Uh I just found something quite OP about a basilosaurus. It has 2400 base health, while the mosasaur has 3600 base health. However, a Basilo gains 480 health per point (wild) while mosasaurs only gain 432, meaning that, at higher levels, a basilosaurus will usually have more health than a mosasaur of the same level. The only tameable creature in the ocean with a higher health than a basilo at higher levels is a tuso.