Are you sure nothing will aggro on you unless you attack it? I have been killed by 3 jellyfish not knowing what they were then I instantly moved all the games I had away from the water and my I think my 1st or 2nd tame which was the lizard that you dont knock out to tame and its great for wood, fiber, and thatch collection died because of jelly fish, I have almost been killed by compy, killed by dilos multiple times and have been saved by parasaurs a few times and saved by a trike once. That doesnt really say nothing aggros unless provoked on mobile. [ all of this was on mobile because I cant get it on pc ]
On valguero, on the beach next to the chalk hills, there are a bunch of dead ichthy's. You get hide, spoiled meat and organic polymer from harvesting them. It's very useful for narcotics, ghillie armour and fabricated weaponry and structures.
Go to herbivore island (The island) at the right bottom. Go to map if unsure. Look around and you should find some itchyosaurus. But be careful, in the water they look like sharks, don’t mistaken them as sharks they have a pointed snout. Like if you found it helpful! :)