I recommend for taming a Rex efficiently and getting hold on them as they run and chase you is with an Argentavis. The Argy has all the things needed such as, a way to keep the distance from the creature/Rex, stamina, weight capacity, movement/movement speed, and if you get An Argy to a high enough level they can slaughter a lot of creatures in Ark. Be sure to put your Argy on passive and not to follow unless you want your creature your trying to tame dead.