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Re: snap-action predation



Greg Paul (GSP1954@aol.com) wrote:

<To clarify matters, by sit-and-wait predation I meant creatures that
either sit and wait for something to come by, or very slowly creep up on
it, and use special, high velocity body parts such as projectile tongues
or unfolding forelimbs to reach out and touch their prey.>

  Come-hither predators, or trap pedators are not the same as ambush
predators, but both may be opportunists. However, ambush predators like
wolves seek prey, then set an ensnaring circle to halter in the animal.
Trap predators, like frogs, some bass, stone fish, caprimulgids in some
settings, etc., are of the kind that Greg describes.

<The idea that the folding arms of avepectoran dinosaurs evolved for
snap-action predation was not absurd, but was always weak>

  insert, in Greg Paul's scheme ...

<in view of their absence in running predators,>

  I counter with long limbed arctometatarsalians like troodontids and
dromaeosaurs, non-arctomet but highly cursorial caudipterids. And these
forms "start out" with these adaptations, _then_ loose them and become
shorter limbed and larger. The smaller pelvis reverses, and the
four-limbed structure becomes two limbed. But cursorial adaptations
nonetheless.

<and the lack of need for such organs in runners.>

  I counter with Dial's Hypothesis. Yeah, yeah, see below....

<Only if such a system was present is an animal that clearly had no other
evidence of a flight heritage would such an explanation be viable. It was
an ad-hoc attempt to try to explain how such a system evolved in 
predators widely thought to have no flight heritage.>

  Not so. In fact, Ostrom's support was the first such exaptive
explanation and at the time few other systems were advanced as the
theropod origin of birds had not been accepted at all. First it was
Ostrom's work that advanced an adaptive explanation for the development of
flight. The flaws in this system are few but focus around feather
development. Feather development need not be co-adaptive to arm-folding,
nor do they need to be adaptive to the same manner. Chure and others'
examinations are turning up semilunate carpals preceeding Coelurosauria,
with a distinct development towards arm lengthing without a predicatory
long arm. Tyrannosaurs are an exception, as is *Sinosauropteryx.* "Normal"
adaptive structure in *Nqwebasaurus* and *Coelurus*/"Tanycolagreus," shows
a trend in increase of the arm and aspect of the semilunate. A ceratosaur,
*Liliensternus*, bears a distal carpal that caps two consecutive
metacarpals and those metacarpals contact along their length though they
are not complete.

<If these dinosaurs all flew or had flying ancestors then the problem
disappears because the folding action simply evolved to tuck up the wings
like an F6F on an Essex class carrier (cue in the Victory at Sea theme).>

  Have you considered you are wrong or are trying to prove the early
development of flight in theropods preceeding maniraptorans? ... err,
"avepectorans", though the clades are not contiguous, and one actually has
no definite concept of content [er, I don't really like apomoprhy-based
clades... :)].

<It is interesting that derived therizinosaurs have a less well developed
wrist folding system than the basal examples. Another one of those
reversal issues that vex cladistics.>

  No vexation, just indicative of a smaller clade within Segnosauria,
defined by reduction of aspect. No cladistic study has considered
therizinosaurs outside a group of theropods which contain a derived
arm-folding mechanism, i.e., Coelurosauria.

<Although I suspect that basal birds had a better developed wing elevating
system than Nick thinks, he is correct that it was not as good as in
modern birds and this is an argument against the Dial hypothesis.>

  This statement would only make sense if there was an experiment with a
time machine, becuase the reference to adaptation of flight, in any sense,
is just as utile with the Dial Hypothesis. It does not presume that a
runner can learn to fly by flapping its arms, but that an animal can
assist it's rear locomotion with fore locomotion, then adapting the last
instead of the former. Many birds use their wings to gather lift for
flight, as in swans "running" on the surface of lakes whiel flapping. That
this is "known" in modern birds does not mean it is only an adaptation for
them, as the nature of this is behavioral, and no fossil can evince Dial's
Hypothesis in preservation; therefore, by extenstion, it cannot be
disproven except to indicate a biomechanical or osteological condition
which prevents it outright. E.g., a bird cannot fluff its feathers if it
lacks them.

  Cheers,

=====
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.

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