Tetrapteryx" with four wings, 1915

The unique wing arrangement found in Microraptor raised the question of whether the evolution of flight in modern birds went through a four-winged stage, or whether four-winged gliders like Microraptor were an evolutionary side-branch that left no descendants. As early as 1915, naturalist William Beebe had argued that the evolution of bird flight may have gone through a four-winged (or tetrapteryx) stage.[19] Chatterjee and Templin did not take a strong stance on this possibility, noting that both a conventional interpretation and a tetrapteryx stage are equally possible. However, based on the presence of unusually long leg feathers in various feathered dinosaurs, Archaeopteryx, and some modern birds such as raptors, as well as the discovery of further dinosaur with long primary feathers on their feet (such as Pedopenna), the authors argued that the current body of evidence, both from morphology and phylogeny, suggests that bird flight did shift at some point from shared limb dominance to front-limb dominance, and that all modern birds may have evolved from four-winged ancestors, or at least ancestors with unusually long leg feathers relative to the modern configuration.[3]

Feeding

Microraptor gui cast
Close-up of a cast

In 2010 researchers announced that further preparation of the type fossil of M. zhaoianus revealed preserved probable gut contents. These consisted of mammalian bones, including possible skull, limb, and vertebral fragments and also a whole foot. The foot skeleton is similar to those of Eomaia and Sinodelphys. It corresponds to an animal with an estimated snout to vent length of 80 mm (3.1 in) and a mass of 20–25 g (0.71–0.88 oz). The unguals of the foot are less curved than in Eomaia or Sinodelphys, indicating that the mammal could climb but less effectively than in the two latter genera.[20]

In the December 6, 2011 issue of Proceedings of the National Academy of Sciences, Jingmai O'Connor and coauthors described a Microraptor specimen containing bird bones in its abdomen, specifically a partial wing and feet. Their position indicate that the dinosaur swallowed a tree-perching bird whole.[21]

In 2013 researchers announced that they had found fish scales in the abdominal cavity of a Microraptor specimen.[22] This new finding corrects the previous position that Microraptor hunted only in an arboreal environment. They also argued that the specimen showed a probable adaptation to a fish-eating diet: the good preservation of the mandible shows that the first three teeth were inclined anterodorsally, a character often associated with piscivory.[22] Microraptor was an opportunistic feeder, hunting the most common prey in both arboreal and aquatic habitats.[22]

In 2019, a new genus of scleroglossan lizard (Indrasaurus) was described from a specimen found in the stomach of a Microraptor. The Microraptor apparently swallowed its prey head first, a behavior typical of modern carnivorous birds and lizards. The Indrasaurus bones lacked marked pitting and scarring, indicating that the Microraptor died shortly after eating the lizard and before significant digestion had occurred.[23]

Unlike its fellow paravian Anchiornis, Microraptor has never been found with gastric pellets, despite the existence of four Microraptor specimens that preserve stomach contents. This suggests that Microraptor passed indigestible fur, feathers, and bits of bone in its droppings instead of producing pellets.[23]

Based on the size of the scleral ring of the eye, it has been suggested Microraptor hunted at night.[24] However, the discovery of iridescent plumage in Microraptor has cast doubt on this conclusion, as no modern birds that have iridescent plumage are known to be nocturnal (though, contrary to media claims about this discovery, the study authors themselves haven't ruled out nocturnality yet, as Microraptor is not similar in diet and behaviour to any modern iridescent birds).[7]

History

Naming controversy

Archaeoraptor-Paleozoological Museum of China
The "Archaeoraptor" fossil; the tail belongs to Microraptor

