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.
How should I handle these guys on gen2? To tame these guys is simple, it’s a normal knockout tame but in the water, they are the best for begging (because unlike the basilosaurus they don’t have swarms of many’s attacking them.) they gather resources and a decent leveled one can mostly survive the taming process for a tusotuethes, although I am having trouble taming them in genisis 2