A little difficult to tame but definitely worth it! I 100% recommend getting a plesiosaur I tamed a lvl 10 and its stats were very high! But if there're more than one make sure to kill one or separate them!
The dossier says they're passive to humans and only attack little fish THIS IS NOT TRUE THEY WILL EAT YOU AND THEY TEAM UP WITH ELECTROPHORUS TO KNOCK OUT YOUR MOUNT AND SHARE IN THE FEAST AFTERWARDS!!