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.
I knocked out a lvl 110 with an engram lvl slingshot with A LOT of repairs and stacks and stacks of stones when I was a level 10 character. It was my first tame of that game. I stood on a ledge where he couldn’t get me and ran him down when he fled!
If your aiming to take down a bronto get as many ranged weapons as you can and get as many ammo as you can firearms deal reasonable damage but the problem is you'll need a lot guns and bullets for this if you can't fight them run away whatever happens DO NOT GO TOWARDS YOUR HOME it'll destroy everything there and kill all your tames instead swim over a river it'll be discouraged to hunt you down or just get on a raft and bail please note that brontos will still be hunting you if your not actively piloting the raft