Microraptor (Greek language, μικρός, mīkros: "small"; Latin language, raptor: "one who seizes") is a genus of small, four-winged dromaeosaurid . Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation (Aptian stage), 125 to 120 million 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, well-preserved fossils of Microraptor provide important evidence about the evolutionary relationship between and earlier dinosaurs. Microraptor had long pennaceous feathers that formed aerodynamic surfaces on the arms and tail but also on the legs. This led paleontologist Xu Xing in 2003 to describe the first specimen to preserve this feature as a "four-winged dinosaur" and to speculate that it may have Gliding flight 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-Avialae 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. One specimen in particular shows evidence of active primary feather moulting, which is one of the few known fossil evidence of such behavior among pennaraptoran dinosaurs.
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.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 and Manospondylus gigas, in which the former became a nomen protectum (protected name) and the latter a nomen oblitum (disused name) due to revisions in the ICZN rules that took place on December 31, 1999. 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 has 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.
The 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 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.Holtz, Thomas R. Jr. (2011) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2010 Appendix. M. gui has been accepted as a distinct species with the specimen reported in 2013 being distinguishable from the type specimen of M. zhaoianus.
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 taphonomy distortion.
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.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 sic seeing what one believes and wants to see". Czerkas also denounced Norell for failing to conclude that Dromaeosauridae 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.
Czerkas's interpretation of the hindleg feathers noted by Norell proved to be incorrect the following year when additional specimens of Microraptor were published by Xu and colleagues, showing a distinctive "hindwing" completely separate from the forelimb wing. The first of these specimens was discovered in 2001, and between 2001 and 2003 four more specimens were bought from private collectors by Xu's museum, the Institute of Vertebrate Paleontology and Paleoanthropology. Xu also considered these specimens, most of which had hindwings and proportional differences from the original Microraptor specimen, to be a new species, which he named Microraptor gui. However, Senter also questioned this classification, noting that as with Cryptovolans, most of the differences appeared to correspond with size, and likely age differences. 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 cm long and 600–700 g in mass).
In a 2024 paper which reported the smallest known juvenile specimen of Microraptor, Wang and Pei included and within a new clade Serraraptoria.
It was originally thought that Microraptor was a Gliding flight, 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.
Describing specimens originally referenced as a distinctive species ( Cryptovolans pauli), paleontologist Stephen Czerkas argued Microraptor may have been a powered flier, and indeed possibly a better flyer than Archaeopteryx. He noted that the Microraptor's fused sternum, asymmetrical feathers, and features of the shoulder girdle indicated that it could fly under its own power, rather than merely gliding. Today, most scientists agree that Microraptor had the anatomical features expected of a flying animal, though it would have been a less advanced form of flight compared to birds. For example, some studies suggest the shoulder joint was too primitive to allow a full flapping flight stroke. In the ancestral anatomy of theropod dinosaurs, the shoulder socket faced downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the column until relatively advanced avialans like the enantiornithes appeared. However, other scientists have argued that the shoulder girdle in some Paraves 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 Patagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an alula, much like a "thumb-like" form of leading edge slot, may indicate that Microraptor was capable of true, powered flight.
Other studies have demonstrated that the wings of Microraptor were large enough to generate the lift necessary for powered launching into flight even without a fully vertical flight stroke. A 2016 study of incipient flight ability in paravians demonstrated that Microraptor was capable of wing-assisted incline running, as well as wing-assisted leaping and even ground-based launching.
Stephen Czerkas, Gregory S. Paul, and others have argued that the fact Microraptor could fly and yet is also very clearly a dromaeosaurid suggests that the Dromaeosauridae, including later and larger species such as Deinonychus, were secondarily flightless. The work of Xu and colleagues also suggested that the ancestors of dromaeosaurids were probably small, arboreal, and capable of Gliding flight, 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. In 2024, Kiat and O'Connor analyzed that Mesozoic birds and Microraptor had remex morphologies that are consistent with modern volant birds, while Anchiornithidae and Caudipteryx were secondarily flightless.
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, 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. However, Hartman and colleagues suggested that Hesperonychus is not a dromaeosaur, but actually an Avialae close to modern like Balaur bondoc based on phylogenetic analyses in 2019.
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.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. The only other two examples are the indeterminate tyrannosauroid specimen GMV 2124 (also known as NGMC 2124) and the holotype of Huadanosaurus, both of which are previously attributed to Sinosauropteryx.
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 bird in its abdomen, specifically a partial wing and feet. Their position implies the bird was swallowed whole and head-first, which the authors 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 lizard ( Indrasaurus) was described from a specimen found in the stomach of a Microraptor. The Microraptor apparently swallowed its prey head first, a behavior typical of modern Carnivore 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 Paraves Anchiornis, Microraptor has never been found with gastric pellets, despite the existence of four Microraptor specimens that preserve stomach contents. This suggests that Microraptor passed indigestible fur, feathers, and bits of bone in its droppings instead of producing pellets.
Based on the size of the Sclerotic 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.
History
Naming controversy
Additional specimens
Study and debate
Description
Distinguishing anatomical features
Coloration
Classification
Paleobiology
Wings and flight
Hindwing posture
Ground movement
Implications
Feeding
See also
Notes
External links
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