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
Everyone says how good the Rex is. And yeah. I'm gonna suck this guy off too. The Rex is basically ARK's right of passage of you want to defeat the bosses and get to the fancy Tek. If there was a tier list for ARK's creatures from S to F, I would have to make a God tier for it and some other dinos. However, I am gonna stop saying my praise there. Despite all the good in the Rex, I feel as if it is the most... generic of the apexes. It has a huge health pool, but the Giga's is larger. It is decently fast and does alot of damage, but the Spino does more damage, and is faster and more agile. The Rex has its pooplock roar, but the Yuty has its fear and courage roars. Now, this isn't me hating on the Rex. I love it as much as the next guy. But I feel as if it needs to step out of the spotlight for a bit to give others the chance to shine.
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)