The initial naming of Microraptor was controversial, because of the unusual circumstances of its first description. The first specimen to be described was part of a chimeric specimen—a patchwork of different feathered dinosaur species (Microraptor itself, Yanornis and an as-of-yet undescribed third species) assembled from multiple specimens in China and smuggled to the USA for sale. After the forgery was revealed by Xu Xing of Beijing's Institute of Vertebrate Paleontology and Paleoanthropology, Storrs L. Olson, curator of birds in the National Museum of Natural History of the Smithsonian Institution, published a description of the tail in an obscure journal, giving it the name Archaeoraptor liaoningensis in an attempt to remove the name from the paleornithological record by assigning it to the part least likely to be a bird.[25] However, Xu had discovered the remainder of the specimen from which the tail had been taken and published a description of it later that year, giving it the name Microraptor zhaoianus.[26]

Since the two names designate the same individual as the type specimen, Microraptor zhaoianus would have been a junior objective synonym of Archaeoraptor liaoningensis and the latter, if valid, would have had priority under the International Code of Zoological Nomenclature. However, there is some doubt whether Olson in fact succeeded in meeting all the formal requirements for establishing a new taxon. Namely, Olson designated the specimen as a lectotype, before an actual type species was formally erected.[27] A similar situation arose with Tyrannosaurus rex and Manospondylus gigas, in which the former became a nomen protectum and the latter a nomen oblitum due to revisions in the ICZN rules that took place on December 31, 1999.[28] In addition, Xu's name for the type specimen (Microraptor) was subsequently used more frequently than the original name; as such, this and the chimeric nature of the specimen would render the name "Archaeoraptor" a nomen vanum (as it was improperly described) and the junior synonym Microraptor a nomen protectum (as it's been used in more published works than "Archaeoraptor" and was properly described).[29]

Additional specimens

Microraptor Skeletons by Qilong
Skeletal restorations of various specimens

The first specimen referred to Microraptor represented a small individual and included faint feather remnants, but was otherwise not well preserved and lacked a skull. In 2002 Mark Norell et al. described another specimen, BPM 1 3-13, which they did not name or refer to an existing species.[30] Later that year Stephen Czerkas et al. named the specimen Cryptovolans pauli, and referred two additional specimens (the first to show well-preserved feathers) to this species. The generic name was derived from Greek kryptos, "hidden", and Latin volans, "flying". The specific name, pauli, honors paleontologist Gregory S. Paul, who had long proposed that dromaeosaurids evolved from flying ancestors.[31]

The type specimens of C. pauli were collected from the Jiufotang Formation, dating from the early Albian and now belong to the collection of the Paleontology Museum of Beipiao, in Liaoning, China. They are referred to by the inventory numbers LPM 0200, the holotype; LPM 0201, its counterslab (slab and counterslab together represent the earlier BPM 1 3-13); and the paratype LPM 0159, a smaller skeleton. Both individuals are preserved as articulated compression fossils; they are reasonably complete but partially damaged.[31]

Czerkas et al. (2002) diagnosed the genus on the basis of having primary feathers (which in the authors' opinion made it a bird), a co-ossified sternum, a tail consisting of 28 to 30 vertebrae and a third finger with a short phalanx III-3.[31] Some of the feathers Czerkas described as primary were actually attached to the leg, rather than the arm. This, along with most of the other diagnostic characters, is also present in the genus Microraptor, which was first described earlier than Cryptovolans.[32] However, BPM 1 3-13 has a longer tail, proportionately, than other Microraptor specimens that had been described by 2002, which have 24 to 26 tail vertebrae.[30]

Subsequent studies (and more specimens of Microraptor) have shown that the features used to distinguish Cryptovolans are not unique, but are present to varying degrees across various specimens. In a review by Phil Senter and colleagues in 2004, the scientists suggested that all these features represented individual variation across various age groups of a single Microraptor species, making the name Cryptovolans pauli and Microraptor gui junior synonyms of Microraptor zhaoianus.[1] Many other researchers, including Alan Feduccia and Tom Holtz, have since supported its synonymy.[4][33]

