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Re: Nothronychus query



Stephan Pickering (StephanPickering@cs.com) wrote:

<Nothronychus, as presented by the Discovery Channel, is depicted as 
ambulating in almost a waddle-like style...and, without hesitation, I
wondered if, when necessary, this taxon could swim.>

  Most likely, most dinosaurs could swim. Today, the most ungainly and
massive of animals can swim, and some quite gracefully (elephants).

<In water, air-sacs would demonstrate variable pressures as would the
rostral>

  Just a terminology note, this would be cranial as a direction along the
axial column, not rostral. The latter term is reserved for the skull and
mandible alone and refers to the direction of the tip of the snout.

<and caudal sacs as the arms moved. On land, the animal's abdominal
musculature might have aided in keeping it relatively upright, contracting
with each step and causing changes in air-sac pressures. In fast-running
dromaeosaurs, one would expect the abdominal musculature to be expirators,
contracting with each breath and not with each step (hence, the
dromaeosaur's air-sac pressures would vary with each step, but for
different reasons).>

  Possible. Only recently have air-sac anatomy been explored in small
maniraptoran theropods (excluding birds). Dromaeosaurids like
*Deinonychus* have been the focus of recent research on costal anatomy and
thoracic airsacs, and Paul (1988) reconstructed possible thoracic and
pelvic airsacs in *Deinonychus* that are corrollary to those between
crocodiles and birds. It is a good start. Carrier and Farmer's work
coupled with the locomotor studies of Gatesy and Hutchinson (both together
and separately) also permit other parts of the anatomy to affect the
pelvic and caudal (thoracic) airsacs, indicating a large suite of complex
muscular and osteological elements and qualities that come into play.

  Therefore, it would be interesting to begin a hypothetical
reconstruction, and provide how the known anatomy of the animal would
affect the airsacs, and how the airsacs would affect the animal. Good
stuff...

<Among extant avian taxa, the abdominal musculature system displays
differences among a wide array of taxa, often "silent" during breathing
when the animal is not moving, activated with running or sudden take-offs.
Thus, my query: has anyone performed a computer-generated, biomechanical
investigation of how Nothronychus walked?>

  No complete enough hindlimb-pelvic skeleton is known for a segnosaur.
The only complete hindlimbs are known in *Beipiaosaurus* and marginally so
in *Segnosaurus*, the latter which lacks pedal phalanges and the former a
complete pelvis. This reduces the ability to compare, as the two animals
have quite different hindlimbs ... one short and robust, longer femur than
the tibia, the other slender, longer tibia than femur, and gracile
metatarsals and pedal phalanges. Certainly in interests many people, and
several variables would need to be taken into account.

  For one thing, trunk carriage in segnosaurs was not horizontal. The
cranial sacrum faced somewhat dorsally, and the dorsal vertebrae show
features that compensate for suprahorizontal carriage, including
compression of the centra. This makes segnosaurs very much in interesting
study in locomotion. The pelvis, similarly bizarre, was opisthopubic, and
the ilia flared laterally as in many large ungulates today. This is
presumably to compensate for an enlarged gut. The centar of gravity
fortunately favors the segnosaurs, in that it would seem to be located in
and around the hip joint, or just cranial to it. Trunk musculature and the
muscles of the hip that participate in the trunk and caudal anatomy would
be affected, and incomplete material does not permit this to be analyzed,
yet. (However, *Neimongosaurus* has a relatively complete tail, as does
*Alxasaurus*, though the latter is distorted, the former is not, it is
also not distinctly described for this purpose and would need to be ran
over with a fine-toothed comb to study for this analysis.)

  As discussed during the Hutchinson and Garcia paper's announcement, a
longer femur than tibia provides a different set of variables on leg
extensor effect, and the short though robust tibia is quite wide,
providing extensive gastrocnemius musculature and a powerful knee flexor.
The ankle does not project cranial from the tibia, which is neccessary to
provide a large moment arm for thrusting against the ground. The
metatarsus is short and provides that relative metatarsal-tibial action is
minimal, and the pedal digits, though long, are very short but are not
very thickened or wider than deep, and the claws indicate a lack of
extreme effect to the substrate. These features all indicate that
segnosaurs were not very quick, were in fact quite minimal in movement,
though I could not yet try to calculate a speed. I could say that they
were most likely not able to outrun a similarly sized or even larger
theropod of their day. *T. bataar* in the day of *Therizinosaurus*,
*Erlikosaurus*, and *Segnosaurus* would easily have outjogged any of its
contemporary segnosaurs, and I think *Beipiaosaurus* was quicker than it's
more derived relatives.

  All this does is beg for quantification...

=====
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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