Well if you are on mobile and dinos of lvl. 30 rarely roam the island, just cook a Dodo Kibble (You get a pursuit named 'Fresh Breakfast') Just put a Dodo egg, some rokcarrots(You can mostly find them on small hills to big mountains, and to be specific, in jungle ferns and to be even more specific, they thrive near mammals). Then craft a cooking pot and put filled water skins, then add some mejoberries and some fiber. Also add cooked meat. Then light the fire. You get your Kibble. Go near that dolphin and feed it. It will get tamed in one or two kibbles (if it's under lvl.30)

More Ichthyosaurus Taming & KO Tips