Lizards (Lacertilia) are the most diverse group of squamates, consisting of more than 4500 species belonging to groups as iguanas, chisel-teeth lizards, chameleons, geckos, night lizards, blind lizards, skinks, anguids, beaded lizards and many others.
Lizards occupy temperate and tropical habitats throughout North and South America, Europe, Asia, Africa, and Australia. They also occur on many tropical islands throughout the Atlantic, Indian and Pacific Oceans.
Most lizards have 4 limbs, although there are a few species of skinks that are limbless. Many lizard species have a long tail. In some species, the tail can easily break. This is a defense mechanism that enables the lizard to escape a predator that catches it by the tail. The tail detaches at weak points along the vertebrae. Often, the lizard regrows the lost portion of the tail.
Lizards defend themselves in a variety of ways. Many are quick runners and dash for cover at the first sign of danger. Other lizards are well camouflaged and escape predators by blending into their surroundings. Some species take a more active stance against threats by expanding themselves to appear larger and more fearsome. If pushed too far, many lizards will resort to biting or clawing their attackers. But of all the defense mechanisms, the most formidable is that of venom. Only three species of lizard are known to be venomous: the Gila monster, the Mexican beaded lizard and the Komodo dragon.
Most lizards reproduce sexually and lay hard-shelled eggs, although a few species give birth to live young.
The fossil record for squamates, including lizards, is relatively poor. It is thought that lizards arose towards the end of the Triassic but there are no known fossil lizards of that age. Instead, the earliest fossil lizards that have been discovered are much younger, dating to between 185 and 165 million years of age, placing them within the middle Jurassic. The closest living relatives of the lizards are the snakes and the worm-lizards.