Microraptor
Encyclopedia
Microraptor is a genus
of small, four-winged dromaeosaurid dinosaur
s. 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.
Like Archaeopteryx
, Microraptor provides important evidence about the evolutionary relationship between bird
s and dinosaurs. Microraptor had long pennaceous feather
s that formed aerodynamic surfaces on the arms and tail but also, surprisingly, on the legs. This led paleontologist Xu Xing in 2003 to describe it as a "four-winged dinosaur" and to speculate that it may have glided using all four limbs for lift. Two species have been named, M. zhaoianus and M. gui, though further study has suggested that all of the specimens belong to a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dromaeosaur, is usually considered be a synonym of Microraptor.
Microraptor was among the most abundant non-avian dinosaurs in its ecosystem, and is represented by more fossils than any other dromaeosaurid, with possibly over 300 fossil
specimens represented across various museum collections.
. Aside from its extremely small size, Microraptor was among the first non-avian
dinosaurs discovered with the impressions of feathers and wings. Three specimens of M. zhaoianus have been described in detail, in addition to two specimens of M. gui and three specimens of M. sp. described by Xu and colleagues in 2003, 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 its feet as well as its forearms and hands. 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 Microraptors head to those of the Philippine Eagle
. Bands of dark and light present on some specimens may indicate color patterns present in life. 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 deinonychosauria
n split between dromaeosaurids and troodontids.
s, one on each of its forelegs and hind legs. The long feathers on the legs of Microraptor were true flight feathers as seen in modern bird
s, 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 hind legs, with flight feather
s anchored to the upper foot bones as well as the upper and lower leg. It has been proposed that the animal glided and probably lived mainly in trees, because the hind wings anchored to the feet of Microraptor would have hindered their ability to run on the ground. It had long pennaceous feathers on arms and hands (10–20 cm (3.9–7.9 in)), with legs and feet 11–15 cm (4.3–5.9 in). Toward the tail end, Microraptor was covered in shorter downy (plumulaceous) feathers, 2–6 cm (0.78740157480315–2.4 in). 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.
When describing specimens originally referred to the distinct species Cryptovolans pauli, paleontologist Stephen Czerkas argued that Microraptor may have been able to fly better than Archaeopteryx
, noting the fused sternum and asymmetrical feathers of Microraptor, as well as features of the shoulder girdle that indicate flying ability closer to modern birds than to 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. The work of Xu and colleagues also suggested that basal dromaeosaurs were probably small, arboreal, and could at least glide, though later discoveries of even more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view.
determined in 2005 that, in order for Microraptor to glide or fly, the fore and hind wings 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 hind wings would also have helped the animal control its gliding flight. Chatterjee also used computer algorithm
s that test animal flight capacity to test whether or not Microraptor was capable of true, powered flight, 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 on occasion in addition to gliding.
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 hind leg 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. 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. Also 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.
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. 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.
Chatterjee and Templin also ruled out the possibility of a ground-based takeoff. Microraptor lacked the necessary adaptations in its shoulder joint to lift its front wings high enough vertically to generate lift from the ground, and the authors argued that a ground-based takeoff would have damaged flight feathers on the feet. This leaves only the possibility of launching from an elevated perch, and the authors noted that even modern birds do not need to use excess power when launching from trees, but use the downward-swooping technique they found in Microraptor.
The unique wing arrangement found in Microraptor raised the question of its importance to the origin of flight in modern birds—did avian flight go through a four-winged stage, or were four-winged gliders like Microraptor an evolutionary side-branch that did not leave 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. 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.
and Sinodelphys
. It corresponds to an animal with an estimated snout to vent length of 80mm and a mass of 20-25 grams. 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 species.
Based on the size of the scleral ring of the eye, Microraptor is thought to have hunted at night.
. 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. 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.
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. Most paleontologists have since ignored the name Archaeoraptor, while the name Microraptor zhaoianus Xu et al., 2000 has attained universal currency.
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. 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.
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.
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 28-30 vertebrae and a third finger with a short phalanx III-3. 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. However, BPM 1 3-13 has a longer tail, proportionately, than other Microraptor specimens that had been described by 2002, which have 24-26 tail vertebrae.
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. Many other researchers, including Alan Feduccia and Tom Holtz, have since supported its synonymy.
