|
<<This is the way exaptations work: an
adaptation allows the animal to do something the adaptation wasn't designed for,
and this use offers an advantage>>
The adaptation is designed for *nothing*( and, in
any case, the "thing" designed fo something would be the character, and not the
adaptation, that is instead how the character fits in the number of way the
omologous character was used by the predecessors of the animal in question); if
the animal can "use" the new character( and I think it always would, being the
character not an extreme alteration, a deformation).
<<even though that use is not necessary for
survival, it is just an advantage>>
Ok but it's a secondarily aquired ability;these
birds were *already* able to fly and *then* "learnt" that they could find fishes
really better and farther than before( exaptation of the ability to fly); this
*doesn't* explain why they should have tried, once caught their fish , to get in
the air, unless they were already able to do it and needed to get
home.
I mean, a mosasaurus trying to eat them would have
been a good reason, such as any other kind of predator that wouldn't have
been able to eat them once they were in the air, but this is one of the reasons
for which cursorial little theropods are thought to have "tried" to
get off the ground (onto a tree, on a higher rocky level, who knows?)
.
Maybe an already semi-acquatic theropod , having
the powerful wing structure and the right movement needed to be able to get in
the air from the water surface(selected as a mean of propulsion in the water),
tried to catch something in the air; this could be not too difficult from
a mechanical point of view( someone knows something about this?..I surely
don't ) but yet, why would you need an explanation already considered as a
possibility in the cursorial scenario??
This would require one more step(the
evolution of the semi-acquatic lifestyle) and thus is surely less parsimonious,
unless you consider the requisites for flight as *only* possible to be
obtained as an exaptation of the swimming abilities.
<<My personal feeling is based on the
evidence I gave -- what is your evidence?>>
I'm not surely the best person to provide you with
all the possible reasons considered to support the ground-up hypothesis, but I
seem to recall some reports from the recent SVP meeting about some studies, one
regarding the ground-up( turning abilities given by the use of the tail and
feathered arms[possibly two different talks I don't remember]) and one the
trees-down( I would have to look for it in the archives, sorry).
However, I think your evidence, from the
point of view the possible evolution of the aqcuatic lifestyle and the
subsequent evolution of flight is not *yet* supported( this obviously doesn't
mean it can't be) by anything more than speculation(intelligent, but still such)
and is therefore a bit weak.
<<Ebel mentions a strong argument against
ground-up -- chickens can fly but don't like to do so when
unnecessary>>
a strong argument??
Has he (or anybody else, if it's possible, but
i think it will hardly ever be) ever tried to compare the predatory
pressure over the different populations of the different
"chickens" species(the wild ones....galliforms[?], I don't know the name of the
group comprising them all), trying to compare them with that under which
the little theropods considered to have been the first fliers
evolved?
I have the impression that domestic chickens would
turn out to be, among all their relatives(those living *not* in particularily
predators-free enviroments) the ones with the worse flying ability.
If today's chickens were freed in the mesozoic in
the region supposed( always hypothetically speaking) to have been the place in
which the litle theropods we're taking about lived(supposing it had to be
particularily different from other areas, but I don't think it would be
necessaryto be so), i think they would have some more troubles surviving
than those little , fast theropods, althought they are(the chickens) able to fly
when necessary.
I said this because I think using chickens as an
example is totally nonsense.
Anyway, I would be really interested in knowing the
kind of enviroment chickens' relatives( and all birds with an analogous body
structure and possibly a similar ecological niche) live in, their usual
predators( and occasional ones, if known) and how these populations are seen in
their habitat complex; I mean, are they usually rare because the predatory
pressure is high and only few can survive and reproduce, mantaining however a
pretty stable population?
Again , back to the chicken analogy, I think it's
pretty useless because it represents an opposite "trend" if compared to that
considered for the little theropods; chickens have secondarily adapted to a
particular lifestyle, while the supposed coelurosaurs were probabily in the same
condition, but had never been able to fly (yet) but the predatory
pressure would have selected the ones that had aquired the features needed to
get in the air(supposing the predatory pressure was the main reason and not
others).
This obviously doesn't mean that taking off was the
only way to survive , but justifies(or may justify, that is, from an
hypothetical point of view the same thing) the selection of the features needed
to begin to fly(or jump higher, maybe on some tree branches;-).
I'm sorry for the long post;
bye
Calzolari Filippo
|