At the beginning of the Eocene, about 53 million years ago, a group of land mammals began their amphibious life. The evolution of cetaceans (from the Greek ketos, sea monster) represents one of the best examples of macroevolution ever documented by fossil records. Pakicetus, one of the earliest whales, looked quite different from today's whales. It was in fact characterized by squat legs and thick fur. Following a slow and continuous evolutionary process, these mammals became skilled swimmers, conquering the oceans, from the cold polar seas to the warm waters of the Gulf of Mexico. The most majestic representative of this group is undoubtedly the Blue Whale, which at over 30 meters in length and 190 tons in weight is, in terms of mass, the largest known animal ever to exist.

< em> Balaenoptera musculus (EN, Endangered IUCN Red List), just like its terrestrial ancestors, breathes out of the water and exhibits a vertical movement of the spine. Thanks to a series of evolutionary adaptations, such as the loss of hair and hind limbs and the modification of the front ones into fins, his body has become perfectly hydrodynamic. Sight and smell are limited, but hearing is sensitive. In fact, it produces infrasound, low frequency sound waves (& lt; 20 Hz), characterized by the ability to propagate over long distances and used for intraspecific communication and navigation.

We will never have the good fortune to admire the mammoth specimens that whalers observed in past centuries during their hunting trips. Decimated by an increasingly intensive fishing, aimed in particular at the largest individuals, the fin whales have reduced both in terms of number and in size. Only in 1966 the International Whaling Commission (IWC) banned the hunting of these cetaceans. Today the populations would finally seem to increase, even if the species remains at risk due to more current problems, such as the deterioration of habitats, impacts with boats and the decrease in the availability of krill, as a result of climate change.