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. 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.
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. 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". Later multiple specimens of Microraptor confirmed Norell's interpretation. Czerkas corrected his own mistake in later versions of the art for his traveling exhibit Feathered Dinosaurs and the Origin of Flight.http://www.fresnomet.org/exhibition/feathered_dinosaurs Czerkas also denounced Norell for failing to conclude that dromaeosaurs are birds, accusing him of succumbing to "...the blinding influences of preconceived ideas." 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 (see Avialae
).
Czerkas' interpretation of the hind leg 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 "hind wing" 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 hind wings 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. Two further specimens, classified as M. zhaoianus in 2002 (M. gui had not yet been named), have also been described by Hwang and colleagues.
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. 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 centimeters long and 600-700 grams in mass). See Dromaeosauridae
, Relationship with Birds.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of small, four-winged dromaeosaurid dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. Numerous well-preserved fossil specimens have been recovered from Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. They date from the early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Jiufotang Formation
Jiufotang Formation
The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
(Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
stage), 120 million years ago.
Like Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, Microraptor provides important evidence about the evolutionary relationship between bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and dinosaurs. Microraptor had long pennaceous feather
Pennaceous feather
Pennaceous feathers are also known as contour feathers. This type of feather is present in most modern birds, and has been shown in some species of maniraptoran dinosaurs....
s that formed aerodynamic surfaces on the arms and tail but also, surprisingly, on the legs. This led paleontologist Xu Xing in 2003 to describe it as a "four-winged dinosaur" and to speculate that it may have glided using all four limbs for lift. Two species have been named, M. zhaoianus and M. gui, though further study has suggested that all of the specimens belong to a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dromaeosaur, is usually considered be a synonym of Microraptor.
Microraptor was among the most abundant non-avian dinosaurs in its ecosystem, and is represented by more fossils than any other dromaeosaurid, with possibly over 300 fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
specimens represented across various museum collections.
Description
With adult specimens ranging 77–90 cm (2.5–3 ft)) and with a weight estimated up to 1 kilograms (2.2 lb), Microraptor was among the smallest known non-avian dinosaursDinosaur size
Size has been one of the most interesting aspects of dinosaur science to the general public. This article lists the largest and smallest dinosaurs from various groups, sorted in order of weight and length....
. Aside from its extremely small size, Microraptor was among the first non-avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
dinosaurs discovered with the impressions of feathers and wings. Three specimens of M. zhaoianus have been described in detail, in addition to two specimens of M. gui and three specimens of M. sp. described by Xu and colleagues in 2003, 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 its feet as well as its forearms and hands. 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 Microraptors head to those of the Philippine Eagle
Philippine Eagle
The Philippine Eagle , also known as the Monkey-eating Eagle, is an eagle of the family Accipitridae that is endemic to forests in the Philippines. It has brown and white-coloured plumage, and a shaggy crest, and generally measures in length and weighs...
. Bands of dark and light present on some specimens may indicate color patterns present in life. 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
Sinovenator
Sinovenator is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period. Two fossils were originally found in the Lujiatun Beds of the lower Yixian Formation in China, about 125 million years ago during the Aptian age.The type species, Sinovenator changii, was...
; 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 deinonychosauria
Deinonychosauria
The Deinonychosauria were a clade of coelurosaurian theropod dinosaurs from the Late Jurassic and Cretaceous periods. These omnivores and carnivores are known for their switchblade-like second toe claws and for displaying numerous bird-like characteristics. The clade has been divided into two...
n split between dromaeosaurids and troodontids.
Wings and flight
Microraptor had four wingWing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s, one on each of its forelegs and hind legs. The long feathers on the legs of Microraptor were true flight feathers as seen in modern bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, 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 hind legs, with flight feather
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
s anchored to the upper foot bones as well as the upper and lower leg. It has been proposed that the animal glided and probably lived mainly in trees, because the hind wings anchored to the feet of Microraptor would have hindered their ability to run on the ground. It had long pennaceous feathers on arms and hands (10–20 cm (3.9–7.9 in)), with legs and feet 11–15 cm (4.3–5.9 in). Toward the tail end, Microraptor was covered in shorter downy (plumulaceous) feathers, 2–6 cm (0.78740157480315–2.4 in). 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.
