Tutorial 15b: the bones of the theropod skeleton

September 8, 2011

Last time, we looked at the bones of the sauropod skeleton, and I mentioned that “thanks to the wonder of homology, it doubles as a primer for dinosaur skeletons in general”.  To prove it, here everyone’s favourite vulgar, overstudied theropod Tyrannosaurus rex, in L. M. Sterling’s reconstruction from Osborn 1906:plate XXIV, published just one year after the big guy’s initial description.  (The pose is somewhat outdated, but it’s a classic):

Click through for the full-sized version (2897 by 1755 pixels), which — like yesterday’s Camarasaurus — you are welcome to print out and hang on your wall as a handy reference.  (Sterling’s original is out of copyright; I hereby make my modified version available under the CC-BY-NC-SA licence.)

The thing to notice is that the Camarasaurus and Tyrannosaurus have exactly the same bones, excepting only that theropods had gastralia (belly ribs) and sauropods probably did not.  If you doubt it, here are the two animals composited together.  Print it out!  Print lots of copies!  Hand them out to your friends!


Osborn, Henry Fairfield.  1906.  Tyrannosaurus, Upper Cretaceous carnivorous dinosaur (second communication).  Bulletin of the American Museum of Natural History XXII:281-296 and plate XXXIX.

22 Responses to “Tutorial 15b: the bones of the theropod skeleton”

  1. Neil Says:

    Really appreciate these Mike, but can you do them three months ago so I can use them in my paleobiology class in June?

  2. Mike Taylor Says:


    Ask me again in three months.

  3. Matt Wedel Says:

    No, dude, you mean, “Ask me again four months ago.” That ought to give you plenty of time!

  4. Sauropod did not have belly ribs?
    That’s news to me – I saw gastralia a few times in the field. However, they separate very badly from the matrix, because they were mostly cartilaginous, and thus are very rarely collected.

    Ceterum censeo…: note that the axis is often called epistropheus in older and medical texts (Janensch, Hennig, Huene come to mind).

  5. Mike Taylor Says:

    Heinrich, interesting stuff! Do you have any field photos of these alleged gastralia? So far as I know the only time they have been reported in a saurpod was in the Eobrontosaurus holotype, and they have been subsequently reidentified as ossified sternal ribs. Unless there’s something more in the literature that I’ve missed you might have a new and exciting discovery lurking somewhere in your photo album.

  6. sorry, no pics! But I know of a quarry map that had a partial gastral basket on it. You know, the typical, crossing-the-midline a bit, one left, one right arrangement that tells you quite clearly that this is NOT a “regular” rib.

    So I will try to remember where I saw that and talk to people there.

    And also, what I saw in the field looked just like that, and it was hellishly difficult to get out of the ground – which is why nobody ever does. The things were about 3 to 5 mm wide, and just faded into the sediment, so you can’t really say where to separate something from the rock. I’d interpret this to mean that the gastralia were almost totally cartilage, with only the slightest bit of ossification in the centers.

  7. […] a sauropod and theropod to show the homology of all the elements.  He’s stuck it up on SV-POW, but is encouraging people to use it in their teaching so I thought I’d repost it here. […]

  8. Adam Yates Says:

    Heinrich said
    “The things were about 3 to 5 mm wide, and just faded into the sediment, so you can’t really say where to separate something from the rock. I’d interpret this to mean that the gastralia were almost totally cartilage, with only the slightest bit of ossification in the centers.”

    That’s really weird on so many levels. The reported diameters are tiny, about what I’d expect in a juvenile Massospondylus, about 2-3m long. We have abundant gastralia of near sauropods (e.g. Aardonyx) and basal sauropods (our new guy and Antetonitrus) and these are much thicker (up to 1.5 cm in diameter) and well ossified.
    Indeed gastralia shouldn’t be cartilaginous ever. They are dermal elements, that originally evolved from scales. As such they ossifiy directly from dense aggregations of mesenchymal cells and are not preformed in cartilage.
    I’m really curious as to what Heinrich saw.

  9. Well, Adam, that makes me even more curious! The overall diameter of rock discoloration was up to 20 mm, but noboy would call the outer area “bone”. I didn’t know about how they form, my theory makes no sense now. I can’t really say what these thing were.

  10. andy Says:

    So that covers both major branches of the saurischia, what about an ornithischian skeleton?

  11. Mike Taylor Says:

    andy-with-a-little-“a”, I’d like to do an ornithischian, but it may have to wait — these are surprisingly time-consuming to prepare, and I have lot of other things I should be doing. Stay tuned.

  12. Zhen Says:

    Thank you for the detailed labels Mike. I’ve been looking for something like this for dinosaurs.

    Is there any chance you can give us a detailed label of the skull? I only remember the maxilla and pre-maxilla, but things get a little foggy after that.

  13. Mike Taylor Says:


    I am shaky on skull myself — this blog is not Sauropod Vertebra Picture of the Week for nothing! But in fact, for that very reason (i.e. to educate myself) I do plan to illustrate and label a sauropod skull at some point. Stay tuned.

  14. Scott H Says:

    This is a really good idea, but aren’t these sort of old and sad skeletal reconstructions to use as a primer on, you know, anatomy?

  15. Mike Taylor Says:

    Well, Scott, I was looking for material that is not encumbered by copyright. And even if the postures are not quite what we’d expect to see these days, you have to admit they are great art.

  16. Scott H Says:

    It’s not just the pose, but several of the bones themselves are not the right shape. I agree that aesthetically the late 19th and early 20th century seem to have been the high-water mark for plates in paleo diagrams, but aesthetics wouldn’t be my first concern for this application.

    Out of curiosity, what do you need public domain images for in this case?

  17. Mike Taylor Says:

    Really? What bones are wrongly shaped in the Camarasaurus? I just looked again and nothing leaped out at me.

    I wanted public domain images so that I can do what I want with them without needing to get anyone’s permission. In particular so I could make my modified versions available under the CC-BY-NC-SA licence.

  18. shaind Says:

    It is interesting that those two very different dinosaurs are stil comparable in structure of skeleton. Those structures really change small through evolution.

    By the way, I found that some korean crank is trying to use your post to insist that sauropods were in fact carnovorous like T. rex…… ( http://treebook.egloos.com/256302 )

  19. […] you’re not a regular and some of these terms are unfamiliar, check out these handy guides [1, 2] to the vertebrate skeleton). That leaves marrow in everything else, although the only bones with […]

  20. […] that, nearly two years ago, we published annotated skeletal reconstructions of Camarasaurus and of Tyrannosaurus, with all the bones labelled. At the time, I said that I’d like to do an ornithischian, […]

  21. […] a bird. We’ve never done either of those — but we should, to go with our Camarasaurus, Tyrannosaurus and Triceratops. Skeletal homology for the […]

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