Re: Progress in evolution and the origin of flight feathers

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

George O. quotes Rob Meyerson:

>> I have a small objection to the word "primitive" 

and responds:

> Let's see some synonyms for "primitive" as an antonym to "derived."

I have mixed feelings about the issue in question.  I agree with Rob
that the word "primitive" conjures up (in the lay public even if not
even subconsciously amongst those in the field) some inappropriate
imagery.  Off the top of my head, though, ancestral is the only other
antonym I can think of that receives common use.  It does lose some of
the problems that "primitive" brings with it, but it suffers from other
problems when you're talking about character states in coeval
organisms.  Aeh what can y' do?

Now since I've been having so much fun battling with George both out
here and in private, let me take issue with:

> Humans are the most complex organisms to ever have evolved on earth.

To be blunt, I think the above statement is rather vacuous.  I argue
against such statements not because I think we have a need for
absolution but rather because I don't think it has any truth to it (or
rather, its truth depends so strongly upon the definition of
complexity that it seems it can only be true by definition -- hence
its vacuity).  I don't particularly want to argue it here, though,
since I think there are plenty of other places where the discussion is
more appropriate (sci.bio.evolution comes to mind, though it's been a
while since I've had time to read that group...).

So let's go back to something more dinosaurian.  George asks:

> Didn't someone (Ostrom?) once suggest archaeopterygid flight
> feathers as insect traps?

Yes.  However, it's my impression that nobody takes the idea seriously
any more.  However, the idea has gotten a fair amount of press, so
let's turn to another idea that Richard Cowen (another prominent
lurker) gave us last winter and which I think could stand some more
consideration.  I'm only excerpting a piece of what Richard sent last
January.  If you want more, look through the jan95 archive (archives
that old were kept by month rather than by day, so be prepared to sift
through a lot...) or better yet look for Richard's book:

  This is a slightly edited version of a section from "History of
  Life" by Richard Cowen, published by Blackwell Science, 1994.
  Copyright Richard Cowen.
  
  The Display and Fighting Hypothesis
  
  Either the arboreal or the cursorial hypothesis would work, and work
  much more easily, if a protobird already had long, strong feathers
  in the right places and already had powerful arm movements. Jere
  Lipps and I suggest that display was involved in the evolution of
  flapping flight as well as in the evolution of feathers. Display
  provided long, strong feathers on arms and tail. Successful display
  was increased by lengthening the arms, especially the hand, and by
  actively waving them, perhaps flapping them vigorously. Flapping in
  display would have encouraged the evolution of powerful pectoral
  muscles.
  
  But a threat display must not be seen as an empty bluff. Fighting is
  the last resort. Living birds often fight on the ground, even those
  that fly well. Wings are no longer clawed but are still used as
  weapons in forward and downward smashes (steamer ducks are
  particularly deadly at this). Beaks and feet can be used as weapons
  too and are most effective when used in a downward or forward
  strike.
  
  A strong wing flap, directed forward and downward, is also the power
  stroke that gives lift to a bird in takeoff. Lipps and I suggest
  that strong wing flapping is a simple extension of display flapping,
  encouraged by fighting behavior. Powerful flapping used to deliver
  forearm smashes could have lifted the bird off the ground, allowing
  it also to rake its opponent from above with its hind claws. The
  more rapidly the wings could be lifted for another blow, the more
  effective the fighting. This would rapidly encourage an effective
  wing-lifting motion that minimized air resistance, so the wing
  action would then be almost identical to a takeoff stroke.
  
  A variant of our idea has also been proposed by Kevin Padian, who
  prefers to think of the wing stroke evolving from the arm strike
  used by a theropod in predation. It's not clear how this could have
  led to whole-body takeoff, however.
  
