Re: Massive answer to the mess of pterosaur mass

[jrc <jrccea@bellsouth.net>]

As usual, comments inserted.
JimC

----- Original Message ----- 
From: "MICHAEL HABIB" <habib@jhmi.edu>
To: <Mark.Witton@port.ac.uk>
Cc: <jrccea@bellsouth.net>; <dinosaur@usc.edu>
Sent: Thursday, January 17, 2008 6:17 PM
Subject: Re: Massive answer to the mess of pterosaur mass


> Hey everyone,
>
> By the same token, my mass estimate and Jim's are also not actually so far 
> off as they might seem, given how much estimate error there can be.

Agreed.

> I do think that Jim's estimate is a bit on the low side; he and I have 
> actually discussed this a bit already, and our disagreement in this regard 
> is minor in the big scheme of things.

Also agreed.

> The caveat there is that body weight in long-distance
> travelers like albatrosses varies a great deal just within individuals. 
> Thus, while I get about 200 kg using the average, the estimate can swing a 
> great deal using a heavily fueled versus skinny set of animals.

Yes.  For example, the huge Whooper swan 'Stonker' was known to drop at 
times from about 29 pounds down to about 13 or 14 pounds during the flight 
from Scotland to Iceland and vice versa.

> I do think that the torso may be a bit larger than Jim gives credit for, 
> though perhaps I'm just reading into his analogy of a large football 
> player too much.

Might be.   I used that as a visual analogy, without intending that too much 
be read into it.  Expect the distance from notarium socket to acetabulum to 
be on the approximate order of 125%  of the articular length of the humerus.

> While the torso was quite short, my estimates suggest that it should be 
> quite deep, as well,

Depth scaling is defined by the relationship between the glenoid, dp crest, 
and the coracoid flange.  The Qsp coracoid flange is preserved.  Look at it 
and the relationship between the Qn and Qsp dp crests and the Qsp 
scapulocoracoid to help scale the depth of the chest after adding in 
notarium, sternum, etc.  The chest is deep, but it should still look like a 
pterosaurian chest, not all that substantially distorted from Qsp, except 
more robust by about the same amount that the Qn humerus is more robust than 
the Qsp humerus.

> and the overall dimensions of the pectoral girdle would be impressive, to 
> say the least.

Yes.

>  The humerus is truly massive; anyone who has seen it on exhibit (or up 
> close) knows what I mean.  That one element would almost fill my thorax 
> and abdomen (though I grant I'm a small person).  The scapulocoracoid 
> would need to be quite deep, and the flanges quite expanded.  The precise 
> allometry is difficult to calculate, but my rough estimate is that the 
> football player would have to be a very good sized linebacker at least :) 
> Add in the huge limbs and giant neck and head, and you have a pretty darn 
> big critter.

Agreed.  And though the torso is relatively large compared to other 
non-azhdarchoid pterosaurs (the azhdarchid torso is roughly about 30% larger 
than a similarly spanned anhanguerid), it still gives the impression of 
being small relative to the size of the long bones.  It's the durned 
azhdarchid head and neck that overwhelm me.

> I've also started toying with some bone cross-section techniques for 
> estimating mass, but this is harder than it sounds because we have little 
> a priori reason to assume a specific safety factor for pterosaurs.  It was 
> probably near that of birds, but we cannot say for certain. 
> Interestingly, my first swing at that gave me a (admittedly rough) mass of 
> about 220 kg.  The interesting thing there is that the technique would be 
> expected to give the maximum (ie. heavy fuel load) weight.  As such, I 
> wonder if perhaps Mark's method does the same, and that our estimates are 
> more congruent than they seem (with 250 or thereabouts being the maximum 
> fueled mass for a large animal).

I do agree that the animal could carry 250Kg, just point out that it would 
not be an optimal loading -- but then, maximum fueled mass never is.

> Regardless, the real punchline, I think, is that these large pterosaurs 
> were not the "ultralights" that is often expected.

You, Mark, Greg Paul, John Conway, and I are in very strong agreement there. 
I've been preaching that since 1999.  These rascals looked like Arnold 
Schwartzenegger on steroids (not that he would ever have taken steroids).

>  Clearly, they were reasonably heavy animals with plenty of power 
> generation.  This holds whether Qn was a 150 kg animal or a 250 kg one.

Yes.
JimC