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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



Augusto Haro wrote:

<Thus, it is more parsimonious to see the long hindlimb feathers as only 
appearing in *Microraptor*, as far as our current knowledge of the fossil 
record reaches.>

  Yes, this is pretty close to the logical premise from which we should start. 
The same is true for *Archaeopteryx*, for the most part, save that it seems 
more "avian" than *Microraptor*.

<In this I was trying to mean that the Neornithes abduction was possible for 
*Microraptor*.>

...

<Now, if you consider the preserved femoral head in *Microraptor* as distorted, 
this seems to impede us to say whether it was incapable of a movement possible 
in birds.>

  However, the avian femur is oriented slightly laterally to the vertical in 
its crouched, neutral position, and to extend, the femur MUST abduct outwards 
to move around the posteriorly swung gut, a side-product of having an 
anteriorly-position center of gravity. This is not the case in *Microraptor* It 
simply does not need to abduct the femur to walk, and there is no reason it 
should. 

  The argument that the semi-spherical caput with slightly elevated neck over 
the trochanteric body of the femur is an old one, and has been argued to be 
inconclusive due to distortion of the Hwang et al. specimens. It is simply not 
informative to argue that the positions and preservation are identical to the 
living animal, and thus we can only argue for what we can compare and derive in 
other, less distorted fossils. These tell us that the femur and the ilium are 
conjoined so much more closely than in birds, especially given the perforate 
acetabulum, such that the femur inserts deeply into the hip socket. 

  Eversion, as Scott Hartman has demonstrated in the past few times this 
argument has come up, causes dislocation of the hip, and that's even using the 
preserved conditions of the femora and ilia. The natural conditions, if they 
are different from the preserved ones, would likely further prevent 
dislocation. Maybe Scott would be willing to post a link showing the 
illustration? This is based on the natural case, and is compared to the femora 
and ilia of other dromaeosaurs.

<However, this does not occur during terrestrial locomotion in Neornithes as 
far as I know.>

  Because in normal avian terrestrial locomotion, the femur barely extends. The 
antitrochanteric contacts are in fact affirmed, and the animal walks using the 
knee instead of the hip as the point from which the leg extends and flexes 
(i.e., the knee and not the hip is the functional "hip" for birds). This forces 
an anterior center of gravity. Gatesy and Middleton have done work on this 
compaction and anteriorization of the avian body in developing unique locomotor 
modules. Contrariwise, *Microraptor* has a long, low, shallow torso, small and 
narrow hip, long femur, and gastralia which promote a form of pelvic pumping 
diaphragmatic breathing systems (see Carrier and Farmer's work on gastric pumps 
in crocs and birds). They simply do not need the avian walking/breathing system 
to move (*Archaeopteryx* also possesses this non-"avian" anatomy.)

<The only feature which may have restricted femoral abduction at full 
retraction is the supraacetabular crest, which as far as I know, is reduced in 
Paraves, at its posterior border). The acetabular perforation does not trap the 
femoral head in an uniquely parasagittal motion.>

  Such a dorsal shelf does not neccessarily have to be large to reduce motion.

<If you consider birds to present a femoral neck more developed than in other 
dinosaurs, and admitting that the proximal extreme of crocodylians is less 
mediolaterally elongated than in either dinosaurs and birds, then if both 
corcodilians and birds can abduct their femora at full femoral retraction, we 
can infer it also should in the intermediate state represented by non-avian 
dinosaurs, even if customarily not employed (as in birds).>

  But we cannot infer this. Both crocs and birds have a naturally retracted 
femur as their neutral condition. This is not true of non-avian dinosaurs. The 
mere presence of a derived supracetabular shelf, the large and sometimes 
extremely large trochanteric body of the femur, the medially oriented caput, 
the cylindrical structure of the latter, and most certainly the perforate 
acetabulum with a deep interlock between pelvis and femur indicate that the 
femur was constrained in virtually all non-avian dinosaurs to parasagittal 
motion. These no NOT indicate than a croc derivative (but not neccessarily the 
originating croc condition! -- See work on *Terrestrisuchus* and other 
crocodylomorphans for derivatives of highly terrestrial and erect-postured 
crocs) must represent the constraint for the originating dinosaurian condition, 
from which birds must derive, if birds arrive at their currect condition by 
modifying their hips to a similar condition. They did not
 retain that condition through their derivation from the bird-croc ancestor, 
and this is the important thing that sets this issue apart from the EPB.

  Cheers,

Jaime A. Headden

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