What type of animal is a Blue Whale?

The Blue Whale is classified as a mammal because it shares key characteristics that define this group. Mammals are warm-blooded vertebrates that breathe air through lungs, have hair or fur at some stage of their life, and most importantly, females possess mammary glands that produce milk to nourish their young. Blue Whales, being marine mammals, exhibit these traits even though they live in the ocean. They breathe air through their blowholes, give birth to live young, and nurse their calves with milk. This classification sets them apart from fish, reptiles, and amphibians, which have different physiological traits and reproductive methods.

Understanding that mammals can inhabit a variety of environments, including aquatic ones, helps clarify why the Blue Whale, despite being fully adapted to life in the ocean, is a mammal rather than other types of animals.