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DrScottHartman β Tuojiangosaurus multispinus
Published: 2007-02-03 00:16:05 +0000 UTC; Views: 13232; Favourites: 132; Downloads: 418
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Description
Skeletal reconstruction of an Asian stegosaurid.Edit: Soft tissue updates.
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Comments: 26
Looks really great.Β This is one of the only reconstructions I've seen that shows Kentrosaurus-style shoulder spikes - are you inferring those from bracketing, or are they really present in the fossil?Β I know they're drawn in the rigorous skeletal, but I want to double check, since like I said they're almost never shown.
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My version
pedrosalas.deviantart.com/art/β¦
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I hope you wouldn't mind me asking this, but I have noticed that your skeletal drawing differs from the technical reconstruction of particular skeletal drawer in the number of spikes forming the thagomizer, respectively 4 in yours and 6 in his. Can you shed some light why is there such difference?
I'm going to draw this stegosaur soon, and I'm planing to use your skeletal drawing as reference, thus my question.
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There was a specimen of Chunkingosaurus that included the end of its tail and three pairs of spines preserved with it (with fragments of a possible fourth pair). It is figured in Dong, Zhou, and Zhang 1983, and the drawing of it there looks almost exactly like the thagomizer in Paul's Tuojiangosaurus.
Paul claims that Chunkingosaurus is a juvenile Tuojiangosaurus in the same field guide that his six-spined Tuojiangosaurus appears, which is probably his justification for the odd thagomizer.
What I'm curious about, though, is whether or not Tuojiangosaurus har shoulder spines. Most reconstructions don't include them, but this one does and in the rigorous version as well. Were the shoulder spines misinterpreted as something else before?
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I saw that in a recent field guide of his, and I'm not sure what it's based on. Nothing in the (mainly Chinese) publication seems to show it, and none of the mounted specimens hint at it either.
So unless there's some unpublished data floating around that I'm unaware of (always a possibility) I don't know where that comes from.
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So his interpretation is either based on unpublished/rumored/known only to him information, or it's simply an artistic license. If the former is true, then it would have been good if he had mentioned it somehow in the text.
I'm going to use your reconstruction anyway, but thank you for clearing this up for me.
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Great work, as usual. Would love to see you work on Kentrosaurus sometime in the near future.
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Kentrosaurus might be number one on my "skeletals I want to do just for me" list. Sadly those tend to fall the "skeletals people are paying me for" list and "skeletals I need for a publication" list
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Are the plates shown here as if in pairs? As in, does it have a total of 32 plates?
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In pairs, yes. And your math checks out too
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I'm beginning to think you're not putting enough epaxial muscles in there -- same for me, actually. I wonder if there should be more? Mallison seems to suggest that if we adopt a croc-like tail, there should be a lot more hypaxial muscle there, at the least, but the epaxial tissue seems thin when considering the mostly-dorsal position inferred for the placement of spikes/plates.
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Also, remember that in this guy at least the plates are not on the midline (I know, stupid lateral orthographic views), so they are in fact embedded deeper in the skin than you would think if you assume they are sitting on top of the neural spines.
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Oh, I know they aren't on the midline. I am no fool, me, though I do play one on the internet. The dorsalmost epaxial muscles though should expand somewhat dorsal to the extent of the neural spine, as do the muscles that run along the dorsal side of the transverse processes or are the dorsal half of the sides of the tail, say the mm. spinalis and articulopsinalis.
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In many (perhaps most thin-skinned) tetrapods the tops of the neural spines can be felt (and sometimes seen, even in health individuals), so I'm not convinced that the spinalis musculature actually exceeded them by a lot (at least not across the length of the entire body...you may have noticed a trend in how I restore necks if you look at the cumulative updates).
As for the more lateral muscles, like the longissimus and iliocostalis, those do rise above the midline in may animals (including reasonably fit humans), but this seems to be more prevalent in mammals. Which isn't to say that those muscles don't need to be larger in life reconstructions, but I'm not yet sold on them actually exceeding the very tall neural spines in many (perhaps most) dinosaurs.
Still, it's a legitimate line of thought, and well within the realm of possibility.
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It's not so much that m. spinalis does not overlay the spine itself, but that it and m. articulospinalis expanded dorsally beyond it in lateral view, and by how much. I'm sure m. spinalis itself did not, but no bets on m. articulospinalis, which runs along the dorsal side of the transverse processes, and may have "bulged" a bit.
