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RE: Senter 2006, Confuciusornis, and humeral mobility



Jason, I think there are a few problems with your hypthesis (I meant to get 
back at this earlier).

  The first issue is that nearly all *Confuciusornis sanctus* specimens are 
preserved with their manus in either ventral or dorsal view, depending on what 
orientation the wing lays. And they are all, to varying degrees, crushed, 
distorting the relative placement of features.

  The second issue is your use of "hypertrophied" in reference to mdII. I'm not 
sure what you mean by this, but there are two possibilities: one is length, in 
that mdII is somehow proportionately longer than another digit than in other 
taxa, and the other is that the digit is morphologically incrassate, expanding 
its apparent features in other dimensions than length.

  I think I can rule out "hypertrophied" length, as mdII is only 2% longer than 
mdIII in the specimen being referenced (Chiappe et al., 1999, fig. 39). Compare 
this to *Archaeopteryx*: München specimen, BSP 1999 I 50: 48%, and Berlin 
specimen, HMN 1880 (counterslab 1881): 57%.

  A few things make me think incrassate proportions (diameter or circumference 
versus length) are not at fault. This includes, but is not limited to, the 
peculiar articulation of mdII-2 and mdII-3 (the ungual): The distal end of 
mdII-2 has no apparent ligament pits, nor does it appear to have paired 
condyles. The proximal end of the ungual is not concave in profile, either 
ascribing a relatively straight articulation (and thus less flexibility at the 
joint, if any), or that the condyle of mdII-2 sat within a bowl-like cotylus on 
the ungual, which I favor here. The proximal end of the ungual is smaller 
dorsoventrally than in either of the other unguals, and this simply supports 
smaller size of distal mdII-2 relative to other penultimate phalanges, in 
keeping with the lack of incrassitude of mdII-2.

  While I cannot contradict the observation of large condyles on mdII-1, I 
would like to note that one of them is larger than the other, but I think this 
is likely evidence of distortion rather than a trochlea; the presence of a 
broad lateral blade on mtII-1, which expands from the distal end of the phalanx 
and incorporates the lateral margin of condyle, suggesting the condyle lacks a 
ligament pit (at least on one side).

  But this is all in comparison to the specified specimen. I am not familiar 
with better specimens, especially published figures, and would like to have a 
better sample. What this specimen says, however, is not supportive of a very 
flexible second digit, at least to the same degree as *Archaeopteryx 
lithographica*.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

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


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Sun, 27 Mar 2011 21:03:37 -0400
> From: jaseb@amnh.org
> To: tijawi@gmail.com
> CC: dinosaur@usc.edu
> Subject: Re: Senter 2006, Confuciusornis, and humeral mobility
>
>
> > Jaime Headden  wrote:
>
> >>   *Confuciusornis sanctus* has ... reduced form of the
> >> second, major digit
>
> The second digit is hypertrophied, not reduced. Only the ungual is
> smaller. The diameters of metacarpal II and Phalanx 1 II are much greater
> than those of digit III. The trochleae are large and well developed (Fig
> 39 Chiappe et al. 1999. Specimen GMV-2132).
>
> I agree that the deltopectoral crest may have functioned in tree climbing
> with the hands but, of course, this is not mutually exclusive with flight
> stroke functions. My hypothesis is that the huge deltopectoral crest could
> have functioned to give the deep pectoralis muscles greater leverage in
> rotating the humeral trochlea dorsally for a powered flight stroke.
>
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>