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Re - Feathers and Flight
Richard again: this is stuff generally related to Kevin Padian's
First, I would be disappointed if Kevin continued to lurk rather than
participate. His comments on this particular topic ware so lucid and
sensible that they force me to explain more clearly what I am trying to
do, and he has such a fund of paleontological knowledge that we could all
benefit from his input on all manner of things Mesozoic and/or vertebrate.
Second, I think other professionals should participate more because we
have learned to treat one another courteously, and by example can perhaps
help the discussion avoid some of the verbal garbage that crops up on
the net (not much in this group, but you have all probably seen some of
Anyway, here are a couple of further thoughts.
The cladistic/phylogenetic school provides evolutionary hypotheses
that are mostly based on morphology, though biochemistry, genetics, etc.
are allowed where available. And yes, evolutionary hypotheses (like the
display hypothesis, for example) must at least be compatible with hard
evidence if they are to be considered seriously. As it happens, the
display hypothesis is. It doesnUt ADD anything (maybe) but that's another
question. Certainly our scenario is not denied, and it brings with it
functional explanations for features that are otherwise puzzling.
Examples: why Archaeopteryx evolved the worst possible tail for flying
with; why it retained claws on the ends of the wings where the longest
primaries would be expected, etc. No phylogeny here, but *explanation.*
I agree that behavioral interpretations are often difficult to establish
beyond all doubt (example of an exception: the dinosaur stampede in
Australia, which *proves* rapid running beyond any doubt). But let's
test the display hypothesis as far as we can. Let's take the diapsids,
which include dinos and birds and lizards and crocodiles etc. Looking
at the distribution of characters within that clade, one can make the
suggestion that they were all (originally = primitively) visual,
displaying creatures (Jacques Gauthier said it, not me). Lizards do it,
birds do it, they all have color vision, and they are daylight,
terrestrial animals. The only exception is the crocs, which secondarily
evolved away from a terrestrial environment and don't display much any
more either. Right, we cannot *know* how dinos or the first birds
behaved, but it is reasonable on these and any other grounds to suggest
that they used display - many people have suggested display in dinos,
especially in the horned ones. Kevin himself says "theropods were
generally active and highly visual creatures". That's behavioral
interpretation, but I have no quarrel with it. It's "only" a hypothesis,
like everything else that goes into the pot. Now the great thing is
that the phylogeny of diapsids MIGHT have suggested that the first birds
did not inherit a tendency to display from their diapsid ancestors, but
when we ask for a check in this way, we find that the first birds
probably did inherit such a behavior. In an admittedly non-rigorous
test here, the display hypothesis has come out with flying colors -
deliberate metaphor :)
Jere and I used evidence from living birds to help us interpret the
biology of Archaeopteryx. That's OK, though Kevin and Tom Holtz point
out there are dangers. In reply to just one of Tom's points, we didn't
look at penguins because they are primitive. We used penguins to answer
only one question. If feathers evolved for thermoregulation, what
would they look like? It's no use looking at most living birds, because
they use their feathers for all sorts of things, and can't give a clean
answer to our question. Let's look at a bird that has feathers used ONLY
for thermoregulation, not for flight, not for display: an Emperor penguin
chick. That's a fair test, it seems to me, and it has an answer: down.
It didn't *have* to be that answer, but it is. You can choose to ignore
that answer, but it won't go away. It suggests (to us) that feathers
didn't evolve ONLY for thermoregulation. Any kind of feather would help
in thermoregulation, but you have to have some other selective factor
acting as well.
"Jacques Gauthier and I showed that the predatory motion of
the deinonychosaurs, whipping forward the sideways-flexing wrist and
the elbow, was virtually the same motion as the flight stroke cinematically
recorded in birds and bats (see the Archaeopteryx Conference volume
edited by Hecht et al. in 1985). This, we think, is the missing piece
of the puzzle in terms of evolving active flight. And it's interesting
that only birds and deinonychosaurs (deleted) have this sideways-
flexing wrist. And these are obviously terrestrial animals."
Our hypothesis does not contradict this fine piece of anatomical
reconstruction: it uses it. A deinonychosaur or a proto-bird hammering
the **** out of a rival would use the same arm-stroke as a d or a
proto-b hammering the * out of a prey animal - and what Kevin's quote
doesn't tell you is that this is the major LIFT stroke. In the predation
scene, lift off the ground doesn't help you. In the fighting scenario,
it could give you the vital edge. (Again, we used observations about
living birds that fight on the ground: a little bit of lift gives you
a big advantage.) So we agree that Kevin and Jacques's analysis is
'the missing piece of the puzzle' that transfers an arm stroke into
some lift - as long as lift gets you something. We specify what
that something is.
Kevin explains very lucidly Jeremy Rayner's problem: why the running
predator would be at the very edge of its envelope before it could
get off the ground: exhaustion at take-off is not a good way to learn
to fly. The beauty of the display-and-fighting idea is that the
lift-off takes place at ZERO ground velocity: it's all *lift*, and
short-lived lift at that, at this stage, ideal pre-flight training
conditions, with forward speed coming later. Our display-and-fighting
hypothesis can provide Jeremy and Kevin with a flying bird from the
ground-based predatory animal they both prefer as its ancestor -
they just can't have it running flat-out to take off.
This also takes care of Tom Holtz's point that Archaeopteryx and
other theropods may not have been running as fast as we once thought.
Jeeze, this is tiring on both the brain and the fingers, but it is
incredibly worth while (for me at least). I'll take up more of Tom's
points another time. And, all of you, thanks for listening, and thanks
for the helpful, constructive responses.
And Kevin - don't worry, the rest of my book is not hanging out there
in the breeze as much as this section, though the origin-of-sex
section is original and therefore suspect!
Richard Cowen - speaking for Jere, too, I hope.