[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Sinosauropteryx feathers?
Kris Kripchak (MariusRomanus@aol.com) wrote:
<Ok... First off, I wasn't looking for a slap to the face here.>
<Thirdly, I'm not going to get into a brawl over this, so the below is all
I am going to say.....>
I should hope it was not taken that I wrote in an aggressive tone, as
this was not my intent. Trust me, I would be compeletely absent from the
conversation if I had anything violent in mind to write here.
The next part was addressed to an earlier post of mine in reply to Mike
Lovejoy's post (I think) or Kris' (just as likely):
<Of course I know about what you said Mr. Headden. Old news really... and
as in an article entitled "The morphogenesis of feathers" in 30 October
2002 Nature pretty much adequately demonstrated via developmental
approaches, that the barbs to rachis model is the one that best fits the
data. Barbs form first in development and thus in integument evolution,
with rachis, a special form of fused barbs, appearing later as an
evolutionary novelty. I know this. Oh, and you said "... those of
*Sinosauropteryx* are stage II structures where various filaments fuse at
the base, but in a fan-shaped structure with a possible helical base
order. No other structures aside from single filaments (stage I) have been
described for *Sinosauropteryx*..." Which is it then? "Stage I" or "Stage
II"? I thought that there was a combination of both observed for the
little guy anyway. In fact, my understanding is that this is the case for
ALL feathered theropods... combinations of feather forms... just like
birds now. Funny how that is. Also, your "Stages" refer to Prum and
Brush's work right? I only ask since I sat in on a talk at SVP by
Hillenius and Maderson about how some of these hypothetical neomorphic
developmental "Stages" are not congruent with the developmental genetics.
I think it was with those beyond "Stage II" where problems arise...
Something about tissue distributions and keratin types... a morphological
"jump" that is not possible... misleading notions about developing feather
shape and form... or something to that effect. Baer's Law might have had
something to do with it too. All I know is that the talk asserted that
Prum and Brush's model is supposedly lacking in the developmental,
morphological and molecular data department. I don't remember for sure,
and I only have the notes I took from the talk at my disposal. But this is
beside the point.>
Prum and Brush are indeed working on a largley observational and
somewhat hypothetical basis, but both have looked at feather development
in detail. After carefully re-reading the paper and Prum's own large work,
it it clear that Yu et al. (not Mingke, _Nature_ is still putting the
personal name first as in Western names, and the same goes for the other
Chinese authors, Wu Ping and Chuong Cheng-Ming) are conformably close to
the work of Prum as I had detailed previously in my reference to "Stages".
The authors of the later paper in fact refer to "rachis" and "barb" during
their Fig. 1 a (Ia, Ib) as a radiating fan or a central rachis with barbs
along the shaft as being a series from the original folical bud, as in
hair development. Such a structure appears as a conical bud that splits
into helical filaments with a single, apical central filament that becomes
what the authors call the rachis (Fig. 1 a (Ia), Prum and Brush's Stage
II) but which Prum chose to not differentiate in comparison to theropod
integument because the base of any structure and development from the
folicle could not be observed. The surrounding filaments eventually
compose into a rachis that forms barbs from its own epithelial tissue
(Fig. 1 a (Ib), Prum and Brush's stage IIIa) that develops overlapping
barbulets (Fig. 1 a (II), Prum and Brush's Stage IIIb or IV) and then
eventually forms a cohesive vane with hooklets (Fig. 1 a (III), Prum and
Brush's State Va and Vb) that in modern birds is the developmental basis
for down, countours, flight feathers, bristles, filoplumes,
brush-feathers, etc.. Aftershafts occur in the Stage V (Fig. 1 a (Ib))
structure where a secondary "prime" filament occurs opposite the primary
"prime" or rachidial filament, and does not develop its own contigent of
filaments, rather than being a stray filament not fused into the primary
structure. Prum and Brush also theorized on the fusion of ranking
filaments in the helical base or "collar" to each other to form the rachis
and differentiate the main shaft with all others.
Yu et al in fact describe the development as differentiation of barbs
from a central rachis, but this does not resolve the basic filaments which
are present without barbulets in down and contour features. Prum and Brush
and Brush before him had gotten the pattern right with only one variation,
and that was composition of the relationship of barbs and rachis
originally, along with a developmental structure between Yu et als Ia and
Ib. No biggie.
Table, where stages refer to Prum and Brush**
Prum and Brush Yu et al.
stage I: multiple filaments in helical collar; X X
stage II: lateral filaments compose rachis; X not
stage III: distinction of venation; X X
stage IV: venation with barbulets; X X
stage V: hooklets and aftershaft; X X
stage VIa, b, c, etc.: contours, down, filoplumes; X X
** Stages as in Yu et al: st-I corresponds to Yu Ia, st-II to Yu Ib,
st-III to Yu II, and st-IV to Yu III along with st-V's hooklets, where Yu
et al. do not describe aftershaft formation in the paper (it's in the
supp. info., though).
Jaime A. Headden
Little steps are often the hardest to take. We are too used to making leaps
in the face of adversity, that a simple skip is so hard to do. We should all
learn to walk soft, walk small, see the world around us rather than zoom by it.
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.