SUPERORDER Lepidosauria: tuataras, lizards and snakes.

ORDER Rynchocephalia: tuataras. Beaked reptiles. Biconcave vertebrae. Parietal eye (third eye) developed, with retina and lens, though covered with scales. Anus is a transversal fissure. Acrodont tooth structure (teeth without alveoli, fused to the edge of the jaw bone). 1 family and 2 species.

FAMILY Sphenodontidae: tuataras. Only living members of a reptile order that became extinct 60 million years ago. Islets of New Zealand. 1 genus, 2 species, Sphenodon punctatus and Sphenodon guntheri.

ORDER Squamata: squamates. Lizards and snakes. Body covered with horny epidermal scales or plates that are moulted periodically. Anus is a transversal fissure. Comprises 95% of living reptiles. 38 families and some 6,600 species.

SUBORDER Iguania: iguanas, chameleons and agamas. Short body, four well-developed limbs. Sharp vision. Large tongue. Eyelids and external auditive holes. 3 families.

FAMILY Agamidae: agamas. Acrodont tooth structure (teeth without alveoli, fused to the edge of the jaw bone). Mainly oviparous. Tail autotomy is absent. Old World tropical regions, except isles. 40 genera, 325 species.

SUBFAMILY Agaminae
SUBFAMILY Leiolepinae

FAMILY Chamaeleonidae: chameleons. Prehensile tail lacking autotomy, bulbous eyes that move independently. Digits partially fused and opposable. Long protractile tongue, used for capturing prey. Acrodont tooth structure (teeth without alveoli, fused to the edge of the jaw bone). Colour change for camouflage. Africa (except Sahara), Iberian Peninsula and South Asia. 6 genera, 128 species.
FAMILY Iguanidae: iguanas. Pleurodont tooth structure (teeth without alveoli, on the inner side of the jaw bone). America, Pacific islands and Madagascar. 54 genera, 550 species.

SUBFAMILY Corytophaninae: basilisks and crested iguanas.
SUBFAMILY Crotaphytinae: collared lizards and leopard lizards.
SUBFAMILY Hoplocercinae: spiny tail lizards.
SUBFAMILY Iguaninae: herbivores. Includes the common or green iguana, Iguana iguana, from Central and South America, and the Galapagos giant iguanas.
SUBFAMILY Oplurinae: Madagascar iguanas.
SUBFAMILY Phrynosomatinae: horned lizards, tree lizards, sand lizards, and spiny lizards.
SUBFAMILY Polychrotinae: anoles. Comprises half of all iguanids.
SUBFAMILY Tropidurinae: curly-tailed lizards, lava lizards.

SUBORDER Scleroglossa: amphisbaenids, anguimorph lizards, geckos, true lizards and snakes. 35 families.

PARVORDER Amphisbaenia: amphisbaenids (worm lizards). Cylindric and slender body, lacking limbs or at least the hind ones. Loose skin surrounding the body, covered with ring scales. Head protected by scutes, sometimes fused. Eyes hidden below skin. One lung. They can moult the tail. Burrowers. Tropical Africa and America, Arabia, Morocco and Iberian Peninsula. 4 families and 143 species.

FAMILY Amphisbaenidae: Africa and America. 120 species.
FAMILY Bipedidae: forelimbs present. Mexico. 3 species.
FAMILY Rhineuridae: Florida.
FAMILY Trogonophidae: Africa and Arabia.

PARVORDER Anguimorpha: anguimorph lizards, monitors, dragons, and Gila monsters. 6 families and 131 species.

FAMILY Anguidae: anguids. Mainly in northern hemisphere. 90 species.

SUBFAMILY Anguinae: glass lizards. Apods.
SUBFAMILY Anniellinae: California apod lizards.
SUBFAMILY Gerrhonotinae: alligator lizards.
SUBFAMILY Diploglossinae: four-legged snake, galliwasps.

FAMILY Helodermatidae: beaded lizards. 2 species, Heloderma horridum (Mexican beaded lizard) and Heloderma suspectum (Gila monster). The only poisonous lizards. Mexico and USA.
FAMILY Lanthanotidae: 1 species, Lanthanotus borneensis (Borneo earless lizard).
FAMILY Shinisauridae: 1 species, Shinisaurus crocodilurus (crocodile lizard). China.
FAMILY Varanidae: monitors and dragons. Africa, Asia and Australia. 34 species.
FAMILY Xenosauridae: knotted scales lizards. Mexico and Guatemala. 3 species.