A new specimen of Microraptor, BMNHC PH881, showed several features previously unknown in the animal, including the probably glossy-black iridescent plumage coloration. The new specimen also featured a bifurcated tailfan, similar in shape to previously known Microraptor tailfans except sporting a pair of long, narrow feathers at the center of the fan. The new specimen also showed no sign of the nuchal crest, indicating that the crest inferred from the holotype specimen may be an artifact of taphonomic distortion.[7][8]

Numerous further specimens likely belonging to Microraptor have been uncovered, all from the Shangheshou Bed of the Jiufotang Formation in Liaoning, China. In fact, Microraptor is the most abundant non-avialan dinosaur fossil type found in this formation.[34] In 2010, it was reported that there were over 300 undescribed specimens attributable to Microraptor or its close relatives among the collections of several Chinese museums, though many had been altered or composited by private fossil collectors.[2]

Study and debate

Microraptor zhaoianus
Fossil specimen

Norell et al. (2002) described BPM 1 3-13 as the first dinosaur known to have flight feathers on its legs as well as on its arms.[35]

Czerkas (2002) mistakenly described the fossil as having no long feathers on its legs, but only on its hands and arms, as he illustrated on the cover of his book Feathered Dinosaurs and the Origin of Flight.[31] In his discussion of Cryptovolans in this book, Czerkas strongly denounces Norell's conclusions; "The misinterpretation of the primary wing feathers as being from the hind legs stems directly to [sic] seeing what one believes and wants to see".[31] Czerkas also denounced Norell for failing to conclude that dromaeosaurs are birds, accusing him of succumbing to "...the blinding influences of preconceived ideas."[31] The crown group definition of Aves, as a subset of Avialae, the explicit definition of the term "bird" that Norell employs, would definitely exclude BPM 1 3-13. However, he does not consider the specimen to belong to Avialae either.[35]

Czerkas's interpretation of the hindleg feathers noted by Norell proved to be incorrect the following year, when additional specimens of Microraptor were published by Xu and colleagues, showing a distinctive "hindwing" completely separate from the forelimb wing. The first of these specimens was discovered in 2001, and between 2001 and 2003 four more specimens were bought from private collectors by Xu's museum, the Institute of Vertebrate Paleontology and Paleoanthropology. Xu also considered these specimens, most of which had hindwings and proportional differences from the original Microraptor specimen, to be a new species, which he named Microraptor gui. However, Senter also questioned this classification, noting that as with Cryptovolans, most of the differences appeared to correspond with size, and likely age differences.[1] Two further specimens, classified as M. zhaoianus in 2002 (M. gui had not yet been named), have also been described by Hwang and colleagues.[6]

Czerkas also believed that the animal may have been able to fly better than Archaeopteryx, the animal usually referred to as the earliest known bird. He cited the fused sternum and asymmetrical feathers, and argued that Microraptor has modern bird features that make it more derived than Archaeopteryx. Czerkas cited the fact that this possibly volant animal is also very clearly a dromaeosaurid to suggest that the Dromaeosauridae might actually be a basal bird group, and that later, larger, species such as Deinonychus were secondarily flightless (Czerkas, 2002). The current consensus is that there is not enough evidence to conclude whether dromaeosaurs descended from an ancestor with some aerodynamic abilities. The work of Xu et al. (2003) suggested that basal dromaeosaurs were probably small, arboreal, and could glide.[36] The work of Turner et al. (2007) suggested that the ancestral dromaeosaur could not glide or fly, but that there was good evidence that it was small-bodied (around 65 cm long and 600–700 g in mass).[15]

Classification

Dromaeosaurs
Size of Microraptor (1) compared with other dromaeosaurs
Shandong Microraptor
Specimen in the Shandong Tianyu Museum of Nature

The cladogram below follows a 2012 analysis by paleontologists Phil Senter, James I. Kirkland, Donald D. DeBlieux, Scott Madsen and Natalie Toth.[37]

Dromaeosauridae

Xiaotingia Xiaotingia

Unenlagiinae Austroraptor Restoration (flipped)

Shanag Shanag

Eudromaeosauria

Saurornitholestinae

Velociraptorinae Fred Wierum Velociraptor

Dromaeosaurinae Deinonychus ewilloughby (flipped)

Microraptoria

Tianyuraptor

Hesperonychus

Microraptor sp.

