An unexpected synapsid

July 3, 2026

Skeletal reconstruction of Sphenacodon in left lateral view, jaws open — a long-bodied early synapsid predator whose neural spines are tall but stop well short of a Dimetrodon-style sail

This wasn’t the pelycosaur you were searching for? I know after my prior post many of you are looking forward to Edaphosaurus, and it’s coming, I swear! But first I had cause to tackle Sphenacodon, so I figured why not push it out to the world first.

To start with the obvious, Sphenacodon isn’t a dinosaur, or even on the evolutionary branch headed towards dinosaurs (or crocodilians, or lizards, ichthyosaurs or tuataras….). It’s very much on the branch that includes us mammals. A close relative of Dimetrodon, it would have played a similar apex-predator role in its environment, although Sphenacodon is found in somewhat less soggy environments (seriously, Dimetrodon is found almost exclusively in swamps, please stop depicting it in semi-arid environments!).

That’s all for now, but in addition to Edaphosaurus, some big changes are coming to SkeletalDrawing.com over the next several weeks, so stay tuned for a more usable website (especially for mobile users).

Cheers!

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10 comments

  1. Kolinfrom the archive

    Happy to see more of your content on prehistoric animal anatomy (now to just wait for Mark Witton to come back too). Do you have any plans on updating, say, Dilophosaurus or Amargasaurus?

    1. Scott Hartmanfrom the archive

      Amargasaurus for sure. My Dilophosaurus is largely ok, although I need to recheck the frill sutures.

    2. DSreplying to Scott Hartmanfrom the archive

      Dear Dr. Scott Hartman

      I have illustrated a Spinosaurus Skeleton and would like you to review it with potential changes and feedback, furthermore has there been any recent updates with the lower limb proportions that Dr. Nizar Ibrahim had suggested, and that the particular specimen was a not a fully grown adult.

      From DS

      hope you can help

      I cannot post the illustration as I am encountering issues with uploading the file.

    3. Scott Hartmanreplying to DSfrom the archive

      You can email me through the contact page - I'll respond and then you can attach your skeletal (or you can upload it somewhere and share the link with me in your first email). I'm happy to take a look.

    4. DSreplying to Scott Hartmanfrom the archive

      Thank you for your help

      I have sent the Skeletal illustration through the contact page I hope you have received it.

      From DS

    5. DSreplying to Scott Hartmanfrom the archive

      Good response I really appreciate your feedback.

  2. Sarcophagusfrom the archive

    Glad you're still alive and posting. Cool synapsid for sure, but I really want that Edaphosaurus lol!

    1. Scott Hartmanfrom the archive

      Soon (TM)

  3. Ildarfrom the archive

    Hello, Dr. Scott! Do you plan to update your Falcarius's skull according to this new information? https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70080 And what are you plans for Eotyrannus skeletal, as the monography about it was published recently?

    1. Scott Hartmanfrom the archive

      It's all on the list of never-ending updates, although the Eotyrannus material didn't become more complete in the process, so I'm not sure there's much to do change on it.

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