Taming this big fluffy T-rex won't be easy when having or riding a dino with you because of its fear roar. It's hard to tame it because it will scare your dino away. So try to get it off a cliff but a cliff where you can see it and shoot it with tranq arrows. But be careful because it can go in the water. Once knocked out give it raw meat or mutton.
It really is that simple though, they can't reach you or your flier on a big enough rock, so if you don't want to make a trap you can just shoot down from a rock or cliff once the carnos are dealt with. Be ready for a goose chase once it starts running.