[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Cost in Aquatic Birds (long)



Phew. I hope I can answer more briefly next time... For those who are
interested and can't steal enough time, the most important parts are the
third and the fourth big paragraphs. :-)

----- Original Message -----
From: "Jaime A. Headden" qilongia@yahoo.com
Sent: Tuesday, March 26, 2002 5:19 AM

> David Marjanovic (david.marjanovic@gmx.at) wrote:
>
> <There are also excellent arguments against both. (Still waiting for the
> paper on vertical running...)>
>
> [...] It is not enough to build up your theory, you must also try to
> take it down. Not that I think you've done anything like I will suggest,
> but you've done a good job of championing Ebel, but have not truly tried
> to tear his theory apart.

Actually, I've modified his hypothesis pretty much. Ebel wants everything to
evolve underwater, feathers, wings, everything, not just flight itself (and
he starts out exclusively from Archie):
        "The sparsely settled islands could have forced *Archaeopteryx*,
respectively her* ancestor, to become an underwater fish hunter. Presumably,
it was advantageous for this new lifestyle if already present enlarged
scales from which feathers could develop served as a device for heat
retention n the beginning that could help to extend the time of solar
exposure in a shadeless environment (REGAL 1985). With progressive
improvement of the plumage this could be used as a means of thermoregulation
as well as waterproof insulation (THULBORN & HAMLEY 1985). The possession of
some kind of feathers was certainly an important prerequisite for a
successful bird evolution. Feathers form a most remarkable innovation and an
important distinctive feature to pterosaurs which also lived in this region
and which must be regarded as direct food competitors." (p. 275f.)

* Germanism -- pteryx is feminine in the original. (Even though most German
speakers regard Archie as masculine.)

IMHO when the dinosaur that took to the water had just some "enlarged
scales", the outcome would have looked more like the enlarged scales on the
caudal sides of crocodile limbs, or at best sea turtle flippers, and
wouldn't have turned into feathers.

"In my opinion, [...] *Archaeopteryx* or her immediate ancestor which was a
terrestrial animal with relatively unspecialized forelimbs turned to
underwater foraging, respectively hunting. [...]
        [...] it is hardly imaginable that such an extensive preadaptation
might have been present in a bird precursor that it could immediately turn
from ground or tree dwelling to flying. Rather the formation of wings and
pectoral structure requires a long-lasting directed evolution which includes
already the execution of the later undulating flight motion." (p. 276)

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.

"This process had to be accompanied by a strengthening of blood circulation
and lungs to extend the length of stay under water [sic]. These changes may
have led to the initiation of endothermy and this, in turn, to an improved
insulation. All these modifications might have developed simultaneously
(FEDUCCIA 1985)."

I obviously can't agree. Not just because Feduccia is cited ;-) -- such an
evolution has no parallel in known ectothermic swimmers, and dinosaurs were
endothermic and had air sacs to boot.

"high-quality and presumably abundant food [...] major skeletal
modifications, above all those of arm and hand. It was important for the
evolution of flight that the tail of the terrestrial ancestor of
*Archaeopteryx* was too weak [and stiff] for the production of propulsion.
The feet also could not be utilized for that purpose [underwater], because
of an unfavourable disposition with respect to the longitudinal body axis
[the legs were much too long and strictly parasagittal]. Therefore,
propulsion had to be generated by arms and hands alone. But this
configuration had the advantage of the propulsion being generated in front
of the centre of gravity and the animal being pulled in a forward direction.
This resulted in a considerable simplification of steering. On the other
hand, propulsion only had to be generated since the animal's weight was
balanced [if not more than balanced] by its buoyancy. The evolutionary aim
consisted in a backward acceleration of as large as possible quantities of
water in a short time to achieve high forward speeds. Certainly with the
original arms and hands the available performance was extremely poor.
Therefore, there was a high evolutionary pressure to enlarge the wing area.
This was accomplished by the extension of wing span and depth [...] [and
musculature]. While it is easily understood that a bird needs large wings to
carry its weight this idea is not so obvious in an underwater hunter.
However, it is the typical configuration of underwater 'flyers' which is
also realized in most rays, apparently due to convergence. Propulsion and in
rays also some lift are generated by large undulating "wings", using either
the pectoral undulatory mode or the pectoral oscillatory mode of real
underwater flying (BRAUN & REIF 1985). Also remarkable in many rays is a
long tail which appears to be necessary for steering. Surely, this
correspondence is not merely a matter of chance." (p. 276f.)

