Temporal range: Lower Cretaceous
Xu et al., 2000
Microraptor was a small feathered dinosaur related to Velociraptor. It had flight feathers, and could glide and probably fly. About two dozen well-preserved fossil specimens have been found in Liaoning, China. They are from the Lower Cretaceous Jiufotang Formation, 125 million years old.
Adult specimens are 42–83 centimeters (1.4–2.7 ft) long, so Microraptor was one of the smallest dinosaurs.
- "The evolution of powered flight in birds from theropod dinosaurs is recognized as the key adaptive breakthrough that contributed to the biological success of this group... Hundreds of small, exquisitely preserved, feathered theropods were discovered in the Early Cretaceous Jehol Group of northeastern China as they died some 125 million years ago, smothered in the "Cretaceous Pompeii"... Both anatomy and phylogeny strongly suggest that these theropods... offer new insights into the origins of feathers and flight, favoring the arboreal ('trees-down') over the cursorial ('ground-up') hypothesis".
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. This led Xu Xing to describe it as a "four winged dinosaur", and to speculate that it may have glided using all four limbs for lift. Their bodies had a thick covering of feathers. A diamond-shaped fan on the end of the tail gave stability during flight.
Sankar Chatterjee found 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). Using this biplane model, he calculated possible methods of gliding, and determined that Microraptor most likely launched itself from a perch, 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, like those on the tibia and the tail, could have been used to control and alter the flight path. The hind wings would also have helped control the gliding flight.
Chatterjee also used computer algorithms to test whether or not Microraptor was capable of true, powered flight, in addition to gliding. The data showed that Microraptor could sustain some level powered flight, so it is possible that the animal flew as well as glided.
- Chatterjee, S., and Templin, R.J. (2007). Biplane wing platform and flight performance of the feathered dinosaur Microraptor gui. Proceedings of the National Academy of Sciences, 104: 1576-1580. 
- Xu, X. et al. 2003. Four-winged dinosaurs from China. Nature, 421: 335-340.
- See Rhamphorhynchus for a similar case.