I was venturing into the woods one day with my carno,my friend,and a Rex named billy (lvl 67 at the time).Then we came across a Hell Rex f**king lvl 185.We were trying to check it's level when it killed my friend and the carno.But billy came in and beat the the hell rex.So if u are trying to tame a Hell Rex this what not to do.
I once tamed a 131 rex, it came out as a 172. I had tamed it in the redwoods on ragnorock and was riding it back to base when I saw what I thought was a saber tooth in a tree. It pounced me off my rex and killed me. It was level 110. I then learned after loosing my rex (who was on passive) that thylacoleos are no joke.