[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: was: Pterosaur.net now: pteroid



Mark,

No one is questioning the bending strength of the pteroid. You can make it out 
of titanium. That's fine.

Bennett (2007) was falsified by his own data as shown Peters (2009 . The 
pteroid did not articulate on the preaxial carpal but on the radiale (proximal 
syncarpal) as supported by Prondvai and Hone (2009), Frey et al. (2006).

So there goes your weight of evidence.

I have no qualms with muscles being attached to carpal elements like the 
pteroid. Especially since it is a former centralia, as is the preaxial carpal. 
They would have taken with them any attached tendons and ligaments during their 
migration to the leading edge.

So you advocate the depression of the pteroid even though it creates an 
anterior V in the leading edge of the wing? 

Even though the leading edge of the propatagium is maintained by tension? 

Remember the rest of the wing is creating drag that is trying to overextend the 
elbow. That is a constant force while flying. The propatagium is the only thing 
that prevents that from happening, as in birds and bats. It's a passive organ.

Mark, think of this in mechanical terms. 

1. That fragile tip of the pteroid ain't gonna hold up if you put lateral 
stresses on it. It can only survive longitudinal stresses. 
2. It's extremely difficult to put a kink in the middle of an object being 
pulled from both ends. It keeps rebounding to a straight line. That kink would 
be right at the tip of the pteroid. 
3. There's no muscle strong enough to pull the pteroid ventrally with such a 
short lever arm originating at the articulation no matter what bone you'd like 
to articulate it on.

We'll get there. 

David







On Jan 15, 2010, at 8:36 AM, Mark Witton wrote:

> Palmer and Dyke (2009) had no qualms with the pteroid being depressed to 
> change the camber of the wing, and they were specifically testing the bending 
> strength of the pteroid. Bennett (2007), by the way, suggests that the 
> pteroid muscle was anchored on the preaxial carpal and cites evidence for 
> such a muscle on both Pteranodon and Nyctosaurus. It seems to me, therefore, 
> that the weight of evidence indicates that the pteroid was both capable of 
> depressing the propatagium and biomechanically sound enough to do so. 
> 
> Mark
> 
> --
> 
> Dr. Mark Witton
> 
> Palaeobiology Research Group
> School of Earth and Environmental Sciences
> University of Portsmouth
> Burnaby Building
> Burnaby Road
> Portsmouth
> PO1 3QL
> 
> Tel: (44)2392 842418
> E-mail: Mark.Witton@port.ac.uk
> 
>>>> David Peters <davidpeters@att.net> 15/01/2010 14:04 >>>
> Okay, given the grooves, and given the muscles attached to the grooves, which 
> bone did the other end of the muscles attach to and does that attachment 
> provide a ventral vector when pulled? Most reconstructions place the pteroid 
> anterior to the radius while in flight.
> So... if the pteroid is [somehow] pulled ventrally, how does that affect the 
> sometimes sharp tip that WAS pointing at the deltopectoral crest? Does that 
> produce a V-shape (in anterior view) in the propatagium? And if so, doesn't 
> that put a lot of stress on that fragile point? 
> 
> I see the anterior propatagium as a straight line providing an inboard 
> leading edge to the wing. It changes shape only when relaxed, when the elbow 
> is flexed during wing folding, as in birds and bats. Those grooves, in my 
> opinion, anchored the pteroid to the rest of the wrist because there was 
> precious little else to anchor it at its articular surface.
> 
> David Peters
> 
> 
> 
> On Jan 15, 2010, at 7:46 AM, Mark Witton wrote:
> 
>> Dave,
>> 
>> There are grooves and rugose protuberances on the proximal ventral surfaces 
>> of pteroids (see Unwin et al. 1996) : these, presumably, anchored 
>> musculature that, because of its insertion on the ventral pteroid face, 
>> would have to depress the pteroid if contracted. 
>> 
>> Mark
>> 
>> --
>> 
>> Dr. Mark Witton
>> 
>> Palaeobiology Research Group
>> School of Earth and Environmental Sciences
>> University of Portsmouth
>> Burnaby Building
>> Burnaby Road
>> Portsmouth
>> PO1 3QL
>> 
>> Tel: (44)2392 842418
>> E-mail: Mark.Witton@port.ac.uk 
>> 
>>>>> David Peters <davidpeters@att.net> 15/01/2010 13:27 >>>
>> Mike,
>> 
>> What tells you the pteroid can be depressed? Which muscle depresses the 
>> pteroid? What bone anchors that muscle? There's nothing out at the tip to 
>> pull it up and down. If you're attempting to manipulate the pteroid near its 
>> articulation, then you've got a very short lever to work with. And finally, 
>> are you articulating the pteroid principally on the radiale? 
>> 
>> At present, your answer doesn't appear to have any evidence to back it up.
>> 
>> David
>> 
>> 
>> 
>> On Jan 14, 2010, at 1:28 PM, Mike Habib wrote:
>> 
>>> On Jan 14, 2010, at 11:42 AM, David Peters wrote:
>>> 
>>>> "The additional membranes (especially the front one) controlled by a 
>>>> special bone called the pteroid would have helped with steering." The 
>>>> pteroid was inboard and would not have been such a great steering aid.
>>> 
>>> Because depression of the pteroid (and hence the propatagium) changes entry 
>>> angle of the inboard wing, the pteroid would be a very good "steering aid" 
>>> - flying taxa turn by altering the fluid force production between the two 
>>> wings, such that they differ, which forces a roll and therefore a turn.  A 
>>> little change in entry angle goes a long way, so the propatagial position 
>>> is, in fact, a factor in maneuverability.
>>> 
>>> Cheers,
>>> 
>>> --Mike
>>> 
>>> 
>>> Michael Habib
>>> Assistant Professor of Biology
>>> Chatham University
>>> Woodland Road, Pittsburgh PA  15232
>>> Buhl Hall, Room 226A
>>> mhabib@chatham.edu 
>>> (443) 280-0181
>> 
>> 
> 
>