Our Cetaceans

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Cetaceans are marine mammals that, in the course of their evolutionary history, have achieved a complete adaptation to aquatic life.

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Cetaceans order is divided into two suborders: Odontoceti (Toothed whales) e Mysticeti (Baleen whales)

The Odontoceti are cetaceans with teeth that actively hunt their prey, such as porpoises, dolphins, killer whales and sperm whales. They eat mainly fish and cephalopods and in relation to feeding specialization, exploit different ecological niches, hunting both in coastal waters and in depths over 1000m.

The Mysticeti and fin whales, are cetaceans of colossal size, equipped with a filtering apparatus, baleen, with which they sift through huge amounts of water to feed on plankton and small fish.

Anatomy and physiology

Cetacean possess small forelimbs which look more like pectoral fins with directional function, while the rears are completely gone. The basin, of which there are only little pelvic rudiments, is reduced to two small equal bones, separate and incorporated in the mass of abdominal tissues. Most species of cetaceans presents a fin implanted on the dorsal line by the middle of the body whose function is related to their swimming. This structure, result of a skin  duplication and subcutaneous tissue, is the crucial directionality organ, especially in the fast forms (typically absent in the slow one). The caudal fin, thicker at the base and flattened distally, is arranged on a horizontal plan and is the primary driver organ of cetaceans. Their front train is virtually immobile even during locomotion, while the rear one, especially the caudal sector , performs, for the purposes of swimming, movements in vertical direction. The locomotor efficiency is given by the tapered shape of the body, which reduces the braking action of the aqueous mean, favoring the sliding of the fluid threads and creating a kind of laminar flow, free of vortices.

The head is directly joined to the body and in many cases fixed to it through the fusion of the cervical vertebrae. The structure of the skull presents peculiar characteristics compared to the one of land mammals: the nostrils, in fact, are located on the top of the head so as to allow the sinusoidal swimming even during breathing and they’re distinct in the suborder of the Mysticeti, and merged together in the Odontoceti; the pre-maxillary and maxillary bones are greatly elongated and the skull is short, more developed in height and width (telescoping); The mouth opening is very wide, lipless and functionally equivalent to those of other  mammals.

The naked skin is very smooth, and able to minimize the creation of turbulence during swimming through the formation of tiny dermal ridges damping the energy developed,  also, the exudation of lubricants oily droplets further reduce the water friction. The coating follicle is absent except for a few bristle shaped tactile hairs (whiskers) attached to the rostrum in the early stages of development. All species of cetaceans have a thick adipose layer that covers the entire body surface, except for the head and fins, which maintains a stable homeothermy, giving  the animal a good flotation and constitutes a substantial nutrient reserves especially for individuals who make long migrations.

The circulatory and respiratory systems are adapted to great depths and long apneas. The exchange of air in the lungs, unlike land mammals,

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takes place in a very short time, with rapid inhalations and exhalations, interspersed with long periods of apnea. The result of this breathing mode determines a respiratory rate very low. When diving, cetaceans do not store large amounts of oxygen in the lungs: thanks to the presence of high concentration of respiratory pigments (hemoglobin in the blood and myoglobin in the muscles) they are in fact able to fix in the tissues about 90% inspired oxygen. Over 70 feet deep, in fact, under the stress of hydrostatic pressure, the lungs and the chest wall are compressed, causing alveolar collapse that interrupts the exchange of respiratory gases between the lungs and blood. The heartbeat is slowed and some districts circulators are isolated through selective mechanisms of vasoconstriction, allowing during diving, a more effective spraying of major organs such as the brain. Finally, a complex circulatory arterial system, mainly present at pectoral, dorsal and caudal fins level as well as at the base of the skull, appears to play a type of thermoregulatory function (through a mechanism of “countercurrent” heat transfer ) and response to immersion (capturing nitrogen bubbles eventually generated following the high pressures reached by the animal).

The excretory system consists of two large kidney, divided into smaller functional units independent of each other, each with an independent vascular system with its papilla and pelvis. The amount of urine is particularly abundant and hypertonic with respect to the external medium: this allows these Mammal to recover from the environment the water necessary to their metabolism, eliminating excess salts.

The morphological changes related to the hydrodynamics of the shapes have led to the development of special adaptations of the reproductive system. The breasts of the female animal and genitals of the males are in fact internal and not disturb the profile of the body. The sex in cetaceans is therefore not immediately recognizable: a closer examination shows that the vulvar slit is near the anus of the female while the slit through which a male's penis is everted, is closer to the navel. The females mammary glands are situated under the subcutaneous fat, they are only two and are placed - one on each side - a little ahead of the genital opening. The nipples are retracted within a smaller cracks lateral to the vulva and become a little protruding only during the nursing period.  The cetaceans baby do not possess appropriate lips to grasp the nipple., hence the specie has evolved a special mechanism that makes mothers able to eject the milk directly into the mouth of the baby by the simple contraction of the muscles through the skin.