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classis reptil

Reptiles are a class of the chordate phylum .  There are approximately 7900 species of reptiles alive today that inhabit a wide range of temperate and tropical habitats including deserts, forests, freshwater wetlands, mangroves and open ocean.
Reptiles, Bird, and mammals are amniotes.  The major derived characteristic of this clade is the amniotic egg, an egg with a shell, housing an embryo in a fluid-field sac, the amnion (inside of which the embryo develops within a protective, fluid-filled sac called the amnion).  The clade of amniote called reptiles includes lizard, snakes, turtle, crocodilians.
In addition to an amniotic egg protected in a waterproof shell, reptiles have several other adaptation for terrestrial living not found in amphibians.  Reptilian skin, covered white scales waterproofed with the tough protein keratin, keeps the body from drying out.  Reptiles cannot breathe through their dry skin and obtain most of their oxygen with their lungs,using their rib cage to help ventilate their lungs. Both the babies and the adults breathe through lungs. 
They have a breastbone called a sternum to protect the heart and lungs.  The reptilian skeleton differs from other vertebrates in various ways. For example, mammals have a single lower jawbone called the mandible but reptiles have several bones in their lower jaw that enable them greater bite mobility. Also, reptiles have only one bone in each ear (the stapes) whereas mammals have three small bones in each ear (the malleus, incus and stapes). Reptiles also have only one occipital condyle (a protrusion on the skull that forms a joint that enables movement of the head) while mammals and amphibians have two occipital condyles.
The female's eggs are fertilized in her body by the male. The eggs are laid in a shell that has a leathery covering to protect it in the wilds.  in some reptiles, the sex is instead determined by the temperature that prevails during the about the middle third of embryonic development. This phenomenon is known as temperature-dependent sex determination.
Reptiles have four limbs, a characteristic that places them among the group of animals known as tetrapods. It should be noted that although some reptiles such as snakes and amphisbaenians have lost their legs during the course of evolution, they are tetrapods by descent.
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Picture 1.  Heat exchange between an organism and its environmentReptiles are cold-blooded or ectothermic which means they are unable to regulate their own body temperature like birds and mammals do. Therefore, reptiles must modify their activity and behavior to accommodate changing environmental temperatures. They must seek shelter during excessive heat (to prevent over-heating) and extreme cold (to prevent hypothermia). But being cold-blooded has its advantages too. It has enabled reptiles to enjoy success in habitats that mammals and birds find challenging. Since reptiles do not need to burn calories to fuel a constant body temperature, they can survive on much less food intake that birds and mammals. For this reason, reptiles are the dominant vertebrate in desert habitats
Reptile skin is covered with scales, structures that grow on the animal's epidermis and consist of a hard substance known as keratin which is similar to human hair and fingernails. Scales are replaced periodically through a shedding process in which the entire skin is shed in one piece or flakes off in small pieces. Reptile scales vary in shape, size, texture and color.

An animal can exchange heat with the environment by four physical processes:
1.      Conduction
Is the transfer of thermal motion (heat) between molecules of object that are in direct contact, as when an animal is physically touching an object in its environment.  Heat is always transferred from an object of higher temperature to one of lower temperature.
2.      Convection
Is the transfer of heat by the movement of air or liquid past a surface.
3.      Radiation
Is the emission of electromagnetic wave.  Radiation can transfer heat between object that are not in direct contact, as when an animal absorbs heat radiating from the sun.  The lizard also radiates some of its own heat into the external environment.
4.      Evaporation
Is the loss of heat from the surface of a liquid that is losing some of its molecules as a gas.  A llizard loses heat as moisteure evaporates from its nostrils.

Table 1.  Reptiles system
System Type
Reptiles System
A reptile has an inner skeleton. It has a breast bone to protect the lungs and heart. The reptiles have feet with claws.
A reptile has a mouth, tongue, teeth, an esophagus, stomach and rectum.
A reptile has a brain and nervous system. It has eyes, can sense sound.
A reptile has a heart
A reptile breathes through a trachea and lungs, including the baby reptiles.
A reptile reproduces sexually with the female's eggs being fertilized by the male internally. The eggs, which have a leathery surface, are then carefully deposited.
A reptile is cold blooded. It is covered with scales. It has kidneys and ureters to get rid of liquid wastes. Snakes can molt or shed their skin.
A reptile has bilateral symmetry.
A reptile varies in size from very small snakes, lizards and turtles up to huge alligators and crocodiles. Their coloration varies, but it frequently allows the reptile to blend in with its environment.

