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Post by Deleted on Dec 1, 2013 18:52:28 GMT 5
 If Brachiosaurus altithorax was only known from an ilium and the Sauropodomorpha were only known from very fragmentary remains, a comparison of ilia would have led you to believe that Brachiosaurus was only slightly larger than Tyrannosaurus, yet the size discrepancy between them is immense, with Brachiosaurus surpassing Tyrannosaurus in terms of body mass by a factor of 7-8 if not more. And the pelvis holds body weight too, doesn't it? But wait? The vertebral centra of Brachiosaurus are only somewhat over thrice the size of those of the Tyrannosaurus! Vertebra holds weight right? Then if, again, Sauropodomorpha were known from barely any material and Brachiosaurus was just as fragmentary as Spinosaurus, then a comparison of individual vertebra would make us think that Brachiosaurus was only around ~250-350% the mass of Tyrannosaurus, wouldn't it? I can now say that comparisons of individual bones from sample animals which are not close relatives can lead to misleading results. Compare individual bone sizes of different taxa as much as you wish, just don't state it to be an actual method of judging the comparative masses, and/or state it to be the only method. |
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Post by coherentsheaf on Dec 1, 2013 18:55:24 GMT 5
If Brachiosaurus altithorax was only known from an ilium and the Sauropodomorpha were only known from very fragmentary remains, a comparison of ilia would have led you to believe that Brachiosaurus was only slightly larger than Tyrannosaurus, yet the size discrepancy between them is immense, with Brachiosaurus surpassing Tyrannosaurus in terms of body mass by a factor of 7-8 if not more. And the pelvis holds body weight too, doesn't it? But wait? The vertebral centra of Brachiosaurus are only somewhat over thrice the size of those of the Tyrannosaurus! Vertebra holds weight right? Then if, again, Sauropodomorpha were known from barely any material and Brachiosaurus was just as fragmentary as Spinosaurus, then a comparison of individual vertebra would make us think that Brachiosaurus was only around ~250-350% the mass of Tyrannosaurus, wouldn't it? I can now say that comparisons of individual bones from sample animals which are not close relatives can lead to misleading results. Compare individual bone sizes of different taxa as much as you wish, just don't state it to be an actual method of judging the comparative masses, and/or state it to be the only method. To be fair if vertebrae are all we have to compare it is fair game. I think the MoA is among the largest if not the largest pliosaur based on vertebral size. |
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Post by creature386 on Dec 1, 2013 18:55:47 GMT 5
But he claims that those estimates are in line with those from other methods! Maybe Cau is referring to the femur methods, which yielded 2,4 t (he thinks that estimates based on measurements are more reliable than GDI methods). That of course doesn't mean Cau believes that Acrocanthosaurus weighed 2,4 t, because he said he only uses measurement based estimates for comparison. Vobby has shown the relevant quotes on CF, you can find them in the comments here: theropoda.blogspot.it/2013/11/aggiornamento-al-post-precedente.html#comment-formThat's right, there are many methods, and it is a mistake to compare the results of different methods. For example, methods based on direct measurements and regression curves (such as those from the vertebrae or of the femur) is a category of methods, while those based on reconstructions volumentriche and densimetric are other methods. The two methods follow different procedures, and one can not directly compare a method with another. That the volumetric methods have considerable margins of error even larger than those based on measurements, and only recently have been refined methods to reduce that uncertainty. That doesn't mean I agree, I just wanted to clarify what he means. |
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Post by Deleted on Dec 1, 2013 19:01:00 GMT 5
