Lizard in the context of Tuatara

Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods, but excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals). All extant (living) amphibians belong to the monophyletic subclass Lissamphibia, with three living orders: Anura (frogs and toads), Urodela (salamanders), and Gymnophiona (caecilians). Evolved to be mostly semiaquatic, amphibians have adapted to inhabit a wide variety of habitats, with most species living in freshwater, wetland or terrestrial ecosystems (such as riparian woodland, fossorial and even arboreal habitats). Their life cycle typically starts out as aquatic larvae with gills known as tadpoles, but some species have developed behavioural adaptations to bypass this.

Young amphibians generally undergo metamorphosis from an aquatic larval form with gills to an air-breathing adult form with lungs. Amphibians use their skin as a secondary respiratory interface, and some small terrestrial salamanders and frogs even lack lungs and rely entirely on their skin. They are superficially similar to reptiles like lizards, but unlike reptiles and other amniotes, require access to water bodies to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators to habitat conditions; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe.

In tetrapods, cervical vertebrae (sg.: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have seven cervical vertebrae, with the only three known exceptions being the manatee with six, the two-toed sloth with five or six, and the three-toed sloth with nine.

In humans, cervical vertebrae are the smallest of the true vertebrae and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a transverse foramen, an opening in each transverse process, through which the vertebral artery, vertebral veins, and inferior cervical ganglion pass. The remainder of this article focuses on human anatomy.

The Mona ground iguana (Cyclura stejnegeri) is a critically endangered species of rock iguana, endemic to Mona Island, Puerto Rico. It is one of the island's few large land animals, and it is the largest endemic terrestrial lizard in the US territory, and one of the biggest rock iguanas within the Antilles. It was previously considered a subspecies of the rhinoceros iguana (Cyclura cornuta).

Snakes are elongated limbless reptiles of the suborder Serpentes (/sɜːrˈpɛntiːz/). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have skulls with several more joints than their lizard ancestors and relatives, enabling them to swallow prey much larger than their heads (cranial kinesis). To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most only have one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution, leading to many lineages of legless lizards. These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal (see Amphisbaenia, Dibamidae, and Pygopodidae).

Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, and the islands of New Zealand, as well as many small islands of the Atlantic and central Pacific oceans. Additionally, sea snakes are widespread throughout the Indian and Pacific oceans. Around thirty families are currently recognized, comprising about 520 genera and about more than 4,170 species. They range in size from the tiny, 10.4 cm-long (4.1 in) Barbados threadsnake to the reticulated python of 6.95 meters (22.8 ft) in length. The fossil species Titanoboa cerrejonensis was 12.8 meters (42 ft) long. Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the Jurassic period, with the earliest known fossils dating to between 143 and 167 Ma ago. The diversity of modern snakes appeared during the Paleocene epoch (c. 66 to 56 Ma ago, after the Cretaceous–Paleogene extinction event). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus.

A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive/cute appearances, intelligence, and relatable personalities, but some pets may be taken in on an altruistic basis (such as a stray animal) and accepted by the owner regardless of these characteristics.

Two of the most popular pets are dogs and cats. Other animals commonly kept include rabbits; ferrets; pigs; rodents such as gerbils, hamsters, chinchillas, rats, mice, and guinea pigs; birds such as parrots, passerines, and fowls; reptiles such as turtles, lizards, snakes, and iguanas; aquatic pets such as fish, freshwater snails, and saltwater snails; amphibians such as frogs and salamanders; and arthropod pets such as tarantulas and hermit crabs. Smaller pets include rodents, while the equine and bovine group include the largest companion animals.

A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains.

Insects are the major pollinators of most plants, and insect pollinators include all families of bees and most families of aculeate wasps; ants; many families of flies; many lepidopterans (both butterflies and moths); and many families of beetles. Vertebrates, mainly bats and birds, but also some non-bat mammals (monkeys, lemurs, possums, rodents) and some lizards pollinate certain plants. Among the pollinating birds are hummingbirds, honeyeaters and sunbirds with long beaks; they pollinate a number of deep-throated flowers. Humans may also carry out artificial pollination.

