Reptiles are a class of vertebrate animals. Compared with their ancestors, ancient amphibians, reptiles are the next stage adaptation of vertebrates to live on land. The reptiles are at a much higher level of organization than the amphibians, but among the higher vertebrates they are the lowest group: their brain is less developed than that of birds and mammals. This is one of the main features of this class. The skin of reptiles, including snakes, is covered with horny scales or hair, protecting the body from drying out and damage. The skeleton reptiles are almost completely ossified. The skull articulates with the spine by one occipital condyle - a sign, in common with birds. The respiratory system of reptiles is more differentiated than at amphibians. There are trachea and bronchi. Another feature of this class lies in the fact that the heart of modern reptiles is three-compartment: 2 atria and 1 ventricle, which is partially or completely (crocodiles) divided by a partition. Turtles, crocodiles and scaly (lizards, snakes) are to modern reptiles. The vast majority of reptiles, including snakes choose life on the ground, preferring the open, sun-warmed landscapes, including arid and almost devoid of vegetation of the desert. All crocodilians and many turtles live in lakes, rivers and swamps. Part of turtles and some snakes constantly live in the seas. Activity of modern reptiles is highly dependent on ambient temperature. Seasonal changes in climatic conditions have a major effect on the activity of reptiles. Most reptiles feed on animal food. Reptiles are very good hunters. So, crocodiles, marine and freshwater turtles eat mostly fish and aquatic invertebrates. Almost all lizards eat mainly insects. Many snakes feed on lizards, smaller snakes, amphibians, small birds and mammals. Devices for killing and swallowing are very large relatively to the size of their bodies. Basic food of boas and some venomous snakes is a relatively large mammals and birds. Some reptiles eat plants and animals (from lizards - Agamas and iguanas). Most reptiles reproduce by laying eggs. The eggs of most scaled reptiles (lizards and snakes) with soft parchment shaped shell and have no protein coat. This is another amazing feature that characterizes this class.
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