Re: feather tracts (and protoscutes)

["Jaime A. Headden" <qilongia@yahoo.com>]

Ken Kinman (kinman@hotmail.com) wrote:

<In the Triassic there were probably many different structures
that were intermediate between feathers and scutes. Longisquama
is "hard evidence" of such structures in my opinion. Such
structures probably evolved many different times among
archosauromorphs, so calling those of Longisquama by the term
"feathers" could be very misleading.>

  Hard evidence of _what_? By _all_ (each and every one dealing
with *Longisquama*) studies except _one_ on the sheer
superficial form of the structures, *Longisquama* is barely an
archosaur, and the crack in the matrix through the skull renders
the key details obscure. The rest of its anatomy is completely
refutable to the idea that this animal had anything to do with
the origin of the birds. As detailed before, Alan Brush has
worked and published on the morphology of feathers, their
development, molecular composition, and finds them not analogous
to an elongated scale, which is all that *Longisquama*'s stuff
is. Not just Alan has worked on this.

  Now noting the rest of what you said above about the analogy
but not homology of these structures, one wonders why you bring
up *Longisquama*?

<In any case, the protofeathers (which I proposed started on the
tail and went up the back) could perhaps equally well be termed
"protoscutes".>

  I'd like to see evidence of this.

<That is why I am trying to get Jaime and others to speculate
more and resist the urge to extrapolate too heavily from
Cretaceous forms back to their Triassic ancestors. This seems to
be why the whole BCF movement is increasingly catching on.>

  You completely misunderstand. I am a proponent of BCF, to most
degrees. I do beleive that arboreality may have driven the
theropod bauplan, mesaxony instead of ectaxony, the beginning of
the hinged wrist, etc..

  I would rather work in the realm of the data and what can be
extrapolated from that than to speculate about something that
cannot in any way be tested, like saying that "quills" developed
from elongated scuts to become rachi and then feathers. The
data, from direct comparison of feathers in embryos, indicates
that they may arise from the essential structure, and folicle,
but are unique to themselves.

<So now maybe you can better understand when some of us look
suspiciously up the assumption that Thyreophora is
holophyletic.>

  I don't see how this applies: the direct ancestors to
dinosaurs were scute bearing, and that's flat scutes.
Crocodylians, *Lewisucus,* and *Marasuchus* all bore a midline
set or pair of flat, keeled scutes. One then sees the most
primitive ornithschians with these, but theropods lack them. It
also confuses me to see how feathers can ossify, and become
scute or osteoderm cores; compared to skin, there is virtually
no calcium in the keratin-based structures of true scutes, hair,
or feathers -- the horny covering of scutes and osteoderms
appears to form from the skin overlaying the growing osteoscute
embedded within, and they form together from there. True scutes
and scales develope from scales, so the osteoderms of
thyreophores and titanosaurs are probably not analogous to
feathers in anyway. I have a reference on this, somewhere ...
but Maderson especially has done much work on archosaurs.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail
http://personal.mail.yahoo.com/