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
A level 2 Bronto was attacked by a dilo and the bronto hit me by accident, and my lvl 20 trike went after it, it killed me, and it killed my trike when I was dead.(I was a noob at the time). Overall: Don’t go near it while it is fighting something when you are a noob.
Beware of these if you are starter. They are not aggressive unless you hit them first. If you are a starter, DONT even think about it. A while ago, it trashed my thatch house, and tried to kill my dodos, dilophosaur and my parasaur. If you want to get rid of it, get across a river, or go further away from where you are, and then shoot it with a ranged weapon. When it comes to you, just quit and rejoin, and it wont disturb you again. They also stomp around, shake your screen and are very loud. They have loads of health and do good damage, and are a great tame if available.