Dinosaurs of the Morrison Had No Lips … or Did They?


Just a minor post. I wanted to present a portion of a larger project on attempting to illustrate typical dinosaurs (especially ornithischians), and I thought “What better method than that well-sampled and intriguing Morrison Formation and its remarkable diversity?” So I started using a minimalistic stippling technique to draw the “busts” of the Morrison paleofauna, focusing on ornithischians. This has the advantage of allowing me to approach well-studied, well-photographed, and decently accessible taxa from the Morrison Formation. This runs into a small problem, that of the composition of the Morrison “fauna,” which is in fact comprised of several temporal (and apparently regional) faunae. To simplify things, I am ignoring all of that.

This series intends to provide a diversity of illustration possibilities. They are not all using the exact same degree of details, nor the same modelling for integument. In some cases, they are meant to create a complex possibility.

Ornithopods

The Morrison ornithischians Dryosaurus altus, Theiophytalia kerri and Camptosaurus dispar.

I think I was pretty successful in creating an “alien” appearance. There are no “cheeks,” and in their place there are neither “lips” nor an absence of anything covering the teeth, a subject I mentioned here. I may have been too conservative on the keratin beaks in these representatives, while I was very elaborate in adding in large “ossicones” or ossicles to the skin, especially along the sagittal margin. The use of a series of prominent ossicles on the spine, especially right above the axial neural spine, is a convention I adopted a while back in connection with Pete Buchholz, although I also fancied a more … extreme … look:

Bust and arms of Dryosaurus altus.

This one played with the idea that the skin would have had less of a squamous appearance and had a more “fluffy” aspect, in connection with Tianyulong — and which I elaborated on in even more detail here.

There’s a definite focus in this series towards the squamation of the integument, and I do not foresee making the smaller ornithischians “feathered” in any manner. Nor the theropods, for that matter, but that’s a discussion for later. Another theme that pervades these is that the palpebral, a bone that articulated to the anterior orbital margin and projects posteriorly and laterally, is made very prominent. This bone is under-emphasized in reconstructions, which often appear to omit the object and it’s effect. In some smaller taxa (e.g., Dryosaurus altus), the bone crosses the entire orbit and can contact the opposite side. In this case, the distal tip is likely connected by a ligament to the postorbital, which is incompletely ossified in ornithischians. This may occasionally be segmented into two elements, and divides the orbit into a lower and upper aperture (Maidment & Porro, 2009).

Composite skull of Heterodontosaurus tucki, modified after Maidment & Porro *2009). Grey indicates the palpebral bone. The skull is mediolaterally crushed, but you get the idea.

The eyeball, however, should not normally be constrained by just the lower (larger), and the scleral ring, defining the inner “visible” diameter of the eyeball, would (or could) extend beyond the apparent position of the palpebral (if articulated correctly. As in Dryosaurus altus (see below) the bone would completely divide the orbit:

Skull of Dryosaurus altus, to scale, showing the complete palpebral bone. Borrowed from nps.gov.

This meant that one could not just show the eyeball below the palpebral, one had to incorporate this into the facial profile, and that meant the use of a “brow.” The brow thus had to incorporate the upper eyelid to some degree, and distort the “perfect circle” that tends to appear in art for dinosaur eyes (or the use of “perfect ovals” when imitating humanistic eyes). Arguably, the “perfect circle” model copies birds to a large degree, but I’ve avoided this for reasons including avian palpebrals tend to be much higher and form portions of the dorsal orbital rim rather than cross the orbit just above mid-height.

Bust of Dryosaurus altus, this time without the fancy “hair.”

This leaves aside the functional implications of the “brow,” which I won’t get into.

I’ve also added in the occasional skin wrinkle, “frills” comprising large triangular or trapezoidal scaled along the chin or throat margin, and also a faux-jawline, but for the most part, the main goal was to obscure the natural openings in the skull (nares, orbit, infratemporal fenestra, etc.) and the shape of the skull itself would be hidden. Admittedly, snakes and lizards typically lack large marginal scales along the jaw line or at the joint, and in this the above illustrations depart enormously and instead correspond to typical “differentiated” art.

The auricle, or “ear-hole” is placed roughly just underneath the paroccipital process, although I expect as some data shows that it was positioned lower and closer to the jaw joint.

All in all, this represents an exercise in depicting soft-tissues and departing from the expectation of classic art for dinosaurs. Here they are scalier, reptilian, rather than prancing nearly scale-less birds. They are still bird-like, but not ridiculously so.

Maidment, S. C. R. & Porro, L. B. 2009. Homology of the palpebral and origin of supraorbital ossifications in ornithischian dinosaurs. Lethaia 43(1):95-111

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4 Responses to Dinosaurs of the Morrison Had No Lips … or Did They?

  1. Matt says:

    Another informative post Jaime.
    I’m really enjoying your exploration of form, anatomy and soft tissue possibilities. The illustrations do your reasoning justice and despite being a little ‘alien’ in nature still resonate as well within the scope of reality and look great too.(the top illustration gives the impression of a group of very disapproving animals, they need pipes and beards to stroke thoughtfully.) Ahem.. sorry.

    Couple of questions, is there much scope for the angular positioning of the palpebral when articulated? Are there definitive attachment points for both ends which pretty much lock the bone in place?

    • The proximal (anterior) end of the palpebral tends to form an open articulation. The surfaces of the articulation appear to be smooth, as if it might be mobile to some degree. Some flexbility in this was suggested, I think, largely due to the fact that skulls would often be missing their palpebrals when they bear obvious articulations for them. The distal end, however, if it reaches the postorbital, always seems to produce a firm articulation, or open suture, that inhibits motion. I take the intial hypothesis then, that the bone is largely immobile but can move to accomodate cranial distortion of the face when under compression (in case there was a knietic component to the skull, or to protect the eyeball).

      • Matt says:

        Thanks Jaime, interesting stuff. I seem to remember Greg Paul commenting on the palpebra giving some ornithischians a very ‘raptorial’ look.
        Looking at the skulls above it looks like we often over state the size of the eyes, it’s pretty cramped under that palpebra, which is why I asked about the angle it may have been held at in life.

        Once again, great post Jaime. The rest of us often ride the coat tails of those artists who are closer to the science.

        • Sadly, without a perfect scleral ring or the ability to otherwise directly infer the size of the eye, I would have to project the eye by the size of the orbit. The palpebral in Heterodontosaurus tucki in the image provided in the post shows what is likely an inwardly rotated element. The distal end should point at the postorbital, but due to compression points into the orbital cavity. Modelling the position and likely sizes of eyeball, shape, and position of the pupil would be an interesting project.

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