Microraptor gui - the four-winged theropod

["Tim Williams" <twilliams_alpha@hotmail.com>]

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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