I have killed so many megalodons, trikes, stegos, carbonemys, sarcos, and even theris. They are deadly things. If you can get one and get a saddle for it, then nice job, you have an oceanic friend that can easily harvest fish meat and normal meat, also keratin. Another thing is that nothing seems to agro on you while your on it, although, sometimes they fight back, other times, the creature won’t attack. For example, a therizinosaurus. Just make sure not to attack any glowing jellyfish.
Please don’t be fooled. All these people saying they won’t get attacked is a feature on MOBILE ONLY. Even on pc or console, there’s still good tames. While they’re not great harvesters and don’t have much health, food, or stamina, they're easily capable of outswimming everything in the ocean. Those stupid megalodons don’t stand a chance.