Lizards 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.
Lizards include more than 20 subgroups, some of which include as iguanas, chisel-teeth lizards, chameleons, geckos, night lizards, blind lizards, skinks, anguids and beaded lizards.
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.
Lizards are classified within the following taxonomic hierarchy:
Animals > Chordates > Vertebrates > Tetrapods > Reptiles > Squamates > Lizards
Lizards are divided into the following taxonomic groups:
- Snakes, monitor lizards, and iguanas (Toxicofera) - There are about 4400 species of snakes, monitor lizards, and iguanas alive today. Members of this group include snakes, iguanas, agamas, chameleons, gila monsters, alligator lizards, monitor lizards. Members of this group include all all venomous reptiles as well as some non-venomous reptiles.
- Geckos (Gekkota) - There are about 1500 species of geckos alive today. Members of this group include western banded geckos, bent-toed geckos, leopard geckos, Tokay geckos, crested geckos, and many others. Geckos lack eyelids and have a transparent membrane that covers their eye, which they lick to clean.
- Amphisbaenians (Lacertoidea) - There are about 180 species of amphisbaenians alive today. Members of this group include amphisbaenids, ajolotes, Iberian worm lizards, Moroccan worm lizards, North American worm lizards and many others. Amphisbaenians are notable for being legless squamates with long bodies and rudimentary eyes.
- Legless lizards (Dibamidae) There are about 24 species of legless lizards alive today. Members of this group inhabit tropical forests in Central America, Southeast Asia, and New Guinea.
- Bronze grass skink (Scincomorpha) - The bronze grass skink is the only species in its group. The bronze grass skink is native to South and Southeast Asia.