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.
This is like the Argy of the sea. It can hold an outstanding amount of weight and can do a lot of damage. Only issue I have with it is the speed and stamina so focus your level ups on those. Also, bring a lot of tranqs since it took me 175 arrows for a level 125 (don’t aim for the head).