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Re: snap-action predation



Martin Human (GMHuman@cs.com) wrote:

<I bow to those with specimens to measure, but what is the point of
"snap-action" arms if the reach of those arms appears to be little further
than the reach of the head plus neck?>

  Though this argument has been broached before, tilting of the body
upward in the front removes this proportional imbalance, and is further
supported by the form of the femora and hip, as detailed in the work of
Gatesy, Middleton, and Hutchinson in the last decade. The longer the arms,
the more flexible the neck, and the greater tilt at the hips, the animal
is no longer constrined by ideas of an allosaur-style cursorial form, but
can be a two-, three-, or five-member attacker: both arms, head and arms,
and head, feet, and arms together. Such exaptation of the forelimbs for
grappling-style attacks (as suggested by Holtz, Williams, and myself on
this list) should involve development of a multi-modal life style as
mechanics become developed for fore- and hindlimb and cranial
specialization. "Dino-birds" were not allosaurs, and their modus vitae
should not be conceived of as such. Meaning, there were no Bakkerian
bronto chases when a deinonych harrassed tenontosaurs, but rather would be
leap and slash, and grapple style attacks. Equipment seems to have been to
hold on, and cause as much damage, but also an attempt to subdue the prey
as quickly as possible. Lions use the same method when the prey is
buffalo. It stands to reason that derived hand equipment, foot equipment,
and cranial specializations (in some forms, a deep snout and large
recurved teeth, or robust teeth and jaw elements) were used in varying
degrees of tandem; should be more plausible to use them exaptively for
hunting.

  Let me also reply in general to the list, on other subjects.

  The same region in other predators for grappling animals, shoulders,
chest and arms, become very large in proportion to others in sabretooth
cats, an example of large-game prey in *Smilodon* sites, versus
smaller-prey kill sites in the chaser-style hunters, as in dogs. Cats
develope both skull and arm anatomy, and there is no reason to suggest
this did not happen in "dino-birds", or at least some of them, and it
certainly is enough to show that there are viable alternatives to what has
been construed in some forms as "the truth."

  And what about feathers? Ville commented on the tail fan of
*Cryptovolans*, and I would suggest that the work of Hopp and Orsen, Luis
Rey, and Scott Hartmann on the concept of a tail fan can be aerodynamic or
utile for either shade or display. If aerodynamic, it need not be for
maneuvering or braking, just distal lift production (Hartmann). I see a
development of a pygostyle as being a biomechanical consideration of
reduction of external forces affecting (distorting proportions of) the
distal tail, but tail fans exist in forms without such a structure; this
suggests to me that tail fans were not dynamically used in balancing
forces as in gravity versus lift, and maybe also not as in directional
controls, which would impose torsional effects and also result in a
pygostylar or other stiffening structure. Thing is, for directional
control, torsion must exist ... it must permit the distal structure to
rotate with intertia and stabilize: cheetahs and birds orient their tails
when maneuvering or banking towards the direction or pivot; it does not
seem to be a matter of lift production in modern birds, as recent studies
have suggested: smaller birds have smaller tails when you would expect
them, and some birds seem unaffected if their tail streamers are removed,
except when breeding is concerned. They are adaptive to display, or to
affect torsional stabilization. I suggest the same may be true of
dromaeosaurids and other still-tailed and short-tailed theropods, which
likely precludes, as Mike Skrepnik illustrated, a tail fan for *Nominga*
as a result of the pygostyle. But oviraptorosaurs should have it basally,
in concurrence with my theory, and one form apparently does without a
pygostyle: *Caudipteryx*.

  In short, aerodynamics do not seem to be all that important, and
feathers should have an origin alternate to that, though maybe concurrent,
of the shoulder adaptations. The development of very large manus
proportions and deeply trenchant claws with roubst phalanges and torsion
resistant bowed elements appears to be in keeping with a cat-style
grappling adaptation, not flight.

  Who knows....

  Cheers,

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