blaze
Paleo-artist
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Post by blaze on Jul 8, 2013 20:58:23 GMT 5
Allosaurus was reconstructed just like the other theropods in the other study by Bates so we could expect its similar density. In Hutchinson et al. (2011), CM 9380 ended up with the same density as Sue despite not being nearly as barrel chested, even then, the skeleton of CM9380 is not significantly larger than Stan and despite Stan having a higher density it was not heavier, the difference between them isn't even that great, just 5%, it might even be just an artifact of the way they created the volumetric models.
The thing is that the models of the (unaffected) specimens that Hutchinson et al. shares with Bates et al. had a lower density in Hutchinson et al. You might have a point if Stan ended up with the same density as in Bates et al. but still it might just be a coincidence as there isn't really any evidence apart from this situation (assuming it does constitute evidence).
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Post by theropod on Jul 8, 2013 21:15:07 GMT 5
MOR 693 has a density of 0,95 for the "contracted ribcage model" (which I use) and 0,93 for the "best estimate". Acrocanthosaurus is 0,91. Hartman's Giganotosaurus seems similarly narrow-bodied to this Big al model. For comparison, the Stan in Bates' other study was 0,9, and Sue is probably less dense than Stan (~10% in Hutchinson et al., 2012). So even if you do not directly compare them, it is clear what this points out to.
Yes, Stan ended up less dense in Hutchinson et al. MOR 555 on the other hand ended up denser. In any case there is a pretty big difference, bigger than 10% in the densities of FMNH PR 2081 and carnosaurs. And it is not said because stan had a lower specific gravity Acrocanthosaurus or Allosaurus would have had in the same study, since the narrow-bodied Wankel rex got even denser.
So going the conservative way, let's lower the density of Acrocanthosaurus and Allosaurus as much as that of stan got lower (0,87/0,904); we would arrive at ~0,877 and ~0,91. Perhaps more realistic anyway. Sue at 0,791 and Giganotosaurus at 0,877-0,91. So if the volume is 9,200 litres for sue and 7,450 for MUCPv-ch1, that would make sue 7,277t, the Giganotosaurus holotype 6,5-6,77t and a specimen that is 6,5% bigger 7,8-8,17t.
This just shows how significant the impact could actually be at the exact same volume.
We could of course make the densities higher or lower, but if, we have to do it for both. I'd prefer them that low to be honest.
btw the carnegie skeleton seems to have just as wide a ribcage (proportionally) as sue when going by the shown skeletons, and is accordingly pneumatic.
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blaze
Paleo-artist
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Post by blaze on Jul 8, 2013 21:47:13 GMT 5
I've already highlighted that Hutchinson et al admits that the poor resolution of the scans of MOR 555 are the major reason for the extra high density of it in the study, I admit I made a mistake in the difference of density of Stan and Sue (its 8% not 5 nor 10. 0.87 vs 0.81) but we don't know what will be the real values as none of the mounts are perfect, and the distribution of tissue applied in the study might not be correct.
How do you figure that the contracted ribcage model of Big Al looks like Hartman's Giganotosaurus? they never figure it other than a frontal view of the ribcage alone, which gives the impression that is not wider than the hips, Hartman's Giganotosaurus actually looks wider than the best estimate one, which is the one figured. You're also ignoring something, the expanded ribcage model didn't result in an decrease of density from the best estimate one.
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Post by theropod on Jul 8, 2013 21:56:36 GMT 5
Sue's density in Hutchinson et al., 2012 is 0,791:
I just compared and it seemed narrower than Acrocanthosaurus, actually closer to Allosaurus. Not specifically that model, since it was not figured in top view, but I wanted to give a range in which it might be.
Of course none of the mounts are perfect, and there is a reason I disagree with the mass estimates from the study. But we have no reason to greatly doubt their relative densities, do we?
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blaze
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Post by blaze on Jul 8, 2013 22:59:51 GMT 5
I read it wrong, damn it haha anyway you still have to address the fact that increasing the ribcage in Allosaurus didn't decrease the density, it seems the (IMO too narrow) contracted ribcage increased the density only because it was impossibly narrow and implied lungs and air sacs too small for the animal, otherwise how do you explain that increasing the size of the ribcage by the same amount didn't result in any change of density? I'll try to make a chart to compare the width of the Allosaurus models, in the mean time, the retracted models is only 74% the width of the best estimate. Edit: Figures A1 and A2 exist because I didn't know how to approach the reduction of the width, in A1 I reduced the profile equally to reflect decrease of width of 13% from each side, on A2 I only reduced 13% on each side at the widest point and made everything else equally wide. The part at the hip only includes the femur, lower leg and fingers were excluded, similarly, from the forelims, only the humerus was included, though I accounted for the posture it had in the mount ("open" arms instead of hanging). Like I said, not even the best estimate is as wide as Giganotosaurus, at least if you compare "hip+upper leg" width to torso width, in Allosaurus this values are almost exactly the same in the best estimate model while in Giganotosaurus the torso is clearly wider than the hip+upper-leg region. Also, there might be an optical illusion making this outlines appear robust compared to those of Hartman, the base of the tail and the posterior part of the torso might be too skinny and the narrow skull of Big Al only adds to the illusion.
