Ran into one while walking the redwoods on my Rex. It just walked around my Rex's feet ignoring us completely. Until, that is, I unseated myself. As soon as I was standing on my Rex's back it took notice. I ended up standing out on my Rex's tail and tranqing it. So apparently like titanboa's they don't aggro on Rex's.
Ok so here’s how you tame them find one that’s on a tree but don’t get too close find a rock to sit on shoot him and he will jump off the tree but won’t be able to attack you then just tranq him out and put spikes around him once he’s out hope this helps