INFRAORDER Gekkota: big eyes lacking mobile eyelids, protected by a lens. Cloacal sacs. Despite morphological differences among families, they share a common bone structure. Mainly nocturnal. 3 families and nearly 1,000 species.

FAMILY Eublepharidae: primitive. Mobile eyelids and feet without lamellae. Central and North America, Africa and Asia. 22 species.
FAMILY Gekkonidae: geckos. Well-developed limbs. Feet with lamellae supported by climbing pads or scansors. Nocturnal. Worldwide except Antarctica. 900 species.

SUBFAMILY Diplodactylinae: split scansors. Australia and New Zealand.
SUBFAMILY Gekkoninae: the largest group. Worldwide except New Zealand. Includes the common geckos (genus Tarentola).
SUBFAMILY Sphaerodactylinae: American geckos.

FAMILY Pygopodidae: forelimbs absent and hindlimbs reduced with layers of loose skin. Slender body resembling snakes. No mobile eyelids. Australasia. 36 species.

INFRAORDER Scincomorpha: nearly half of all lizard species. Pleurodont tooth structure (teeth without alveoli, on the inner side of the jaw bone). Lower hemi-jaws fused. 7 families and 1,800 species.

FAMILY Cordylidae: rock flat lizards, South Africa eel lizards, shell lizards. Hard shell with ostheoderms. Africa and Madagascar. 60 species.
FAMILY Dibamidae: small burrowers with reduced limbs. Southeast Asia, isles of Australasia and Mexico. 11 species.
FAMILY Gymnophthalmidae: Central and South America. 130 species.
FAMILY Lacertidae: Old World "true" lizards. Well-developed legs, small dorsal scales, big ventral and head scales. Eurasia and Africa, specially in the Mediterranean region. 200 species.
FAMILY Scincidae: trend towards limb reduction. Usually smooth imbricated scales giving them a fish-like aspect. Worldwide. 1,300 species.
FAMILY Teiidae: equivalent to lacertids in the New World. 100 species.
FAMILY Xantusiidae: night lizards (some species are active by day). America. 19 species.

INFRAORDER Serpentes (Ophidia): snakes. Long and slender body lacking limbs. No external ears. Lower jaws linked by ligaments, which together with a flexible skull structure allows them to swallow large prey. Eyes without eyelids, covered with a membrane. Bifid protractile tongue with olfactory functions. Conical teeth on jaws and palate. Worldwide except polar regions. 15 families and 2,500 species.

SUPERFAMILY Acrochordoidea: 1 family.

FAMILY Acrochordidae : wart snakes. Aquatic, freshwater or sea water. Warty scales, no ventral scutes. Loose skin, body flattened dorsoventrally. Constrictors. Southeast Asia and Australia. 3 species.

SUPERFAMILY Booidea: vestigial hindlimbs (spurs flanking anus). 7 families and 60 species.

FAMILY Aniliidae: false coral snakes. Burrowers. Fused skull bones. Northern South America and Southeast Asia. 9 species.
FAMILY Boidae: New World boas. Viviparous and constrictors. The South American anaconda (Eunectes murinus) can measure up to 10 m. There are also Old World species, like sand boas.
FAMILY Bolyeriidae: small constrictors. Only in one island of the Indian Ocean. 2 species.
FAMILY Loxocemidae: 1 species, Loxocemus bicolor. Semi-burrower. Central America.
FAMILY Pythonidae: Old World pythons. Oviparous. Constrictors. The Asian reticulate python, Python reticulatus, measures up to 10 m.
FAMILY Tropidophiidae: wood snakes. Resembling boas but far shorter. Constrictors. From Southern North America to Northern South America. 20 species.
FAMILY Uropeltidae: shield-tailed snakes. Burrowers. Fused skull bones. Asia.

SUPERFAMILY Colubroidea: 4 families.