When describing specimens originally referred to the distinct species Cryptovolans pauli, paleontologist Stephen Czerkas argued that Microraptor may have been able to fly better than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, noting the fused sternum and asymmetrical feathers of Microraptor, as well as features of the shoulder girdle that indicate flying ability closer to modern birds than to 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
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
were secondarily flightless. The work of Xu and colleagues also suggested that basal dromaeosaurs were probably small, arboreal, and could at least glide, though later discoveries of even more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view.
Hind wing posture
Sankar ChatterjeeSankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
determined in 2005 that, in order for Microraptor to glide or fly, the fore and hind wings must have been on different levels (as on a biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
) and not overlaid (as on a dragonfly
Dragonfly
A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...
), and that the latter posture would have been anatomically impossible. Using this biplane model, Chatterjee was able to calculate possible methods of gliding
Gliding (flight)
Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...
, and determined that Microraptor most likely employed a phugoid
Phugoid
A phugoid or fugoid is an aircraft motion where the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "uphill" and "downhill." This is one of the basic flight dynamics modes of an aircraft , and a classic example of a positive...
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
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
and the tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
, could have been used to control drag and alter the flight path, trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
, etc. The orientation of the hind wings would also have helped the animal control its gliding flight. Chatterjee also used computer algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
s that test animal flight capacity to test whether or not Microraptor was capable of true, powered flight, 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 on occasion in addition to gliding.
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 hind leg 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. 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. Also in 2010, Alexander's team responded to these criticisms, noting that the related dromaeosaur Hesperonychus
Hesperonychus
Hesperonychus was a genus of small, carnivorous dromaeosaurid dinosaur. There is one described species, Hesperonychus elizabethae; the type species was named in honor of the woman who collected it in 1982...
, 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.
Ground movement
Due to the extent of the hind wings 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.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. 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.
Chatterjee and Templin also ruled out the possibility of a ground-based takeoff. Microraptor lacked the necessary adaptations in its shoulder joint to lift its front wings high enough vertically to generate lift from the ground, and the authors argued that a ground-based takeoff would have damaged flight feathers on the feet. This leaves only the possibility of launching from an elevated perch, and the authors noted that even modern birds do not need to use excess power when launching from trees, but use the downward-swooping technique they found in Microraptor.
Implications
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
William Beebe
William Beebe
William Beebe, born Charles William Beebe was an American naturalist, ornithologist, marine biologist, entomologist, explorer, and author...
had argued that the evolution of bird flight may have gone through a four-winged (or tetrapteryx) stage. 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
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, 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
Pedopenna
Pedopenna 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...
), 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.
Feeding
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 EomaiaEomaia
Eomaia is an extinct fossil mammal, discovered in rocks that were found in the Yixian Formation, Liaoning Province, China, and dated to the Barremian Age of the Lower Cretaceous about . The fossil is in length and virtually complete. An estimate of the body weight is between . It is exceptionally...
and Sinodelphys
Sinodelphys
Sinodelphys is an extinct mammal from the Early Cretaceous. To date, it is the oldest metatherian fossil known, estimated to be 125 million years old...
. It corresponds to an animal with an estimated snout to vent length of 80mm and a mass of 20-25 grams. The unguals of the foot are less curved than in Eomaia
Eomaia
Eomaia is an extinct fossil mammal, discovered in rocks that were found in the Yixian Formation, Liaoning Province, China, and dated to the Barremian Age of the Lower Cretaceous about . The fossil is in length and virtually complete. An estimate of the body weight is between . It is exceptionally...
or Sinodelphys
Sinodelphys
Sinodelphys is an extinct mammal from the Early Cretaceous. To date, it is the oldest metatherian fossil known, estimated to be 125 million years old...
, indicating that the mammal could climb but less effectively than in the two latter species.
Based on the size of the scleral ring of the eye, Microraptor is thought to have hunted at night.
Naming controversy
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 unrelated feathered dinosaur species assembled from multiple specimens in China and smuggled to the USA for saleFossil trade
Fossil trading is the practice of buying and selling fossils. This is many times done illegally with stolen fossils, and many important scientific specimens are lost each year...
. After the forgery was revealed by Xu Xing of Beijing
Beijing
Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...
