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: journals.plos.org/plosone/arti…
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.
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?
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.
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.
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?
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.
Of course I'm always happy to update it later if more/better evidence emerges.
On some reconstructions Stegosaurus had too short tail, now it looks more functional in defense. Good job
"Sophie" is a stunning specimen
This sparks a memory of when was given the opportunity to look at a stegosaurus fossil behind the curtains last year (at a fossil/mineral shop called Red Gallery in Hamburg, Germany). What was curious about this specimen though is that it seemed to have an additional row of tail spikes? My memory is a bit foggy unfortunately, but I clearly remember the guide talking about it as if it was a recent discovery. It also had a bite mark from an Allosaurus on one of its back plates that had healed.
I guess that's just a long-winded way of saying I don't know.