Monday, January 19, 2009

Muscle reconstructions: doing the homework

I know I have been lazy with the postings here, and I really need to finish my Pachyrhinosaurus reconstruction. But I have been faced with a bit of a problem since I've decided to reconstruct this dinosaur one layer at a time, i.e. I wanted to be as accurate in the muscle reconstructions as possible so that the fleshed out version would look realistically three-dimensional even over the skin. Basically, I don't know enough about the postcranial musculature. Previously, I would have just roughly fleshed the whole creature out, from the outside in - basically imagining what a dinosaur would have looked like in life and just sketching it. This way, I didn't really need to be accurate in the myology just as long as the animal looked good enough. However, reconstruction from the skeleton up requires a bit more accuracy on the muscle reconstruction, or at least I would want to be as accurate.

If you have been following my blog for any period of time, you would know by now that I am quite obsessed with jaw muscles. I've dissected numerous specimens of birds (and a couple of crocs) and thus am quite familiar with the attachment sites, general architecture, and relative sizes of the jaw muscles. But dinosaurs (or indeed any animal) is not just the jaws or the head. There is something annoying (ha!) called the postcrania. While the spatial organization cranial/mandibular muscles can be three-dimensionally complex, they are fairly simple, as far as identification goes, in that there are only about a dozen well-defined muscle groups, about half of which are the large adductor (jaw closing) muscles. And when drawing dinosaur jaws, even at a wide open gape, only a couple of these muscles are visible, because most of them are tucked away inside the cranial adductor cavity! So thats all the contribution I get from my thesis when doing full-body reconstructions. But the rest of the body is covered in powerful postcranial musculature, most prominent of which are the appendicular (or arms/wings and legs) musculature. And I don't have much knowledge on the detailed myology of these systems - of course, I've glanced over some papers on reconstructing these muscles in dinosaurs but I don't know exactly which muscle originates where and inserts where...

Unfortunately, as I don't have time or any plans in the immediate future of actually dissecting and documenting first hand the postcranial musculature in birds or crocs (unless of course I suddenly switch to locomotor biomechanics for my postdoc), I have to resort to the next best option: read the existing literature on postcranial musculature, or doing the homework. There are plenty of literature out there on postcranial musculature, primarily appendicular musculature. And there are also an increasing number of papers dealing with the cervical (neck) musculature, most notably by Tsuihiji but also by Snively and Russell. The ribcage and tail musculature is something that is a bit more rare, I think, as I can't think of any publications off the top of my head - I'll have to go through my references to make sure. But I do know that one of my colleagues has been working on dinosaur ribcage reconstructions based on a myological/biomechanical model.

Anyway, some good places to start in reading on archosaur appendicular myology are:

Vanden Berge, J. C. & Zweers, G. A. 1993. Myologia, in Baumel, J. J. (ed.) Handbook of avian anatomy: nomina anatomica avium, pp. 189-247, Nuttall Ornithological Club.

McGowan, C. 1979. Hind-limb musculature of the Brown Kiwi, Apteryx australis mantelli. Journal of Morphology, 160: 33-73.

McGowan, C. 1982. The wing musculature of the Brown Kiwi Apteryx australis mantelli and its bearing on ratite affinities. Journal of Zoology, 197: 173-219

(these are one of the first studies to attempt to identify and correlate bone surface features with specific muscles)

and of course, some good papers on reconstructing appendicular musculature in dinosaurs, for instance:

Jasinoski, S. C.; Russell, A. P. & Currie, P. J. 2006. An integrative phylogenetic and extrapolatory approach to the reconstruction of dromaeosaur (Theropoda: Eumaniraptora) shoulder musculature. Zoological Journal of the Linnean Society, 146: 301-344.

(Sandra Jasinoski is a good friend of mine and so I know that the work that went into this paper is extremely thorough and of very high quality)

8 comments:

Raptor Lewis said...

I think if some fossils were preserved well enough then we could see where the ligaments and tendons attached to the bones like...in...Sue!! *sob* Oh...Sue....Why did they have to take her away...and all because of a legal dispute between the Field Museum and another party.

Manabu "Mambo-Bob" Sakamoto said...

!!! I thought Sue was still at the Field...did something happen?

Anyway, yes, in some well-preserved specimens you can confidently identify muscle scars, tendon/ligament attachment sites. Even in well-casted replicas like BHI 3033, or "Stan".

But unfortunately, not all muscles leave muscle scars, especially the Musculus adductor mandibulae posterior (MAMP) on the quadrate. They just don't leave enough of a discenible mark...the only reason I know it should be there is by analogy to modern reptiles.

Zachary said...

You don't happen to...HAVE...that dromaeosaur shoulder musculature paper, do you, Manabu? :-D

When dealing with your pachyrhino, the hindlimb musculature will be pretty similar to other large ornithischians. The leg muscles behind the femur (I'm not good with muscule names) will attach to the ischium in a divergent way because the ischium in ceratopsians differs pretty wildly from, say, ornithopods. But overall, they probably held their hindlimbs similarly.

However, the pectoral girdle would have been set up similarly to a crocodile in that they used a "high-sprawl" for the forelimbs. There was a great paper in Paleontologica Electronica awhile back dealing with forelimb anatomy in centrosaurines.

Manabu "Mambo-Bob" Sakamoto said...

Indeed I do have that paper. I actually have a physical reprint as we used to share an office. But I also have the pdf so I can e-mail it to you.

And thanks for the tip on ceratopsian limb posture. I'll have to hunt down that Pal Electronica paper! Do you know the citation for that?

sinornis said...

'Ello Manabu, it's Roger. Do you have the two McGowan papers on wing musculature published in J Zool? They're not available online as far as I can see.

Manabu "Mambo-Bob" Sakamoto said...

I have the '82 J. Zool. paper as a photocopy - I don't think I have any other J. Zool. papers by him though...

sinornis said...

Huzzah! One less trip to the library!

Bob said...

Mambo-Bob, There is an amazing article published on 8/20/09 by one of the world's leading paleontologists and authors on the sciencs, ethics, and reality of creating a living dinosaur without dino-DNA. This article is very credible and controversial. I have a blog post about it at http://dnadata.wordpress.com. Must reading for anyone into dinosaurs