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RE:Ceratopsian mass estimates



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