If you want to tame it, then make sure you have cannons or boulders to knock it out as tranq arrows and darts will not do. Aim for the head and once down, put the saddle on it and you’ve got a titanosaur. I do not recommend for swimming deep as they will die.
If you try taming these guys, tame a Quetzal first and equip it with a platform saddle. Then, put 2 storage boxes on it and a cannon. Make sure you make LOTS of cannon balls. Then, shoot the titan in the head.