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Microraptor gui - the four-winged theropod




All I can say is "Wow!"

Xu et al. (2003).  Four-winged dinosaurs from China. Nature 421: 335- 340.

Abstract. Although the dinosaurian hypothesis of bird origins is widely accepted, debate remains about how the ancestor of birds first learned to fly. Here we provide new evidence suggesting that basal dromaeosaurid dinosaurs were four-winged animals and probably could glide, representing an intermediate stage towards the active, flapping-flight stage. The new discovery conforms to the predictions of early hypotheses that proavians passed through a tetrapteryx stage.

Material. IVPP V13352 (holotype) and V13320 (referred specimen), both represented by an almost complete skeleton.

Locality and horizon. Dapingfang, Chaoyang County, western Liaoning (30 km southwest of Chaoyang City); Jiufotang Formation18 (Early Cretaceous).

Diagnosis. Distinguishable from _Microraptor zhaoianus_ in having prominent biceps tuberocity on radius, much shorter manual digit I, strongly curved pubis, and bowed tibia.

Now the REALLY interesting stuff...

The body of _M. gui_ is covered by plumulaceous feathers that are about 25?30 mm long. Certain cranial feathers have pennaceous vanes. Large pennaceous feathers are also attached to the distal tail, forelimbs and hindlimbs. The forelimb feathers (remiges) form a pattern similar to those of modern birds. The primaries are longer than the secondaries, and (in the holotype at least) some primaries display ASYMMETRY, with the leading vane much narrower than the trailing vane. The proximal secondaries have symmetrical vanes and the distal ones display weak asymmetry; these feathers are also pennaceous. The hindlimb feathers are arranged in a pattern similar to those on the forelimbs; and the vanes of the distal feathers display ASYMMETRIC vanes. The proximal hindlimb feathers are shorter and have symmetrical vanes. Tail feathers (rectrices) are also preserved, attached to the 15th to 18th caudal through the end of the tail, and some are very long.

The authors suggest that "The forelimb and the leg feathers would make a perfect aerofoil together, analogous to the patagium in bats or gliding animals. [For me, the sifaka comes to mind] These features together suggest that basal dromaeosaurids probably could glide, representing an intermediate stage between the flightless non-avian theropods and the volant avialans. Apparently some non-avian theropods evolved large and highly specialized pennaceous feathers on the leg for aerodynamic function; these features were later reduced and lost in birds, which depend completely on forewings for flight." Hence, the authors strongly favour an arboeal origin for avian flight, with gravity used to the advantage of small feathered theropods in the incipient stages of aerial behavior.





Tim








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