Thursday, February 12, 2009

T. rex is Cool the Third: Jaws!

Holy Lip Gloss, Batman! I haven't posted in a long time. This will be post three of four on the subject of dinosaur faces. For now, that is.

And soon I will share my thoughts and feelings concerning some amazing medieval manuscripts I've had the chance to ogle recently.

Remember
Jurassic Park from waaay back in 1993? It affected dinosaur imagery in far-reaching ways. Not only did it help convince a lay audience that dinosaurs were active animals rather than sluggish monsters, but it brought scientific ideas to the popular perception of dinosaurs. Despite these steps, it was still a movie, and it's ultimate goal was entertainment. In the last post, I talked about the flesh covering the jaw attachment site. The JP T. rex design had a very idiosyncratic version of this anatomy. In the picture below, you can see the characteristic zig-zag JP jawline. You can also see that the actual lower jaw does not zig-zag:
This zagged jawline was proliferated due to the popularity of JP. It filtered into scientific publications as well. Here's a recent depiction of T. rex from, unfortunately, I don't know where: It has that same zigging and zagging lower jaw line. Why are they depicting it that way? Well, unlike most theropods (the lineage of mostly carnivorous dinosaurs that now includes birds), T. rex has a thick tooth line and a particularly thick and prominent jugal bone:
This bone is part of what accounts for the wide, boxy cheeks of T. rex. These cheeks also turn T. rex eyes forward significantly, giving the animal a degree of stereoscopic vision: The wide jugal projects over the lower jaw in a remarkable way: The articulation and overlap of the upper jaw over the lower indicates how the flesh should appear. There is, generally speaking, a huge overlap of the upper jaw over the lower jaw in carnivorous dinosaurs: In at least one T. rex specimen, the overlap is so great, that teeth from the upper jaw actually project below the lower jaw. Here is another view, where the red is the amount of the overlap of the jaws: So what we have is osteological evidence for the appearance of the jaw attachment. The artists behind JP took this overlap line and made the lower jaw follow it. I suspect that this also had mechanical purposes: the animatronic dinosaur model had to close and articulate its jaws, and maybe different kinds of cheek were harder to pull off. But I've never felt that the JP design was either scientifically supported or aesthetically ideal. But that doesn't mean that I've always succeeded in my attempts, either.

In the drawing below, I made the cheek covering similar to the flesh covering the rest of the head. When shading the jaw, I think I understated the jugals projecting over the lower jaw.
The problem is that if this drawing were correct, the cheek flesh would have to extend over the jugals and down to the lower jaw thusly: Which is pretty far out there anatomically. What's next is to update the drawing and have both versions. If any of you have an opinion, let me know!

For now, here's Sue, the Tyrannosaurus rex, with "her" particularly wide face:

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