's Institute of Vertebrate Paleontology and Paleoanthropology
Institute of Vertebrate Paleontology and Paleoanthropology
The Institute of Vertebrate Paleontology and Paleoanthropology of China is a prominent research institution and collections repository for fossils, including many dinosaur and pterosaurand cat poo specimens...
, Storrs L. Olson
Storrs L. Olson
Storrs Lovejoy Olson is an American biologist and ornithologist from the Smithsonian Institution. He is one of the world's foremost avian paleontologists....
, curator of birds in the National Museum of Natural History
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
of the Smithsonian Institution
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
, 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. 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.
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
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
. 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
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
, before an actual type species was formally erected. Most paleontologists have since ignored the name Archaeoraptor, while the name Microraptor zhaoianus Xu et al., 2000 has attained universal currency.
Additional specimens
In 2002 Mark Norell et al. described another specimen, BPM 1 3-13, which they did not name or refer to an existing species. 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
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
volans, "flying". The specific name, pauli, honors paleontologist Gregory S. Paul
Gregory S. Paul
Gregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
, who had long proposed that dromaeosaurids evolved from flying ancestors.
The type specimens of C. pauli were collected from the Jiufotang Formation
Jiufotang Formation
The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
, dating from the early Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
and now belong to the collection of the Paleontology Museum of Beipiao, in Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China. They are referred to by the inventory numbers LPM 0200, the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
; LPM 0201, its counterslab (slab and counterslab together represent the earlier BPM 1 3-13); and the paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
LPM 0159, a smaller skeleton. Both individuals are preserved as articulated compression fossils; they are reasonably complete but partially damaged.
Czerkas et al. (2002) diagnosed the genus on the basis of having primary feathers (which in the authors' opinion made it a bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
), a co-ossified sternum, a tail consisting of 28-30 vertebrae and a third finger with a short phalanx III-3. 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. However, BPM 1 3-13 has a longer tail, proportionately, than other Microraptor specimens that had been described by 2002, which have 24-26 tail vertebrae.
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. Many other researchers, including Alan Feduccia and Tom Holtz, have since supported its synonymy.
Numerous further specimens likely belonging to Microraptor have been uncovered, all from the Shangheshou Bed of the Jiufotang Formation
Jiufotang Formation
The Jiufotang Formation is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. . It is a member of the Jehol group. The exact age of the Jiufotang has been debated for years, with...
in Liaoning, China. In fact, Microraptor is the most abundant non-avialan dinosaur fossil type found in this formation. 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.
Study and debate
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.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. 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". Later multiple specimens of Microraptor confirmed Norell's interpretation. Czerkas corrected his own mistake in later versions of the art for his traveling exhibit Feathered Dinosaurs and the Origin of Flight.http://www.fresnomet.org/exhibition/feathered_dinosaurs Czerkas also denounced Norell for failing to conclude that dromaeosaurs are birds, accusing him of succumbing to "...the blinding influences of preconceived ideas." The crown group
Crown group
A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...
definition of Aves, as a subset of Avialae
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
, 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 (see Avialae
Avialae
Avialae is a clade of dinosaurs containing their only living representatives, birds , and the most immediate extinct relatives of birds.-Competing definitions:...
).
Czerkas' interpretation of the hind leg 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 "hind wing" 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
Institute of Vertebrate Paleontology and Paleoanthropology
The Institute of Vertebrate Paleontology and Paleoanthropology of China is a prominent research institution and collections repository for fossils, including many dinosaur and pterosaurand cat poo specimens...
. Xu also considered these specimens, most of which had hind wings 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. Two further specimens, classified as M. zhaoianus in 2002 (M. gui had not yet been named), have also been described by Hwang and colleagues.
Czerkas also believed that the animal may have been able to fly better than Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, 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
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
might actually be a basal bird group, and that later, larger, species such as Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
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. 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 centimeters long and 600-700 grams in mass). See Dromaeosauridae
Dromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
, Relationship with Birds.
External links
- A model of Microraptor/Cryptovolans pauli by Boban Filipovic
- Jacqui Hayes: Bird wings evolved from biplane dinosaurs COSMOS magazine
- The Four-Winged Dinosaur - PBS web site for the Nova documentary
