REPTILES

The reptiles (Reptilia) or sauropsida are a group parafilético of vertebrates amniotas provided with epidermal scales of keratin. They were very abundant in the Mesozoico, epoch in which the dinosaurs arose, pterosaurios, ictiosaurios, plesiosaurios and mosasaurios. According to the traditional taxonomía the reptiles are considered to be a class; according to the systematic cladística, they are a group parafilético without value taxonomico.

Characteristics:

The majority of the reptiles have adapted to the terrestrial life, but finally one has discovered that some of them live in the water. A resistant and scaly skin is one of his adjustments. Others of the adjustments that they have contributed to the success of the reptiles in firm land are that there include developed well lungs, a circulatory system of double circuit, a system excretor that preserves the water, strong extremities, fertilization hospitalizes and terrestrial eggs with shell. In addition the reptiles can control his shaped temperature changing place 

• Control of body temperature: The aptitude to control his body temperature is an enormous advantage for the active animals. The animals about which we have spoken till now are ectotérmicos. The ectotérmicos use the conduct to control the temperature of the body. To warm up, they are stretched under the Sun the whole day or remain under the water during the night. To cool, they move towards the shade, swim, or shelter in underground burrows.

• Supply: Most of the reptiles are carnivorous and possess a digestive simple and short tract, since the meat is simple enough of separating into its elements and digesting. The digestion is slower than in the mammals, which reflects his slow metabolism during the rest and his disability to divide and chew his food. This metabolism has very low requirements of energy, allowing that the big reptiles, as the crocodiles and the big constrictive serpents, could live of a big food per months, digesting slowly a dam of great size.

• Breathing: He lungs of the reptiles are spongy and have major surface for gas exchange that the amphibians. This is due to the fact that the majority of the reptiles cannot exchange gases across the skin, since they do the majority of the amphibians of humid skin. Many reptiles have muscles that surround the ribs and expand the thoracic cavity to inhale, or collapse the cavity to exhale. Several species of crocodiles also possess cutaneous doublings that separate the mouth of the nasal conduits; this way they breathe for the nostrils while they have the opened mouth.

• Traffic:The reptiles they possess an effective circulatory system of double circuit. One of the routes takes and gathers blood of the lungs. Another route takes and gathers blood of the rest of the body. The heart of the reptiles contains two auricles and one or two ventricles. The majority of the reptiles have the only ventricle with a partial septo; it allows to separate the blood become oxygenated of the blood not become oxygenated during the cycle of pumping. 

• Excretion: He urine takes place in the kidneys. In some reptiles, the urine flows across a few pipes directly towards a sewer similar to that of the amphibians. In other cases, the urinary bladder stores the urine before eliminating it for the sewer. The urine of the reptiles contains ammonia or uric acid. The reptiles that live principally in the water, as the crocodiles and caymans, excrete most of his nitrogenous waste in the shape of ammonia, a toxic compound. The caymans and crocodiles drink great water, and this dilutes the ammonia of the urine and helps to expel it. In contrast, many other reptiles, especially those who live exclusively in firm land, do not excrete ammonia directly; they turn the ammonia into a compound called uric acid.

• Beside creeping, the reptiles are characterized fundamentally for:
•  - thick skin protected by a horny protective cap of scales.
•  - oviparous reproduction with internal fertilization.
•  - pulmonary breathing during all his life.
•  - blood stream blood double and incomplete with heart divided in 3 chambers 
• - skeleton formed by four extremities and constituted by ossified cranium and vertebral column.
•  - nervous system constituted by twelve couples of cranial nerves.
•  - rigid bosses of conduct established from the birth overcoat the reproductive ones.

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