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DrScottHartman's avatar

Roofed-reptile overhaul

Stegosaurus, one of the most popular non-theropod dinosaurs. 

2016 update: As strange as it must seem given how often Stegosaurus has been portrayed and how many specimens are known (for well over a century!), but we actually knew surprisingly little about the basic proportions of Stegosaurus until very recently. That's because previous specimens were either not prepared out all the way (to preserve taphonomic data) or were mounted as composite specimens.

That all changed last year when Maidment, Brassey, & Barrett published the Sophie specimen:…
Among other things it turns out that Stegosaurus has more cervicals and fewer dorsals had been previously been thought. This results in a less tall-bodied and longer-necked animal. In retrospect perhaps this isn't shocking - Kentrosaurus appears to also have had a longer neck than some early reconstructions suggested, and of course Miragaia took this one extra step in its neck-elongation.

Another odd feature is that the tail has a distinct down-curve in the posterior portion. I've gone over the distal caudals several times and the downcurve does not seem like a preservational artifact, so I'm including it in the reconstruction. One interesting side-effect of this is that the thagomizer is now oriented at a more useful angle for swinging at an attacker (I do not consider the laterally-facing spike suggestion to be likely), and notably other stegosaurs also seem to have their distal tail spikes end up facing closer to horizontal as well, either through tail articulation or by changing the angle of the spikes.

So now Stegosaurus does not stand out quite as drastically from its close relatives. It still looks pretty cool though, if you ask me.
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Taliesaurus's avatar
is this a fully grown specimen?
Paleo-reptiles's avatar
Dear Scott

What is your opinion about this new illustration?

Do you think the half of plates were covered like this model? How and why?

the end of tail have a bend but different of your model. what is your opinion?

The stegosaurus was covered with fur like this model? please pay attention to fur in end of the tail in this illustration
Stegosaurus stenops by Kana-hebi
DrScottHartman's avatar
Most of Stegosaur plates were almost certainly covered in keratin, not skin. That said, how deeply the base of the plates were sunk into the skin isn't really known, so the idea that there was extra skin/muscle that covered part of the bottom of the plates is at least possible.

The tail is just being swung around - I drew the tail in the neutral position, but there's no reason it has to stay rigidly in that position.

Fur...since we know that there was dinofuzz/fur/quills at the base of the ornithischian tree (e.g. Tianyulong) it's at least possible that thyreophorans had such structures, though it's also possible that having dermal armor precludes other epidermal structures. The Wyoming Dinosaur Center has some fairly extensive skin impressions of a stegosaur, and it shows only scales, but I don't know that any are from the tail, so this would have to fall in the realm of "speculative but plausible".
Kana-hebi's avatar
Exactly what Scott said. The reason I added filaments (not only to the tail tip but along the vertebral line) was because we know basal ornithischians were profusely covered with fuzz/quills/simple feathers so it is possible sparse covering was still present in some parts of the body (think about what occurs in modern elephants for example).

One thing to note is that in my reconstruction the visible part of the dorsal plates were covered in keratin. They just have a jagged edge. It is possible these structures were used for sexual or territorial display, so I wanted to be highly ornamented (although the surface is mostly smooth).
RizkiusMaulanae's avatar
Kana Herbi's Stegosaurus is pretty much speculative, Amin my brother. We don't know if the plates were covered with skin or soft tissues, but again its a speculation. The end of the tail bending upwards is pretty much not a problem at all. As for the furs, like the skin/soft tissue covering the plates, is also speculative. I think a small amount of furs in the body is more plausible, similiar to a small amouny of hairs in an elephant body. Get it?
DrScottHartman's avatar
We pretty much know that the majority of the plates were covered in keratin. Histological work (and basic phylogenetic bracketing) shows that stegosaur plates are just elaborated scutes, and those are always covered in a keratinous sheath. Otherwise I generally agree.
TimeToGoHero's avatar
It seems to have the right about of plates, if anything it was the other way around when depicting the number of Stegosaurus' plates. And since generally each Stegosaurus species has a different number variation of plates I wouldn't be suprised if those that all the Stegos in movies and books weren't the same species.
DrScottHartman's avatar
Could be, but that doesn't justify their proportions - those were derived from composite specimens, and can't be trusted for accuracy.
tigris115's avatar
Could someone point me to some decent references for S. ungulatus that are up to the minute? Also, is it true that the Sophie specimen is significantly deformed?
thedinorocker's avatar
In the paper listed above the authors said S.ungulatus is a junior synonima of S.stenops...
What do you mean with deforme? Tafonomic distorsion is present in a somewhat degree in (almost) any specimen
tigris115's avatar

