Without doing the usual thing of telling a massive story, I'll only say this. I almost tamed a lvl 145 Rex, but I made some mistakes.

I only took as many narco arrows as I needed, when I should of brought 3 times as many, for the shots I missed, and the times when I had to run away and come back, giving it's torpor time to wear start going down.

I should of left at the crack of dawn, or sooner. I fought it for so long, I was still fighting it at midnight.

I should of brought a backup Crossbow, or 2. When my crossbow broke, I had to sprint back home to repair it, which cost me valuable time, torpor, and lead to my final mistake.

I should of kept a better track of where any nearby alphas or other Rex were. I almost lost it when it ran in the direction of an alpha Raptor and it's pack, but managed to kite it away, and later in the evening, either by luck or instinct, it fled to the safety of a nearby 150 alpha Rex.

I eventually had to give up after using 60 more arrows than I should of needed, needing to replace my crossbow, chasing it around till midnight, (at which point I was having to switch between the torch and crossbow to shoot blind) and chasing it towards an Alpha Rex.

Next time, I'm leaving before dawn, bringing 3 crossbows, 300+ narco arrows, and maybe killing the alpha Rex and alpha Raptor first (though honestly, I'm scared to try, and lose my best dinos. Why did there have to be a level 150 alpha Rex so close to my starting zone base?! And a level 145 Rex not too far away from it, teasing me with the chance to have an OP Rex so early into the game)