Microraptor gui Fred Wierum Microraptor

Microraptor zhaoianus

Cryptovolans

Graciliraptor Graciliraptor

Sinornithosaurus Sinornithosaurus

See also

References

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Adasaurus

Adasaurus ( AH-də-SAWR-əs; "Ada's lizard") is a dromaeosaurid theropod dinosaur from the Late Cretaceous Period of Central Asia. It was a small bipedal carnivore with a sickle-shaped claw on the second toe of each hind foot, and was perhaps 1.8 m (5.9 ft) long. The genus name Adasaurus is taken from Ada, an evil spirit in the mythology of Mongolia, and the Greek word sauros meaning 'lizard'. The species name, for the single species, (A. mongoliensis), refers to the country of origin. Adasaurus was named and described in 1983 by Mongolian paleontologist Rinchen Barsbold.

Adasaurus is a member of Dromaeosauridae, a group that is closely related to living birds. Other dromaeosaurids include Deinonychus, Velociraptor, Microraptor, and Buitreraptor. The relationships of Adasaurus are poorly understood. Traditionally, Adasaurus is assigned to the Dromaeosaurinae, which includes heavily built animals such as Dromaeosaurus and Utahraptor but several recent studies have suggested that it may be a member of the Velociraptorinae instead.Two specimens of Adasaurus have been found, both from the Nemegt Formation in the Gobi Desert of southern Mongolia. The holotype, IGM 100/20, is an incomplete skeleton with partial skull, including the vertebral column except the back of the tail, all three bones of the pelvis, the shoulder girdle and the hindlimbs. The second specimen, the paratype IGM 100/51 also described in the original paper, consists of the back end of another skeleton, including the hindlimbs. Both specimens are currently in the collection of the Mongolian Geological Institute in Ulaanbaatar, Mongolia.

The age of the Nemegt is not known for certain, but it is commonly thought to belong to the Maastrichtian stage of the Late Cretaceous Period., and Adasaurus would therefore have lived between 72 and 66 million years ago. Other dinosaurs found in this formation include the tyrannosaur Tarbosaurus, the ornithomimid Anserimimus, the troodontid Zanabazar, and the hadrosaur Saurolophus.

Anchiornis

Anchiornis is a genus of small, four-winged paravian dinosaur. The genus Anchiornis contains only the type species Anchiornis huxleyi, named for its similarity to modern birds. Anchiornis fossils have been only found in the Tiaojishan Formation of Liaoning, China, in rocks dated to the Late Jurassic, about 160 million years ago. Anchiornis 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. Anchiornis huxleyi translates to "T.H. Huxley's near-bird" in Greek.

Archaeoraptor

"Archaeoraptor" is the informal generic name for a fossil from China in an article published in National Geographic magazine in 1999. The magazine claimed that the fossil was a "missing link" between birds and terrestrial theropod dinosaurs. Even prior to this publication there had been severe doubts about the fossil's authenticity. Further scientific study showed it to be a forgery constructed from rearranged pieces of real fossils from different species. Zhou et al. found that the head and upper body actually belong to a specimen of the primitive fossil bird Yanornis. A 2002 study found that the tail belongs to a small winged dromaeosaur, Microraptor, named in 2000. The legs and feet belong to an as yet unknown animal.The scandal brought attention to illegal fossil deals conducted in China. Although "Archaeoraptor" was a forgery, many true examples of feathered dinosaurs have been found and demonstrate the evolutionary connection between birds and other theropods.

Barremian

The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 125.0 ± 1.0 Ma). It is a subdivision of the Early Cretaceous epoch (or Lower Cretaceous series). It is preceded by the Hauterivian and followed by the Aptian stage.

