Depending on your level and Materials you have. large bear traps are pretty cheap to craft. Craft five or more depending on how comfortable you feel.
And use any method of tranquilizing you like.
Tip: when your timing something it never hurts to go a little bit above of what you need in materials.
1. Find the fluffy t Rex. When you find one make sure you’re pretty close but not too close for it to notice you.
2. Place down all the bear traps in a line.
3. Once all your Bear traps have opened. Try to get the attention of the fluffy t Rex. Just shoot it once or go up to it (if you’re brave enough). Once you have its attention run to the first beer trap in the row of bear traps you’ve place down.
4. Once it’s caught in the bear trap you wanna run to the last bear trap in the row. You Want to have the bear traps between you and the fluffy t Rex. And that way you can start shooting it. and as it breaks each bear trap and try’s to come toward you it steps on another Bear trap getting it’s self stuck.
And depending on what tranquilize method you use you probably won’t have to worry too much about it running away but they’re pretty slow. I use this method for almost every dinosaur I tame that can fit in a large bear trap.
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.