I say this dude in valguero at a beach, it was busy killing a sauropod (giant long necked herbivores) and I walked over to check it because my bro said it was not a Rex, it was a Rex and it started chasing me, I ran like heck and crossed a body of water so it could not get me, THE END
You can use the normal darts or arrows. But the fastest way to tame a Rex .
Get under its belly as fast as you can and rub its belly, instant tame :) all you new player try it out and you'll be riding like a king like us vets !!