Discovered this by accident, but a Sinomacrops will scream at and scare away all the mantas that surround the Basi. Not required, but the easiest way I found was to set my Sino to have "auto scream" enabled and "scream requires aggro" disabled. When you get semi close it'll scream which will make all, or most of the Mantas flee for long enough to feed the Basi. Hope this helps and happy whaling!!
Ride dolphin or manta, water creature won't attack you while riding a water dino, then go near basilo feed it, Don't unride or you'll see your self dying, put food on your hot bar then click it when near basilo u can feed basilo without unriding. Up! So no noobs will be eaten by manta or megalodon lol
Basilosaurus are found in the oceans surrounding herbivore Island
Basilosaurus are passive tames that arent aggressive towards you at all and they are carnivores so feed them meat.
Basilosaurus are surrounded by mantas and they will attack you when you feed or attack the Basilosaurus, there are plesiosaurs,megalodons,leedsicthis and tusothuthis where the Basilosaurus are,
Basilosaurus are slow so you're underwater mount can keep up with it.
Abilities when tamed:
Basilosaurus are immune to jellyfish stings and eel shocks and cannot be grabbed by squid, they produce oil in there inventory but it spoils, they regenerate health fast near the surrface, they can shoot rainbows out of their blowhole using one of their attacks
Disabilities when tamed:
Basilosaurus lose health when they are in deep water
Okay, so I saw one in a river opening on Crystal Isles. I thought the mantas attack you as soon as you go near. So I slowly approached the tail near the river bank. The mantas didn’t agro on me, I thought I was just far enough away. No. Oh no no no noooo. It turns out the mantas ATTACK the second you feed it. Please don’t do what I did haha
There's a river on the west end of the redwoods that's considered ocean so they'll spawn in it. Just gate off each end to trap the basil, kill whatever's in the water, and you don't even need a water tame.