If Brachiosaurus altithorax was only known from an ilium and the Sauropodomorpha were only known from very fragmentary remains, a comparison of ilia would have led you to believe that Brachiosaurus was only slightly larger than Tyrannosaurus, yet the size discrepancy between them is immense, with Brachiosaurus surpassing Tyrannosaurus in terms of body mass by a factor of 7-8 if not more. And the pelvis holds body weight too, doesn't it? But wait? The vertebral centra of Brachiosaurus are only somewhat over thrice the size of those of the Tyrannosaurus! Vertebra holds weight right? Then if, again, Sauropodomorpha were known from barely any material and Brachiosaurus was just as fragmentary as Spinosaurus, then a comparison of individual vertebra would make us think that Brachiosaurus was only around ~250-350% the mass of Tyrannosaurus, wouldn't it? I can now say that comparisons of individual bones from sample animals which are not close relatives can lead to misleading results. Compare individual bone sizes of different taxa as much as you wish, just don't state it to be an actual method of judging the comparative masses, and/or state it to be the only method. To be fair if vertebrae are all we have to compare it is fair game. I think the MoA is among the largest if not the largest pliosaur based on vertebral size. If the animals are sufficiently closely related then yes. You can compare the vertebra of the Monster of Aramberri to those of other pliosaurs to get an idea of size, since they have similar proportions and are quite closely related to each other. What Cau is trying to do in his posts would be akin to comparing the MoA vertebrae with those of Mauisaurus with the purpose of getting the comparative masses. |
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Post by theropod on Dec 1, 2013 19:21:53 GMT 5
I really can't understand how he can seriously believe Comparisons of single bones among very distantly related taxa with totally different anatomy and ecology had smaller margins of error than a proper volumetric modeling approach...
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Post by coherentsheaf on Dec 1, 2013 19:52:28 GMT 5
To be fair if vertebrae are all we have to compare it is fair game. I think the MoA is among the largest if not the largest pliosaur based on vertebral size. If the animals are sufficiently closely related then yes. You can compare the vertebra of the Monster of Aramberri to those of other pliosaurs to get an idea of size, since they have similar proportions and are quite closely related to each other. What Cau is trying to do in his posts would be akin to comparing the MoA vertebrae with those of Mauisaurus with the purpose of getting the comparative masses. Pliosaurs are not that tightly related as well. |
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Post by Deleted on Dec 1, 2013 20:06:01 GMT 5
If the animals are sufficiently closely related then yes. You can compare the vertebra of the Monster of Aramberri to those of other pliosaurs to get an idea of size, since they have similar proportions and are quite closely related to each other. What Cau is trying to do in his posts would be akin to comparing the MoA vertebrae with those of Mauisaurus with the purpose of getting the comparative masses. Pliosaurs are not that tightly related as well. That may be but you can always pick the pliosaur clade where MoA is (likely) a member of or (likely) a close relative of. Anyway they're still more tightly related than Tyrannosaurus/Acrocanthosaurus and Spinosaurus(correct me if I'm wrong). Anyway they all have similar morphology and similar lifestyle even if they're not that tight in relation, which would induce convergent evolution. This is clearly not the case between Spinosaurus and Tyrannosaurus/Acrocanthosaurus. |
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Post by coherentsheaf on Dec 1, 2013 20:41:23 GMT 5
Pliosaurs are not that tightly related as well. That may be but you can always pick the pliosaur clade where MoA is (likely) a member of or (likely) a close relative of. Anyway they're still more tightly related than Tyrannosaurus/Acrocanthosaurus and Spinosaurus(correct me if I'm wrong). Anyway they all have similar morphology and similar lifestyle even if they're not that tight in relation, which would induce convergent evolution. This is clearly not the case between Spinosaurus and Tyrannosaurus/Acrocanthosaurus. Re similar lifestyle: Not enough evidence here large pliosaurids are very fragmentary and their exact ecology is not that well understood. Degree of relatedness is also quite up to debate. More recent evidence suggests so but it is far from certain. |
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Post by theropod on Dec 1, 2013 20:46:00 GMT 5
I think what he means is that we know for sure Tyrannosaurids and Spinosaurs have completely different ecology and morphology, while (also correct me should I be wrong) in pliosaurs no comparable degree of variation is known (but in fact the large ones are pretty fragmentary alltogether, with the sole exception of Kronosaurus, so we end up mostly using Kronosaurus and perhaps smaller specimens like Liopleurodon, without having much of a choice).
