Reptiles are animals that are related to birds, but their bodies differ in several ways. Reptiles do not use internal energy to stay warm, so their food intake is considerably lower than that of mammals. They typically feed on small insects, other animals, and plants, though some species only eat plants. Reptiles are categorized into four basic groups: snakes and lizards, crocodiles and alligators, turtles, and tortoises. Some of the smallest species include the tuatara and crocodile.
Squamata are the most diverse order of extant reptiles. They are characterized by flexible jaw structures, moving quadrate bones, and scales or shields. They represent 95 percent of all species of reptiles. They include snakes, lizards, and turtles.
The morphological characteristics of squamates suggest that the group split about 206 million years ago at the Triassic-Jurassic boundary. Most snakes are legless, and they lack functional eyelids or eardrums. Squamates have evolved specialized skills for active foraging, enabling them to hunt cryptic prey.
Most squamates exhibit a seasonal reproductive cycle. Eggs are laid in spring, and the young hatch when food resources are most plentiful. Temperate zone squamates also display a prenuptial pattern of gametogenesis, where maximal secretion of steroid hormones occurs prior to spring mating. Alternatively, some tropical squamates mate in the fall and give birth during the wet season.
Squamata are divided into 60 families. They live in a variety of habitats, including deserts, grasslands, and thornscrub. They are diurnal or crepuscular at twilight and can be terrestrial or aquatic. The diversity of squamates is greatest in semi-arid areas.
Most squamata have a V gene repertoire consistent with the other Squamata. However, their TCR repertoire is different from their mammal counterparts. In addition, their gamma and delta T cell receptors are absent.
The Crocodilia reptiles are large, predatory semi-aquatic reptiles that evolved 95 million years ago. They are the closest living relatives of birds. The archosaur family consisted of a number of extinct species that are now part of the Crocodilia.
Crocodilians are carnivores and feed on carrion and live animals. They are very efficient hunters with superior senses. They can hear their prey even from inside its eggshell. Their snouts are also equipped with special sense organs that help them detect their prey.
Crocodilians live in the tropics and subtropics of Africa, South America, and Asia. Their habitats include freshwater, brackish, and saltwater environments. They spend most of their lives in water but some species are capable of moving on land. They are often called “crocodiles”, but this does not necessarily mean that they are venomous. 파충류샵
Male crocodiles mate with multiple females. They are not monogamous, but they often work together to catch prey. During mating season, male crocodiles will mate with several females. In contrast, female crocodiles will form an exclusive bond with one female. Once a female crocodile has laid her eggs, she will guard the nest from predators. Once the young have been hatched, the female will take them to water.
The crocodile has a long snout, but they can differ in proportions and shape. Their bodies and backs are thick and hard, and they are covered in scales. They also have an excellent hearing ability and use a variety of vocalizations to communicate.
The Rhynchocephalia is a group of lizard-like reptiles. Although there is only one species left today (the tuatara of New Zealand), they were quite diverse in the Mesozoic. During this time, they were the largest and most varied group of reptiles on Earth.
The rhynchocephalians are classified as a sister taxon to the squamates, and share many derived characteristics. These include a full body ecdysis, imperforate stapes, and a fused pelvic bone. They also have extra centres of ossification in the epiphyses of the limb bones.
Rhynchocephalians differ in the arrangement of their teeth. Some are acrodont, while others are conical. The conical shape of their teeth allows them to pierce small prey. Their teeth are located on the inner side of the jaw bones. The rest of the rhychocephalians have teeth that are acrodont, but they are less common.
The tuatara, the only remaining member of the order Rhynchocephalia, is genetically variable and endemic to New Zealand. It provides key insights into the evolutionary history of rhynchocephalians. They were widespread in the early Mesozoic era and exhibited a wide geographic range. Since the Early Jurassic, their geographical range has shrunk dramatically. However, recently, they have been reintroduced to several mainland and island sanctuary populations.
Rhynchocephalians evolved from the Squamata order about 250 million years ago, and are therefore an important evolutionary link to the extinct stem reptiles. The genome of the tuatara is expected to be sequenced by 2020, and the discovery of 450 exogenous tuatara retroviruses provides a unique opportunity to understand the evolution of vertebrate viruses.