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Sketchy-raptor's avatar

Stegosaurus Muscular Anatomy

Here's a chart illustrating the superficial muscular anatomy of Stegosaurus stenops from a number of major anatomical aspects. Built around the scans of Sophie (NHMUK PV R36730, see here:…), this reconstruction was previsualised in 3D, and ties in to the research I'm undertaking as part of my PhD.

A few notes, that I may add to over time (or if/when I make inevitable revisions to the image in the future):

1. Yes, Stegosaurus really is this wide. While only half of Sophie's iliosacral block is preserved, the preacetabular process is longer and flares out at a much wider angle than is often implied in some Stegosaurus imagery. Even reasonably accounting for deformation, the pelvis of Stegosaurus has some impressive girth (insert "Hips don't lie" reference here).

2. About one third of the humerus is buried in the musculature of the pectoral girdle, and the humerus is slightly abducted. The articulation point of the humerus and scapula-coracoid are closer to the midline than one might expect at the first glance of this illustration (unlike the displayed skeleton itself, where the scapulae-croacoids, and thus the humeral heads, are mounted too widely-spaced). The scapula-coracoid layout and enlarged deltopectoral crest of Stegosaurus  implies some pretty hench shoulders, even if one restores things conservatively. I'll be posting my illustration of the underlying skeleton in due course, which hopefully will communicate the relationships with the bones more clearly.

3. Directional pitting in the cortical bone of the plates of Stegosaurus implies the presence of Sharpey's Fibres or equivalent connective tissue at the base. This may suggest that as well as being anchored deep within the dermis, the plates would have had a tendinous attachment to other deeper dorsal tissues, possibly the epaxial muscles or fascia, perhaps similar to extant crocodiles. However, the form of these connective tissues and their attachments remains pretty ambiguous, as stegosaur plates are really quite unique in the grand scheme of osteoderms. With that in mind, for now I have not attempted to illustrate a hypothetical attachment.

Hopefully this will be useful as palaeoart reference!

Useful dinosaur muscle resources:…

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TarbosaurusBatar's avatar

Wow, great piece. I had no idea the front feet were so odd. It's not an exact match but it reminds me of sauropod feet in a way. Thanks for creating a useful reference.

When will you update this?

Saulcontilde's avatar

Hi Matt. I love your job. I have a doubt. The thigh muscles did not fully cover the back of the hips? Did it occur in all stegosaurids? I take this opportunity to wish you a happy new year!

Sketchy-raptor's avatar

Hello, and happy new year to you as well :).

In Stegosaurs the ilia broaden, and the iliac blade is folded over to form what's called a supratrochanteric flange. As a result of this, the surface from which most of the major thigh muscles originate faces downwards (instead of sideways like you would expect to see in most other dinosaurs) and the rim of the ilium from which those large superficial muscles (the iliotibialis) of the thigh originate becomes oriented laterally instead of dorsally. Other large bodied quadrupedal ornithischians show this same trend, but none of them take it to the same extreme as Stegosaurs and Ankylosaurs.

Heilos's avatar

I think I stared for a good hour just admiring all the time, detail and effort that went into this anatomy illustration. Incredible work! The top down and under side views are really impressive and not something i see many people tackle on anatomy sheets.

atomiic-angel's avatar

Thank you so much for these, it can get tiring picking and choosing through papers and older interpretations and only skeletons for what to be drawing. Hope you can do more theropods in the future.

it is my all-time favorite dino!!

Xiphactinus's avatar

Awesome and very helpful work! But, wait, Stegosaurus had only two manual unguals?

Sketchy-raptor's avatar

Thank you very much! :)

Yes, this does appear to be the case for Stegosaurus. Stegosaurian manus are quite rare, but in the Stegosaurus stenops holotype (USNM 4934), most of the manus was preseverved in articulation, and the third digit appears to terminate in a shortened, blunted phalanx lacking features that we would associate with an ungual.

Xiphactinus's avatar

That's really new to me... Thank you for clarifying!

Evodolka's avatar

awesome muscle work here :la:

SonicCaleritas's avatar
There muscles actually look pretty similar to our own
Well in the upper body anyway
Sketchy-raptor's avatar

Absolutely! Almost every muscle here, even if the forms are different, will have a homologue in humans, as they were inherited from the shared amniote common ancestor.

SonicCaleritas's avatar
True almost all quadropedes have a similar musculature just with different proportions
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