Wings and flight Microraptor had four
wings, one on each of its forelimbs and hindlimbs, somewhat resembling one possible arrangement of the quartet of flight surfaces on a
tandem wing aircraft of today. It had long
pennaceous feathers on arms and hands with legs and feet . The long feathers on the legs of
Microraptor were true flight feathers as seen in modern
birds, with asymmetrical vanes on the arm, leg, and tail feathers. As in modern bird wings,
Microraptor had both primary (anchored to the hand) and secondary (anchored to the arm) flight feathers. This standard wing pattern was mirrored on the hindlegs, with
flight feathers anchored to the upper foot bones as well as the upper and lower leg. Though not apparent in most fossils under natural light, due to obstruction from decayed soft tissue, the feather bases extended close to or in contact with the bones, as in modern birds, providing strong anchor points. It was originally thought that
Microraptor was a
glider, and probably lived mainly in trees, because the hindwings anchored to the feet of
Microraptor would have hindered their ability to run on the ground. 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. 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. He noted that the fused sternum of
Microraptor, asymmetrical feathers, and features of the shoulder girdle indicated that it could fly under its own power, rather than merely gliding. Today, most scientists agree that
Microraptor had the anatomical features expected of a flying animal, though it would have been a less advanced form of flight compared to birds. For example, some studies suggest the shoulder joint was too primitive to allow a full flapping flight stroke. In the ancestral anatomy of theropod dinosaurs, the shoulder socket faced downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds. Studies of maniraptoran anatomy have suggested that the shoulder socket did not shift into the bird-like position of a high, upward orientation close to the
vertebral column until relatively advanced avialans like the
enantiornithes appeared. However, other scientists have argued that the shoulder girdle in some
paravian theropods, including
Microraptor, is curved in such a way that the shoulder joint could only have been positioned high on the back, allowing for a nearly vertical upstroke of the wing. This possibly advanced shoulder anatomy, combined with the presence of a
propatagium linking the wrist to the shoulder (which fills the space in front of the flexed wing and may support the wing against drag in modern birds) and an
alula, much like a "thumb-like" form of
leading edge slot, may indicate that
Microraptor was capable of true, powered flight. 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. 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
anchiornithids and
Caudipteryx were secondarily flightless.
Hindwing posture Sankar Chatterjee suggested in 2005 that, in order for
Microraptor to
glide or fly, the forewings and hindwings must have been on different levels (as on a
biplane) and not overlaid (as on a
dragonfly), and that the latter posture would have been anatomically impossible. Using this biplane model, Chatterjee was able to calculate possible methods of gliding and determined that
Microraptor most likely employed a
phugoid style of gliding: launching itself from a perch, the animal would have swooped downward in a deep U-shaped curve and then lifted again to land on another tree. The feathers not directly employed in the biplane
wing structure, like those on the
tibia and the
tail, could have been used to control drag and alter the
flight path,
trajectory, etc. The orientation of the hindwings would also have helped the animal control its gliding flight. Chatterjee also used computer
algorithms that test
animal flight capacity to test whether or not
Microraptor was capable of true, powered flight, as opposed to or in addition to passive gliding. The resulting data showed that
Microraptor did have the requirements to sustain level powered flight, so it is theoretically possible that the animal flew, as opposed to gliding. 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
avialan close to modern
birds like
Balaur bondoc based on phylogenetic analyses in 2019.
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 's hypothetical "
Tetrapteryx" with four wings, 1915 The unique wing arrangement found in
Microraptor raised the question of whether the evolution of flight in modern birds went through a four-winged stage, or whether four-winged gliders like
Microraptor were an evolutionary side-branch that left no descendants. As early as 1915,
naturalist William Beebe had argued that the evolution of bird flight may have gone through a
four-winged (or tetrapteryx) stage. 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 dinosaurs 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. 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 6 December 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. Unlike its fellow
paravian Anchiornis,
Microraptor has never been found with
gastric pellets, despite the existence of four
Microraptor specimens that preserve stomach contents. This suggests that
Microraptor passed indigestible fur, feathers, and bits of bone in its droppings instead of producing pellets. However, the discovery of dark and glossy plumage in
Microraptor may suggest otherwise, as no modern birds with comparable plumage are known to be nocturnal. ==See also==