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

Feather origins? (fwd)



 
     Here is a slightly abridged and modified version of a posting I made
in February:
----------------------------------------------------------------------------
 
  _Bristles_ (definition from my ornithology text): A stiff, tapered
rachis that usually lacks barbs entirely, although they may be present
around the base.  They serve a variety of functions, mainly sensory
(similar to a cat's whisker), and as filters around the eyes and nostrils
(ostrich and hornbill "eyelashes" are bristles).
     Bristles are the structurally least complex kind of feather, and I
think it is reasonable that the earliest feathers may have been bristles,
or bristle-like.  Bristles in modern birds mainly serve two functions;
tactile devices similar in function to whiskers, and filters to keep dust
and other crap out of the eyes and nostrils.  
     Do bristles develop an epidermal collar like contour feathers do?
Unlike trees, feathers grow from the base, not the top.  Differentiation
into a contour feather begins with the development of an "epidermal
collar" deep inside the follicle.  This is a crown shaped structure, and
the barbs grow off of it.  One side of the crown continues  to grow up,
and the bases of the growing barbs come around and attach at the base to
FORM THE RACHIS.  The imporatant lesson here, which may be problamatic to
my idea, is that the _rachis_ is formed from the _barbs_; the barbs do
not "sprout" off of the rachis like twigs off of a branch.  This implies
that barbs came first. 
     However, if you didn't form the epidermal collar, wouldn't you just
get a huge barb?  Are bristles really naked rachi, or big barbs?  Can
anyone who knows a little more about bristle epidermal development answer
that?  
    The whole point to bringing this back up is that I don't think the
fact that the _Sinosauropteryx_ things lack the structure associated with
most feathers is neccesarily so strange.  They basically look like hairs
(or bristles) rather then CONTOUR feathers, right?  
    By the way, I would appreciate it if someone could give me references
for Longisquama and any other flying archosaurs or archosauromorphs (with
the exception of drepanosaurs) that might have been considered as bird
(or even pterosaur) fore-runners.  I'd like Gracilosuchus or any other
potentially arboreal crocodilians as well.  Thanks!

LN Jeff
O- 
"My dad says good is what you feel in your heart, and evil is what you
sense in your gut."
"Well, your dad's brain is so tiny that naturally his other organs would
have to pitch in..."