Sooo easy! I tamed one BEFORE I unlocked the saddle! Just get a ballista burret, load it with trang arrows, and shoot a bronto! It will attack you, so hide behind a appropriate rock or cliff and shoot again, and again, and again! When it runs from you, continue shooting. It will knock out and feed it mejoberries!
These are the easiest tame ever, just get far away, shoot it with a crossbow repeatedly, when it gets close run and shoot, then boom u knocked out a brontosaurus (I literally have 5 of them that’s how easy they are to tame) please