Sunday, April 20, 2008

More on jaw muscle reconstructions

I have some more old images of mine, this one is of the jaw muscle reconstructions in Deinonychus. The skull is reconstructed from Ostrom's (1969) original figures. And jaw muscles are based on personal observations in numerous modern bird species. Off the bat it's obvious I've only referred to birds and not crocodilians or other diapsids because of the way I've reconstructed the MAMES attaching with a tendonous attachment onto the coronoid process. The muscle attached to the dorsal and medial surfaces of the surangular just medial and posterior to the MAMES is the MAMEM. In contrast, the MAMES in crocodilians attach along the dorsal surface of the surangular with the MAMEM attaching just medial to that. I suspect given the arrangement of cranial bones that the muscles arrangements in theropods would be more similar to crocs (and other diapsids) than to birds. The MPT is reconstructed as wrapping around the ventral side to attach to the lateral surface of the angular as in crocs.

Another picture I drew of muscle reconstructions in theropods, or rather another one of them hypothetical dissections, is one in Allosaurus. Again it is evident the muscles are based on birds from the MAMES attachment. Like in a previous post, the skin is peeled off halfway and the tongue and hyobranchial apparatus have been removed to reveal just the jaw adductor muscles. I just think this is a rather comical drawing, more so than the last one.

You might think that all this is pointless and we will never know what the muscles in theropods were like, but a large part of biomechanics actually rely on muscle data and the more we know about them the better it is.

3 comments:

Zach said...

Gorgeous pictures, especially the second one! I always like seeing muscle reconstructions of dinosaurs. Has anybody done one for hadrosaurs? As I understand it, their mandibles worked in a wierd way...

Mambo-Bob said...

Thanks, Zack! The second one was actually quite difficult mostly because of its odd angle...you rarely see dinosaur drawings at this angle. But the muscles weren't that difficult as I have first hand observations from various angles.

Ostrom (1961) has some detailed jaw muscle reconstructions using Corythosaurus. They're more schematic than artistic but I really like them as Ostrom looks at all the major jaw muscles from a variety of angles!

The ref is: Ostrom, J. H. 1961. Cranial morphology of the hadrosaurian dinosaurs of North America. Bulletin of the American Museum of Natural History 122:35-186

And of course, the classic refs for jaw biomechanics in hadrosaurs are Weishampel (1983) and Norman and Weishampel (1985).

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Spencer