A tooth (pl.: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.

The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw.

Sauropoda (/sɔːˈrɒpədə/), whose members are called sauropods (/ˈsɔːrəpɒdz/; from sauro- + -pod; lit. 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their body), and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Alamosaurus, Apatosaurus, Argentinosaurus, Brachiosaurus, Brontosaurus, Camarasaurus, Diplodocus, Dreadnoughtus, and Mamenchisaurus.

The oldest known unequivocal sauropod dinosaurs are known from the Early Jurassic. Isanosaurus and Antetonitrus were originally described as Triassic sauropods, but their age, and in the case of Antetonitrus also its sauropod status, were subsequently questioned. Sauropod-like sauropodomorph tracks from the Fleming Fjord Formation (Greenland) might, however, indicate the occurrence of the group in the Late Triassic. By the Late Jurassic (150 million years ago), sauropods had become widespread (especially the diplodocids and brachiosaurids). By the Late Cretaceous, one group of sauropods, the titanosaurs, had replaced all others and had a near-global distribution. However, as with all other non-avian dinosaurs alive at the time, the titanosaurs died out in the Cretaceous–Paleogene extinction event. Fossilised remains of sauropods have been found on every continent, including Antarctica.

Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 200 species described as of June 2015. The members of this family are best known for their distinct range of colours, being capable of colour-shifting camouflage. The large number of species in the family exhibit considerable variability in their capacity to change colour. For some, it is more of a shift of brightness (shades of brown); for others, a plethora of colour-combinations (reds, yellows, greens, blues) can be seen.

Chameleons are also distinguished by their zygodactylous feet, their prehensile tail, their laterally compressed bodies, their head casques, their projectile tongues used for catching prey, their swaying gait, and in some species crests or horns on their brow and snout. Chameleons' eyes are independently mobile, and because of this the chameleon's brain is constantly analyzing two separate, individual images of its environment. When hunting prey, the eyes focus forward in coordination, affording stereoscopic vision.

Monitor lizards are lizards in the genus Varanus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the southern United States as an invasive species. About 80 species are recognized.

Monitor lizards have long necks, powerful tails and claws, and well-developed limbs. The adult length of extant species ranges from 20 cm (7.9 in) in some species such as Varanus sparnus, to over 3 m (10 ft) in the case of the Komodo dragon, though the extinct megalania (Varanus priscus) may have reached lengths of more than 7 m (23 ft). Most monitor species are terrestrial, but many are also arboreal or semiaquatic. While most monitor lizards are carnivorous, eating smaller reptiles, fish, birds, insects, small mammals, and eggs, a few species also eat fruit and vegetation.

The Cretaceous Terrestrial Revolution (abbreviated KTR), also known as the Angiosperm Terrestrial Revolution (ATR) by authors who consider it to have lasted into the Paleogene, describes the intense floral diversification of flowering plants (angiosperms) and the coevolution of pollinating insects (especially anthophilans and lepidopterans), as well as the subsequent faunal radiation of various frugivorous, nectarivorous and insectivorous terrestrial animals then at the lower food web levels such as mammals, avialans (early birds and close relatives), squamate reptiles (lizards and snakes), lissamphibians (especially frogs) and web-spinning spiders, during the Cretaceous period.

After the K-Pg extinction event devastated the Mesozoic terrestrial ecosystems and wiped out nearly all animals weighing more than 25 kg (55 lb), the survivors among these smaller animals that thrived during the KTR recovered first to reoccupy the ecological niches vacated by the extinction of non-avian dinosaurs and pterosaurs, and therefore became the dominant clades of the Cenozoic terrestrial faunas. Flowering plants also quickly became the mainstream florae during the Cenozoic, replacing the previously more prevalent gymnosperms and ferns.

Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten extant salamander families are grouped together under the order Urodela, the sole surviving order from the group Caudata. Urodela is a scientific Latin term based on the Ancient Greek οὐρά δήλη: ourà dēlē "conspicuous tail". Caudata is the Latin for "tailed ones", from cauda: "tail".

