Why are whales so big? 

Given the vast expanse of ocean on our planet, compared to the somewhat limited land space, you may be forgiven for thinking animals in water have the potential to grow bigger and bigger.  Yet new research has revealed that mammal growth is more constrained in water than on land, and we may have already reached the maximum.

Source: Why are whales so big? Study reveals secrets of giant mammals and why nothing will ever be bigger than a blue whale | Alphr