Today, scientists classify reptiles into four major groups known as "orders." These four reptile orders are as follows:
  1. Crocodilia       à: crocodiles, gharials, caimans and alligators: 23 species
  2. Sphenodontia  à:tuataras from New Zealand: 2 species
  3. Squamata        à:lizards, snakes and amphisbaenids ("worm-lizards"): about 7,900 species
  4. Testudines       à:turtles and tortoises: approximately 300 species
The common reptiles are snakes, turtles, lizards alligators and crocodiles.
1.      Snakes
Snakes are covered with scales, many times of various colors. As humans shed some of their skin, the snakes also shed their outer skin many times during the year. This is called molting. The snakes finds a stone or twig to rub up against and then pushes and pulls against it until the skin comes off.
The snake is one reptile that has no legs. It makes up for this by its scales on the underside of its body called scutes. It also has very strong muscles that help it move. They can move in curves from side to side or up and down. Snakes move quite slowly compared to other animals. The fastest they can move is several miles per hour.
The snake has no eyelids, but has a transparent covering to the eye to protect it. Some have round eye pupils and some have oval pupils. The snake has a long forked tongue that it uses to smell things with.
The snake has a very big mouth with two rows of teeth on each side of its upper jaw and one row on its lower jaw. The teeth, however, are not used for chewing, but to hold onto its prey. The snake eats its prey whole. The teeth slant backward to push the prey back into the snake. Its jaws stretch very far open so that the snake can take in animals bigger than itself.
Snakes solely eat animals. Many snakes such as the garter snake open their mouths and swallow their prey whole. Others such as the boa and python, wrap their bodies around their prey and squeeze it to death. They snakes are usually larger and more powerful. Snakes such as the rattlesnake, water moccasin, cobra, copperhead and coral snake, have huge fangs that poison in them. These snakes attack their prey and the hollow fangs fill with poison from poison glands around the fangs. The prey dies and the snake eats it.
2.      Lizard
There is a huge size range for lizards from tiny skinks to Komodo dragons that are up to 5 meters long. Lizards generally live in the tropical zone where it is very warm.
Lizards differ from snakes in that they have four feet and can move quite quickly. One well known snake is the chameleon. Its tale is one and one half the size of its body, which is around two inches. It changes its color constantly.  The Gila monster is a poisonous lizard and lives in the American Southwest. It is several feet long and has brown or black skin with colored splotches. It has poisonous glands in its jaw which can kill a man when the Gila monster gives a hard bite.
The horned toad is really a lizard, despite its name. It is found in the western United States. It has scales of different lengths and some of them have live birth of their babies versus laying eggs as most reptiles do.  The iguana is a lizard of the tropics. It resembles a tiny dragon
3.      Turtles
Turtles live on land, in fresh and salt water. If they live on land, they are called tortoise and some fresh water turtles are called terrapins.
Turtles can range in size from a few inches to three meters. All turtles have two shells with their bodies sandwiched in between. Its head can be pointed or shaped like a triangle. It has a jaw that forms a beak, but has no teeth. It has good eyesight with upper and lower eyelids. It has a third eyelid called a nictitating membrane that covers the eye.
The turtle walks quite slowly due to its body shape and its short legs. It has five toes on each leg and claws on the toes. Turtles' toes are webbed to a greater or lesser degree.
Some turtles have tails, while others don't. Turtles all lay their eggs on land in shallow holes covered with sand. Turtles eat insects, worms, plants, fish and frogs.
4.      Alligators and crocodiles
Alligators and crocodiles are in the same reptile subgroup. They mostly live in tropical or semitropical regions. Alligators are mostly found in the southern United States and the crocodiles in Africa, India, South America, and southern United States. They are among the largest reptiles. Their bodies are covered with scales and they have webbed toes. They live in swamps and along the banks of rivers.
The crocodile spends more time in the water than the alligator. The crocodile has a narrower, more triangular head and a pointer snout. The crocodile is grayish-green in its color. The crocodile is more active than the alligator.
The alligator is brownish in color and moves more slowly than the crocodile.
Both the alligator and crocodile eat fish and nearby land animals. They can also attack man.

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