Easy way to tame (Works if you have Argentavis or Quetzal):
Step 1: Go to the swamp with your Argentavis or Quetzal and search the area for Dimetrodon. Once one is found, pick it up and carry it somewhere safe (recommended: The Dead Volcano, or your base. Just make sure everyone is set to passive).
Step 2: Let it wander around for a while. Knock it out every so often to check on its hunger. If it is not hungry upon knockout, let it wake up and heal for a while. Repeat until it is completely starving.
Step 3: Once one of your checkups on the Dimetrodon via knockout reveals that it is completely starving, grab whatever meat you have as fast as you can (prime meat if its a high level). The starving status causes the Dimetrodon, as well as all other creatures tamed via knockout, to constantly eat every second until they are either tamed or not hungry anymore.
I did all of this myself at the Dead Volcano, which it arrived there via my male Quetzal, Flappy. Argentavis can also pick them up for delivery. Hopefully this helps.