Why Did Some Mammals Move Back Into The Ocean?

Every branch of life has its beginnings in the ocean, but the majority of us chose to remain on land. Manatees and other marine species, however, didn't appreciate the agreement and opted to return to the water.

It doesn't make much evolutionary sense for them to have done that, therefore biologists are at a loss as to why. Early whales, for instance, would have struggled to even swim underwater since they had limbs and body types that were long developed for surviving on land. All marine mammals still need to utilize their lungs to breathe, just like all other animal species found on land, hence they no longer possessed any organs to help them survive underwater.