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Post by Deleted on Dec 1, 2013 21:04:48 GMT 5
That may be but you can always pick the pliosaur clade where MoA is (likely) a member of or (likely) a close relative of. Anyway they're still more tightly related than Tyrannosaurus/Acrocanthosaurus and Spinosaurus(correct me if I'm wrong). Anyway they all have similar morphology and similar lifestyle even if they're not that tight in relation, which would induce convergent evolution. This is clearly not the case between Spinosaurus and Tyrannosaurus/Acrocanthosaurus. Re similar lifestyle: Not enough evidence here large pliosaurids are very fragmentary and their exact ecology is not that well understood. Degree of relatedness is also quite up to debate. More recent evidence suggests so but it is far from certain. Okay. But if the most recent evidence indicates so then it's safe to follow it(but not take it as fact, because as you said, it's not really certain). |
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Post by Deleted on Dec 21, 2013 23:05:06 GMT 5
Some words and statements from Scott Hartman: __ About the "robust" and "gracile" morphs: comments.deviantart.com/1/124138016/3308263532"First of all, you are assuming there really are robust and gracile morphs, which has not been established statistically. Even if there are two morphs, we have no idea at this point whether they represent genders or something else entirely. It does seem reasonable that a more robust specimen may potentially be stronger than a similarly-sized gracile specimen, but we are a long ways from being able to say that about T. rex."
This should stop that "female tyrannosaurs are bigger than males" thing. __ And about the size of Spinosaurus aegyptiacus specimen IPHG 1912: comments.deviantart.com/1/381444515/3288653546"Well the type specimen is relatively well constrained - it's clearly in the same size class as the largest theropods. Whether the larger snout fragment scales up linearly to such a monster size is indeed still a matter of conjecture."He clearly does not think that it's half the size of Tyrannosaurus, but rather in the same size class as the largest theropods(aside from S. aegyptiacus itself obviously). Which means ~8+ tonnes. |
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Post by Grey on Dec 22, 2013 6:45:28 GMT 5
He's talking about length, he does not have performed yet a weight figure for Spinosaurus.
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Post by Deleted on Dec 22, 2013 8:14:56 GMT 5
He's talking about length, he does not have performed yet a weight figure for Spinosaurus. Well, I assumed he talked about the probable mass range since he defines size as mass. |
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Post by spinodontosaurus on Dec 22, 2013 8:16:20 GMT 5
This should stop that "female tyrannosaurs are bigger than males" thing. The only specimen with a known gender, MOR 1125, is female, and a robust morph. Most 'robust morphs' - including MOR 1125 - are small, so if anything it would appear that females are the smaller ones in Tyrannosaurus, albeit a sample of just 1 isn't exactly very vast, so conclusions like this may be a bit premature. Well the type specimen is relatively well constrained - it's clearly in the same size class as the largest theropods. Whether the larger snout fragment scales up linearly to such a monster size is indeed still a matter of conjecture. ^What we should keep in mind when reading this is that nobody is really doubting that the type specimen is among the largest theropods - even Cau (I think? He only seemed to be arguing it wasn't the biggest, and besides it's vertebrae are still as big as Acrocanthosaurus', which is definitely a very large theropod. At least that's the impression I got). Even 6 tonnes as Blaze mentioned puts it close in size to the Giganotosaurus type specimen and various Tyrannosaurus specimens - I would call that being in the same 'size class' myself, as I would if higher estimates of 8 tonnes+ are true. |
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Post by Deleted on Dec 22, 2013 8:25:09 GMT 5
This should stop that "female tyrannosaurs are bigger than males" thing. The only specimen with a known gender, MOR 1125, is female, and a robust morph. Most 'robust morphs' - including MOR 1125 - are small, so if anything it would appear that females are the smaller ones in Tyrannosaurus, albeit a sample of just 1 isn't exactly very vast, so conclusions like this may be a bit premature. Well, you could draw such an impression if you go by the known specimens, although I wouldn't take it myself. But I don't know why people stubbornly stick to the "males were the smaller gender" line of thought when we haven't even identified any male Tyrannosauri at all yet. |
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