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Re: Fwd: the largest Pterosaur


----- Original Message ----- From: "Mark Witton" <Mark.Witton@port.ac.uk>
To: <dinosaur@usc.edu>
Sent: Tuesday, April 24, 2007 3:48 AM
Subject: Re: Fwd: the largest Pterosaur


Hi Mike,

To be honest, the remains of these giants are so scrappy that I feel
we're clutching at straws trying to guess their size and mass. I mean,
the Hatzegopteryx (finally spelt correctly - third time lucky) skull
appears to be relatively robust compared to that of Quetzalcoatlus,

Not really. No part of the northropi skull is preserved, so it's hard to make comparisons. The gracile skull you see on the full scale skeletal 'replicas' of northropi can be blamed on me. It's just an isometric blowup of Wann's reconstruction of the skull of Quetzalcoatlus species, scaled up in length by a factor of 2.05 (which is nothing more than the average of the relative lengths of the northropi r/u plus the humerus, divided by the average of the relative lengths of the Q species r/u plus the humerus -- (2.14+1.96)/(1+1) = 2.05). Had we had more time before the scheduled opening ceremony of the TMM, the enlarged skull would have been made more robust, about 15% taller and wider by an approximately similar amount. Coincidentally, that would have resulted in a northropi skull 'replica' very similar in size and robustness to the preserved Hatzegopteryx skull bits.

but who knows if this reflects gross dimensions elsewhere? 

In this case, it doesn't represent anything but an artistic deadline......

To me, the humerus of Hatzegopteryx and Quetzalcoatlus look a bit different: 

To me as well.

Hatzegopteryx has a relatively slender deltopectoral crest compared to
Quetzalcoatlus, but, conversely, appears to have a thicker diaphysis
(like yourself, these observations are based on photographs).

Agreed. I'm basing my own visual comparison on a northropi humerus cast that I have here at the house, but upon photos and some measurements of the Hatz humerus.

Of course, this situation is not aided in that the Hatzegopteryx is pretty beaten
up: I really think we need more material before any definitive
conclusions can be drawn.

Yes. What we can presently say is that there are several species of very large, similarly sized pterosaurs distributed about the world, so pterosaurs of this general size were perhaps not all that rare.

Still, if Hatzegopteryx did have a greater wingspan, I reckon it
would've weighed more. Increased body size generally corresponds with
increased mass (though not in a linear relationship, of course) and,
with all the additional flight musculature needed to flap those
expansive wings, I think an azhdarchid with a 14 m wingspan would weigh
a lot more than an 11 m specimen.

Assuming similar builds, probably on the loose order of 95% more (with mass increasing by roughly about the 2.7 to 2.8 power of the wingspan). Keep in mind though, that it is the hyperdevelopment of the azhdarchid delto-pectoral crest and coracoid flange that appears to have allowed them to carry the additional mass and wing loading, so I'd expect span and mass of the large azhdarchids to be very closely correlated with the size of the delto-pectoral crest and those weren't all that similar in Hatz and northropi. As a aside, the Q species scapulocoracoid is so closely related in size and shape to the proximal humerus and dp crest, that it implies that a very good approximation of the northropi scapulocoracoid could be recreated based upon the shape of the proximal humerus and dp crest. The one in the northropi skeletal 'replicas' is not shaped at all like the real thing would have been (that durned deadline again). This correlation implies that the Hatz scapulocoracoid could be reconstructed based on the Hatz humerus -- subject to error built into the Hatz humerus degradation of course. In any event, it leads toward a reduced estimate of Hatz mass and wingspan.

I think we sometimes forget with all
these measurements that something like a 3 m difference (to use the
example here) is actually quite a big distinction: the walls in the room
I'm sitting in now are about 3 m tall, which is a significant dimension.
It's all relative, of course: 3 m might mean a lot to comparisons
between 10 -14 m pterosaurs, but comparatively little to gigantic, 30 m
+ sauropods. All the same, even accounting for increased pneumatisation
and all that, I think it's hard to avoid a extra mass if your azhdarchid
has a wingspan one-storey broader than another (if that makes any
sense).

It makes sense. As I've mentioned before, the northropi humerus can be morphed to support the mass associated with a wingspan of up to about 13 meters. If anyone says they've found anything larger than that, I'd want a chance to inspect the materials and do some structural calculations before buying into the larger estimate. I'm not saying that spans larger than 13 meters are impossible, or even improbable -- but, they sure do raise some red flags when compared to the known giant pterosaurs.

That's about all I want to say about Quetz for now. I think any detailed discussions should be deferred until after Wann publishes a description of Quetz.
JimC