Biplane

A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a biplane wing structure has a structural advantage over a monoplane, it produces more drag than a similar unbraced or cantilever monoplane wing. Improved structural techniques, better materials and the quest for greater speed made the biplane configuration obsolete for most purposes by the late 1930s.

Biplanes offer several advantages over conventional cantilever monoplane designs: they permit lighter wing structures, low wing loading and smaller span for a given wing area. However, interference between the airflow over each wing increases drag substantially, and biplanes generally need extensive bracing, which causes additional drag.

Biplanes are distinguished from tandem wing arrangements, where the wings are placed forward and aft, instead of above and below.

The term is also occasionally used in biology, to describe the wings of some flying animals.

David Attenborough's Conquest of the Skies 3D

David Attenborough's Conquest of the Skies 3D is a British natural history television series tracking the evolution of flight in animals. Attenborough analyses gliding reptiles, parachuting mammals, acrobatic insects and the world of birds.

Dinosaur coloration

Dinosaur color is one of the unknowns in the field of paleontology as skin pigmentation is nearly always lost during the fossilization process. However, recent studies of feathered dinosaurs have shown that we might be able to infer the color of some species through the use of melanosomes, the color-determining pigments within the feathers.

Dromaeosauridae

Dromaeosauridae is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek δρομεῦς (dromeus) meaning 'runner' and σαῦρος (sauros) meaning 'lizard'. In informal usage they are often called raptors (after Velociraptor), a term popularized by the film Jurassic Park; a few types include the term "raptor" directly in their name and have come to emphasize their bird-like appearance and speculated bird-like behavior.

Dromaeosaurid fossils have been found across the globe in North America, Europe, Africa, Asia, South America and Antarctica, with fossilized teeth giving credence to the possibility that they inhabited Australia as well. They first appeared in the mid-Jurassic Period (late Bathonian stage, about 167 million years ago) and survived until the end of the Cretaceous (Maastrichtian stage, 66 ma), existing until the Cretaceous–Paleogene extinction event. The presence of dromaeosaurids as early as the Middle Jurassic has been suggested by the discovery of isolated fossil teeth, though no dromaeosaurid body fossils have been found from this period.

Graciliraptor

Graciliraptor (meaning "graceful thief") is a genus of theropod dinosaur from the early Cretaceous Period. It is a microraptorine dromaeosaurid.

The type species Graciliraptor lujiatunensis was first named and described in 2004 by Xu Xing and Wang Xiaoling. The generic name is derived from Latin gracilis and raptor. The specific name refers to the village Lujiatun where the fossil site is located. Its fossil, holotype IVPP V 13474, was found in Beipiao, Liaoning Province, China.

Indrasaurus

Indrasaurus is a genus of extinct lizards, containing one species, Indrasaurus wangi. Its fossil remains were found as stomach contents of a Microraptor fossil specimen found in the Liaoning province, China in 2003. It was found by a team of paleontologists led by Professor Jingmai O'Connor from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), together with researchers from the Shandong Tianyu Museum of Nature. The stomach content of the Microraptor was not recognised by scientists when it was first uncovered. On further examination by scientists in 2019, the Microraptor stomach contents were revealed to contain the fully swallowed remains of a previously unknown lizard species. Following this, the new species was formally described and named in 2019.. The species was named after Prof. Wang Yuan of IVPP, also the director of the Paleozoological Museum of China at the time of identification of the species and an expert on the paleoherpetofauna of China. The name Indrasaurus was inspired by a Vedic legend in which god Indra was swallowed by a dragon-like creature during a great battle (the dragon in the legend being equated with the Microraptor specimen that had swallowed the lizard specimen).

Jiufotang Formation

The Jiufotang Formation (Chinese: 九佛堂组, pinyin: jiǔfótáng zǔ) is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with estimates ranging from the Late Jurassic to the Early Cretaceous. He et al. (2004) used argon - isotope radiometry to confirm biostratigraphic age estimates. They confirmed an Early Cretaceous, Aptian age for the Jiufotang Formation, 120.3 +/-0.7 million years ago. Fossils of Microraptor and Jeholornis are from the Jiufotang.

