Re: Cost in Aquatic Birds (long)

["Jaime A. Headden" <qilongia@yahoo.com>]

David Marjanovic (david.marjanovic@gmx.at) wrote:

<In contrast, I start out with a coelurosaur that already had full plumage
and wings at least as large as those of
http://dinosauricon.com/images/bambiraptor-bb.html before it took to the
water. Makes the whole affair much simpler, and allows it to take much,
much shorter (instead of half the Jurassic); I consider "a long-lasting
directed evolution" pretty improbable.>

  The problem with this is that animals which take to the water for any
form of flight, and have large limbs, tend to _reduce_ these limbs until
they are short, stubby, muscular, and structurally unique. You don't see
this in *Archaeopteryx*, and in fact the broad structure of the wings
would have been counter-productive to aquatic thrusting. They would have
produced excessive drag and would have caused the animal to sit there
foundering in the water as do many modern birds when they can't swim,
paddle, or dive. Archie just has not the equippage to do much of anything
in the water. Proposing an aquatic thrust theory for the development of
aerial mechanics ignores the nature of the appendicular propulsors in
living vertebrates, which are shorter and stubbier in the adapted forms.

<Why doesn't this destroy the whole hypothesis? -- I can simply assume
that wings of considerable size were present even before that, and there
was a selective pressure to retain them.>

  The problem is is that the animal would have had these prior to entering
the water. So why have them to begin with. Ebel's theory only works if the
animal is a terrestrial form and has developed the larger arms as an
adaptation to increase in brachial-thrust. This ignores the viscocity of
water and the tendency to compensate by reducing the area of the wing and
achieving similar thrust through muscular effort. Elongation of limbs with
the increase in the feathers is exactly the opposite effect, and would
serve to operate in a less dense environment, a more fluid fluid, if you
will.

<In most of today's wing-propelled divers this pressure that keeps them
from evolving penguin-like flippers is the necessity to be able to fly.
(Penguins, Great Auks and others have somehow managed do circumvent
this.)>

  Erm, I think you're taking dippers too far back. They are the exception.
They also have short, tapered wings. Water forces constraits on size of
structures that operate within in in certain shapes. To adapt better to
movement within water, the thunniform morphology of a bullet-shaped body,
short tapered propulsive structures, and compact body without
non-propulsive or aerodynamic protrusions is not just better, it's
required, and a host of aquatic animals do this. No animal has ever gone
into the water, become so highly derived to acheive capable aquatic
flight, then come back out and flown. Ihe case of the various flying
fishes is different, as is that of *Isurus*, the mako shark.

<I assume one or both of these caused the ancestor of all flying theropods
to retain long wing feathers, at least during part of the year,> and to
swim with them, as so many birds do today. (Many auks molt all their wing
feathers at once and are then flightless for weeks.)>

  Auks molt every other feather, retaining the ability to swim during the
moulting phase. However, what reason can you see that aquatic effects
would no0t have reduced the arm as they do on any other animal that
becomes adapted to swimming.

<Though considering that confuciusornithids didn't, lacking one may still
allow being a good enough flier (aquatic or not) for many (certainly not
all) purposes. And, after all, lacking a keel is the plesiomorphy :-)>

  Or that confuciusornithids couldn't fly and the lack of a sternal keel
indicates a problem of aerial maneuvering. They were possibly capable of
lauching themselves from tree to tree, but may not have been capable of
extensive maneuvering around. They may nonetheless have been more able
than Archie was with its smaller sternal area.

<to my mind you imply that every dumb little winged theropod (including
Archie) can fly underwater without having to converge on a penguin! =8-)>

  Quite the opposite, if you read above. The penguin is the not the needed
plan, it is required for the equitable flying thrust in an aquaeous
environment. Or that is the conclusion produced from body types developed
by underwater fliers, anyway.

<Just like digits aren't necessary for a pike (correct? *Esox lucius*
anyway),>

  Like it has a choice in the matter ... lol.

<digits bring an advantage in its way of life and can therefore evolve in
an animal that occupies (sorry, makes up) this ecological niche.>

  Not neccessarily. They are a solution to bottom dwellers, for muddling
and maneuvering. Watching hellbenders can provide much insight into this
as they do the very things that the tetrapodomorphs may have done before
coming to land. Not just maneuvering through the vertical water column.

<It is (apparently) the plesiomorphy for... let's call it
Maniraptoriformes (and ignore my peculiar phylogenetic hypotheses). But it
is a synapomorphy of that clade within Theropoda, even within
Archosauriformes, for which serrated teeth are the norm. Therefore I think
the serrations must have been lost at some point, either as an adaptation,
or because the teeth were too small for serrations to have an effect
anyway. Should the former be correct, it suggests that all
Maniraptoriformes didn't just start out looking like Archie, but also
eating the same.>

  Actually, only *Caudipteryx,* ichthyornithiforms, hesperornithiformes,
and enants have this. Other forms have serrations, including
*Protarchaeopteryx*, *Pelecanimimus*, and *Sinovenator*; microserrations
have not been corroborated for *Archaeopteryx,* but neither have they been
refuted. So this condition is an adpatation, not a plesiomorphy, not just
within Maniraptoriformes, but within Tetanurae (including spinosaurine
spinosaurids).


=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

__________________________________________________
Do You Yahoo!?
Yahoo! Tax Center - online filing with TurboTax
http://taxes.yahoo.com/