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Re: Longisquama



Ronald Orenstein wrote:

> At 07:13 AM 11/03/03 -0600, David Peters wrote:
> >As in Sharovipteryx, there is no way that Longisquama was a
quadruped.
> >The hind limb is twice the length of the forelimb, which due to toro
> >length and elevation, barely reached the level of the knee when
bipedal.
> >The torso is also long with a center of balance just anterior to the
> >ilium, far from the humeral glenoid. So, with two pterosaur sister
taxa
> >now obligate bipeds
>
> Why?  You could say the same sort of thing (roughly") about
Stegosaurus -
> or, for that matter, frogs.  Why couldn't unequal limb length be
associated
> with climbing, as it is in tree frogs, instead of bipedality?
>

Good point. But I think you'll have to see the reconstruction. In
appearance
it approaches the condition in Sharovipteryx and the short-armed
theropods.
Due to the ilial bend, if Longisquama is tipped forward to the
quadrupedal
condition, the tail is either forced straight up, like a cat's, or tips
forward over the dorsal series
-- very unorthodox. The bipedal stance is just the most conservative I
could
visualize.

Plus, the enormous elongation of the anterior ilium is an indicator of
bipedalism in diapsids. Stegosaurus, as Ron will recall, had bipedal
ancestors. Frogs are another matter.

In Longisquama, the tail is attenuated. No deep hemals nor wide
transverse processes are present, matching pterosaurs. Thus the
caudofemoral muscle mass is reduced so the tail muscles are _not_
pulling the hind limbs backwards, .>> thus undulation, as in primitive
quadrupedal diapsids is probably _not _ taking place, as in pterosaurs,
despite the long torso.

The pedes are probably placed medially, as in pterosaurs, because the
outer pedal digits, although longer than the medial ones, are much
shorter than in sister taxa predecessors, such as Macrocnemus.

David Peters
St. Louis



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> Ronald I. Orenstein                           Phone: (905) 820-7886
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