A shorter Scelidosaurus skull

Scelidosaurus nests next to Daemonosaurus as the most basal ornithischian in the large reptile tree. It’s obviously quite a bit more derived than Daemonosaurus with those plant-eating teeth and tiny antorbital fenestra (Fig. 1). Probably more bulky, too (Fig. 2).  But no other taxon in the large reptile tree (338 taxa) is closer with the exceptions of Heterodontosaurus (Fig. 2) and Hexinlusaurus.

This is one of the dinosaurs I rescored a few weeks ago. I was under the impression that it had a longer rostrum. I’d like to see some papers on this.

Figure 1. Scelidosaurus in situ with bones traced and colorized. Only the left half of the dorsal skull has been traced. The break in the rostrum occurs right where Daemonosaurus and Heterodontosaurus have dentary fangs, so, with phylogenetic bracketing, one has to wonder whether Scelidosaurus had them too.

Figure 1. Scelidosaurus in situ with bones traced and colorized. The naris is not clear. Only the left half of the dorsal skull has been traced. No palpebral? This skull is somewhat distorted, taken with a wide-angle lens. 

A shorter skull gives Scelidosaurus something of a new look.

Figure 2. Basal ornithischia and Pampadroameus, a sister to their common ancestor. Daemonosaurus likely resembled Pampadromaeus, with its long neck.

Figure 2. Basal ornithischia and Pampadroameus, a sister to their common ancestor. Daemonosaurus likely resembled Pampadromaeus, with its long neck.

So, the origin of the Ornithischia remains in that gray unknown area represented by the unknown postcrania of Daemonosaurus. Scelidosaurus and Heterodontosaurus have the basic ornithischian pelvis. Pampadromaeus probably doesn’t since it is also basal to sauropods. Daemonosaurus is apparently where the magic transformation takes place in the pelvis.

Figure 3. Daemonosaurus and kin. Here a selection of basal dinosaurs is divided into clades. Yet, note the resemblances. These taxa are not too far from one another.

Figure 3. Daemonosaurus and kin. Here a selection of basal dinosaurs is divided into clades. Yet, note the resemblances. These taxa are not too far from one another.

Addendum
Mike Hanson has kindly sent a less distorted side view skull. Here it is (Figure addendum). Thank you, Mike.This is to demonstrate that I make mistakes (this one more or less on purpose to encourage the reception of better data, see above) and that I correct them once revealed, as I have done before. Even with the distortion adjustment, the skull is still shorter and smaller in the rostrum than the data I had before. All I want is the best data. Again, thank you, Mike. Keep it coming. 

The revised skull of Scelidosaurus taken from more distance for less distortion.

Figure addendum. The revised skull of Scelidosaurus taken from more distance for less distortion.

 

 

References
Norman D 2001. Scelidosaurus, the earliest complete dinosaur in The Armored Dinosaurs, pp 3-24. Bloomington: Indiana University Press.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B, published online 
Thulborn, RA 1977.
 Relationships of the lower Jurassic dinosaur Scelidosaurus harrisonii. Journal of Paleontology. 51: 725-739

wiki/Daemonosaurus
wiki/Scelidosaurus

5 thoughts on “A shorter Scelidosaurus skull

  1. This is why examining the physical specimen is such an important thing, the dorsal part of the skull ought to be much lower and flatter than restored here, also, the angle from which it was photographed is somewhat oblique, making the entire skull distorted so that it appears anteroposteriorly compressed. Here’s a photo of the same specimen from a better angle: http://newsimg.bbc.co.uk/media/images/44683000/jpg/_44683297_dino_getty.jpg
    Furthermore, even if the photo you used were the only reference for the specimen in existence and the physical specimen were lost, this is one of two S. skulls known (the other is the neotype described by Owen), and both present the shallow morphology. This is precisely why scientists do not rely on photographs, and if they must use them, it is with extreme caution.

  2. “Scelidosaurus nests next to Daemonosaurus as the most basal ornithischian in the large reptile tree. It’s obviously quite a bit more derived than Daemonosaurus with those plant-eating teeth and tiny antorbital fenestra (Fig. 1). Probably more bulky, too (Fig. 2). But no other taxon in the large reptile tree (338 taxa) is closer with the exceptions of Heterodontosaurus (Fig. 2) and Hexinlusaurus.”
    According to your own methods of nesting similar-looking taxa together this should raise red flags to you. Scutellosaurus certainly looks morphologically more similar to Scelidosaurus than any other taxa you have listed.
    In the “orthodox” taxonomy we find Scelidosaurus as a rather derived ornthischian. It isn’t even the basalmost thyreophoran, let alone at the base of ornithischia. Having this massive armored beast at the base of ornithischia creates some problems with reversals in losing then gaining armor multiple times instead of having armor conserved through one lineage. Which is most parsimonious?

  3. Not sure which taxon leads to other armored taxa. I haven’t tested that far. One or the other may have been the last of its kind. I don’t know. Scuttellosaurus nests apart from Scelidosaurus due to a larger number of traits than intermediate taxa, so no, they don’t look more alike. The size difference is major. They do share armor. This may be a case of convergence. That will have to be tested. I’ll produce a post on that soon. Thanks for the idea.

    • “The size difference is major.”
      A lion and a housecat are more closely related than a housecat and a Chihuahua. Gross size isn’t terribly important. I look forward to your post.

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