FAMILY Atractaspididae: burrowing asps. Africa and Middle East.
FAMILY Colubridae: colubrid snakes. Includes most of the snakes. In general non-poisonous; the poisonous ones have opistoglyph (rear) teeth. Flexible skull, pelvic waist absent. Worldwide except Antarctica. 1,600 species.

SUBFAMILY Boodontinae: large and diverse group. Includes harmless and opistoglyph species. Africa and Madagascar.
SUBFAMILY Calamariinae: East Asia dwarf snakes. They feed on invertebrates. 80 species.
SUBFAMILY Colubrinae: very diverse and extended. Includes harmless snakes (like the milk snakes Lampropeltis) and opistoglyph snakes (like the tree snakes Boiga).
SUBFAMILY Homalopsinae: aquatic, opistoglyph. They feed on fish or crustaceans. Asia and Australia. 40 species.
SUBFAMILY Natricinae: diverse group. Includes the European collared water snake (Natrix natrix), water snakes and knotted snakes. All the New World species are viviparous. North America, Europe and Asia.
SUBFAMILY Pareatinae: they feed on snails. Southeast Asia, Central and South America.
SUBFAMILY Pseudoxenodontinae: small or medium-sized. They feed on frogs and toads. Asia.
SUBFAMILY Xenodermatinae: protuberant snout scales. India and Southeast Asia.
SUBFAMILY Xenodontinae: includes, among others, the North American hognose snakes (Heterodon). America (including West Indies and Galapagos).

FAMILY Elapidae: cobras, mambas, taipans, coral snakes and sea snakes. Highly poisonous. Proteroglyph teeth (front and fixed). Most of them feed on cold-blooded animals. Terrestrial or marine. Distributed worldwide in warm regions.

SUBFAMILY Acanthophiinae: Australasian elapids. Includes species that have undergone convergent evolution with vipers or colubrids. Death adders (Acanthophis), taipans (Oxyuranus), shield snakes (Aspidelaps), Australian copperhead (Austrelaps), island tiger snakes (Notechis), eastern brown snake (Pseudonaja textilis).
SUBFAMILY Bungarinae: terrestrial kraits (Bungarus), water cobras (Boulengerina). Africa and Asia.
SUBFAMILY Elapinae: Asian and African cobras (Naja and Ophiophagus), African mambas (Dendroaspis), ringhal (Hemachatus haemachatus), American coral snakes (Micrurus and Micruroides).
SUBFAMILY Hydrophiinae: "true" sea snakes. Body flattened laterally. Viviparous and fully aquatic. They live in shallow waters, except the yellow-bellied sea snake, Pelamis platurus, which is pelagic. Indian and Pacific Oceans.
SUBFAMILY Laticaudinae: sea kraits and broad-tailed sea snakes. Cylindrical, with a flattened tail. Aquatic, but they reproduce and rest at the shores. Oviparous. Indian and Pacific Oceans.
SUBFAMILY Notechinae

FAMILY Viperidae: vipers and pit vipers. Highly poisonous. Long solenoglyph (hollow) teeth, front and retractile. Thick body, suitable for stalking prey.

SUBFAMILY Azemiopinae
SUBFAMILY Crotalinae: pit vipers. Between eyes and nasal holes they have two thermosensitive pits, which they use for detecting prey by their body warmth. Cottonmouth and copperhead (Agkistrodon), rattlesnakes (Crotalus and Sistrurus), and allies. America, Europe, Africa and Asia. 140 species.
SUBFAMILY Viperinae: typical vipers. From the coldest regions (Vipera berus) to the tropics (African puff-adder Bitis arietans, Gaboon viper Bitis gabonica, rhinoceros viper Bitis nasicornis). Europe, Africa and Asia. 60 species.

SUPERFAMILY Typhlopoidea: worm snakes. Flat snout, cylindrical body, rudimentary eyes. Burrowers. Non-poisonous. They feed on invertebrates. 3 families.

FAMILY Anomalepididae: blind worm snakes. Central and South America. 20 species.
FAMILY Leptotyphlopidae: slender blind snakes. America, Africa, Arabia and Pakistan. 64 species.
FAMILY Typhlopidae: blind snakes. Africa, Asia, Australia and Central America. One of the species, Ramphotyphlops braminus (flowerpot snake), is present throughout the world. 150 species.