Re - Feathers and Flight

[cowen@geology.ucdavis.edu]

Richard again: this is stuff generally related to Kevin Padian's 
comments. 

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 
the others.)

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. 

Kevin wrote
"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.