Whales are marine mammals that belong to the order Cetacea. Whales are divided into two suborders: the baleen whales are filter feeders with huge comb-like structures (baleens) instead of teeth. This first suborder includes the largest animals on earth, such as the blue whale and the humpback whale. The second suborder of the toothed whales includes sperm whales, and Orca whales (which are actually dolphins). The common name 'whale' does not include dolphins, however, they all evolved from the same terrestrial mammal called Pakicetus.

All whales have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings called blowholes, on top of their heads. Due to their ancestry, whale morphology is an excellent example of the evolution of homologous structures. The whales hindlimbs are reduced to a pelvic bone that has no function for motility anymore.

Humpback whale jumping in water.

Figure 1: Whale jumping out of the body of water.

Human hunting of whales has brought many species to the brink of extinction.