''Microraptor'' (
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
, μικρός, ''mīkros'': "small";
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, ''raptor'': "one who seizes") is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of small, four-winged
dromaeosaurid
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 ('), meaning ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. Numerous well-preserved
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
specimens have been recovered from
Liaoning
Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...
,
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. They date from the early
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
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 ...
(
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 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...
stage), 125 to 120 million
year
A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...
s 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''.
Like ''
Archaeopteryx
''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'', well-preserved fossils of ''Microraptor'' provide important evidence about the evolutionary relationship between
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s and earlier dinosaurs. ''Microraptor'' had long
pennaceous feather
The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs.
Description
A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the skin ...
s 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
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is a ...
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
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
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.
[
]
History
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 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
}
Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
's Institute of Vertebrate Paleontology and Paleoanthropology The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...
, Storrs L. Olson
Storrs Lovejoy Olson (April 3, 1944 – January 20, 2021) was an American biologist and ornithologist who spent his career at the Smithsonian Institution, retiring in 2008. One of the world's foremost avian paleontologists, he was best known ...
, curator of birds in the 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. It has free admission and is open 364 days a year. In 2021, with 7 ...
of the Smithsonian Institution
The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...
, published a description of the Microraptor's 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.[Olson, S.L. (2000). "Countdown to Piltdown at ''National Geographic'': the rise and fall of ''Archaeoraptor''." ''Backbone'', 13(2) (April): 1–3.] However, Xu had discovered the remains 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''.[Xu, X., Zhou, Z., and Wang, X. (2000). "The smallest known non-avian theropod dinosaur." ''Nature'', 408 (December): 705-708.]
Since the two names designate the same individual as the type specimen, ''Microraptor zhaoianus'' would have been a junior objective synonym
The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently.
* In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linnae ...
of ''Archaeoraptor liaoningensis'' and the latter, if valid, would have had priority under the International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...
. 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
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
, before an actual type species was formally erected.[Creisler, B. (2002).]
Archaeoraptor still a nomen nudum
" Message to the Dinosaur Mailing List, 4 Jan 2001. accessed 23 Sep 2009. A similar situation arose with ''Tyrannosaurus rex
''Tyrannosaurus'' is a genus of large theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosaurus'' live ...
'' 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.[Taylor, M. (2002).]
" So why hasn't ''Tyrannosaurus'' been renamed ''Manospondylus''?, 27 Aug 2002. accessed 30 Sept 2014. 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).[Williams, T. (2002).]
Archaeoraptor v Microraptor
" Message to the Dinosaur Mailing List, 1 Jan 2001. accessed 30 Sept 2014.
Additional 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
Mark Allen Norell (born July 26, 1957) is an American paleontologist, acknowledged as one of the most important living vertebrate paleontologists. He is currently the chairman of paleontology and a research associate at the American Museum of Na ...
et al. described another specimen, BPM 1 3-13, which they did not name or refer to an existing species.[Norell, Mark, Ji, Qiang, Gao, Keqin, Yuan, Chongxi, Zhao, Yibin, Wang, Lixia. (2002). "'Modern' feathers on a non-avian dinosaur". ''Nature'', 416: pp. 36. 7 March 2002.>] 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 (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''volans'', "flying". The specific name, ''pauli'', honors paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Gregory S. Paul
Gregory Scott Paul (born December 24, 1954) is an American 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 dino ...
, who had long proposed that dromaeosaurids evolved from flying ancestors.
The type specimen
In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...
s of ''C. pauli'' were collected from the 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 ...
, dating from the early 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 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...
and now belong to the collection of the Paleontology Museum of Beipiao, in Liaoning
Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...
, China. They are referred to by the inventory numbers LPM 0200, the holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
; LPM 0201, its counterslab (slab and counterslab together represent the earlier BPM 1 3-13); and the paratype
In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype nor a syntype). Of ...
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
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
), a co-ossified sternum, a tail consisting of 28 to 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 to 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.
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
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...
distortion.
Numerous further specimens likely belonging to ''Microraptor'' have been uncovered, all from the Shangheshou Bed of the 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 ...
