It is a fact that the blue whale is the largest of animals to have ever existed. The size of the blue whale has baffled scientists for centuries. However, it is theorized that since the blue whale is a marine mammal, it would make sense that it would be huge in size. This theory is based on the idea that marine mammals will be allowed to grow large in size due to buoyancy than if they lived on land. But, this idea has not been accepted so simply. The reason why many marine mammals are large in size may be because of energy conservation. Ocean water is colder than marine mammal body temperature (ex. whales, manatees, and seals) and water is better than air in conducting heat away from an organism.