If you wanted to tame a level 300 bronto with only your fist and mejoberries you would need to punch it 11785 times and feed it 1334 mejoberries over the course of 8 hours and 15 seconds. This could in theory work quite nicely if the bronto got stuck from some rocks, until you realize the amount of recoil damage from punching. But this isn’t over yet, if we were to create a small stone structure with a bed inside we could respawn infinitely allowing us to punch the bronto with our many lives. We would also put some spare beds in the structure just in case one breaks or stops working. Now I have wasted your time and mine by typing this. But at least you know.
You can use tranq arrows and perch up on a cliff and fire at it from there. It will be stuck on the rocks and will not be able to attack you. Do not hit it on a lowered platform. Go higher enough so that it can't hit you. Then shoot it until it goes a bit far so you can confirm it's fleeing. Then go nearby and keep shooting until it falls unconcious. Hope this tip helps.