Sixty-two Attack Strageties (Rex): The Rex is a good Tame, but is also a good kill. Read my TWO attack strategies on how to kill this ruthless beast.
1) Bring two baryonx with 2590 hp and 296 damage. While mounted on one, whistle TARGET for the first baryonx to attack from FRONT. Then sneak behind the Rex. Attack on one side while the other attacks the front.
2) Get a bullesta and ammo and chain bola. Bola a Rex (this can be used for tame) and then go aggro on the beast. Send animals, shoot with ammo, and, a great tip, use arrows on it from a high, HIGH rock to practice targets!
Lure alpha trex into the middle of the ocean by carrying a herbivore app in the talons of an Argentavis (I used a Parasaurolophus) then use an aquatic mount like Beelzebufo or megalodon to bite the alpha Rex to death, with the water mounts increased speed underwater it can easily evade trex attacks