To tame diplocaulus you have to make sure you have a lot of fish meat or normal meat. Then if you are taming it in the wild you should build a small little area with walls or spike walls around the perimeter in case anything tries to attack it because diplocaulus are usually a top ten prey item for most things in the swamp. Finally find a diplocaulus and then rather take some time to push it into the small area protected by walls or just get a pteranodon ride the pteranodon and pick up the diplocaulus and then drop it into the small area then tranq it, feed it, and tame it. Up if this was helpful

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