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

["Jaime A. Headden" <qilongia@yahoo.com>]

[appologies for the long post]

Augusto Haro wrote:

<But they can rather abduct much once they retracted so that the facies 
articularis antitrochanterica is no longer in contact with the antitrochanter. 
So, yes, you should not have completely-splayed out hindlimbs, but each 
hindlimb may have formed a, say, 90° angle or somewhat more (not know of 
quantities) with the other in anterior view. Not the best for gliding but best 
than strictly parasagittal limbs.>

  In modern birds, yes. But modern birds, unlike any dromaeosaur, 
*Archaeopteryx*, and especially *Microraptor*, have an elevated, 
proximally-directed femoral caput with a distinct neck separating the 
trochanteric body distally from a semi-spherical caput proximally. This gives 
the femoral head a good deal of rotational ability, and especially the ability 
to evert when the leg is flexed, as you state. But this is not possible in 
non-avian dinosaurs, which possess not only a medially directed caput, but lack 
the attenuation between caput and trochanteric body of the femur, and this 
matches up quite nicely with the ventral surface of the acetabular margin of 
the ilium. In other words, the femur was married to the ilium, and they could 
not be parted without serious damage to the leg (this was stated in Hwang et 
al.'s monograph on two further *Microraptor zhaoianus* specimens, among other 
sources).

  I know Martin and Burnham have presented the premise that apparently a 
reconstructed ilium articulating with a reconstructed femur seems to purport 
that the ilium possesses no deep acetabulum, so that the shelf that articulates 
with the femoral caput is very short; this apparently allows lateral eversion 
of the femur dorsally, with the femur extended and not flexed, which fits into 
the idea of a sprawling femur. This evidence, presented in the Nova program, 
has yet to be published, but evidence from Hwang et al. and the femur data from 
published specimens already puts this theory to a serious test of 
reconstructing evidence from a preconceived position (i.e., *Microraptor* 
sprawled).

<Third, as far as I know, *Archaeopteryx* is more basal within the Avialae than 
*Microraptor* is within Deinonychosauria.>

  Current phylogenies on this portion of avian ancestry argues that this is not 
true:

--+--Deinonychosauria
  |  `--+--Troodontidae
  |     `--+--Microraptoria
  |        `--Dromaeosauridae
  `--+--Archaeopteryx
     `--Aves

  The above represents a concensus on what most studies over the last 20 years 
have produced in one form or another. Some phylogenies have posited alternate 
positions, including placing Oviraptorosauria between Aves and 
Deinonychosauria, Troodontidae between Dromaeosauridae and Aves, and 
Dromaeosauridae between Troodontidae and Aves. Paul has posited that 
*Archaeopteryx* represents a declination from the dromaeosaur+bird condition, 
rather than at the base of its emergence, but this phylogeny has yet to be 
backed up with any sort of completeness as have the "total data" phylogenies of 
the Theropod Working Group, includiong studies by Hwang et al. and Xu et al. on 
*Microraptor*, etc.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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