King of the Jungle

Alright, another lit search turned up a pretty cool article. Though it is not directly related to iguanas, I think it offers some cool insights in to the musculature of the forelimb in a variety of species. The study was conducted to analyze the evolution of pectoral and forelimb muscles from bony fish to non-mammalian tetrapods and then further to monotreme and therian mammals, including humans.
Bony fish or sarcopterygians have very few muscles in their "upper bodies." They have a fin abductor and adductor and then some undifferentiated hypaxial and epaxial muscles. This makes sense when you consider that fish aren't doing a lot of heavy lifting. This also explains why there was a large change upon the evolution of tetrapods (creatures that walk on four legs). Species that walk must support half their weight on their forelimbs and their pectorals and back muscles have to support their entire body weight on their limbs. Many species have heavily developed shoulder and back muscles due to their large body mass. For example, hippos have a huge weight in their trunks and they have to move this when they walk. The muscles around the trunk have to not only stabilize this mass, but also move it against the force of gravity, mud, water, etc. That's a lot of requirements and is the reason that nature went from fish with 2 clear forelimbs muscles to over 40. And these forty muscles has not undergone a large amount of change since then, mainly because the same requirements are still present (Diogo, 2009).
All of the current forelimb muscles -- biceps, triceps, coracobrachialis, extensor carpi ulnaris, flexor carpi radialis, extensor digitorum, and about twenty others -- derived from the first two forelimb muscles in fish, the fin abductor and adductor. Oddly enough, the pectoral muscles developed from the "postcranial axial" muscles. These are the muscles that are below the head and towards the center of the body. I have to say, the whole article was very odd. It is not very often that I think about how I am descendant from fish. Does that strike anyone else as ironic? You know how we now eat fish and consider them fairly low on the food chain, it's very Lion King ;)
AA
Diogo, R., Abdala, V., Aziz, M. A., Lonergan, N. and Wood, B. A. “From Fish to Modern Humans – Comparative Anatomy, Homologies and Evolution of the Pectoral and Forelimb Musculature.” Journal of Anatomy (2009), 214.5: 694–716. Web. 23 Mar 2012.