Reptiles are a diverse group of egg-laying vertebrate animals. Their classification is based on a wide range of features including skull structure and a distinct type of cloaca.
Modern chelonians such as turtles, tortoises and terrapins are classified based on how they retract their heads in their shells. They have one temporal fossa present high up on their skulls.
Class Reptilia contains the lizards, snakes, crocodiles and turtles. These are creeping terrestrial animals that live in the warmer regions of the world. They are uricotelic. They excrete the nitrogenous wastes as urea. They have three chambered hearts and a nervous system with 12 pairs of cranial nerves.
These are the first vertebrates to occupy ecological niches far from water. They advance from amp 레오파드게코 hibians by having dry scaly bodies that are adapted to life on land, by being ectothermic (cold-blooded), and by having internal fertilization and amniotic eggs.
The lepidosaurids, the surviving group of lizard-like reptiles from the Permian period gave rise to birds and dinosaurs. They are bipedal and have two temporal fossae in the skull.
Lepidosauria (lizards, snakes and tuatara) is the largest and most diverse order of reptiles at present, comprising >9000 species and filling a wide range of ecological niches. The clade is split into Rhynchocephalia and Squamata, with lizards and snakes placed in the latter (Squamata).
A new fossil locality from the Vellberg Mountains in Germany has led to a shift of divergence estimates for Squamata. The new data indicate that this group originated in the Early/Middle Triassic, well after the end-Permian mass extinction.
Squamata are characterised by a wide variety of derived features, such as paired male hemipenes; tongue notched distally for lingual prehension; a wide range of locomotor behaviours; and fracture planes in the caudal vertebrae that allow the tail to be thrown off at the moment of capture by predators. They also use camouflage and are able to feign death. 레오파드게코
The Squamata are a highly successful group of reptiles, with over 7000 species around the world. They are represented by the familiar lizards (including gekkotans, skinks and chameleons) as well as snakes and amphisbaenians. Squamates also have the remarkable ability to reproduce asexually, using a process known as parthenogenesis.
Ancestral squamates were ambush predators that relied on visual cues to capture prey. However, the evolution of a skull hinge that allowed them to open their jaws widely and a suite of chemosensory adaptations gave Scleroglossa greater access to microhabitats and prey that could not be detected by visual means. This enabled them to forage actively and led to higher activity levels.
Molecular studies of higher-level Squamate phylogeny have confirmed the overall patterns observed by earlier morphological analyses. Our large-scale maximum likelihood estimate of Squamate phylogeny, shown below, includes all the major groups:
The order Testudines is characterized by a special bony shell developed from their ribs that acts as a shield. Its use allows them to stay submerged for long periods of time and protects them from predators.
Besides the shell, they have special scales covering their skin and scutes – horny plates that act as an additional defense. They can survive surprisingly deep scrapes and bruises, and even large cracks in their carapace can often be filled in by new bone.
While the word turtle is commonly used to describe any member of this clade, it can lead to confusion since many members are also called terrapins, tortoises or sea turtles. To avoid confusion, many veterinarians, scientists and conservationists now use the term chelonian to refer to all members of this group.
The order Rhynchocephalia is a small group that contains the only living reptile, the New Zealand tuatara Sphenodon punctatus (or S. guntheri). Tuataras were originally classified as lizards in 1831, but remained misclassified until 1867, when Albert Gunther of the British Museum noticed their similarities to birds, turtles, and crocodiles and proposed the order Rhynchocephalia for them and their fossil relatives.
Rhynchocephalia is traditionally nested within Lepidosauromorpha, which also includes the modern reptiles of the order Squamata (lizards and snakes). However, molecular phylogenetic analyses now place the tuatara in a separate group, the clade Sphenodontia. This group is characterized by a hooked beak-like structure at the tip of the snout, formed by enlarged premaxillary teeth. Sphenodontia is derived from Greek sphenos (beak) + kephale (head). It has long been thought that rhynchocephalian morphology was essentially conservative, but recent studies have revealed considerable diversity among rhynchocephalian taxa.
Crocodilians are the order of large, primarily aquatic reptiles that includes true crocodiles (family Crocodylidae), alligators and caimans (family Alligatoridae), and the false or gharial crocodiles and gharials (family Gavialidae). They appear to be the closest living relatives of birds, and the two groups probably share a common ancestor that lived during the Campanian stage of the Late Cretaceous period.
They are characterized by robust skulls with long snouts and strongly toothed jaws, short necks that extend without constriction into thick laterally compressed tails, and powerful front feet with four separate toes. The 23 living species are predominantly carnivorous, and most spend much of their lives in water. They have efficient four-chambered hearts, like mammals and birds. Adult crocodilians are typically territorial and solitary, with males defending basking spots, nesting areas, nurseries, and overwintering sites.
Tuatara are reptiles endemic to New Zealand. Although they resemble most lizards, they belong to a distinct lineage and are the only living members of an order that flourished 200 million years ago in the Triassic. Their closest living relatives are squamates (lizards and snakes).
They have an unusual body plan, with a large head and small body. They are nocturnal and mainly insectivorous. They can withstand cold temperatures and their skin is adapted to absorb water.
Like their distant reptilian relatives, tuatara excrete uric acid to prevent dehydration. They also have a suite of genes that help them cope with heat, including a thermosensitive TRP gene. Genetic work has shown that tuatara populations are distinct, with strong inbreeding and local adaptation. The tuatara genome will facilitate future studies of tuatara evolution.