Microraptor did not sprawl!

[DinoBoyGraphics@aol.com]

     Since I and others have been discussing posture in Microraptor, I pulled 
out Hwang et als. AMNH Novitate #3381, "New Specimens of _Microraptor 
zhaoianus_ from Northeastern China."  Should be available on Bio-one for those 
whose universities subscribe.

    If I could draw everyones attention to page 23, figure 27 a & b, there are 
two excellent photgraphs of the proximal portions of femora from two specimens 
of Microraptor.  Fig 27a is the proximal femur (of CAGS 20-8-001) in lateral 
view, and 27b is another specimen (CAGS 20-7-004) with the proximal femur in 
anterior view.  Both show perfectly normal theropod femora, including the 
deeply offset femoral head with ventral flange.  There is no unique morphology 
evident.

     With this (typical theropod) morphology, there are two excellent reasons 
why Microraptor could not splay its hindlimbs laterally.  First, the 
pubo-ischiadic junction would be broken if the femure were splayed laterally, 
as the ventral flange of the femoral head would be forced through it (to be 
fair, the greater and/or lesser trochanters might have broken part of the 
illium instead, but the point remains: you cannot splay the leg laterally and 
keep it in the acetabulum).

     Two, the morphology of the proximal femur shows that the pelvic musclature 
inserted on it in the normal theropod manner.  If the femora were splayed 
laterally (ignoring the whole broken pelvic-girdle issue for the moment), the 
proximal-most portion of the femur would be rotated entirely into the 
acetabulum, shearing off all te musclature that inserts on the greter and 
lesser trachanters, etc.  Even if somehow the tendons stayed attached, they 
would be unable to actually rotate the limb laterally, as any contraction at 
this stage would instead pull the femur back out of the acetabulum.  I guess 
that's three reasons.

Please, please, please, stop with the spread-eagle microraptors.  Whatever the 
critter did with those hind leg "wings," it wasn't employing them with the legs 
splayed laterally.  

Cheers,

Scott Hartman
Zoology & Physiology
University of Wyoming
Laramie, WY 82070

(307) 742-3799