https://www.highend3d.com/maya/tutori...ongputer/bone/

Try looking at this tutorial, its for a dragon but I think it might help you out. Also if you look at Jurassic Park or the dinosaur show on discovery channel you will notice that the t-rex's spine will move the upper torso from side to side, he also leans forward considerably when he walks. I would use a spline IK solution from the root joint up and a IK solution for the head. You get some really great movement with that solution. A book called Inspired 3d character setup has a great rig for that. It also has a great solution for the pelvis movement by using expressions. If you live in the US go to borders with a pen and paper and look at that book for some ideas regarding your T-Rex and or maybe the tut will help. Let me know if that helped out, and if you can help me out in thread Rigging a Gun holster it would be appreciated.