Reptile Classification

Reptiles are tetrapod vertebrates that have horny epidermal scales, internal fertilization, lungs instead of gills for respiration, and an externally shelled egg (except those species that give birth to live young). They are divided into several subclasses.


Crocodiles, alligators, tuatara (a lizard-like reptile found only in New Zealand), and snakes are classified in this class. Its phylogenetic position is contentious.

Class Reptilia

Class Reptilia includes all non-mammalian amniotes that are not birds or mammals. It contains the largest group of living animals, the Order squamata (lizards and snakes). This group is found worldwide and varies in size from a small gecko to a saltwater crocodile. Most members of the Order squamata have scaly skin that is shed periodically. Some, like the snakes, have a moveable quadrate bone to open their mouth wide. Oth 게코도마뱀 er species, such as the lizards, can also swallow large prey items whole.

Most squamates are oviparous (egg-laying). However, some, such as the tuatara of New Zealand, give live birth. Traditionally, the term reptile has been used to describe all tetrapods that are not mammals or birds, and that have a dry, scaly skin. These include crocodiles, alligators, tuatara, lizards and snakes. However, phylogenetic analysis now indicates that this traditional view is inaccurate. Instead, a more accurate classification would be to use the term ectothermic vertebrates.

Sub-class Testudines

The order Testudines, or Chelonian, is a group of about 360 living and recently extinct species of turtles and tortoises. They are characterized by the fact that most of their bodies are shielded in a special bony shell developed from their ribs. The shell, called a carapace or plastron, is a rigid box that cannot be ejected like the skin of some other reptiles and can withstand considerable damage.

Testudines are also distinguishe 게코도마뱀 d by the fact that most male and female individuals of a given species exhibit sexual dimorphism, with some species of tortoise being noticeably larger than others. Their longevity and resistance to many environmental extremes have made them a symbol of endurance, and they feature prominently in the mythology, art, and folklore of many cultures.

Sub-class Crocodilia

The sub-class Crocodilia contains the orders Alligatoridae (alligators, caimans, and dwarf gharials), Crocodylidae (crocodiles and gharials) and Gavialidae (the Malayan gharial). These animals are large semi-aquatic reptiles found in the tropics of Africa, Asia, South America, Southern Florida, and Australia. Their unique features include the ability to swallow stones, called gastroliths, that act as ballast, and a very acidic stomach that aids post-digestion processing of their prey. Males are much larger than females. They also have a form of sex determination that is temperature related.

The crocodilian lineage separated from that of the archosaurs in the Late Triassic. They are the most ancient of living reptiles. The Malayan gharial, also known as the false gharial, lives in freshwater bodies throughout Peninsular Malaysia, Sumatra and Borneo. It feeds on fish, water birds and proboscis monkeys. It is listed as Vulnerable on the ICUN list. DNA studies suggest that the Malayan gharial is closely related to the American crocodile (Crocodylus acutus). In this phylogenetic tree the red shaded box on the right contains the American crocodile.

Sub-class Sphenodontia

In the past, college-level textbooks usually equated this group with reptiles, since they were the only amniotes that did not include mammals or birds. However, cladists recognize that mammalians are actually a clade (Mammalia), and birds are a separate clade (Aves). So the traditional class Reptilia is only one section of the larger clade Amniota.

The sub-class Sphenodontia consists of two living species, the tuatara (Sphenodon punctatus and Sphenodon guntheri). Native to New Zealand, these are among the most unusual reptiles on earth, showing unique adaptations for life in a cold environment.

Tuataras are known for a number of odd features, including the fact that they grow slowly and reproduce very infrequently. Their eggs are laid in a parchment-like shell that takes ten years to form, and females typically only breed every four or five years. They also have a remarkable ability to regenerate lost limbs. Tuataras are close relatives of modern snakes and lizards, which belong to the sub-class Lepidosauria.

Sub-class Lepidosauria

Lepidosauria is a subclass (or superorder) of Reptilia that contains the orders Squamata and Rhynchocephalia. Its living members include tuatara, lizards, snakes and amphisbaenians. It is also the sister taxon to Archosauria, which includes birds and Crocodilia.

Many lepidosaurs rely on camouflage for defense, including the ability to change skin color to match their surroundings. Some can even autotomize their tails for protection. Other defensive mechanisms include gular pumping and the ability to feign death.

Fossils like the aquatic Marmoretta from the Middle Triassic of the UK and the paraboloid kuehneosaur Pamelina from the Early Triassic of Poland show that stem-lepidosaurs existed long before the rise of the modern form. Until recently, molecular data placed turtles within the Anapsida (and not in the more basal group of the Diapsida), but recent morphological studies place them firmly with the rest of the lepidosaurs. They are now referred to as Lepidosauridae.

Sub-class Squamata

Squamata is a clade of tetrapods (four-legged vertebrates) that includes the familiar groups of lizards, snakes, and amphisbaenians. These groups are found all over the world and range from burrowers to bipedal runners, and from climbers to active predators. Despite their diverse appearances, all squamates have several derived features that are unique to the group, such as paired penes and movable quadrate bones that allow them to open their mouths wider than any other reptiles.

Historically, squamates have been divided into two crown-group suborders: Lacertilia (lizards) and Ophidia (snakes). However, modern molecular phylogenetic analysis has shown that the distinction between the two groups is paraphyletic and that the term “lizard” can be used informally to refer to any squamate. Genetic data also support a sister-group relationship between Dibamida (geckotans) and Scincoidea (scincids, cordylids, gerrhosaurids, and xantusiids), as well as a clade containing iguanians, snakes, and anguimorphs – a division that reflects the way that many morphological characteristics have evolved.