What is a reptile?
The reptiles are the ancestors of birds and mammals. We include in the group of reptiles lizards (lizards), snakes (snakes), turtles and crocodiles. While no current studies that could diverge latter two groups, the fact that the group Reptilia today embraces them all.
Characteristics of reptiles
Reptiles crawl in principle, although many lizards (such as monitor lizards) and crocodiles are capable of running with raised floor belly and legs roughly erect. However, it is the position of their feet about hips which gives them away as reptiles. In reptiles, the legs out laterally from the trunk and this is what often gives the appearance of crawling creatures.
The reptiles are also called cold-blooded, a definition that refers to the temperature of your body depends on the temperature of the environment in which they are, so you have to move in their environment to regulate their body temperature. Reptiles are poikilothermic animals.
They are tetrapods animals although there are many cases in the kingdom of reptiles that certain species have lost their legs like snakes and several species of lizards (lizards). There are also some species only with front legs, and snakes with spurs or vestiges of the hind legs.
They have a thick, scaly skin that protects them from the environment. The skin is permeable reptiles and amphibians and reptiles are independent of the aquatic environment but some are adapted to live in freshwater, and very few reptiles at sea.
Reptiles have pulmonary respiration, not metamorphose.
The blood circulation of a reptile is the type called double circulation and incomplete as they have the corazoón divided into 3; not like crocodiles almost have a heart divided into 4 chambers, almost like that of mammals and birds.
There are ovoviviparous, oviparous and viviparous reptiles.
Evolution of reptiles
The reptiles are descended from an amphibious ancestor who leaves the water more than 250 million years ago. They are now adapted to any type of habitat and is found throughout the world except in the coldest regions of the earth.