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Re: was: Pterosaur.net now: pteroid



On Jan 16, 2010, at 8:21 AM, Augusto Haro wrote:

> 2010/1/15 David Peters <davidpeters@att.net>:
>> That facet Chris and Jim are looking at on the preaxial carpal is not the 
>> facet for the articulation of the pteroid.
> 
> David, I for sure have seen much less pterosaur specimens than you,
> but, judging from what is published, it seems to me that an articular
> facet is better marked on the medial side of the preaxial carpal of
> one old specimen of Pteranodon, as shown by Bennett (2007), than on
> the anteroventral surface of the proximal syncarpal of Anhanguera, in
> the same paper. I was unable to see a differentiated articular surface
> in other published sources.

Yes, Augusto, the medial side of the preaxial carpal has a facet. The question 
is, can the pteroid be articulated there. The answer is yes, but the pteroid 
can also be articulated in the cup of the preaxial carpal, as many have shown. 
The answer to where the pteroid was articulated, no matter how poorly, comes 
from the observations of undisturbed pterosaur fossils. Tell me if ANY of these 
have the pteroids closer to the preaxial carpal or closer to the radiale. Then, 
finally, please reconstruct the carpus of Nyctosaurus to see if your 
reconstruction differs from mine in JVP (29(4)). This is a repeatable, 
verifiable experiment. 

Some pterosaurs may not have a distinct articulating surface on the anterior 
side of the radiale because no bone originally articulated there in basal 
tetrapods. The pteroid and preaxial carpal migrated there from positions in the 
central carpus. There are no analogs among living tetrapods that I am aware of. 
That is why these bones are easily disarticulated. 
> 
>> Absolutely NO specimens preserve the carpus articulated in this fashion. 
>> None. Zero.
> 
> I think that the pteroid is also preserved contacting the radius in
> Eudimorphodon, as you show in your paper, and contacting no bone in
> many pterosaurs, so I doubt in situ associations. In the Anhanguera
> specimen shown by Bennett (2007) you do not have the pteroid
> articulated to the preaxial carpal.

The examples you cite are due to post-mortem disturbances. It happens more 
often than not. With regard to the Anhanguera specimen, you are correct. The 
specimen preserved the pteroid closer to the radiale. However, it is Bennett 
who advocates the preaxial carpal articulation, not me.
> 
>> Send jpegs of exceptions if you can possibly find them. They don't exist. If 
>> they did, Chris would have included them in his  2007 paper.
> 
> I would have to re-check, but I found an example of pteroid contacting
> the lateral carpal at its articular end, in Wellnhofer 1975, Tafel 20,
> fig. 3, a Rhamphorhynchus specimen in the American Museum.
> 
> Wellnhofer, P. 1975. Die Rhamphorhynchoidea (Pterosauria) der
> Oberjura-Plattenkalke Süddeutschlands. Palaeontographica, Abt. A, 148:
> 1-33; 148: 132-186; 149: 1-30.

So what does this mean, if not post-mortem disturbance? 
> 
>> And try to imagine the big angle iron pteroid of Nyctosaurus articulated as 
>> Bennett suggests. So, it's back to the drawing board.
> 
> Bennett (2007) wrote there was a rostroventrally directed facet for
> the pteroid in the preaxial carpal of Nyctosaurus, if I remember
> correctly, which will still have the pteroid pointing medially.

Please reconstruct these pieces to see if what you are saying is correct. It 
may be that that was a facet that, via soft tissue, connected to the anterior 
bend in the Nyctosaurus pteroid, not the short process ball joint. 
> 
>> Given that it's not a bone/bone articulation, what is that little spot on 
>> the inboard preaxial carpal all about? Consider the possibility of a short 
>> ligament between the preaxial carpal and the pteroid, attaching at the 
>> pteroid bend and beyond.
> 
> Humm... but as far as I remember, it is a smooth facet, right? should
> not a ligamentary surface be more rugose?

Look at other tetrapod (centralia) carpals. Are they rugose or smooth? 

Bottom line: Follow what undisturbed fossils tell you. 

Please send jpeg examples that differ from my hypothesis and support the 
Bennett hypothesis. If I'm wrong, the evidence will show it.

David Peters