Microraptoria

Microraptoria (Greek, μίκρος, mīkros: "small"; Latin, raptor: "one who seizes") is a clade of basal dromaeosaurid theropod dinosaurs. The first microraptorians appeared 125 million years ago in China. Many are known for long feathers on their legs and may have been semi-arboreal powered fliers, some of which even capable of launching from the ground. Most microraptorians were relatively small; adult specimens of Microraptor range between 77–90 centimetres long (2.53–2.95 ft) and weigh up to 1 kilogram (2.2 lb), making them some of the smallest known dinosaurs.

Paraves

Paraves are a widespread group of theropod dinosaurs that originated in the Late Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and scansoriopterygids, the group also contains the avialans, among which are the over ten thousand species of living birds. Primitive members of Paraves are well known for the possession of an enlarged claw on the second digit of the foot, which was held off the ground when walking in some species.

Pedopenna

Pedopenna (meaning "foot feather") is a genus of small, feathered, maniraptoran dinosaur from the Daohugou Beds in China. It is possibly older than Archaeopteryx, though the age of the Daohugou Beds where it was found is debated. A majority of studies suggest that beds probably date from between the late Middle Jurassic (168 million years ago) and early Late Jurassic Period (164-152 million years ago).The name Pedopenna refers to the long pennaceous feathers on the metatarsus; daohugouensis refers to the locality of Daohugou, where the holotype was found. Pedopenna daohugouensis probably measured 1 meter (3 ft) or less in length, but since this species is only known from the hind legs, the actual length is difficult to estimate. Pedopenna was originally classified as a paravian, the group of maniraptoran dinosaurs that includes both deinonychosaurs and avialans (the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.

Serikornis

Serikornis is a genus of small, feathered anchiornithid dinosaur from the Upper Jurassic Tiaojishan Formation of Liaoning, China. It is represented by the type species Serikornis sungei. Its name means "Ge Sun's silk bird", a reference to the plumulaceous-like body covering evident in the fossil. The specimen's nickname, "Silky", refers to the striking resemblance of the delicate hindlimb filaments to the modern Silky breed of domestic chicken.Serikornis, first described in August 2017, is noteworthy for the variety of feather types represented in its holotype, a single complete articulated skeleton preserved on a slab along with extensive integumentary structures. The specimen's feather imprints include wispy bundles along the neck, short and symmetrical vaned feathers on the arms, and both fuzz and long pennaceous feathers on its hindlimbs. While its anatomy and integument share features with birds as well as derived dromaeosaurs such as Microraptor, cladistic analysis places the genus within the cluster of feathered dinosaurs near the origin of avians. It was unlikely to be a flier.

Shanag

Shanag is a genus of dromaeosaurid theropod dinosaur from the Early Cretaceous Period of Mongolia.

The type species of Shanag is S. ashile. It was named and described by Alan Turner, Sunny Hai-Ching Hwang and Mark Norell in 2007. The generic name refers to the black-hatted dancers in the Buddhist Cham dance. The specific name refers to the Ashile Formation, the old name for the layers where Shanag was found, used by Henry Fairfield Osborn.The holotype of Shanag, IGM 100/1119, was discovered in the Öösh Formation, the stratification of which is uncertain but probably dating to the Berriasian-Barremian. Shanag bears a strong resemblance to basal Chinese dromaeosaurids such as Microraptor and Sinornithosaurus, suggesting a close similarity between the fauna of the Öösh deposits, dated tentatively to 130 million years ago, and the Jehol Biota of China (such as the animals found in the roughly contemporary Yixian Formation), during the Early Cretaceous. The holotype specimen, about six centimetres long, is composed of an associated uncompressed upper and lower jaw fragment, containing a nearly complete right maxilla with teeth, a partial right dentary with teeth and an attached partial splenial.Shanag was a small predator. In 2010 Gregory S. Paul estimated its length at 1.5 metres, the weight at five kilogrammes. Shanag shows a mixture of dromaeosaurid, troodontid and basal avialan traits.Turner et alii assigned Shanag to the Dromaeosauridae. Their cladistic analysis indicated that it was a basal dromaeosaurid but higher in the tree than the Unenlagiinae. Later analyses recovered it in the Microraptorinae.

