Reptile Classification

게코도마뱀 Reptiles are cold-blooded (ectothermic) vertebrates that occupy almost every type of habitat. They comprise over 11,500 living species.

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In modern zoological classification we use phylogenetic methods, in which animals are grouped by their ancestry rather than their characteristics. By this convention, reptiles include all crocodiles and alligators, as well as birds, lizards and snakes, plus the tuatara of New Zealand.

Class Reptilia

Class Reptilia includes the snakes, lizards, and turtles that make up about 6,550 of the planet’s 8,500 living species. They’re a diverse group that can be found in most habitats, from forests to deserts to seas. Reptiles are tetrapod vertebrates, which means they have four limbs and are descended from four-legged ancestors. They are also amniotes, which are animals whose embryos develop surrounded by membranes, either carried inside the mother or laid outside as part of an egg.

Most reptiles are oviparous (they lay eggs) but a few, such as snakes and some extinct aquatic clades, are viviparous, where they lay their young alive. They are also ectothermic, meaning that they can’t regulate their own body temperature like mammals and birds can. Instead, they rely on the sun and other sources to warm them up, and they cool down by hiding in the shade or in water.

The class Reptilia is divided into four orders, with only three of these orders occurring in North America – the Order Crocodilia (crocodiles and alligators), the Order Sphenodontia (frogs and toads), and the Order Squamata (turtles, lizards, snakes, and tuataras). These are further subdivided into a number of different sub-classes. The most well-known reptiles are crocodiles and alligators, but there’s also a range of lizards and snakes in the Squamata, and even turtles in the Testudines.

Sub-class Chelonia게코도마뱀

Chelonia is a subclass of the Reptilia order and includes all turtles, tortoises and terrapins. These animals differ from other reptiles because their bodies are enclosed in a shell above and below. This shell protects their heads, tails and legs from predators and the elements. Most chelonians are oviparous and lay eggs that hatch inside their shells.

The green sea turtle (Chelonia mydas) belongs to the genus Chelonia and to the family Cheloniidae. This turtle is one of five species and has a cosmopolitan distribution in warm seas. This species demonstrates a dramatic shift in diet from the pelagic to the adult benthic stage, with post-hatchlings (occupying pelagic convergence zones) eating worms, crustaceans and aquatic insects while adults are herbivorous and eat algae and grasses.

AnAge entries for 149 growth increments of the green sea turtle, Chelonia mydas, were analyzed to determine if the dietary transition is related to morphological changes, such as carapace length and plastron width. The results suggest that growth in these linear measurements is primarily influenced by body mass. Growth rate is predicted to be higher in animals with larger carapaces and plastron widths.

Chelonians are a race of turtle-like humanoids. They first appeared in the artwork of Phil Bevan for the cover of Prelude The Highest Science (1993). Their depiction is a bipedal saddleback Galapagos tortoise with long limbs and a tri-flipper. They have a pointed skull, black eyes and smooth green skin. Later depictions of chelonians, such as those by Tony Masero for the cover of Zamper (1995) and Lee Sullivan for The Last Word (2006), show spiked arms and a domed helmet.

Sub-class Archosauria

A subclass of diapsid reptiles that began to evolve in the late Permian period. The group includes dinosaurs and the living crocodilians and birds. Also known as archosaurids or thecodonts, they are distinguished from other vertebrates by a pair of openings in their skull temporal area and serrated (saw-edged) teeth set into sockets. They also have a process on the shaft of their femur, called the fourth trochanter, that served as an attachment point for major tail muscles (the caudofemoralis).

Early archosauromorphs like Euparkeria evolved several key diagnostic features including a long narrow skull with well-developed frontal lobes and two new openings in their skull, the mandibular and antorbital fenestrae. These features helped archosauromorphs occupy ecologically dominant positions and replace the previously successful synapsids in most terrestrial niches by the Middle Triassic, shortly after the end-Permian mass extinction.

The crown clade Archosauria, represented today by crocodylians and birds, are the last surviving members of the archosauromorph lineage. They are a diverse group with remarkable adaptations, from the herbivorous armoured pseudosuchians to the carnivorous rauisuchids and ornithodirans of the Late Triassic. This diversification went hand in hand with unappreciated high skull shape diversity among stem archosaurs during the Middle Triassic. This varied cranial morphology is most likely related to differing feeding ecologies and environmental adaptations of early archosauromorphs.

Sub-class Lepidosauria

Lepidosauria is a subclass of the Reptilia order, and contains the living lizards, snakes and amphisbaenians. It is named after the Greek word for scaled lizards, and includes the tuatara, which is the only surviving member of a group that was once a diverse and widespread part of the Mesozoic fauna. Lepidosauria is the closest living relative of the clade Squamata, and can be distinguished by a number of unique features, including transverse cloacal slits and a distally notched tongue.

In traditional classifications, the tuatara is ranked as a suborder of Squamata (or Rhynchocephalia), and lizards (Lacertilia or Sauria), snakes (Serpentes or Ophidia) and amphisbaenians (Amphisbaenia) are placed at equal categorical rank within this group. Such traditional classifications, however, were crafted by workers who focused on evolutionary taxonomy rather than on phylogenetic systematics, and they do not reflect the true phylogenetic relationships among these groups.

The tuatara is considered to be the sister of the lizards, and it can be classified as a relict from the Mesozoic subclass Rhynchocephaliana, which also included the crocodiles and alligators. Today, rhynchocephalians are extinct everywhere except in New Zealand, where the only two surviving members of the group are the tuatara and a genus of small lizard. This makes tuataras the smallest living reptiles, but they are not the least numerous, and they have developed a wide range of adaptations to survive in New Zealand’s unique environments.