The marine world has extraordinary animals, including cetaceans . These beings, mostly of enormous dimensions, are mammals that inhabit the waters of planet Earth and that have always aroused the interest of science. Notable are sperm whales and dolphins, species of proven intelligence with unique physical characteristics. The fascination they arouse has reached the cinema, although it has also harmed them, since some have been diminished by the action of man, until they are placed in danger of extinction.

What are cetaceans?

Aquatic animals that make up the order Cetacea are called cetaceans They are considered placental mammals, because they have a placenta. It is said that it was Aristotle who coined the term “cetacean” , which comes from the Greek “ketos” , and refers to “sea monster” . This term is used to name the species of water that could breathe through their lungs. They are similar to fish, but have unique shapes depending on the type. Whales, porpoises and dolphins stand out.

  • Source
  • Evolution
  • Types of cetaceans
  • Species
  • Characteristics of cetaceans
  • Habitat
  • Feeding
  • Reproduction
  • Cetaceans in danger of extinction
  • Examples


The origin of cetaceans dates back to about 50 million years. They developed in what was formerly called the ocean or sea of ​​Tethys. Initially, they were terrestrial mammals and little by little they adapted to the aquatic habitat. This terrestrial origin is based, among other things, on the ability of cetaceans to “absorb” air from the surface and the movements they make when swimming. Its spine “shifts” in a way similar to that of mammals and not that of fish.


There are various theories about the evolution of cetaceans. One of the most accepted is the one that links them to the Mesonychians, particularly those of the Mesonychia form. These extinct animals were angled carnivores similar to wolves, but with very large hooves . Their triangular shaped teeth resemble those of whales. On the other hand, after the study of several DNA samples, in the 90’s, it was determined that the evolution would come from artiodactyls, specifically from a group called Hippopotamidae. Other ancestors related to cetaceans are: Indohyus (Raoellidae), Pakicetidae (Pakicetidae), Ambulocetus (Ambulocetidae), Remingtonocetidae (Remingtonocetidae), Protocetidae (Protocetidae) and Basilosaurids (Basilosauridae).

Physical evolution

From being terrestrial animals, cetaceans became semi-aquatic, and then fully aquatic. Its physical structure was changing to adapt to its new condition, but without being completely transformed. For example, the front legs became fins , but inside the bones of their predecessors remain. Subsequently, the rear shape became a “horizontal tail fin.” This type of orientation makes it easier for you to swim to the surface to get air. For this they also developed a hole (some have two) in the upper part of their bodies to breathe. The coxal organ (pelvic bone) that they possessed became vestigial, whose current function is to anchor their genital organs.

Types of cetaceans

There are several classifications for cetaceans, however, they are usually classified into two broad groups:

  • Los Misticetos: In this group the whales are located. There are fewer of these species of cetaceans and they are the most striking and exuberant due to their enormous size. The fundamental characteristic of mysticetes is that they lack teeth and instead have beards. They often inhabit icy waters. Many of its species have been unseen for decades. They are carnivores despite being toothless. Beards are made of keratin. They are very strong and filter the water that escapes from their mouths and at the same time they capture the animals they consume to feed themselves.
  • The Odontocets : In this group are the cetaceans that have teeth. The size of its species is variable, ranging from sea cows, through dolphins to orcas. They all have a dorsal fin and are distinguished by having a very swollen forehead. This is because they have an organ called a melon that acts like a sonar. It provides them with an echolocation. With the melon the odontocetes emit sounds that collide with the bodies and objects and when the sound waves return they allow them to perceive the location of the things that surround them. Like the mysticetes, they are also carnivores.


