Many of the people here are saying to just go and shoot them. Just do it. I would agree. When if tamed mine I was scared that it was to fast, but you can easily beat it while sprinting. shoot it, run away, repeat. easy. Tranq arrows will work fine just bring enough. And be prepared to make more just incase.
The way I do it as I use a rock drake from aberration it’s Jump and glide can get me away quickly and the fact that I can shoot at the Rex while still on my mount work great. The invisibility of the Rock drake also allows me to get that crucial first shot without it bum rushing me
I was going to tame a spino and successfully I tamed it by shooting from a cliff nearby then after putting the food I saw a rex closely and then with my bryonx I again climbed the cliff and shoot a few more tranc arrows I was not planning to tame it but since it went unconscious I used 3× smoothing bam and I got my spino and rex at the same time and I only used 44 tarnc arrows which also included a few misses. And now I not afraid of any dino on the island.
Dont be scared of them, get a flyer and make sure to have a high health and stamina, fly at him (make sure its only one or your dunso) and let him take a bite of your flyer once in a while then lead him into a square wall of dino gates with a trap in it. Once he is stuck quickly close up the open gate, laugh at him and shoot him (alot)
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.)
The 3x smoothing bam works like magic and if don't have enough amber just wait and use bio toxins I have tamed with both ways just the thing you should be worried about is tranc arrows you must have enough of them atleast 30 to 35 since non of us are 100 present accurate all the time.