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Microraptor: Sprawling Revisted

  Viewers of the NOVA program "The Four-Winged Dinosaur" will recall a 
similarity in this argument, one approached previously with several other 
papers but wwithout the aggressive testing, of flight plan models in a 
sprawl-legged microraptorian.

  In Alexander et al. (2010), the authors approach this topic by using a 
transfer-prepared specimen (previously undescribed) called LHV 0026.  Now, a 
short note on transfer preparation:  The process involved does little to 
actually preserved the fossil itself, save to separate it from the unstable 
rock matrix it is preserved in/on.  In this casde, the material is removed 
completely from the underlying matrix, and replaced onto a new one.  Anyone 
interested in Jiufotang preservation will note that all specimens are virtually 
flat (they are not intact in all three dimensions, although they produce a 
light relief from the surface of matrix that is left after the layers are 
removed which overlie the bedding plane where the integument is splayed out 
upon.  Transfer preparing the specimen removes the final section of matrix 
UNDER the fossil (all integument is lost) and remounts it.  This is often done 
to care for larger fossils (in order to make all sides of a fossil available, 
but retain the "bonebed" look) but also smaller fossils in extremely fragile 
rock (such as the oil shales of the Messel).  So far, the bedding rock of the 
Jiufotang does not require transfer to preserve the fossils, but the idea here 
is that the material can become visible on all sides.  This does nothing to 
reveal the shape of the bones, which are still flattened and in many cases 
crushed.  There are virtually no Jiufotang fossils which are not like this.

  As such, the process of transfer casting to preserve the model of an 
articulatable specimen is flawed on the outset, without the assumption that no 
distortion has occured, but aside from the discussion in the supplemental 
information, no further details of the preparation and casting of this iconic 
specimen are made, and no photos of the material are made (just the modeled 

  Further arguments on the model as a glider are based on the articulation of 
the splay of the femur, but fortunately the authors refrained from arguing that 
the specimen itself shows this splay.  What they do argue, however, is a form 
of sleight of hand:

  "Primitively, early archosaurs are sprawling, with the legs set laterally and 
elevated at around 75° (6), a preadapted posture for gliding.  Modern birds 
normally have the thigh elevated and sprawled to the side in different degrees; 
for example, it is nearly perpendicular to the midline in loons and grebes (7). 
 This variation shows that the degree of splaying needed to use the hindlegs in 
gliding is not unusual when compared with that in modern birds.  The absence of 
an antitrochanter and a supraacetabular shelf (SAC) in the eumaniraptorans, 
including dromaeosaurids, would make elevation and splaying of the legs even 
easier (8)."

[6. Bakker, R. T. 1971. Dinosaur physiology and the origin of mammals. 
_Evolution_ 25: 636–658.
7. Hertel, F. & Campbell, K. E, Jr. 2007. The antitrochanter of birds: Form and 
function in
balance. _Auk_ 124:789–805.
8. Longrich, N. 2006. Structure and function of hindlimb feathers in 
*Archaeopteryx lithographica.* _Paleobiology_ 32:417–431.]

  One will note first that the word dinosaur does not appear anywhere in this 
sentence, which is in keeping with one of these authors' previously reported 
statements arguing that birds derived from nondinosaurian 9even 
nonarchosaurian) terrestrial vertebrates (just no idea what it is, but 
apparently it cannot be a dinosaur). Secondly, a large leap is made, seemingly 
with a continuous morphology presented:  The sprawling femur of early 
archosaurs followed by the elevated and rotated femur in birds.  It is almost 
as if the femur was continuously splayed in evolution from this basal to this 
derived from, and thus there is no way the femur could in fact be parasagittal 
in orientation.  Thirdly, it excludes the option that the femur could evolve 
from a splayed into an erect posture, despite this being the case with 
dinosaurs, or that if it did, it would be 1) unlikely to shift into a sprawling 
posture, or 2) that the femur was not in fact sprawled.  The argument, then, is 
that the femur is sprawled in this specimen (an eversion of 25 degrees in the 
paper and supplement) because basal archosaurs and birds have an everted femur.

  Problems abound with this despite the apparent models: 

  1) The authors argue that the ilium lacks a supra-acetabular shelf. -- Hwang 
et al (2002, _A M Novitates_ 3381) shows that this is in fact incorrect in 
specific when applied to two well-preserved specimens referred to *Microraptor 
zhaoianus*, and Paul (2002, _Dinosaurs of the Air_) does so in general, 
examining specimens of *Archaeopteryx* and *Velociraptor*; the shelf exists, 
even though it is short.

  2) Eversion of the femur in an archosaurian-like sprawl requires an elevated 
caput -- The authors do not demonstrate the morphology of the femur (or, in 
fact, the morphology of anything in the paper; they go so far as to hypothesize 
a V-shaped tail fan for their models despite one of the specimens they 
photograph, *Microraptor gui* holotype IVPP V13352, as having a diamond-shaped 
tail fan -- the image in the supplement is cut at this point), which would be 
required to determine the actual splay of the femur they argue is apparent 
based solely on an attempt at phylogenetic bracketing (trumped by actual 
morphology).  This is further contradicted by Hwang et al. (2002, _A M 
Novitates_ 3381) where the caput is essentially horizontally oriented, as it is 
in *Velociraptor mongoliensis*.

  At this point, the argument in the paper tests a model being thrown in 
various methods, and the flight path analyzed.  I am tempted to side with Jim 
Cunningham as the relevant voice of skepticism here, as arguing for a stable 
glide model is in fact the wrong idea when attempting to derived an evolving 
flyer.  A dynamic, modular flight system (as in birds) required a chaotic, 
unstable system to operate in, and modulating the body to compensate.  
Nonexistent or gently controlled air flow is not a good way to determine 
performance of a glide path, especially since NO living glider today maintains 
an absolutely fixed physical posture during its trajectory, and this goes 
triple for parachuting animals.

  In their conclusion, Alexander et al. state:  "Obviously, the living animal 
was capable of active control, but we suggest that the tandem wing 
configuration may have been advantageous because it requires less active 
stabilizing ability."  I am not quite sure how one can develop a system of 
unstable flight control from a passively stable system.  Abilities to develop 
control over the wing and perform a dynamic powered operation seem to require a 
powered operation to precede it, although perhaps I am simply being too 


  Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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