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Post by theropod on Jul 9, 2013 0:15:42 GMT 5
That's indeed strange. The expanded ribcage doesn't add airspace relative to total volume, while the contracted ribcage removes airspace. well then, let's use the 0.933 of the best estimate and it will still end up at around 0,9 when lowering it for the same percentage as the stan model between the Bates 2009 and Hutchinson 2012 studies. My point was not to conclude some precise figure, but thanks for pointing out that oddity anyway.
My point was merely that it appears the wider ribcage at least in part is due to pneumaticity, and taking both at the same density might produce overestimates for T. rex.
btw in lateral view it seems the-7,5% model is about right, it looks like the gastralia would fit comfortably if adjusting the rib posture, tough it really looks a tad narrow in dorsal view. I will go with the 1,4t for the contracted ribcage, since that's in between the two.
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Post by theropod on Jul 9, 2013 0:40:19 GMT 5
You've got a point on the model. Could it be Allosaurus simply has the bulkier tighs compared to its TL?
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blaze
Paleo-artist
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Post by blaze on Jul 9, 2013 0:40:40 GMT 5
Though the initial method of gathering data is the same (laser scanned) I don't think we can use values interchangeable between the two studies like that.
The expanded ribcage increases the volume of the thoracic cavity by 20% (about 100L, or 7% of total volume) which also increases the size of the airs sacs accordingly, though not enough to offset the added mass (increase of 64kg which sounds like much but is only 4% more).
About the things... I don't know.
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Post by theropod on Jul 9, 2013 1:21:27 GMT 5
^That's what I meant, it increases the total volume more than the pneumaticity, so the total mass gets greater. Imo trying to find a solution based on the pneumaticity in the studies is probably better than assuming both at the same density. When ignoring MOR 555, and using Stan to normalise them, you can at least get some sort of objective comparison how dense they would be with similar methodology. the real densities could deviate in either direction. All credit goes to the respective authorsThe differences between all of them when scaled to the same lenght appear smaller than I would have tought (tough Hartman's Giganotosaurus is really very slim considering it likely has more spine curvature than the other models). And it does seem the Allosaurus models have pretty big tighs rather than particularly slender torsos.
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blaze
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Post by blaze on Jul 9, 2013 1:59:00 GMT 5
That comparison includes the lower legs and feet of both Allosaurus and Acrocanthosaurus, the later does seem to have pretty big thighs but I'm not sure how accurate they are it seems like the legs are on the anterior half of the reconstructed thigs and the posterior half is as big or bigger despite being empty. The Allosaurus mount also seems to have a tail that's too long (about 57% of body length) though I don't know how that affects the comparison.
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Post by theropod on Jul 9, 2013 14:31:48 GMT 5
If the tail is too long that should make the body smaller in the comparison. The shape of the legs seems to be just that of the tighs, and the lower legs should not be visible, or only marginally. But the thighs protrude much more in the models than in Hartman's top view, so it is not the body that is wider.
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blaze
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Post by blaze on Jul 10, 2013 2:50:37 GMT 5
Then I wonder how much did Hartman remove from the legs, he said that the dorsal views are not just an skeletal painted black.
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Post by theropod on Jul 10, 2013 14:32:24 GMT 5
He obviously made the less protruding, but the mediolateral size of the gluetal and iliotibial complexes also seems exagerated in the scans if you ask me.
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blaze
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Post by blaze on Jul 10, 2013 21:59:31 GMT 5
That could explain it.
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Post by theropod on Jul 11, 2013 0:36:52 GMT 5
The whole dorsal view would looks smoother in life, the tight should would be less mediolaterally expanded but perhaps longer anterocaudally, and the pronounced steps at the anterior and posterior end of the torso should be filled with fascia and musculature.
Those models are approximations, so we cannot expect a perfect life-reconstruction of the animal from them.
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