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''.[Czerkas, Sylvia J. ed. (2002) "Feathered Dinosaurs and the Origin of Flight" The Dinosaur Museum Journal Volume 1. Blanding, Utah, USA. The Dinosaur Museum, August 1, 2002] 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'' ic''seeing what one believes and wants to see''". Czerkas also denounced Norell for failing to conclude that dromaeosaurs
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 ('), meaning ...
are birds, accusing him of succumbing to "''...the blinding influences of preconceived ideas.''" The crown group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
definition of Aves, as a subset of Avialae
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
, 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.
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 The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...
. 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.[ 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'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'', 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 () 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 ('), meaning ...
might actually be a basal bird group, and that later, larger, species such as ''Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'' 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 cm long and 600–700 g in mass).
Description
With adult specimens estimated up to ) and with a weight estimated up to , ''Microraptor'' was among the smallest-known non-avian dinosaurs. Holtz estimated it at .[Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,']
Winter 2010 Appendix.
/ref> An estimate by Benson ''et al.'' in 2012 was that ''Microraptor'' had a maximum length of . Aside from their extremely small size, ''Microraptor'' were among the first non-avialan
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...
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
The Philippine eagle (''Pithecophaga jefferyi''), also known as the monkey-eating eagle or great Philippine eagle, is a critically endangered species of eagle of the family Accipitridae which is endemic to forests in the Philippines. It has br ...
. Bands of dark and light present on some specimens may indicate color patterns present in life, though at least some individuals almost certainly possessed an iridescent black coloration. 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
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discov ...
. ''Microraptor'' is particularly similar to the basal troodontid ''Sinovenator
''Sinovenator'' (meaning "Chinese hunter") is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period (geology), Period.
Discovery and naming
Two specimens of a troodontidae, troodontid were described in 2002 in pale ...
''; 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.[Hwang, S.H., Norell, M.A., Ji, Q., and Gao, K. (2002). "New Specimens of ''Microraptor zhaoianus'' (Theropoda: Dromaeosauridae) from Northeastern China." ''American Museum Novitates'', 3381: 44pp.]
Coloration
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
Starlings are small to medium-sized passerine birds in the family Sturnidae. The Sturnidae are named for the genus ''Sturnus'', which in turn comes from the Latin word for starling, ''sturnus''. Many Asian species, particularly the larger ones, ...
, and indicated iridescence
Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...
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.
Classification
The cladogram below follows a 2012 analysis by paleontologists Phil Senter, James I. Kirkland, Donald D. DeBlieux, Scott Madsen and Natalie Toth.
Paleobiology
Wings and flight
''Microraptor'' had four wing
A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...
s, one on each of its forelimbs and hindlimbs, somewhat resembling one possible arrangement of the quartet of flight surfaces on a tandem wing QAC Quickie Q2
A tandem wing is a wing configuration in which a flying craft or animal has two or more sets of wings set one behind another. All the wings contribute to lift.
The tandem wing is distinct from the biplane in which the wings are ...
aircraft of today. It had long pennaceous feather
The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs.
Description
A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the skin ...
s on arms and hands with legs and feet . The long feathers on the legs of ''Microraptor'' were true flight feathers as seen in modern bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
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 hindlegs, with flight feather
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tail ...
s 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.
It was originally thought that ''Microraptor'' was a glider
Glider may refer to:
Aircraft and transport Aircraft
* Glider (aircraft), heavier-than-air aircraft primarily intended for unpowered flight
** Glider (sailplane), a rigid-winged glider aircraft with an undercarriage, used in the sport of glidin ...
, 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.[Xu, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F. and Du, X. (2003). "Four-winged dinosaurs from China." ''Nature'', 421(6921): 335-340, 23 Jan 2003.] 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. 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. 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.
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
''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
''. 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 vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
l column until relatively advanced avialans like the enantiornithes
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...
appeared. However, other scientists have argued that the shoulder girdle in some paravian
Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the aviala ...
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
The patagium (plural: patagia) is a membranous body part that assists an animal in obtaining lift when gliding or flight. The structure is found in extant and extinct groups of flying and gliding animals including bats, birds, some dromaeosaurs ...
