No your options if u do not have a quetzal to use and knock it out find a cliff and drag the Rex over with either a Dino of yours or hit it with a tranq if u are high enough u will get to shoot it without home hitting u
To tame one make a trap out of wood gates, stone if a higher level, that looks like this (from above) /_\ afterwards, put a large bear trap in the middle. Then, using one last gate, fill in the gap on the top. (Obviously you can rotate the trap making the gap on the bottom or top.) Afterwards just knock it out! Good luck taming! 🦖
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.