When trying to kill a bronto, get one normal bow, and about 50 arrows, and you should be good, the one thing is to run into a forest and every once a while shoot it until it starts catching up, then just keep running, also Spears come on handy
I was taking 11 dilos, all between lvls 5-40 to try to explore the south cave in The Island. When I looked out from behind a rock, I saw a big blue egg sitting in an opening. I picked it up, and the nearby bronto did nothing. I got hungry, and bronto eggs restore 100 hunger, so I ate it. THEN the bronto got mad. It chased after me and my dilos attacked it. It killed 6 of the dilos before I finished it off with a regular bow. Got the trophy and named the five remaining dilos, including my strongest lvl 38, Bronto Killers 1-5
I always tried to find out the personalities of the different dinos, and that caused me to flourish for a long time without trouble. Though the brontosaurus aggravates me greatly. While the Compy is the playful, curious dino who just wants to see if you have treats, and the Velociraptor is viciously loyal, going to great lengths to protect you once tamed, this bronto is the complete opposite. I always found them the arrogant ones. When i leave my home to gather resources, one will stop what its doing and cut in front of me, just daring me to do something about it. If you try to make them your friend, they snack you with their tail (which im not that bothered about, i was asking for that one.) they are the ones who seem to expect all of us to bow to them. One day i will tame a nice huge pack of like 70 dinos and murder a few of these jerks. Then maybe i will tame one or two.