How to tame a Rex:bring out a dinosaur that have a lot of health and low melee,whistle that Dino in passive and park it in a good distance,shoot the Rex and let it attack your dinosaur,while in distraction shoot the Rex and bear trap it and move your dinosaur steps away(for recover),when the Rex broke the large trap let it attack your dinosaur again and shoot”move your dinosaur steps away,when the Rex broke the large trap”Do this 2 step again and again when the Rex is knocked out.
If you use the bear trap strategy which is if you lead it into a Dino gateway that is shaped in a triangle and with a bear trap in the middle (Large Beartrap) and when it is stuck you must put a dinogate behind it to trap it and then knock out. (hope this helped and "If" I win could it be an Xbox voucher, thanks.)
You can use the normal darts or arrows. But the fastest way to tame a Rex .
Get under its belly as fast as you can and rub its belly, instant tame :) all you new player try it out and you'll be riding like a king like us vets !!
Create a 3x3 mobile taming pen 3 walls high on a raft with a Dino gateway on one side and ramps on the other. Use a flyer to lead it up the ramp into the pen then move it to a safe area to tame. I got 2 150s without a single issue.