To knock out these easily, you should use an ichthyosaurus and crossbow with tranq arrows. You will need a lot of tranq arrows. Stay on the ichthyosaurus so the dunkleosteus won’t attack you. Don’t let anything dangerous get in the way. Hope this helps.
Very easy to tame if you know what your doing. First tame an Ichthyosaur. Then grab a crossbow and some tranq arrows and find one and knock it out. It is not be able to attack if you are on the Ichthy. As you are taming it, be sure to remain on the Ichthy unless feeding narcs, so other creature don’t hurt you. Vote up if this helped