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
The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive of ''ala'', meaning "wing". The al ...
, much like a "thumb-like" form of leading edge slot
A leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading-edge slot is a spanwise gap in each wing, allowing air to flow from below the wing ...
, may indicate that ''Microraptor'' was capable of true, powered flight.
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
Wing-assisted incline running (abbreviated as "WAIR") is a running behavior observed in living birds as well as a model proposed to explain the evolution of avian flight. WAIR allows birds to run up steep or vertical inclines by flapping their win ...
, as well as wing-assisted leaping and even ground-based launching.[
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
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 ('), meaning ...
, including later and larger species such as ''Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
'', were secondarily flightless. The work of Xu and colleagues also suggested that the ancestors of dromaeosaurids were probably small, arboreal, and capable of gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is al ...
, although later discoveries of more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view. 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.[
]
Hindwing posture
Sankar Chatterjee
Sankar Chatterjee (born May 28, 1943) 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 ...
suggested in 2005 that, in order for ''Microraptor'' to glide
Glide may refer to:
* Gliding flight, to fly without thrust
Computing
*Glide API, a 3D graphics interface
*Glide OS, a web desktop
*Glide (software), an instant video messenger
*Glide, a molecular docking software by Schrödinger (company), Schr ...
or fly, the forewings and hindwings must have been on different levels (as on a 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 ...
) and not overlaid (as on a dragonfly
A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonfly are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threate ...
), 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
In aviation, a phugoid or fugoid is an aircraft motion in which the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "downhill" and "uphill". This is one of the basic flig ...
'' 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
A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is expres ...
structure, like those on the tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and the tail
The tail is the section at the rear end of certain kinds of animals’ bodies; 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, r ...
, could have been used to control drag and alter the flight path
In the United States, airways or air routes are defined by the Federal Aviation Administration (FAA) in two ways:
"VOR Federal airways and Low/Medium Frequency (L/MF) (Colored) Federal airways"
These are designated routes which aeroplanes ...
, trajectory
A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete traj ...
, etc. The orientation of the hindwings would also have helped the animal control its gliding flight. Chatterjee also used computer algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
s that test animal flight
A number of animals are capable of aerial locomotion, either by powered flight or by gliding. This trait has appeared by evolution many times, without any single common ancestor. Flight has evolved at least four times in separate animals: insec ...
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.
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''. 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. Later in 2010, Alexander's team responded to these criticisms, noting that the related dromaeosaur ''Hesperonychus
''Hesperonychus'' (meaning "western claw") was a small, carnivorous dinosaur. It was a member of the family Dromaeosauridae, along with its larger relatives ''Deinonychus'' and ''Velociraptor''. There is one described species, ''Hesperonychus eli ...
'', 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 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.
Implications
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
Charles William Beebe ( ; July 29, 1877 – June 4, 1962) was an American naturalist, ornithologist, marine biologist, entomologist, explorer, and author. He is remembered for the numerous expeditions he conducted for the New York Zoological S ...
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'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'', and some modern birds such as raptors, as well as the discovery of further dinosaurs with long primary feathers on their feet (such as ''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 majori ...
''), 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, and a full study on them was later published in 2022 by David Hone and colleagues. These consisted of the remains of a mammal, primarily a complete and articulated right foot (including all tarsals, metatarsals
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...
, and most of the phalanges
The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.
...
) as well as the shafts of additional long bones and potentially other fragments. The foot skeleton is similar to those of ''Eomaia
''Eomaia'' ("dawn mother") is a genus of extinct fossil mammals containing the single species ''Eomaia scansoria'', discovered in rocks that were found in the Yixian Formation, Liaoning Province, China, and dated to the Barremian Age of the Lower ...
'' and ''Sinodelphys
''Sinodelphys'' is an extinct eutherian from the Early Cretaceous, estimated to be 125 million years old. It was discovered and described in 2003 in rocks of the Yixian Formation in Liaoning Province, China, by a team of scientists including Zhe ...
''. It corresponds to an animal with an estimated snout to vent length of and a mass of . 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 and so was likely not arboreal but potentially scansorial.
