[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Senter 2006, Confuciusornis, and humeral mobility




Jason, I think you misunderstood my notation:

  I compared two specimens of *Archaeopteryx,* the München and Berlin 
specimens: In both, the second digit, or mdII, is 48% and 57% longer than the 
third digit, or mdIII. In *Confuciusornis sanctus*, this proportion is only 2% 
(md3/md2). I did not calculate the metacarpal in this. I also looked at a few 
other birds, but for reasons including loss of the third and fourth phalanges 
of digit three in various forms, this value was less useful.

  If I were to use digit length, not excluding the ungual, then this value 
changes: In Archaeopteryx* (specimens above, and respectively), the proportion 
of digit II (md2)/MCII is 64% and 82%; in *Confuciusornis sanctus* (using GMV 
2131 and GMV 2132, again, repsectively), the proportions are 161% and 181%. 
These measurements _do_ fall into the values you argue, but as noted they 
include the unguals.

  If I were to test the individual proportions of the phalanges 
(mdII-2/mdII-1), what might we get? For *Archaeopteryx* (same specimens) we 
get: 48% and 25%, respectively. For *Confuciusornis sanctus* (GMV 2132), we get 
30%. This shows a median measurement.

  This argues that the phalanges are not, as you argued, hypertrophied. They 
are short or fall in the range of another, earlier bird without a more 
specialized brachial-pectoral apparatus.

You wrote:

  "I made no comparisons to Archaeopteryx. [...] 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."

  Why are you excluding *Archaeopteryx* from this at all? Presumably, it lies 
closer to *Confuciusornis sanctus* than does *Microraptor [I assume you are 
using] zhaoianus* -- I know Paul disagrees, and maybe you place emphasis on 
*Microraptor* for this reason, but you shouldn't; if the conditions are 
convergent, they are less useful for your work than you may think. For 
reference, I used Hwang et al., 2002:

  CAGS 20-7-004: mdII-2/mdII-1: 24% ; md3/md2: 12% ; md2/MCII: 27%

  In my original measurements, it should be noted, *Confuciusornis sanctus* 
lacks an elongation of mdII-2 relative to mdII-1. It is, in short, short. 
Otherwise, the proportions of the digits or the phalanges (on a purely linear 
level) are similar across most of these taxa. They supported feathers, so 
presumably there was a constraint involved (number of feather attachments would 
be my guess), and these birds (and nonavian paravian) are all close to one 
another in size.

  But let's care for a second that only the diameter of the crest on mdII-1 is 
relevant, and no other measurements aside from the length. While Paul (2002) 
argues that the crest is present in *Archaeopteryx* (I am unclear which 
specimen; pg.106-407, Paul references Zhou & Martin, 1999, which I do not 
have), and in *Sinornithosaurus millenii* (holotype, his "adult specimen," into 
which he puts all *Microraptor* species and specimens), larger in the latter 
than the former. Using Paul's figure, length/diameter (at its greatest points; 
a fault, I know) in *Sinornithosaurus millenii,* *Archaeopteryx* whatever, and 
*Confuciusornis sanctus* are: 3.71, 5.7, and 3.

  Using this measurement, then yes, I would say the phalanx is broader relative 
to the condition of, say, *Archaeopteryx* or *Microraptor.* But to simply say 
the phalanx is incrassate and subject this then to calling the digit 
hypertrophic is grossly incorrect, as it infers both a length value (which is 
not apparent) and other proportional values, none of which were mentioned. I 
explain above that only in the diameter of mdII-1 does the manus of 
*Confuciusornis sanctus* even barely exceed the conditions of other taxa. I 
could go further: I could demonstrate using other baselines (such as MCI 
length, or md1-1 length) the shortness of the elements here in contrast to 
other taxa.

  I do not think using diameter alone is a valid test of your argument.

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: Mon, 28 Mar 2011 08:57:26 -0400
> Subject: RE: Senter 2006, Confuciusornis, and humeral mobility
> From: jaseb@amnh.org
> To: qi_leong@hotmail.com
> CC: jaseb@amnh.org; dinosaur@usc.edu
>
> 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
>