In real life these were vicious carnivores that would have killed and eaten a human on sight and lived mostly in shallow waters and swam up rivers looking for food they were also twenty metres long, good thing the developers didn't make them more realistic or crossing rivers would be a dream until you have a flyer.

I keep thinking I hear Lugia. Also this thing kills tusos and alpha megs easy. Only advice for alpha megs is to stay near the surface of the water for healing boost while fighting and when the Meg tries circling to reposition itself just stay where you are and let the stamina be restored. It’s not just the mouth that does damage, it’s the hips too. Might name my next one Shakira!

If one spawns 3 mantas will automatically spawn near it, and start following it and group up near its belly. If you feed a basilo every ichthy/megalodon/manta near the basilo will automatically take one damage (the game inflicts the damage as if it was inflicted by you), then get angry at you and start chasing you. You should then run away if your tame can't kill the mantas quickly because mantas do more damage through armor like saddles than other creatures, so your tame's health might get shredded in seconds.

I have a tip to share on how to deal with the Mantas and Megalodons that are surrounding the area where the Basilosaurus roams. Make sure to go with a high level Baryonyx because of its underwater stun ability and damage in general. Make sure to damage one manta so they will all start following you. Then lead them away and kill them. Killing the Megs is easier in my opinion, plus you can gather them all in one place, stun them and start killing them!

On The Island, I always find very quickly in the waters near South Beach, around 65 longitude. They're generally not difficult to spot, due to the swarms of Mantas and Ichthyosaurs. Though it's only happened to me once, I've found one stuck between a large rock and the beach itself, at the south edge of the rocky penninsula near 50 longitude.