Sinornithosaurus

Sinornithosaurus (derived from a combination of Latin and Greek, meaning 'Chinese bird-lizard') is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period (early Aptian) of the Yixian Formation in what is now China. It was the fifth non–avian feathered dinosaur genus discovered by 1999. The original specimen was collected from the Sihetun locality of western Liaoning. It was found in the Jianshangou beds of the Yixian Formation, dated to 124.5 million years ago. Additional specimens have been found in the younger Dawangzhangzi bed, dating to around 122 million years ago.Xu Xing described Sinornithosaurus and performed a phylogenetic analysis which demonstrated that it is basal, or primitive, among the dromaeosaurs. He has also demonstrated that features of the skull and shoulder are very similar to Archaeopteryx and other Avialae. Together these two facts demonstrate that the earliest dromaeosaurs were more like birds than the later dromaeosaurs were.

Sinornithosaurus was among the smallest dromaeosaurids, with a length of about 90 centimetres (3.0 ft). In 2010, Gregory S. Paul gave higher estimations of 1.2 metres and three kilogrammes.

Timeline of dromaeosaurid research

This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like Velociraptor. Since the Native Americans of Montana used the sediments of the Cloverly Formation to produce pigments, they may have encountered remains of the dromaeosaurid Deinonychus hundreds of years before these fossils came to the attention of formally trained scientists.In 1922 Matthew and Brown named the new genus and species Dromaeosaurus albertensis, considering it a new type within the family Deinodontidae, a now defunct family name that once applied to the tyrannosaurs. Not long after, Velociraptor was discovered in Mongolia by the Central Asiatic Expedition. Dromaeosaur research was fairly quiet until the 1960s, when John Ostrom described the new genus and species Deinonychus antirrhopus. This discovery played a major role in setting off the Dinosaur Renaissance because Deinonychus was obviously a vigorous, active animal, and exhibited characteristics linking it to the origin of birds. As such it brought support for controversial reinterpretations of dinosaurs as warm-blooded and ancestral to birds. Its distinct nature and similarity to Dromaeosaurus led Ostrom to follow Edwin Colbert and Dale Russel's suggestion that the Dromaeosaurinae be regarded as its own family separate from the Deinodontidae.After Ostrom's initial research on Deinonychus, evidence continued to mount for a close evolutionary relationship between dromaeosaurids and birds. The dromaeosaurid Sinornithosaurus milennii, described in 1999 by Xu, Wang, and Wu, is a notable example as the fine-grained Chinese limestone from which it was collected preserved its life covering of feathers. Discoveries of feathered dromaeosaurids continued into the 2000s. Xu, Zhou, and Wang named the new genus Microraptor in 2000. Three years later, Xu and others would report a new species in this genus that exhibited a bizarre "four winged" body plan with long pennaceous flight feathers on both its front and hind limbs.

Zhenyuanlong

Zhenyuanlong (meaning "Zhenyuan's dragon", from Chinese Pinyin 龙 lóng "dragon") is a genus of dromaeosaurid dinosaur from the Yixian Formation of Liaoning, China. It lived during the Aptian age of the early Cretaceous period, approximately 125 million years ago. It is known from a single specimen belonging to the species Zhenyuanlong suni (Chinese: 孫氏振元龍). This type specimen preserved a nearly complete skeleton that contains traces of feathers, including long tail feathers and large wings. In addition to further complicating diversity of Liaoning dromaeosaurids, this specimen provides the first evidence of well-developed pennaceous feathers in a large, non-flying dromaeosaur, raising the question of what function such wings would serve.

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