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Feathers [was: Re: Q's arising from Archaeopteryx feathers]



At 05:09 PM 10/1/96 -0400, George Olshevsky wrote:

>There is >no< "well-argued hypothesis" explaining how feathers developed,
>period, just a lot of Just So Stories, BCF included (by the way). The

        I do not agree.  There is a significant body of scholarly work
devoted to the endothermic dinosaur theory.  Along with it have come
comments about the evolution of feathers.  I have yet to see major scholarly
work onthe subject, but considering that nearly every biology textbook has
the "scales-to-feathers" diagram, I assume that the homology is well
established (PG, feel free...). 

[Allow me to interject... No, that ain't right.  The topic has come up
 here on a few occasions.  See, for example:

 http://www.cmnh.org/fun/dinosaur-archive/1994Dec/0232.html
   and better yet:
 http://www.cmnh.org/fun/dinosaur-archive/1995Jan/0188.html
 -- MR ]

      Gregory Paul's _Predatory Dinosaurs of the
World_ may not have the *most* well argued hypothesis (sorry GSP), but it
certainly is one.  I have not heard of a hypothesis which says they evolved
specifically *for* flight.
        "Just So" stories tend to be a phenomenon associated with poor
theoretical knowledge, and/or incomplete or simplisitic thought.  They
almost always involve a simplification of a process.  Try this: "If
dromaeosaurs were warmbloodled [hypothesis] and since they were small enough
[fact], perhaps they had feathers [grounded theory based on fact, with no
controverting evidence], which would then explain the presence of feathers
in their close cousins the birds [fact] from the earliest definitely known
member of the clade [fact] as exaptations [evolutionary theory] from the
insulation of their (presumably cursorial [theory based on analysis of data,
but by no means necessary to the central point]) common ancestor."  For you
refernece hounds, I will reference this idea to everything Bakker and Greg
Paul have ever written.
        Anyway, that is most assuredly not a "Just-So" story.  It does not
over-simplify the evolutionary process, nor does it offer simple
explanations to complex issues.  It takes an end product, and based on
available data, hypothesises a beginning situation.
        Sorry if that was too abrupt.  I'm still in confrontation mode.  :)

>development of feathers for insulation requires a need for insulation, which
>has never been established in avian ancestors because we know too little
>about their energy budgets. All arboreal animals, however, >do< face the
>Falling Problem, which a number of adaptations, including aerodynamic
>feathers of various kinds in various places on the body, can alleviate. The
>case for feathers arising as a solution to the Falling Problem is presently
>just as good as the case for feathers arising as insulation.

1)       All of the full-body "hairlike" integument that exists is used as
insulation (although it does have other uses...).
2)        There are many arboreal animals which have not developed feathers
or other integument to soften their falls (yes, some have, but how many
gliding animals have *not* exapted their scales into feathers.  No, don't
bring up scale gliders either, those are not feathers at all.).
3)        Birds are warm blooded.  There is no a priori reason why this
would have to develop as a part of becoming volant, and it has been
suggested (no refs, anyone, anyone?) that it may be necessary for flapping
flight.  I'd rather not rehash dinosaur endothermy, though...
        All of these things make the conclusion that feathers were
origionally developed for a purpose other than flight (or falling out of
trees) the more parsimonious theory.  Display is certainly possible, and so
is insulation.

        Wagner

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| Jonathan R. Wagner                    "You can clade if you want to,     |
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