sábado, 4 de diciembre de 2010

The mammals

 With the mammals the evolutionary line of the vertebrates is completed at the moment. They are the dominant tetrápodos in the terrestrial way, with a great diversity of forms and especially with a great capacity of adjustment to the diverse means.They represent the maximum degree of adjustment to the terrestrial life obtained till now by the animal kingdom. Nevertheless, some groups have returned to the sea, as the cetacean ones, whereas others, the quirópteros, have conquered the air way. The great diversity and, especially, the enormous capacity of adjustment have allowed to the mammals to expand all over the world and to take advantage of the diverse mas available resources. Departing from a basic structure, they have developed forms as diverse as a dolphin, a shrew, an elephant and the own human being.
The stretching of the neck of the giraffes they have not supposed increase of the number of the vertebrae but an increase of his length.
Some mammals have adapted to the life in the water, as the case of the dolphins, acquiring his body a fish-shaped aspect, reflection of the adjustment to the way.

The birds

 The birds are almost the only vertebrates that dominate the air way and all his anatomical this structure adapted to the flight. The transformation of the previous extremities in wings is the characteristic fgeneral, except in some species that have limited or turned in fins.They come from the reptiles but they have evolved up to obtaining a new characteristic, the homeotermia, or aptitude to keep the corporal temperature constant independently of the conditions of the environment. As for his nervous system, this one also many evolved mas, which it reflects in a complex conduct and a learning capacity with regard to the reptiles very top. The flight is another characteristic that determines in a decisive way his physiology and his anatomy.
The bee-eater feeds of insects that he hunts in flight, constructs his nests in the bank of the rivers or sandy walls.


 The reptiles are a former group of vertebrates terrestresque they reached in the past a great summit, dominating the whole planet. The later appearance of birds and mammals from them and with solutions mas advanced, it reduced them to his current distribution. The reptiles constitute a big step in the conquest of the terrestrial way on the part of the animals, since they manage already to become free completely of the water. His extremities possess also a major capacity of support, being able to raise the body of the soil and improve this way the locomotion.
The serpents, they are tetrapodos that have lost his four extremities as a secondary evolution.


 The amphibians are the first terrestrial vertebrates, but that depend still narrowly on the aquatic way, since only in they can be reproduced. His four extremities are alone sufficient to move with slowness for firm land.
 It has cartilaginous skeleton, with the cranium joined the vertebral column by means of two cóndilos and with the ribs, when they exist, without joining the breastbone. Is observed in them already the beginning of reproduction of the number of cranial bones that they characterize to the terrestrial vertebrates. They can have tail or not.

The fish

 The fish are the vertebrates that dominate in the aquatic way. East has given them a typical form that one adapts perfectly to the life in. The vertebral column plays a role very importantly in the locomotion, being the fins especially elements of direction.The fish in wide sense include the Agnatos, lacking in jaws, and the fish in strict sense, which the systematic one groups in two extinguished classes and living two. The function of the fins couples of the fish is it of using as stabilizers since they are the movements as that of a serpent of the body the principal element propellent.
The escorpora is camouflaged perfectly in the sea bed thanks to the form and the color that adopts his body.


That of thorns on the skin is one of the characteristics of this group, exclusively marine and that I reach a great development in last epochs. The adults present symmetry of five radioes, though in some groups they can modify it. In the body of the adults a backbone is observed, that it departs from the mouth, from that they think up five radiuses provided with elements ambulacrales.In some groups, since for example, the starfishes, these radiuses are the arms of the animal. Nevertheless there are others (since it is the case of the irregular hedgehogs) in that this symmetry pentarradial is modified.
The sea urchin has the body covered with mobile thorns with which it can move slowly on the bottom, using him at the same time as defensive weapon opposite to the predators.


The insects are one of the groups animal that have obtained major evolutionary success in our planet. They occupy practically the totality of the terrestrial existing habitats, being complementary in firm land to the crustaceans.The insects, or hexápodos, have the body divided in three regions: head (with antennas, jaws, maxillary and lips), thorax (with three couples of legs, two couples of wings and two couples of espiráculos). They have eyes simple and composed in the head, excrete by means of Malpighi's pipes and the fertilization is internal. In the development they happen for several larval phases. Almost they all are terrestrial and in a secondary way some of them live in the waters, in general continental and in an exceptional way in the sea.
Numerous insects happen for different larval phases before reaching the adult condition. A caterpillar of butterfly appears here.