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

RE: Senter 2006, Confuciusornis, and humeral mobility

Hi Jaime,

Yes I did misunderstand your notation. I took your use of Md for Mc. My

Now let's get to our real misunderstanding.

When I initially was so bold as to blatantly state that Confuciusornis'
second manual digit is not reduced, it was in the context of a discussion
about function - specifically the possible flexion of this finger during
the flight stroke.

I assumed that you meant that it was reduced in a developmental/functional
way - as the third digit is in the hand of Cathayornis or Longipteryx. I
thought you were suggesting that it was reduced perhaps because it
received less of the mechanical stress (stress placed on it by muscular
tension, force directed through it by loaded feathers, etc.) that induces
modeling and haversian remodeling. I believe you had mentioned the lack of
extensor pits and I thought your observations were along that same train
of thought.

You were instead talking about reduction from the ancestral state. In that
case, I agree that comparison to Archaeopteryx is best. But you are also
equating hypertrophy to length, and there we do disagree.

The humerus of the ostrich, for example, is much longer, proportional to
the ulna and manus, than in the flying ancestor of ratites, yet it still
must be described as reduced, mustn't it? So perhaps the converse can be
true as well: that a bone can be shorter yet more robust, more voluminous,
thicker - walled, perhaps more densely reinforced by internal trabeculae,
with large flanges that probably support the follicular ligaments of
primary feathers, and therefore more functional importance overall. I am
not saying that I have evidence of most of these features in the case of
PhII-1 of Confuciusornis, but all are possible.

When considering functional reduction or function - related hypertrophy,
the distinctness of the articular processes and muscle insertion points is
probably also key. Again, in fig 39 of Chiappe et al. 1999 I see that the
proximal end of Ph II - 2 is much broader than any other penultimate
phalanx, and the distal end of Ph II - 1 seems correspondingly broad. Both
show large condyles.

I agree that it would be nice to see more specimens. And I'm not certain
that the second digit could flex powerfully, it just looks possible to me.
I am looking at the two specimens preserved in IVPP V 11374 (Fig. 173 in
The Jehol Fossils, Academic Press (Elsevier) 2003). They show also that
the proximal PhII 2 and distal PhII 1 are very broad, though perhaps

But I certainly do concede that the second digit of Confuciusornis is much
shorter, proportional to the other fingers, than it is in Archaeopteryx.
Sorry to put you to so much trouble measuring so many specimens when I
meant to concede that point without hesitation. And I am fascinated by
your observation about the ungual of digit II sitting in a bowl-like

So I suggest a truce. If using diameter alone is, let's say, grossly
incorrect, then using length alone must be as well.

Thank you for this stimulating exchange. You are a most knowledgeable
anatomist and patient in explaining your points.