Reptiles are cold-blooded vertebrates with scaly bodies and paired limbs, breathing through lungs, laying shelled eggs (though some “squamates” give birth to live young). They are uricotelic, excreting waste as urea.
The class Reptilia contains most surviving reptiles, including lizards, snakes, turtles and chameleons. It also includes the dinosaurs and crocodiles.
Class Reptilia represents the first animals to fully adapt to life on land, evolving from amphibians 320 million years ago. The living species are found in four orders, three of which occur in North America: order Testudines (turtles), order Crocodilia (crocodiles and alligators), and order Squamata (lizards and snakes). Their thick, dry scaly skin protects them from desiccation, physical injury and can even have chromatophores for 레오파드게코 colour.
Their short limbs allow them to crawl quickly, and their heart is 4-chambered with separate ventricles. Their skin can have horny scales, shields or plates, and they have a well-developed tail.
Fossil evidence and comparative analyses show that birds belong with reptiles rather than with mammals, forming part of a monophyletic group called the diapsida. Because of this, most systematists now place them within the class Reptilia. Similarly, molecular evidence shows that the lepidosauria and squamata are more closely related to each other than they are to archosaurs, and that crocodiles and birds evolved from the same ancestor. Most reptiles are oviparous, but some of the squamates are capable of giving live birth through ovoviviparity or viviparity (egg retention and internal fertilization). The lizards in the subclass Squamata have adapted to this by developing a placenta similar to that of mammals.
The group Archosauria (“ruling reptiles”), which contains all dinosaurs and pterosaurs, and 레오파드게코 the extinct crocodylians, is distinguished by a variety of anatomical features. The defining morphological characteristics include serrated teeth, an antorbital fenestra (opening in the skull in front of the eyes), and mandibular fenestrae, openings in the lower jaw bones that reduced skull weight and allowed for more flexibility (kinesis) when chewing.
The earliest true archosaurs appeared in the Olenekian (Lower Triassic) and were carnivores that probably defended themselves against rival mammals by their powerful, sharp teeth. Later they diversified, becoming the ecologically dominant terrestrial vertebrates of the Triassic until the K-Pg mass extinction.
Older morphological definitions of Archosauria included the bird lineage (class Aves) and some crocodylians such as proterosuchids and euparkeriids, but these groups have since been placed outside Ornithosuchia and crown-group Archosauria by cladistic analysis. As a result, birds and crocodylians are now in the subclass Reptilia. They were the only groups of basal archosaurs to survive into the Cretaceous and beyond, when they and a handful of other archosaurians became dominant in the air and on land – dinosaurs ruled the land, pterosaurs dominated the sky, and crocodylians dominated swamps, rivers, and seas.
A clade consisting of the modern lepidosid reptiles (lizards, snakes and the New Zealand tuatara). They currently comprise >9000 species worldwide, which fill a wide variety of ecological niches.
Unlike the monophyletic archosaurs, lepidosids are not bipedal and have two complete temporal openings, a fully functional palate and ovipary. They also have a specialized auditory epithelium that resembles that of the primitive tuatara, crocodiles and turtles. It consists of an elongated array of up to 1000 sensory hair cells, which can detect sound reflected off surfaces.
In general, lepidosaurids are herbivores and omnivores that can consume plants or insects. The tuatara, however, is a carnivore that eats a broad range of prey species and can do so by using a special shearing mechanism, which involves anterior movement of the lower jaw after it has closed.
The Lepidosaurida, Scleroglossa, and Squamata are all subclasses (or superorders) of the Class Reptilia. Squamata is the most diverse of the four surviving reptile orders and includes the lizards, snakes, and amphisbaenians. This group has the most varied modes of survival among all reptiles, with specialized forms such as geckoes, chameleons, and skinks that can live on dry rocky surfaces or burrow through dirt to evade predators. In the case of snakes, the evolution of a flexible jaw structure has allowed them to kill larger prey and hunt more efficiently by using their forked tongues to quickly engulf food or feces and then hold it in their mouths with powerful jaw muscles.
Squamata is also distinguished by its vivipary, in which some species give birth to living offspring. This allows squamates to live in cooler regions, and it has evolved multiple times among lizards and snakes. In addition, a number of squamate species, such as the New World natricine snakes and genus Eumeces, attend or “guard” their eggs to provide them with moisture and heat, helping them to develop more rapidly.
Turtles and tortoises (Chelonia) belong to the order Testudines, one of the oldest reptile groups. Known from fossils dating back to the early Triassic period, they are much older than lizards and snakes. Their body is shielded by a special bony shell, called a carapace, developed from their ribs. The shell is covered by scutes – horny plates of keratin – which helps them survive even severe injuries. They are poikilotherms, meaning that they can control their body temperature by adjusting behavior.
Turtles are divided into two suborders, Pleurodira and Cryptodira. The distinction is based on the method of head retraction: pleurodires can retract their heads laterally, while cryptodires can only hide them behind the shell. Currently, the families Pelomedusidae, Chelidae, and Dermatemydidae are pleurodires; the remaining family, the Dermochelyidae, is cryptodires.
Members of the order Testudines are often referred to as turtles, tortoises, or terrapins. Which name is used depends on the language of the speaker: British English typically describes them as turtles, while American and Australian English often use terrapin or tortoise.