At least 80 species of cetaceans have been counted. The best known according to their type are:

  • Mysticetes
    • Pygmy right whale (Caperea marginata)
    • Greenland whale (Balaena mysticetus)
    • Pacific right whale (Eubalaena japonica)
    • Fin whale (Balaenoptera physalus)
    • Humpback whale (Megaptera novaeangliae)
    • Blue whale (Balaenoptera musculus)
    • Gray whale (Eschrichtius robustus)
  • Toothachets
    • Pilot whale (Globicephala melas)
    • Common killer whale (Orcinus orca)
    • Dusky dolphin (Lagenorhynchus obscurus)
    • Southern dolphin (Lagenorhynchus australis)
    • Striped dolphin (Stenella coeruleoalba)
    • Atlantic dolphin (Lagenorhynchus acutus)
    • Bottlenose or bottlenose dolphin (Tursiops truncatus)
    • Vaquita marina (Phocoena sinus)
    • Common porpoise (Phocoena phocoena)
    • Spectacled porpoise (Phocoena dioptrica)
    • Pygmy sperm whale (Kogia breviceps)
    • Sperm Whale (Physeter macrocephalus)
    • Dwarf sperm whale (Kogia sima)
    • Blainville’s beaked whale (Mesoplodon densirostris)
    • Gray’s beaked whale (Mesoplodon grayi)
    • Gervais’s beaked whale (Mesoplodon europaeus)

Characteristics of cetaceans

Although the aquatic universe is home to a large number of cetacean species, there are characteristics that identify them. These are:

  • Most have a large body mass that allows them to have a high capacity to store and use oxygen, which prevents hypoxia.
  • They have a large reserve of fat that prevents them from suffering from hypothermia when diving very deep.
  • Its trachea is much shorter than that of terrestrial mammals and does not communicate with the esophagus, but with the blowhole. Through that hole they breathe.
  • Their heart diverts blood to the lungs, brain, and muscles when they swim.
  • His body is hydrodynamic. Its body shape makes it faster when swimming and prevents many of the evils caused by sudden pressure changes.
  • They lack vocal cords. They communicate, locate and hunt by echolocation , thanks to the fact that they have a special organ called melon.
  • The young are born with fur, but they lose it months later.
  • They are endowed with caudal and pectoral fins. The number of fins varies with the species.


Cetaceans are found in the seas and oceans of the entire planet Earth . There are species adapted to both cold and tropical waters. Some species also inhabit freshwater rivers , such as the pink dolphin and the Ganges dolphin . Almost all cetaceans migrate annually from their areas where they feed to others where they have their young.


At birth they feed on breast milk . When ready, mysticetes (barbados) usually feed on krill, seedlings and small fish. Odontocetes hunt larger fish and almost all kinds of marine animals. They chew very little, they usually swallow their prey almost whole.


They reproduce sexually and by internal fertilization. Because they copulate in water, their genitals are designed so that fluids don’t leak . Males have their sex organs in a slit and females in a cavity in the abdomen below their kidneys. It reaches reproductive maturity between 6 and 13 years of age. Their life expectancy is (according to species and size) between 30 and 80 years. Gestation also changes from one species to another. For example, the orca spends 16 months in the state and the bottlenose dolphin has a calf after a year of pregnancy.

Cetaceans in danger of extinction

Statistics from 2008 indicate that a quarter of known cetaceans are threatened with extinction. Of the figure, 10% are classified “Critically Endangered . ” However, the statistics could be more serious, since it must be considered that there is very little data on half of the cetaceans that we are aware of today. Indiscriminate hunting, collisions with boats, entanglement in fishing nets, deterioration of the habitat, acoustic alteration and loss of food are among the causes of the evil.


Among the threatened species, the blue whale stands out. This beautiful aquatic animal is considered the largest that has ever existed on our planet. It can reach up to 33 meters long. The largest known dinosaur measured 26 meters.

The fin whale (Balaenoptera borealis) is another on the dire list. Although their massive hunting was halted thanks to various protection measures, their capture by man still persists.

In the category of “Vulnerable” are the black porpoise (Neophocaena phocaenoides), the dolphin or dolphin of La Plata (Pontoporia blainvillei) and the Irrawaddy dolphin (Orcaella brevirostris).

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