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Re: Origin of feathers



Regarding our "Brooding came first" concept for wing feather elongation,

jjackson@interalpha.co.uk wrote:
<the theory does not satisfy the "bootstrap test" - would the adaptation have
had an advantage from the moment it first appeared>

    We think so.  Again, our starting point is an animal with short contour
feathers all over its body.  From Oviraptor we know that the arms were held in
a position that brought them into contact with the eggs on each side of the
animal.  Consider an ancestral creature that had no long feathers (sorry again
that I can't show you our accompanying figure).  It would only be able to
cover the eggs in a small nest (few eggs, small eggs) and the arms would be
nearer to the side of the body.  Under selective pressure to have larger
numbers of eggs, or larger eggs, there would be a need to move the arms
outwards to encircle the larger clutch.  This leaves a gap between the arm and
body, at first small, then growing to the large size seen in Oviraptor.  ANY
small increment of feather lengthening on the arm and hand would have enabled
the proto-Oviraptor to cover a slightly larger egg size or clutch number.  A
series of small arm-feather lengthening mutations would have allowed a gradual
expansion of the area COVERED by the proto-Oviraptor's arms.  Thus, in our
view, the selective pressure that brought arm feathers out to great length was
the selective advantage of covering an increasingly bigger clutch (size and/or
number).  No need to invoke anything outside the bone evidence such as insect
chasing, tree climbing etc.  Just something we know Oviraptor did - brooding.
In our view (perhaps I shouldn't speak for Mark Orsen here, but I think he
would agree) Oviraptor, at least postcranially, can be considered to be an
oversized example of EXACTLY the intermediate that John Ostrom proposed twenty
years ago (he didn't have the benefit of Oviraptor to look at or I am sure he
would have thought of this himself).

Dinogeorge wrote:
<feathers on the arms . . . would interfere with other useful forelimb
functions such as subduing prey>

    I think too much anthropomorphic emphasis has been placed on the use of
hands by theropods.  Look on either side of theropods for examples and you
will find that hands are used minimally in prey-capture.  Crocodiles capture
prey mouth-first, as do lizards.  On the other side, birds are mouth-first
grabbers, as well.  Why invoke something for which there are few or no
examples to explain dinosaur predation?  Not parsimonious, I think.  Sure,
velociraptor MAY have latched on with its hands (but why not use its big,
nasty jaws instead?) The real question is, what did Archaeopteryx's ancestor
do?  Climbing trees is not as parsimonious as running around like a
roadrunner, with the arms doing nothing most of the time.  This leaves them
free to assist in other critical functions like brooding.

    Dinogeorge also suggested that exaptation from flight to brooding is
easier than from brooding to flight.  Not necessarily.  A wonderful book
entitled "The Roadrunner," by Wyman Meinzer shows how an Archaeopteryx-sized
cursorial hunter escapes counterstrikes from its prey by leaping into the air,
then flapping to stay aloft a short while longer.  Think small.  The smaller
an animal is, the more its large arm feathers can make a difference in "hang
time."  Given a fully lengthened set of feathers used only for brooding, it is
not at all hard to see how Archaeopteryx's immediate ancestors could have
exapted them for flight.

    So George, perhaps BCF actually stands for BROODING CAME FIRST.

Tom Hopp