It is ambiguous whether the mammal had been predated upon or scavenged by the ''Microraptor'', although the lack of other definitive body parts consumed may suggest the low-muscle mass foot may have been eaten during a late stage of carcass consumption, possibly through scavenging. The find is a rare example of a theropod definitively consuming a Mesozoic mammal, the only other being a specimen of the compsognathid
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other ...
''Sinosauropteryx
''Sinosauropteryx'' (meaning "Chinese reptilian wing", ) is a compsognathid dinosaur. Described in 1996, it was the first dinosaur taxon outside of Avialae (birds and their immediate relatives) to be found with evidence of feathers. It was cover ...
''.[Larsson, Hans, Hone, David, Dececchi, T. Alexander, Sullivan, Corwin, Xu, Xing. "THE WINGED NON-AVIAN DINOSAUR MICRORAPTOR FED ON MAMMALS: IMPLICATIONS FOR THE JEHOL BIOTA ECOSYSTEM" "Program and Abstracts. 70th Anniversary Meeting Society of Vertebrate Paleontology October 2010" 114A.]
In the December 6, 2011 issue of ''Proceedings of the National Academy of Sciences'', Jingmai O'Connor and coauthors described a specimen of ''Microraptor gui'' containing bones of an arboreal enantiornithean
The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...
bird in its abdomen, specifically a partial wing and feet. Their position implies the bird was swallowed whole and head-first, which the thors interpreted as implying that the ''Microraptor'' had caught and consumed the bird in the trees, rather than scavenging it.
In 2013 researchers announced that they had found fish scales in the abdominal cavity of another ''M. gui'' specimen. The authors contradicted the prior suggestion that ''M. gui'' hunted only in an arboreal environment, proposing that it was also an adept hunter of fish as well. They further argued that the specimen showed a probable adaptation to a fish-eating diet, pointing to the first three teeth of the mandible being inclined anterodorsally, a characteristic often associated with piscivory.[ They concluded that ''Microraptor'' was an opportunistic feeder, hunting the most common prey in both arboreal and aquatic habitats.][
Both of these studies regarded each gut contents as instances of predation. However, Hone and colleagues (2022) questioned the reliability of these interpretations and wrote that both could just as equally be attributed to scavenging. Further, they argued against ''Microraptor'' being a specialist in either or both arboreal or aquatic hunting, citing the broad range of vertebrate gut contents (i.e. fish, mammals, lizards, birds) as evidence for a generalist hunting strategy, and that neither required that ''Microraptor'' being a specialist for hunting in either habitats.]
In 2019, a new genus of scleroglossa
Scleroglossa is a group of lizards that includes geckos, autarchoglossans (scincomorphs, anguimorphs, and varanoids), and amphisbaenians. Scleroglossa is supported by phylogenetic analyses that use morphological features (visible anatomical featu ...
n lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
('' 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
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s 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.
Unlike its fellow paravian
Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the aviala ...
''Anchiornis
''Anchiornis'' is a genus of small, four-winged Paraves, paravian dinosaurs, with only one known species, the type species ''Anchiornis huxleyi'', named for its similarity to modern birds. The Latin name ''Anchiornis'' derives from a Greek word m ...
'', ''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.
Based on the size of the scleral ring of the eye, it has been suggested ''Microraptor'' hunted at night. 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.
See also
* 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 ...
References
External links
* Dromaeosauridae, ''Relationship with birds''
A model of ''Microraptor''/Cryptovolans pauli by Boban Filipovic
*Jacqui Hayes
Bird wings evolved from biplane dinosaurs
COSMOS magazine
The Four-Winged Dinosaur
- PBS website for the ''Nova'' documentary
*NewScientis
nationalgeographic.com 2012-03-08 Ed Yong, A shiny dinosaur four-winged Microraptor gets color and gloss
nationalgeographic.com 2008-10-08 Ed Yong, Microraptor–the dinosaur that flew like a biplane
{{Taxonbar, from=Q310537
Jiufotang fauna
Early Cretaceous dinosaurs of Asia
Microraptorians
Feathered dinosaurs
Fossil taxa described in 2000
Animal flight