Short answers, pulled from the story.
A reptile is a tetrapod vertebrate animal with an ectothermic metabolism and amniotic development. The Reptile Database lists about 12,000 extant species, traditionally grouped into four orders: Testudines, Crocodilia, Squamata, and Rhynchocephalia.
Birds are the only surviving group of Dinosauria, a clade of diapsids more closely related to crocodilians than to other living reptiles, so birds are nested among reptiles under the clade Archosauria. Because of this, modern cladistic systems often redefine Reptilia as a clade that includes birds, and the 2004 definition by Modesto and Anderson includes birds.
The first reptiles evolved about 310 to 320 million years ago, in the steaming swamps of the late Carboniferous period, from advanced reptiliomorphs. Footprints from Nova Scotia dated to 315 million years, attributed to Hylonomus, are among the oldest known reptilian tracks.
Reptiles have a low resting metabolism because they are ectothermic, so they require far less fuel than warm-blooded animals of the same size. A crocodile needs from a tenth to a fifth of the food a lion of the same weight requires and can live half a year without eating.
Snakes lack an outer ear, a middle ear, and a tympanum, but have an inner ear with cochleas connected directly to the jawbone. They feel vibrations from sound waves through the ground using mechanoreceptors that carry the signals along the spinal nerves to the brain.
Geckos, skinks, and some other lizards shed part of the tail through a process called autotomy when captured, allowing them to flee while the detached tail thrashes and distracts the predator. The tail regrows in most species but contains cartilage rather than bone and never reaches the original length.
Gila monsters produce compounds that reduce plasma glucose, one of which is used in the anti-diabetes drug exenatide, sold as Byetta. Snakebite can be treated with antivenom made by injecting snake venom into a horse, and snake venom's cytotoxic effect is being researched as a potential cancer treatment.