  A few living birds use their wings extensively as weapons. The
  steamer ducks of the South Atlantic are large, powerful birds with
  heavy, bright orange, horny knobs on the wings of both sexes. These
  are used by both sexes in display and fighting. Steamer ducks
  (especially males) fight a lot among themselves for mates and
  territory, and they often kill other species of water birds, holding
  them by the neck and beating them to death with the wing knobs. Some
  species of steamer duck are flightless; in other species, the males
  are often too massive to fly, even though juveniles and females can
  fly well. Selection has favored fighting ability over flying ability
  for many steamer ducks. Flight is perhaps less important for them
  than for many birds, because they live in shoreline habitats where
  food is plentiful all year round.
  
  Archaeopteryx fits our display-and-fighting hypothesis well.  It was
  well adapted for display. Like any small theropod, it was well
  adapted for fighting with its teeth and the strong claws on hands
  and feet. Archaeopteryx did not have long primary feathers on its
  fingers, probably because they would have hidden the claws in
  display and would most likely have broken in a fight.
  
  Did Archaeopteryx Fly?
  
  Archaeopteryx, then, was a fierce little fast-running, displaying
  bird, which probably spent its life scurrying around the Solnhofen
  shore, hunting for small prey such as crustaceans, reptiles, and
  mammals. In hunting style, Archaeopteryx was probably much like the
  roadrunner of the dry country of the American Southwest, but its
  ecological setting was closer to that of a steamer duck - a
  shoreline with year-round food supply. Archaeopteryx did not compete
  in the air with the pterosaurs that are also found in the Solnhofen
  Limestone.

  From Display to Flight

  In our theory, display and fighting were simple selective agents
  that encouraged the evolutionary transition from small dinosaurs to
  birds. The idea fits with our current knowledge of the biology and
  behavior of living birds. Display, and fighting if necessary, is
  very important, even within a species. Bald eagles and frigate birds
  often try to rob other birds of food instead of catching prey
  themselves. Because the penalty for wing injury is high, many birds
  can be intimidated by display into giving up their catch rather than
  fighting to defend it.
  
  Display and fighting in birds, whether for territory, dominance, or
  food, takes a lot of energy, but only for brief periods or seasons,
  and it provides an enormous payoff in survival and selection.
  Sexual display in most living birds must be done correctly, or no
  mating takes place. New behaviors are quick to evolve, and they are
  evolutionarily cheap, because they usually do not require any
  important morphological changes in their early stages. Bowerbirds,
  for example, show distinct behavioral differences in display between
  closely related species.
  
  The display hypothesis suggests that a protobird gained flight
  behavior, anatomy, and experience at low ground speed and low
  height, ideal preflight training. The selective payoff for
  successful mastery of the flight motions gave significant
  advantages, even before flight itself was possible. From that point,
  the many advantages of flight were added to those of social or
  sexual competition.
  
  Lipps and I envisage Archaeopteryx as a small, fierce predator,
  capable of liftoff but not true flight. Once liftoff was achieved,
  flapping flight quickly followed. There is no need to suggest any
  difficult evolutionary sequence to complete the final transition to
  full powered flight. In more advanced birds than Archaeopteryx, the
  pulley system of the shoulder evolved for quick wing upstrokes,
  while the wishbone evolved into a spring. The breastbone evolved as
  the anchor for the flight muscles. The forearms became longer,
  lighter, and more fragile in bone structure, becoming specialized as
  wings, and losing the finger claws. The feathers became more
  aerodynamically suited to powerful swishes through air. Meanwhile,
  the feet and beak became the dominant fighting weapons, as in most
  living birds today.
  
  The display hypothesis for the origin of flight is particularly
  attractive because it demands few of the assumptions required by the
  arboreal or cursorial hypotheses, yet it is fully compatible with
  the morphology of Archaeopteryx and the biology of living birds.
  
  NOTE: If you want to quote this hypothesis, I'd suggest that you use
  the phrase Cowen and Lipps in Cowen (1994), and refer to my
  textbook.  I hope that Jere and I will be able to get the
  full-jargon version out in a journal some day. Meanwhile, Jere and I
  are responsible for the idea, and you have to blame me for the
  detailed wording that I prepared for my text.