Easiest way to take down one of these: get a cross bow or a bow if ur not a high level 2, I recommend using tranq arrows to knock out one of these and use a melee weapon to not waste ammo and also look for a cliff that the bronto can't reach and get top of it now shoot it with tranq arrows and kill it while it's KOd might be cruel but hey, you just got yourself free prime meat or just tame it if u want
Tip : Don't put wooden / metal spike walls near your base if you live in an area with a lot of sauropods.
this is why : since they like to wander around, There's a chance that they will get stabbed by the spikes when they wander near your base. And they will get mad at you, kill your tames, and wreck your base.
so please be careful and think twice before setting up spikes near your base.
Do not try and take its egg i did and next you know i got chased to a cliff and then I jumped down then I got stuck in between two rocks then two seconds later I was a pancake and the egg wasn't even fertilized a like a day keeps the killer bronto away.
In early game i found a ascendant bow then i started killing brontos for leveling up fast just grab a explorer note get on a high cliff where it cannot reach you and keep shooting and also a good source for hide (i play on mobile so i got the ascendant bow by pursuits early on in game >lv20)