As for the cervical epaxial musculature/ligaments, I think you're a bit wrong on those, but for me I have only a few circumstantial arguments to make:
I don't think a mammal-like arrangement for a "nuchal" ligament exists in sauropsidans, and instead the epaxial "nuchal" ligaments will conform more or less to the curve and shape of the spine. There wouldn't be a withers, as there isn't in birds, turtles, etc.. Accomodation to loading can occur ventrally, as in a cantilever, and as such the enormous cervical ribs and their ligamentous attachments are a novelty that has been at times put into the context of supporting these enormous necks, though it's obvious that guys like Mike Taylor and Matt Wedel disagree; they have the problem of working with birds, which have these really pathetic little cervical ribs and lack the ultrastructural support elements of sauropod verts (neural spine anatomy, deep intercentral articulations, elongate prezygapophyseal articulations, cervical rib morphology, etc.). I understand size is an issue, but biomechanically speaking, I'd see what the muscles would have to be like before I start installing extra structures not indicated by Sauropsida extant morphology. If one cannot reconstruct a reasonable muscle system, constrained by probably morphology, with constant ratcheting of size against the mass of the neck it produces; then, and only then would I assume perhaps additional, more novel structures can apply. Unless, of course, you have info I do not....
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Ahh...but I'm not reconstructing saurischians with mammal-like nuchal ligaments, but rather avian-like ones, just hypertrophied in some sauropodomorphs. In particular I recommend Tsuihiji 2004 (in JVP) to see how easily the avian system produces taller nuchal ligaments (and concurrent muscles).
In ornithiscians I do think the arrangement was slightly more mammal-like, and presented the evidence in a relatively unknown proceedings volume at a Tate Museum conference quite some time ago, but with any luck the better parts will show up in a paper again in the not-too-distant-future.
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Oh, I'm aware of how the avian neck can produce tall epaxial ligament systems spanning the neck itself. This is very common in birds that maintain a largely C-curved neck, as in many passerines, precellariiformes, or so forth. But that has the effect of pulling the neck around into a curve, to reduce the slack. In birds with thin, hyperelongate necks that are stretched out (e.g., ostriches, swans, geese) the nuchal system stays pretty close to the vertebrae. Birds with very long and slender necks also have relatively smaller heads, and thus hold less mass at the ends not handled at the cervicocranial joint (and are mostly omnivores/herbivores or specialists on small prey, thus need smaller heads). But birds with proportionately larger heads, and/or are macropredators, use a C-shaped neck and may need the "tall" nuchals to suspend the middle-section of the neck between head and shoulders. I should also note that in birds, the tallest part of the nuchal system is in the middle (Zusi's work, here). I might think instead suspensory posture of the neck promotes taller nuchals, but straighter necks probably had nuchal systems closer, if not nearly parallel, to the cervical series. Just thinking out loud here. Would love to put this into more direct context; it's part of my major disagreement with the neck reconstruction models of Taylor et al. -- I much prefer that of biomechanists like Schwartz-Wings, Christian and Dzemski.
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No, ratites with elongated necks and bifurcated neural spines specifically have nuchal ligaments that extend well above the neural spine (and which support an expansion of the axial musculature above them as well), and the thickest portion tends to be in the posterior part of the neck, where the added mass will have the smallest impact on the outstretched necks.
I have to say that I'm not a very big fan of some of Schwartz-Wings myological reconstructions, although I do like much of what Christian and Dzemski have published.
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My understanding from Tsuihiji's work on rheas is that his depiction, but not description, of the "deep" posterior tendons of the nuchal system in rheas concurs with your argument. He reconstructs, for example, that the musculature that ascends up the neck and around the tendons is not really as high as the vertebra is tall at the posterior neck. The reconstruction he provides is a deliberately schematic reconstruction, for even when a rhea's neck is raised up, the tendons do what Wedel and Taylor call "bowstringing", in being largely conforming to the curvature of the neck, but with a smaller arc: [link] . the sauropod reconstruction follows the schematic, but I am sure it is not meant to say that the structure copies this relative height in vivo. Not in these taxa. As mentioned, in deeply C-curved "shortnecked" birds, the nuchal system is more shallowly bowstringed, higher above the verts.
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I wasn't talking about the schematic diagrams (although you are correct that they could be taken that way). For the sake of brevity (and to save some good stuff for blog entries and/or paper submissions) I'd just refer you to figure 2c & d. Note how even with such low neural bifurcated neural spines that the nuchal ligaments and axial muscles at an extra 70% of the vertebral height to the neck. With tall-spined sauropods I have no problem envisioning this ratio being much larger, and I believe macronarians have their own suite of adaptations along those lines to increase the leverage of those muscles and ligaments.
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I agree with you in general. I would like to know the variation is birds with much longer necks, or those whose aspect ratio (length:depth at, say, a posterior cervical; something to qualify down the road) is very low.
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Bulking up the epaxial musculature over the tail and back is mostly done lateral to the neural spines (e.g. it isn't very obvious in a side view skeletal), although I have been going back and adding a bit more. As for this guy (and other stegosaurs) I actually had the same thought...perhaps it'll need another update later in the year.
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Β‘Orales! al parecer si tenia pΓΊas en los hombros.
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Excellent as usual! Your skeletal drawings are the best I ever saw!
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