Anatomy

The origins

65 million years ago, at the time of the dinosaurs extinction, Cetaceans were terrestrial animals like all mammals. The extreme competition for food given by the disappearance of primary predators started that evolutionary process that led to the birth of the first semi-aquatic ancestors of dolphins and whales, the Archaeocetes.
Some important adaptations to life at sea soon appeared. The Protocetes in fact were endowed with an elongated body, in which the fur had almost disappeared. The hind limbs, now useless for walking on earth, were still present but considerably reduced. The head appeared elongated and the nostrils, not yet converted into a blowhole, began to move back from the apex of the muzzle to better adapt to breathing in the water.
Twenty-five million years ago, the Archaeocetes definitively gave way to today's cetaceans: Baleen Whales and Toothed Whales.

The body: swim and apnea

Cetaceans are mammals perfectly adapted to aquatic life and they don’t have relations with the land: reproduction, development, feeding, hunting and play always take place in water. The only remaining link with the surface world is breathing.
However, the apnea skills do not derive from the large size of the lungs. Rather, they derive from the amount of oxygen-using proteins present in the blood and muscles (hemoglobin and myoglobin). On surface, the cetaceans do a series of close breaths and then dive, emptying their lungs with increasing depth. This is an indispensable natural adaptation. This allows to reduce the presence of gas in the lungs, which over a certain pressure would cause trauma. The diving ability is further improved thanks to the presence of floating ribs, which make the rib cage considerably adaptable to high pressures. In the case of the Sperm Whale these adaptations combined with the spermaceti find their maximum expression.
Cetaceans can reach speeds of up to 40 and 50 km / h, thanks first of all to the tapered and hydrodynamic shape of the body. Furthermore, the natural adaptation has drastically reduced the protruding appendages and strengthened those useful for swimming.
Thermal insulation, essential not to take energies to swim and apnea, and originally ensured by the presence of fur, is now guaranteed by a thick layer of subcutaneous adipose panniculus, called "blubber", which in some species of whales even reaches 50cm thick and 50% of body weight.

The echolocation

Researchers soon realized that the animals were able to spot obstacles and preys even in darkness or in murky waters. Eco-localization consists in the ability to use self-produced sounds, in the form of "clicks", to capture information on objects in the surrounding environment.
The clicks, real sound waves, are produced in the larynx. The air is compressed producing vibrations, and from here they are directed towards the frontal area of ​​the head where the "melon" is found, a sac in the head of the Odontocetes (toothed whales) that contains a particular fat capable of acting as a megaphone to amplify and direct the sounds. So, the beam of waves is launched into the environment and hits the objects that are in its path and is reflected, returning to the animal that produced it. Here the echo is received through the vibration of the mandibular canal, which acts as a receiving antenna and transmits the sound to the ear. Then, the brain can analyze the sound waves received and deduce all the information contained in them, such as the distance of the objects, their shape, size and even their structure. It has in fact been shown that a bottlenose dolphin in total darkness is able to identify a small ball with a diameter of 2 centimeters at a distance of over 72 meters.
The head of the Odontocetes (toothed whales), like the sonar of ships and submarines, represents a perfect apparatus for the emission and reception of ultrasounds. It is therefore not surprising that many of the military technologies that make use of sonar were inspired by the study of the biosonar of cetaceans.

The feeding: Baleen Whales and Toothed Whales

The food way during evolution have undergone profound changes, found especially in the mouth part. The dentition, in principle heterodont, has in fact evolved into homodont (ie not differentiated teeth) and monophiodon (absence of milk dentition) in Odontocetes. The Baleen Whales instead have even replaced the teeth with particular horny structures suitable for filtration: the baleen.
Odontocetes, with teeth, feed on large prey such as large fish and squid. The hunting techniques are numerous and individuals often cooperate in capturing preys. For example, the Killer whales and Bottlenose dolphins organize real coordinated attack groups during the hunting phase. Odontocetes often use ultrasound to stun the prey which is then grabbed and eaten. The teeth, however, have the mere function of retaining the prey and not that of chewing it as for the rest of mammals.
The Odontocetes have strong food preferences for fine fish such as mullet and sea bream, but they do not fail to hunt octopus and squid of which they are particularly gluttonous.
The Misticeti (Baleen whales), instead equipped with baleen, have a diet consisting of tiny preys such as krill and small fish. Whales and Fin whales capture an enormous amount of water in the large mouth which is then ajar. The water is then pressed by the tongue and expelled through the baleen, which retain nutrients like a filter comb. The feeding techniques of the Misticeti are varied and ingenious. Some groups filter the water continuously while keeping their mouths open, others are real predators that launch with their mouth wide open on groups of small fish previously grouped with particular movements. In fact, the Humpback whales rotate in a circle while expelling the air. This creates a column of bubbles that rise to the surface, inside which the fish are frightened and imprisoned, becoming easy prey.

The reproduction

Reproduction occurs in the warmer seasons and it can therefore vary according to latitude. In the Mediterranean sea, most of the species breed in late spring or early summer. The average gestation in the different species is twelve months, the youngs therefore born in the same period in which reproduction occurs. The longest gestation is that of the Sperm Whale, which reaches eighteen months. Often the delicate phase of birth is followed by all members of the group actively assisting the mother. Dolphins usually organize the group with a female who stays next to mother and her baby until weaning, effectively playing the role of "aunt".
The rate of growth first of the fetuses and then of the young in large cetaceans is staggering. A baby whale grows 70 kilograms and 3 centimeters in length per day, feeding on more than 100 liters of milk every day. Once the baby is weaned (6 months for the Misticeti; 3 years for the Odontocetes) it learns to hunt and feed independently and with the passage of time the young reaches sexual maturity and begins a life of its own regardless of the birth group.

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