I can't agree with all of the above. Using unspecialized coelurosaur arms
for wing-propelled diving (yeah, that's the term :-) ) should be pretty
useless. When the glenoid for such an arm faces laterally rather than
ventrally for whatever reason, then the outcome should, as the common
objection onlist is, look much more like a penguin (or a seal or a
plesiosaur); large wings would not evolve. Maybe this speculative dinosaur
http://specdinos.0catch.com/Spec/Torrentraptor.html is a good idea of what
would happen (though that one's flippers are even narrower than a
penguin's). (Interesting idea about the reverted hallux, though. :-) )
        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. 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.) This can obviously
not have been the case before flight had evolved. What other things are
large wings good for? -- Brooding (to be precise, shielding eggs and young
from heat and rain) and/or various sorts of display, the same thing(s) they
evolved for. 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.)
        Was Archie able to twist its tail about its long axis for lateral
steering, as Ebel assumes, without ever mentioning anatomy? And do
bottom-living rays really steer with their thin, stiff tails?

And now the really difficult part... Paraphrasing Ebel, when you can fly
underwater and your wings are large enough to carry you on in air, you can
already fly in air; you don't need to beat your wings as hard, but on the
other hand much faster.

> <Again I don't think Archie could qualify as aquatic. Just as semiaquatic
> as a dipper.>
>
>   Dippers are not semi-aquatic, as they feature no adaptation to a life in
> the water. More on this below...

Fine, fine. Then you strengthen my argument. :-)

> <(sterna is already the plural, of sternum)>
>
>   I think that all three are used. Both sterna and sternum are stems from
> sterno (something broad) in Latin.

According to the dictionary sterno means "I strew", "I throw
something/someone to the ground". Past participle is stratum... you know
that word :-)
        My dictionary doesn't know either sterna or sternum... I've seen
only sternum so far as the singular.

> Birds with a larger lateral keel surface area are
> better fliers, including aquatic fliers.

Erm... yeah. Penguins do have very large keels. 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 :-)

>   A lot of birds have the ability to seal their nostrils. The thing is,
> all dipper aquatic behavior is just that: behavior. And that does not
> fossilize. This is part of Ebel's theory's flaw: the dipper has no real
> features except sustenance of breath to permit it to swim into deep water
> and take prey.

I think this is an important part of Ebel's hypothesis' _very strength_ --
to my mind you imply that every dumb little winged theropod (including
Archie) can fly underwater without having to converge on a penguin! =8-)
        I use what I've picked out of Ebel's hypothesis solely to explain
how the behavior of flapping evolved, if you will, and to give me an idea in
which ecological niche flight can actually be an advantage, but not
necessary, so it can evolve there. Just like digits aren't necessary for a
pike (correct? *Esox lucius* anyway), digits bring an advantage in its way
of life and can therefore evolve in an animal that occupies (sorry, makes
up) this ecological niche. And unlike the old (probably distorted) idea that
"fish" first went ashore and then evolved lungs, _after_ they had begun to
_need_ them. :-)

> <...which is a foot-propelled diver.>
>
>   Mostly. Cormorants also use their wings as aerofoils (I've seen them
> dive, though not in person) as part of the upsurge from a dive. They use
> this to increase their surfacing speed.

Interesting.

> <I am aware that many arguments for FUCHSIA are negative. :-)>
>
>   I see flaws, and I report. That's part of the scientific process. It
> permits refinement, or rejection.

Of course. Nothing against that.

>   I don't know how many times I've seen osprey dive. They plunge at an
> angle into the water, grasping with the feet, if the object is too deep to
> snatch from the surface, and use their wings to propel them to the
> surface.

Yet one more bird which does that (as a behavior)! :-) (I've never seen an
osprey dive. They are pretty rare over here.)

> <It does have the unserrated teeth of a fish-eater, though.>
>
>   Fish-eaters typically need _lots_ of interlocking teeth ... avian
> fish-eaters, though, lack 'em, so it's not required.

Good arguments...

> As for the lack of
> serrations, there are lot's of basal birds and maniraptoran theropods with
> non-serrate teeth, so this is evolutionary first, ecological secondarily
> if at all.

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.

-------------------
Full ref for Ebel:

Klaus Ebel: On the origin of flight in *Archaeopteryx* and in pterosaurs, N.
Jb. Geol. Paläont. Abh. 202(3), 269 -- 285 (Dezember 1996)