RE: *Microraptor* the biplane: published

[Tim Williams <twilliams_alpha@hotmail.com>]

Mickey Mortimer wrote:

> Anyone notice Chatterjee and Templin assign Microraptor amd Pedopenna to 
> Dromaeosauria in the cladogram?  Is this the first time the taxon has been 
> published?

Like David, I'm guessing this is a mistake; "Dromaeosauria" may be a typo 
for Deinonychosauria or Dromaeosauridae.  Note, however, that Xu and Zhang 
(2005) actually recovered _Pedopenna_ as lying outside both Aves and 
Deinonychosauria.  Thus, I'm not sure what the justification is for allying 
_Pedopenna_ closer to _Microraptor_ than to birds (Aves).

Also, Chatterjee and Templin (2007) mention that _Caudipteryx_  shows 
"contour feathers on the hindlimbs".  But I wasn't aware that any 
_Caudipteryx_ specimen shows pennaceous feathers of any variety associated 
with the hindlimbs.  The best _Caudipteryx_ specimens lack both metatarsal 
and tibial feathers (NGMC 97-4-A, NGMC-9-A, IVPP V 12344), even though 
feathers are clearly preserved elsewhere (e.g., forelimbs, tail).

This might seem like nit-picking on my part (and it is), but the authors do 
raise _Caudipteryx_ in the context of supporting the hypothesis that a 
four-winged 'biplane' configuration is primitive for Eumaniraptora, and 
therefore ancestral to the two-winged 'monoplane' configuration of birds.  
The alternative hypothesis is that the _Microraptor_-style biplane 
represents a dead-end experiment in aerial locomotion, and (consequently) 
that the direct ancestors of birds never passed through this 'biplane' 
stage.  However, given that metatarsal contour feathers are limited to 
microraptorans and _Pedopenna_, I don't think either hypothesis could be 
said to be superior to the other.  No incontrovertible fossil bird shows the 
'biplane' arrangement.  Even though the Berlin specimen of _Archaeopteryx_ 
shows long hindlimb feathers (as does an unnamed enantiornithean IVPP V 
13939), these are not attached to the metatarsus, only to the 
tibia/tibiotarsus.  Therefore, there is no 'biplane' arrangement, which 
requires a ventral wing formed by metatarsal contour feathers.

Having said all that, the idea of biplane-style gliding in microraptorans is 
compelling - although I don't think we have enough evidence to argue that 
birds must have passed through this stage on the way to powered flight.  In 
fact, microraptorans and _Pedopenna_ may represent experiment(s) in theropod 
flight (probably "trees-down") that were independent of the manner in which 
birds (Aves) achieved flight ("trees-down", "ground-up", or a combination of 
the two).  But if we do find long metatarsal feathers in a basal bird, then 
it would be a huge boost to the biplane hypothesis for the origin of bird 
flight.

> I liked how they didn't pretend Cryptovolans didn't exist. ;)

All we need is a review of the specimen, to see if it is a junior synonym of 
_Microraptor_ or not.

Cheers

Tim

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