Dododex
ARK: Survival Evolved & Ascended Companion
Rate Tips
Baryonyx are really good for taming these! Once they start running, a Bary is fast enough to chase them, and since it allows rider weaponry you can keep firing. Since Dunkleos are pretty chunky, it's hard to miss a shot on them even while moving. Aim anywhere except the head. I tamed a 135 with a harpoon launcher loaded with tranq spear bolts, SCUBA gear, and my 276 Baryonyx I use for caves.
For mobile players: From experience they won't attack you on Ichthyosaurus (which also allows rider weaponry,) so you can chase one down and tame it with an Ichthy and a crossbow. Harpoon launchers don't exist on mobile.
For both versions, you could also use a Tusoteuthis and grab/hold the desired Dunkleo, but this takes a long time since they have high torpor and I wouldn't recommend it. You could also be interrupted by other hostile creatures such as Megalodons or Plesiosaurs if you do this. If you don't press attack, the Tuso will inflict torpor but no damage. You'll need more tranquilisers than you think.