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RE: Senter 2006, Confuciusornis, and humeral mobility



Hi Jaime,

By hypertrophied I mean that all the elements of the second digit, with
the exception of the ungual, are  larger and more robust than either of
the others, not reduced relative to them. The diameter of PH 1 II must be
three times that of PH 1 III. Though the metacarpal may be only 2% longer
that Mc III, it is longer nonetheless, not reduced.

I made no comparisons to Archaeopteryx. That must surely be the point of
our misunderstanding. You are comparing all elements to Archaeopteryx, and
describing any differences as reductions or enlargements from the
condition in Arcaheopteryx, while I am not.

But the expansion of the diameter of Ph 1 II is a feature seen in both
Microraptor and Confuciusornis and it is therefore interesting to me.

-Jason




>
> 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
>>
>


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