AutobÃºs elÃ©ctrico

The Taxon of the Cetacea ( Cetacea of the Greek kêtos , whale) is traditionally an order of Mammifère S placental, considered as Monophylétique. The Cetacea have all a joint adaptation specific to the dulçaquicole seamen circle and , but evolved/moved starting from terrestrial mammals.

Evolutionary history and taxonomy

The Cetacea have as an ancestor a terrestrial animal. The analysis Phylogénétique of genes coding certain proteins mitochondriales gathered them within same a Clade with the Artiodactyles (Ongulés with even fingers) in the group of the Cetartiodactyla . In addition, the study of natures derived in their nuclear Génome (the Rétrotransposon S) watch that their more close relatives are the Hippopotame S. a study based on morphology however calls in question this close relationship and suggests a greater proximity with the fossil Anthracothères and an evolution of the hippopotamuses from an other connects, within the Cetartiodactyla to be determined. The Cetacea would thus have diverged very early from Anthracothères, following the example Suidés and Ruminants. It should however be specified that this study included only fossil representatives of the Cetacea, Archéocètes which are not themselves not ancestors of the current Cetacea.

The oldest known fossils go back to approximately 60 My. The taxon includes/understands approximately 80 species of which more half are of world distribution.

Description

Morphology

The body of the Cetacea smooth and is tapered, which facilitates the penetration in the Eau. The forelimbs and the tail of the Cetacea evolved/moved in Nageoire S. the caudal fin called pallet , very powerful, is horizontal, contrary to those of the Poisson S. It ensures the propulsion while the side fins ensure the balance and the maintenance of the direction. The dorsal aileron acts as stabilizer like the Quille of a boat. Like the other mammals, the Cetacea breathe using Poumon S and must regularly make surface to breathe.

Delivered Cetacea is adapted to the lifestyle of the animal. It can be asymmetrical left-right-hand side as for the common Rorqual. For several species, it makes it possible to recognize the specimens. The majority of the oceanic Cetacea have the dark back and the white belly, so that the preys and the predatory ones when they see them top confuse them with the sea-bed and when they see them of lower part see only one reflection of water surface.

Directions

The direction more developed in the Cetacea is the Audition, equipped with the function of echolocation, kind of natural Sonar, particularly developed in the Cetacea with teeth. They emit clicks of echolocation of which a part is reflected by the obstacles. The analysis of these returns gives them a kind of image acoustic of their environment. They seem to have lost their sense of smell.

Anatomy

The ancestors of the Cetacea, in a few million years adapted terrestrial environment to the seamen circle. Starting from a terrestrial morphology, they lost certain characteristics to gain others of them.

The skeleton

The modifications on the level of the skeleton are definitely visible.

The pelvic members are considerably reduced: there remain nothing any more but some pelvic bones residual to which is connected the ischiocavernosus muscle which maintains the penis in place inside the genital slit in the males. This muscle is similar to that found in the other mammals of which, inter alia, ongulés and the Man. On the other hand, the thoracic members are preserved, though atrophied, and one finds the Scapula (" omoplate" of the Man), the Humérus, the Radius, the Ulna (" cubitus" of the Man), bones of the Carpus, the Metacarpus S and the Phalange S which multiplied (hyperphalangie). The whole forms a pectoral, equivalent fin of that of the Poisson and whose role is not the propulsion but the maintenance of balance in the space and the direction of the movements. The other fins are not ossified. It is on the level of the Crâne that one differentiates mainly Odontocètes from Mysticètes. One notices also a certain asymmetry between the parts left and right-hand side of cranium (at certain species). Bones of the face (jawbone, incisive, mandible, etc…) lengthened and telescope with the bones of cranium on the dorsal face of cranium to form what one calls the vent, resulting from the migration on the dorsal face of the osseous nostrils during the Oligocène.

Skin

The épidermique layer is fine, smooth and elastic and exudes oil which increases their hydrodynamism. This adaptation is also present in many fish. In order to avoid the creation of microphone-turbulence when speed increases i.e. to preserve a regular flow of water on their skin, evolution with developped at the point several mechanisms. The skin of the Cetacea adapts its consistency thanks to their flexible derm which is made of papillae and richly innervés channels able to enter in Turgescence. The skin is also traversed of a multitude of tiny wrinkles which direct the flow of water.

The skin of the Cetacea is also sensitive to the touch. Certain zones, for certain species, are still equipped with sensitive hairs.

The skin of the Cetacea reaches 2 to 4 millimetres on average, and 12 millimetres at the Bélouga.

Reproductive bodies

The genitals are interns, located behind the genital slit, in the males like the females so that it is sometimes difficult to distinguish the sex from the specimens. In the female of the Cetacea, contrary to the other mammals, the white Corps S do not disappear and testify to the reproductive history to each animal. The cetologists can thus estimate the number of gestations of Cetacea.

The Brain

The brain of the Cetacea is very powerful. With the elephants and the primates, the Cetacea belong to the rare animals whose conscience of themselves was scientifically highlighted. The experiments on the Grand dolphin show that they are also able to be put at the place of human, to learn, to invent but they are also aware of their own states of knowledge (Métacognition). In addition, it is known that the Cetacea are able to communicate, that all the groups of the same species do not use the same signals inevitably, including vocal, to communicate, to control a grammar and to even be able to name by singing exercise a partner. The brain of the Cetacea evolved/moved whereas they were already marine mammals, in a way independent of that of the primates since 95 My and it is thus remarkable that it allows performances comparable with those of the primates on these points. It is a remarkable example of evolutionary Convergence.

In fact the Néocortex of the Cetacea exceeds by its degree of Gyrification all the other mammals, including that of the human ones. The thickness of the various layers of the neocortex however differ from that the primates, I and the IV are thinner, II denser. In fact intra-hemispherical connectivity seems to support in the cachalot for example. The brain of the Cetacea is also characterized by the strong density of the cells gliales

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