I tamed A bronto once by tranquillizing him.

So basically a had a crossbow and a bunch of tranq arrows, and I was thinking about taming a bronto. So I used Dododex to see how many tranqs I needed. However, I forgot to put in the level. I got my some more tranqs, and started shooting. A bunch of rocks near my base made the terrain uneven which actually helped a ton. I also had 300 max hp. Anyway after I used the amount of tranqs that should have KOd him, I got worried. I did have some extras, but I quickly got down to my last arrow. I was sure I was gonna die, but I still shot my last arrow. The bronto kept attacking but I was saved by the rocks. Then, the final effects of the last arrow finished and he started running due to high torpor. I ran after him and clubbed him until he fell unconscious, and tamed him without another problem.