I use to go to the beach, swim out a little bit until it agro. Then swim to land again and the cnidarias are following me to land. When it I am standing on land it stops. Then I can easily kill it without taking any damage.
For the people complaining about the iguanadon being one of the highest rating, its because of aberration. The iguanadon harvests a bunch from the red hallucinagenic mushrooms that are unique to aberration.
This is a amazing thing! Like really, For example when you tame a Wolf, you can feed it biotoxin and it Will increase the torpur up to 80. Thats how i tame most animals, though its easier when you're in a tribe, they might have baryonix's or even a basilisc! It'll be much easier when you have a tribe and many biotoxin, trust me.