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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.
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