RE:Ceratopsian mass estimates

[Andy Farke <andyfarke@hotmail.com>]

> From: GSP1954@aol.com
> In other words using limb dimensions to
> estimate mass only gives very general ball park estimates and must never 
> ever be
> used to restore mass for purposes that require more accurate estimates

Exactly!

> The premise of the 85 paper is that mass correlates consistently with limb
> strength, but this is silly because animals vary enormously in structural
> strength.

> So chimps can rip apart humans of egual mass because they have far more
> strongly constructed skeletons operated by a much more massive musculature.

Chimp skeletons have always struck me as rather gracile, personally. . 
.gorilla skeletons are pretty beefy, but then the largest of them have a few 
hundred pounds on humans!

> observed by myself and Per Christiansen, ceratopsid limbs, vertebra and 
> even
> the ribcage are way overbuilt for animals of their mass.

The question then becomes, what is the "standard" against which this is 
measured? I will totally agree that the big USNM specimen looks overbuilt. 
But most of the "small" ceratopsids--like the NMC Chasmosaurus, for 
instance--look downright gracile. But I have not spent a lot of time 
comparing these postcrania, either. . .

Something which bugs the heck out of me is the absence of information on 
internal architecture in dinosaur bones (although I seem to recall that Eric 
Snively and others addressed this in some of their papers--please correct me 
if I'm wrong). Yes, ceratopsid bones are mostly solid, but they still have a 
less-dense area in the middle. And most theropod bones certainly aren't 
solid all the way through. I think it would be *extremely* illuminating for 
someone to rigorously work up the cross-sectional properties of dinosaur 
bones (along with other large critters). I suspect that they're probably 
playing by the same rules as large mammals, but who knows until someone 
takes a look at it. . .that is, perhaps a ceratopsid just *looks* more 
robust than a comparably sized elephant, but these distinctions disappear 
when one starts evaluating the distribution of bone mass across the 
cross-section. Perhaps this explains some of the discrepancies in 
Alexander's equation, too.

Jaime Headden wrote:

> unquantified "how much mass can a muscle scar carry" debate. No one has 
> noted
> the degree of rugosity or height of relief (or even what "degree of 
> rugosity"
> is) much less determined how much muscle IS there based on comparative 
> anatomy,
> except for  Greg and Hutchinson ... yet both come to different conclusions.

Based on my limited experience (and hear-say around the department), a 
muscle scar carries however much muscle tissue it darned well pleases. 
Muscle scars can show the presence of a muscle, but they are pretty bad 
about showing actual muscle size.

>   I would like to see Greg's method and models illustrated in more detail,
> since it seems to be a critical part of his work. A paper in biomechanics 
> using
> the mass-estimating models and how he came to his published figures would 
> be a
> decent work and wholly in line with his calculation work he's been doing
> lately. Plus, I've always been curious. Compared to, say, 3D-spline 
> modelling,
> such methods may offer a digital versus physical model for mass 
> reconstruction.

Absolutely--I think that physical or computer models offer an important 
alternative to the limb bone measurement method. I guess the main thing I 
would like to see is more validation studies for both. There are plenty of 
relatively decent plastic models of elephants floating around out there--I'd 
be interested to know what ranges of masses one arrives at when dunking 
these in water. I'll second Jaime's request for a full paper on the mass 
estimates--it'd be a useful contribution to the literature!

At any rate, this has been a most illuminating thread. As I said at the 
beginning, I put only the smallest bit of faith in the mass estimates I 
originally posted. I mainly just wanted to stir the pot a little and see 
what people thought! After all, this Alexander method is pretty commonly 
cited. . .

Perhaps I'll try dunking my Anchiceratops model (a Cliff Green original!) in 
water and see what I get for a mass. . .

Andy

_______________________________________________
Andrew A. Farke
Graduate Student
Department of Anatomical Sciences
Stony Brook University
Stony Brook, NY