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Re: Pterosaur morphological evolution

On Jul 7, 2011, at 5:15 AM, Mark Witton wrote:
> On a related note, has anyone ever wondered why
> Raeticodactylus/Caviramus has such a narrow humeral diaphysis? It's
> seriously stick thin. It's still got a large DPC and flight finger,
> though, so I don't know that it necessarily reflects flightless habits.
> Interestingly, its femur is probably more robust than its humerus, a
> feature only otherwise seen in Preondactylus. Looks to me like
> Raeticodactylus/Caviramus is just begging for some a nice biomechanical
> investigation of its limb strength: it would be particularly interesting
> to know if it could quad launch.

I've been wondering that myself, actually - but I have not had a chance to look 
at the Raeticodactylus material in detail.  It's a weird animal.  Perhaps it 
was more bipedal than other taxa.

On Jul 8, 2011, at 2:35 AM, Tim Williams wrote:

> _Raeticodactylus_ also has a femoral head that is perpendicular to the
> shaft, as in dinosaurs (this was noted in the original description:
> Stecher, 2008).  So maybe it was better at bipedal launching?

Good point.  Again, perhaps it was a biped launcher, instead.   It is also 
possible for a quad launching animal to use a more balanced force output from 
the hindlimbs and forelimbs - it doesn't have to be forelimb dominated, but 
quadrupedal launching should tend to favor a forelimb-dominated cycle because 
it improves multimodal efficiency (i.e. robust forelimbs improve both launching 
and flight for a quad locomotor, so the most mechanically efficient mode is 
robust forelimbs and gracile hindlimbs).  Competing demands could lead to 
robust hindlimbs, or perhaps Raeticodactylus was just largely bipedal.  

Interesting stuff all around!

--Mike H.

Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181