The class Reptilia contains crocodiles, alligators, tuatara, lizards, snakes and amphisbaenians. It also includes modern turtles (Chelonia), as well as extinct sea reptiles, and dinosaurs.
They are cold-blooded and have horny, rough skin. They are ectothermic and lay eggs with internal fertilization.
They are divided into two groups, one with holes in their skulls (Diapsida) and the other without (Archosauria). Birds belong to the latter group.
Squamata
Squamata (lizards, snakes, and their allies) are a large and successful order of reptiles with many different types of body forms. The group includes long-tailed surface dwellers, burrowers, climbers, aquatic forms, and gliding types. They can be found on all continents except Antarctica in a wide variety of h 도마뱀분양 abitats and lifestyles, adapted to their environments by evolutionary adaptations such as scales, limb reduction, a wide range of behavioral modes, and adaptations for different food sources.
Squmata are the only vertebrates with paired penes, and they also have a number of unique characteristics not shared with other reptiles. Most notably, all squamates have a movable quadrate bone that hangs down from the skull like a curtain, allowing them to open and close their jaws more quickly and to a wider gape. The ability to streptostylize their jaws enables them to swallow relatively large prey items that would otherwise be too large to fit through their narrow mouths, and it also frees the tongue for other activities such as chemosensing.
Squamata is a monophyletic group, meaning that all squamates are descendants of a common ancestor. They have more than 70 shared derived features, including the streptostylized jaws, a single temporal opening or reduced opening, a highly specialized skull, and a pair of eversible copulatory organs at the base of their tails (hemipenes). Some squamates, such as New World natricine snakes and some anguimorph skinks, guard their eggs, while others, such as a few skinks in the genus Eumeces an 도마뱀분양 d all snakes, enhance development by providing water or heat to their developing embryos.
Testudines
Testudines (Chelonia) are reptiles that are distinguished by a special bony shell developed from their ribs. The earliest turtle fossils date from the Triassic period, making them one of the oldest reptile groups and a more ancient group than snakes, lizards, or crocodiles. Today, about 300 species live worldwide, mostly in salt water or in freshwater. Their unique body form distinguishes them from other animals, and their shells serve as protection from predators and even changing weather conditions.
The ribs of a testudine form a hard shell, or carapace, that interlocks to protect the limbs and head. Many of the shells are brightly patterned and recognizable. The carapace is covered with scutes — horny plates of keratin — that provide added strength and protection. Testudines can survive surprisingly severe damage to their shells, and deep cracks or missing portions of the shell often fill in with bone and heal.
Most newly-emerged aquatic testudines are carnivorous, but adult turtles are typically herbivorous grazers that feed on algae, leafy greens, and flowers. Some, such as the leatherback sea turtle (Dermochelys coriacea), are primarily solitary foragers in the open ocean. Testudines are famous for their longevity, and research into the genes of long-lived turtles is beginning to shed light on how they do it. In addition to a healthy diet, the secret seems to be that their organs do not wear out with age, unlike most other mammals and vertebrates.
Crocodilia
Crocodylians (order Crocodylia, family Crocodylidae) comprise 23 species of large, ponderous carnivorous reptiles. They are among the largest of living animals, with robust skulls, long snouts and powerful jaws, short necks and a long, robust, laterally compressed tail that extends from the shoulders. They are found worldwide in water but are most abundant in the tropical rivers and marshes of the southeastern United States.
They have an extremely strong grip and can crush bones with their powerful jaws. They have a specialised skull with a hinge between the atlanto-occipital joint, enabling the jaws to open wider than would be possible in other reptiles. The muscles that close the jaws are much stronger than those that open them. The snout shape differs between species; crocodiles have slender snouts while alligators and caimans have broad snouts. The teeth of the lower jaw fit into pits in the upper jaw and are not visible when the mouth is closed.
Their skin is tough and can withstand abrasions, with the outer layer being covered in small plates called scutes. They have a muscular tail that is largely used for propulsion. They can also use it to control their buoyancy in the water. They can sink by moving their lungs towards the tail and float by pushing them back to the head. They can also swim in a “tail walk” by holding their legs against the body and reducing drag. Crocodiles can communicate with other members of their species using a loud yelp or grunt; this may help them to identify and locate food.
Sphenodontia
Sphenodontia (“wedge-tooth”) arose during the Mesozoic and is characterized by one living genus, tuatara (Sphenodon). Also called Rhynchocephalia, sphenodontians are an offshoot of the evolutionary line leading to true lizards and snakes.
Although tuataras appear very lizard-like in gross appearance, several unique features define them as distinct taxa within Lepidosauromorpha. These include the caudal anatomy, a habit of losing the tip of the tail when threatened, and transversal cloacal slits.
In addition, the skull of tuataras is highly elongated with an elongate posteroventral process reaching to the level of the Meckelian canal. The anterior dentaries are slender and do not meet at the center of the quadrate-quadratojugal complex, as seen in other sphenodontians. The dentary apex also has a well-developed coronoid process, and the ventral surface of the Meckelian canal is a slender crest that curves upwards, similar to other sphenodontians.
The fossil record of sphenodontians is fragmentary, and the only articulated skulls of this clade are of the early Neogene tuatara fossils described by McEwen and colleagues10. However, the holotype of N. sani and its ontogenetic series of maxillae and dentaries, with successional teeth on the dentaries, hatchling teeth on the maxillae, and alternating teeth on the mandible, provide a unique window into sphenodontian skull evolution. Phylogenetic analyses (maximum parsimony, non-clock Bayesian inference, and relaxed morphological clock BI with tip dating) all support the placement of N. sani within Sphenodontinae, with the smallest specimens (inferred as juveniles) having relatively short dentaries and large dental regions of successional and hatchling teeth. The larger sized specimens, inferred as adults, have dentaries that are 30% longer than the smallest individuals and show tooth wear indicating advanced ontogenetic stages.