Exdaix, I don't know of any tutorials that go into skin and muscle deformation, although that doesn't mean they don't exist. The basic approach is to use influence objects as muscles and deform them with SDK's from the joints rotation.
As for reference, I watched a lot of Jurassic park. The third one has a bunch of dinosaur turn tables in the bonus features which show ILM's Trex from the movie which was useful.

Glad you both liked it.

Thanks,

Richard