What is a reptile?

A reptile is a vertebrate which, like amphibians, is ectothermic, its body temperature influenced by the temperature of its surroundings. Its body is covered with dry skin, from which grow scales.
Body wastes, eggs and sperm all leave the body of a reptile through the final section of the gut, which is called the cloaca. A reptile's kidneys can change body wastes from liquid to solid form. Land reptiles' urine forms part of the limy waste material passed out of their bodies, but aquatic reptiles usually pass fluid urine as well as solid wastes.
The sperm produced by a male reptile fertilizes a female's eggs inside her body (in amphibians, fertilization takes place outside the body). The fertilized eggs of most reptile species are enclosed in shells and are laid on land. However, some species retain their eggs within their bodies until the young hatch.
Most reptiles eat other animals, though a few eat plant material.
Most reptiles have four limbs. Snakes have no limbs (though pythons have remnants), and some lizards have reduced limbs, only two hind limbs, or scaly flaps instead of hind limbs.
Lungs and hearts
When it breathes, a reptile expands its ribs, drawing air into its lung. After oxygen and carbon dioxide have been exchanged in the lungs, the reptile breathes out by contracting its ribs. In a few water-living species, some exchange of gases takes place through the skin or even the cloaca.
Turtles, lizards and snakes have three-chambered hearts. In the single lower chamber, oxygenated blood coming from the lungs may mix with deoxygenated blood from the body.
Crocodiles have four-chambered hearts, like those of birds and mammals. Normally oxygenated and deoxygenated blood do not mix, but during a long dive, when fresh air is not available, a special valve allows deoxygenated blood to pass back into the crocodile's body tissues.
Desert survivors
Australia's many dry areas are full of reptiles which are adapted to arid conditions in a number of was:
·Their body wastes have very little water in them.
·They obtain water from their food, and from licking dew. The scales of some lizards channel water to the mouth.
·Because of their low energy requirements, reptiles can survive food scarcities during drought.
·Small reptiles feed on ants and termites, which are plentiful in the desert. The small reptiles are then eaten by larger reptiles.
·A reptile becomes active when the temperature is right for its species. In the desert, it may forage at night, and shelter in a burrow during the day, or spend daytime shuttling from sunshine to shade and back again. Some lizards climb some distance off the ground into vegetation to avoid ground heat.
Wetlands predators
The floodplains of northern Australia support a greater weight of predators in a given area than do Africa's Serengeti Plains.
The African predators are mammals such as lions and hyenas. The Australian ones are reptiles, such as water-living pythons, file snakes, freshwater turtles, crocodiles and a variety of lizards, including the Frilled Lizard. These creatures eat each other, as well as insects and other invertebrates, fish, frogs and small mammals.