Dolphins 16 Month 2012 Calendar. Dolphins are essentially aquatic mammals that are closely related to both whales and porpoises. It is thought that there are approximately forty different species of dolphin which vary in size from 1.2 meters to 9.5 meters. These mammals are known for their intelligence and their highly sophisticated underwater radar. They can be found all over the world and mainly stay in the shallower seas of the oceans continental shelves. This marvellous calendar is sure to delight lovers of these popular mammals.