Salamander diversity is highest in eastern North America, especially in the Appalachian Mountains; most species are found in the Holarctic realm, with some species present in the Neotropical realm. Salamanders never have more than four toes on their front legs and five on their rear legs, but some species have fewer digits and others lack hind limbs. Their permeable skin usually makes them reliant on habitats in or near water or other cool, damp places. Some salamander species are fully aquatic throughout their lives, some take to the water intermittently, and others are entirely terrestrial as adults.

Squamata (/skwæˈmeɪtə/, Latin squamatus, 'scaly, having scales') is the largest order of reptiles; most members of which are commonly known as lizards, with the group also including snakes. With over 11,991 species, it is also the second-largest order of extant (living) vertebrates, after the perciform fish. Squamates are distinguished by their skins, which bear horny scales or shields, and must periodically engage in molting. They also possess movable quadrate bones, making possible movement of the upper jaw relative to the neurocranium. This is particularly visible in snakes, which are able to open their mouths very widely to accommodate comparatively large prey. Squamates are the most variably sized living reptiles, ranging from the 16 mm (0.63 in) dwarf gecko (Sphaerodactylus ariasae) to the 6.5 m (21 ft) reticulated python (Malayopython reticulatus). The now-extinct mosasaurs reached lengths over 14 m (46 ft).

Among other reptiles, squamates are most closely related to the tuatara, the last surviving member of the once diverse Rhynchocephalia, with both groups being placed in the superorder Lepidosauria.

Rhynchocephalia (/ˌrɪŋkoʊsɪˈfeɪliə/; lit. 'beak-heads') is an order of lizard-like reptiles that includes only one living species, the tuatara (Sphenodon punctatus) of New Zealand. Despite its current lack of diversity, during the Mesozoic rhynchocephalians were a speciose group with high morphological and ecological diversity. The oldest record of the group is dated to the Middle Triassic around 244 million years ago, and they had achieved global distribution by the Early Jurassic. Most rhynchocephalians belong to the suborder Sphenodontia ('wedge-teeth'). Their closest living relatives are lizards and snakes in the order Squamata, with the two orders being grouped together in the superorder Lepidosauria.

Rhynchocephalians are distinguished from squamates by a number of traits, including the retention of rib-like gastralia bones in the belly, as well as most rhynchocephalians having acrodont teeth that are fused to the crests of the jaws (the latter also found among a small number of modern lizard groups like agamids).

Herpetology (from Ancient Greek ἑρπετόν herpetón, meaning "reptile" or "creeping animal") is a branch of zoology concerned with the study of amphibians (including frogs, salamanders, and caecilians (Gymnophiona)) and reptiles (including snakes, lizards, turtles, crocodilians, and tuataras). Birds, which are cladistically included within Reptilia, are traditionally excluded here; the separate scientific study of birds is the subject of ornithology.

The precise definition of herpetology is the study of ectothermic (cold-blooded) tetrapods. This definition of "herps" (otherwise called "herptiles" or "herpetofauna") excludes fish; however, herpetological and ichthyological scientific societies often collaborate. For instance, groups such as the American Society of Ichthyologists and Herpetologists have co-published journals and hosted conferences to foster the exchange of ideas between the fields. Herpetological societies are formed to promote interest in reptiles and amphibians, both captive and wild.

A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head, is photoreceptive, and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production for thermoregulation. The hole that contains the eye is known as the pineal foramen or parietal foramen, because it is often enclosed by the parietal bones.

The parietal eye was discovered by Franz Leydig, in 1872, from work with lizards.

Pseudocopulation is a behavior similar to copulation that serves a reproductive function for one or both participants but does not involve actual sexual union between the individuals. It is most generally applied to a pollinator attempting to copulate with a flower adapted to mimic a potential female mate. The resemblance may be visual, but the key stimuli are often chemical and tactile. The form of mimicry in plants that deceives an insect into pseudocopulation is called Pouyannian mimicry after the French lawyer and amateur botanist Maurice-Alexandre Pouyanne.

A non-mimetic form of pseudocopulation has been observed in some parthenogenetic, all-female species of lizard. The behaviour does not appear to be necessary to trigger parthenogenesis.