Thanks for the information. I just wanted to use a larger species. Can I just scale up the stenops to 10m?
thedinorocker's avatar
The Sophie specimen is a subadult near 6 meters long...
10 meters seems a bit to high but there Are surely specimens buggerato Than Sophie
Sekley's avatar
Do changes to the proportions change the biomechanics a little? I'd imagine the more typical torso shape would allow it to be slightly faster than previous reconstructions?
Angrydinobirds's avatar
Does this mean that Stegosaurus thagomizers really pointed more vertically, as in much older reconstructions, than horizontally?
Paleo-reptiles's avatar

Dear Scott Hartman

Plates shape are different in these two models. Even Pelvis shape that was discovered, have differences with each other.

Therefore, Are you Sure these two models are the same species?

Why do you delete the previous model of your website and deviantart?

DrScottHartman's avatar
Excellent questions Amin, and some of the questions are easier to answer than others. Remember that before Sophie specimen that all current mounts (and all the skeletals based on them...including my earlier one) were based composite mounts (that is, mounts made up of several specimens) and on specimens that were not fully prepared from the rock (e.g. the "road-kill" specimen at the USNM), so they all had to make assumptions to fill in or cross-scale the gaps in our knowledge.

Sophie is very complete, and shows that some of those assumptions are just wrong - e.g. the number of vertebrae in the neck and torso (and thus the relative lengths of the body and neck). The pelvis is generally squished or incomplete in a number of specimens, so I'm not 100% sure whether the differences are due to some sort of variation in age, sex, species, etc. Certainly the relative length of the retroverted pubis and ischia could have varied between the sexes, since the depth of those bones directly impacts the size of eggs that could have been laid - but with so few good specimens we just don't know for sure.

The plates really do seem too variable to be explained away like this, and also we have lots of good plates (though rarely such a complete series as in this example). Several researchers have suggested that there might be some sort of sexual dimorphism involved between males and females, which would explain why there is such a large variety of plate sizes in the Morrison. But until we get enough specimens to test this hypothesis (as opposed to different ages, species, etc.) we won't know for sure.
Paleo-reptiles's avatar
Thank you very much brother Scott to spent your valuable time for me.

Your answers every time show me that you are a great scientist. I am very lucky for having a wise friend like you :)

I feel writting a new book about prehistoric reptiles are not easy like past. everyday, a new information will be discovered and theories change very fast. In past, we have new changes every decades. but Now, it is every month. publish a new book is not easy in such condition. but It is necessary we have a new book even if next years its information and pictures are out of date according the more research.

I hope you and your friends in USA publish a new encyclopedia about new modeles of prehistoric reptiles . Now, the interesting books that G. S. Paul published cannit give us a correct imagination about anatomy of these wonderful animals.  
Dinosaurzzz's avatar
Would all stegosaurs have this tail shape, or just Stegosaurus?
DrScottHartman's avatar
Kentrosaurus seems to have a bit of a curve also, but it's not this strong. I'd guess that the character is pretty variable, especially since the number of "spikes" varies in other taxa, and so tail-use might have varied quite a bit as well.
Dinosaurzzz's avatar
Huh, ok. What about Hesperosaurus, would it also have a curve?
DrScottHartman's avatar
Dinosaurzzz's avatar
Would it be equally as accurate to restore it with and without one?
Paleo-reptiles's avatar
Dear friend, Scott!

somtimes, if fossils exist in museums , why everytime, reconstractions show strange changes? I was surprised how the great experts were blind for watch things that they see them now.

