When I was starting the game a saw a iguanadon and wanted to kill it because I needed meat so I ran up to it and poked it with my spear and died, I respawned and saw a rock so I hoped on it and I didn't slip off so I ran up to the iguanadon and poked it again and bolted to the rock and hoped on and started poking, after a while the iguanadon started to run so I hoped of the rock and killed it, the next day I found out that iguanadons have infinite stamina and was so mad at myself for not taming it.
I tamed a highlvl one one easy with some crops fron the fjördur. After exploring the areas around me i found a 55 Alpha raptor. It took a while but i easily killed it. Of course i never would try Alpha rex.