Microraptor

Dinosaurs > Microraptor

Microraptor was a genus of small, four-winged paravian (possibly dromaeosaurid) dinosaurs. 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 years ago. Three species have been named (M. zhaoianus, M. gui, and M. hanqingi), though further study has suggested that all of them represent variation in a single species, which is properly called M. zhaoianus. Cryptovolans, initially described as another four-winged dinosaur, is usually considered to be a synonym of Microraptor.

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

Microraptor were among the most abundant non-avian dinosaurs in their ecosystem, and the genus is represented by more fossils than any other dromaeosaurid, with possibly over 300 fossil specimens represented across various museum collections.

With adult specimens ranging 77–90 centimetres long (2.53–2.95 ft) and with a weight estimated up to 1 kilogram (2.2 lb), according to Holtz, Microraptor was among the smallest known non-avian dinosaurs. Aside from their extremely small size, Microraptor were among the first non-avialan dinosaurs discovered with the impressions of feathers and wings. Seven specimens of M. zhaoianus have been described in detail, from which most feather impressions are known. Unusual even among early birds and feathered dinosaurs, Microraptor is one of the few known bird precursors to sport long flight feathers on the legs as well as the wings. Their bodies had a thick covering of feathers, with a diamond-shaped fan on the end of the tail (possibly for added stability during flight).

Microraptor

Clade: Dinosauria
Suborder: Theropoda
Family: Dromaeosaurid

Size: 77–90 cm (2.53–2.95 ft) long

Weight: 1 kg (2.2 lb)

When: Cretaceous Period
125 to 120 million years ago

Where: China

Diet: Carnivore

Microraptor had four wings, 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 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 hind legs, with flight feathers 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.

Whether or not Microraptor could achieve powered flight or only passive gliding has been controversial. While most researchers have agreed that Microraptor had most of the anatomical characteristics expected in a flying animal, some studies have suggested that the shoulder joint was too primitive to have allowed flapping. The ancestral anatomy of theropod dinosaurs has the shoulder socket facing downward and slightly backward, making it impossible for the animals to raise their arms vertically, a prerequisite for the flapping flight stroke in birds.

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.

In March 2012, Quanguo Li and team became the first scientists to determine the plumage coloration of Microraptor, based on the new specimen BMNHC PH881, which 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 blackbird, and indicated iridescence in the plumage of Microraptor. Though the researchers state that the true function of the iridescence is yet unknown, it seems reasonable to conclude that the tiny dromaeosaur was using its glossy coat as a form of communication or sexual display, much as in modern iridescent birds.


Source: Wikipedia