Please answer to my quesions:

1- You had a nice stegosaurus like reconstraction by G. S. Paul. but Now, You delete it. Why?

2- Why the shape of large plates in back of your new version  is different of your previous version?

3- Even numbers of paltes changed. Why?

4- in your previous version, large plates have a much of dark part that show they grow like horn of rhino . but now, do not exist such high dark part in large plates of your new version.... but why?

I like the curve shape of end of its tail because it is logical for attack to predators now. but How stegosaurus can lay down or sit down with such curve?
DrScottHartman's avatar
So the reality is that museums are just doing their best, and despite public perception the main purpose of most publicly funded museums is to support scientific research, not to constantly update their displays (which would be enourmously expensive). As a result, displays are often put together by people who are not scientists themselves, and they often copy what has been done in other museums previously rather than reading the current scientific literature. In this case, most museum displays of Stegosaurus from the early 1900s until the 1980s largely just repeated mistakes that Marsh had made, sometimes with some of the corrections made in papers from the 1910s and 1920s (but there still were lots of unknowns at the time). Because Stegosaurus is so distinctive with its plates and spikes and tiny head, dinosaur books almost always tried to portray them, and museums wanted casts to mount, so the image of Stegosaurus became much more entrenched in our collective imagination then the science itself warranted - sort of the same way that swamp-dwelling sauropods did.

Several paleontologists and artists started revising what we know about stegosaurs starting in the 1970s, but these weren't usually done because of new specimens, they were just correcting anatomical inferences that were no long seen as correct (like the lizard-like sprawling forelimbs), but areas where we just didn't know the answer (like vertebral count) couldn't be corrected without newer, more complete specimens.

I was also surprised by how extreme the changes were - it's not often that a well-known species goes through this sort of change anymore, but as I said here and elsewhere, if we'd looked a bit closer it would have been clear that there were more gaps in our knowledge of Stegosaurus anatomy than people realized. 

Now for your questions:

1) My previous reconstruction was based on a composite of several excavated by and displayed at the Museum of Ancient Life at Thanksgiving Point, Utah. I used the specimen because I had access to casts of it, but I was still stuck with the assumptions they made. My best guess is that they used Greg Paul's skeleton to try and decide how to combine the incomplete specimens they used, which is why they had similar vertebral counts, etc. I deleted it because the new skeletal based on Sophie is definitely more correct, even if some of the differences (like the shape of the plates) might be real. Perhaps some time I will get to revisit those specimens with our new knowledge from Sophie, but until I do (and see them first hand so I know which specimens are which) I have pulled it from my website because it's now out of date.

2) Different specimens. There's actually quite a lot of variation in plate shape and size in Stegosaurus, and it might suggest that the males and females of each species had differently shaped plates (and presumably there were differences between the species themselves), but as is usually the case we don't have a large enough sample to test this statistically. And in the case of the Morrison itself we also don't have good enough temporal constraints, since the Morrison is ~9 million years long and each lineage of dinosaur probably also shows variation over that timespan (indeed, that's probably why it looks like sauropod diversity is so high in the Morrison - because Apatosaurus, Camarasaurus, etc., were all evolving across that time into 2-4 distinct "morphs" that we've named different species).

3) The Sophie specimen has the most complete set of plates, and it shows there were more than people had inferred from earlier, more complete specimens.

4) That just reflects changing ideas about how thick the keratin layer was - some of the histological work has hinted that it wasn't as thick as my previous skeletal showed. It's just a coincidence that the new specimen came out before I got around to changing the keratin thickness on the old one.

5) The curve is just the neutral position, it's not fused into that shape. I'm sure it could at least partially straighten it when laying down.

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