”Reptiles are tetrapod (four-limbed vertebrate) animals in the class Reptilia, comprising today’s turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives.
The earliest known proto-reptiles originated around 312 million years ago during the Carboniferous period, having evolved from advanced reptiliomorph tetrapods that became increasingly adapted to life on dry land.
Modern members exhibit some form of cold-bloodedness , so that they have limited physiological means of keeping the body temperature constant and often rely on external sources of heat.
By using temperature variations in their surroundings, or by remaining cold when they do not need to move, reptiles can save considerable amounts of energy.
The oldest known animal that may have been an amniote is Casineria (though it may have been a temnospondyl).A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales. These tracks are attributed to Hylonomus.It was a small, lizard-like animal, about 20 to 30 centimetres (7.9 to 11.8 in) long, with numerous sharp teeth indicating an insectivorous diet.
Reptiles are generally considered less intelligent than mammals and birds. The size of their brain relative to their body is much less than that of mammals, the encephalization quotient being about one tenth of that of mammals, though larger reptiles can show more complex brain development. Larger lizards, like the monitors, are known to exhibit complex behavior, including cooperation. Crocodiles have relatively larger brains and show a fairly complex social structure. The Komodo dragon is even known to engage in play, as are turtles, which are also considered to be social creatures and sometimes switch between monogamy and promiscuity in their sexual behavior.”