if you know what you're doing, taming a rex doesn't require a trap. i recommend taming one as soon as you unlock tranq arrows--shoot from a cliff or ledge if you can, but if you have stamina you can just run and shoot. the saddle doesn't unlock until late game, but you'll have a powerful bodyguard until then. if you're hunting with your rex, it'll level up, and by the time you DO get the saddle, it'll be shredded 🔥