Reptiles are one of the six basic groups of animals. Reptiles are cold-blooded vertebrates that diverged from ancestral amphibians about 340 million years ago. There are two characteristics that distinguished early reptiles from amphibians and enabled them to colonize terrestrial habitats more extensively than their ancestors, scales and the ability to lay hard-shelled eggs. Scales protect reptiles from abrasion and loss of body moisture. Hard-shelled eggs provide a protective environment in which the embryo can develop.
FACT: Reptiles are divided into four groups.
Turtles are among the most ancient of the reptiles alive today and have changed little since they first appeared some 200 million years ago. They have a protective shell that encloses their body and provides protection and camouflage. Turtles inhabit terrestrial, freshwater, and marine habitats and are found both in tropical and temperate regions.
Squamata are the most diverse of all the reptile groups and include lizards, snakes and worm-lizards. There are nearly 7,600 species of squamates alive today. The earliest squamate fossils date back to the beginning of the Jurassic Period. Squamates shed their skin periodically and have jointed skulls and jaws that enable them to capture larger prey and bite with great power.
Crocodilians first appeared during the late Cretaceous Period, about 84 million years ago. The group includes alligators, crocodiles, gharials, and caimans. Crocodiles are the closest living relatives to birds.
Tuataras are a group of reptiles that are lizard-like in appearance but they differ from members of the Order Squamata in that their skull is not jointed. Tuataras were once widespread but today only two species of remain. Their range is now restricted to just a few islands in New Zealand.
FACT: There are about 8,000 species of known reptiles alive today.
Of the four groups of reptiles, the squamates (lizards, snakes and worm-lizards) are the most diverse. There are nearly 7,600 species of squamates, including about 2,900 species of snakes, 4,500 species of lizards, and 158 species of amphisbaenians. Turtles is the second most diverse group of reptiles, with about 294 species. There are 23 species of crocodilians and 2 species of tuataras.
FACT: The first reptiles appeared approximately 340 million years ago during the Carboniferous Period.
Reptiles are thought to have evolved about 340 million years ago during the Carboniferous Period from a group of reptile-like amphibians called the Reptiliomorphs. Early reptiles included organisms such as Hylonomus, Petrolacosaurus, Archaeothyris, and Paleothyris. The oldest evidence of reptiles is a set of footprints found in Nova Scotia.
FACT: Reptiles are tetrapods.
Reptiles have four limbs, a characteristic that places them among the group of animals known as tetrapods. It should be noted that although some reptiles such as snakes and amphisbaenians have lost their legs during the course of evolution, they are tetrapods by descent.
FACT: Reptiles are cold-blooded.
Reptiles are cold-blooded or ectothermic which means they do not generate their own, internal heat. This is one of the main ways reptiles differ from other animal groups such as mammals and birds (both of which are endothermic, meaning they are able to produce their own internal heat). Reptiles must rely on their environment for warmth. That's why they bask in the warmth of the sun during the day and seek shelter at night to avoid cold. Reptiles also must avoid overheating, so if daytime temperatures climb too high, they must seek shelter to avoid absorbing too much heat.
FACT: Reptiles have scales.
Reptile skin is covered with scales, structures that grow on the animal's epidermis and consist of a hard substance known as keratin which is similar to human hair and fingernails. Scales are replaced periodically through a shedding process in which the entire skin is shed in one piece or flakes off in small pieces. Reptile scales vary in shape, size, texture and color.
FACT: Reptiles are amniotes.
Amniotes are a terrestrial vertebrates whose eggs are characterized by having several layers of protective membranes (the amnion, chorion and allantois). Reptiles, mammals, and birds are all amniotes.
FACT: The Mesozoic Era is the 'Age of Reptiles'.
The Mesozoic Era, which began 245 million years ago, is known as the Age of Reptiles, a chapter in Earth's history when reptiles dominated terrestrial habitats. It was during this time period that dinosaurs arose and diversified. The Age of Reptiles ended with the extinction of the dinosaurs, 65 million years ago.
FACT: In many reptiles, the sex of the young is determined by the temperature the embryos are exposed to during incubation.
In mammals and birds, the sex of offspring is determined at the time of fertilization but in some reptiles, the sex is instead determined by the temperature that prevails during the about the middle third of embryonic development. This phenomenon is known as temperature-dependent sex determination.
FACT: Some of the largest reptiles alive today include the leatherback turtle, the Komodo dragon, and the saltwater crocodile.
The leatherback turtle is the largest turtle species. Adult leatherbacks grow to an average length of 2 meters and can weigh between 250 and 700kg. The Komodo dragon is the largest lizard species and can grow in excess of 3 meters in length and 70kg in weight. The saltwater crocodile is the largest of all living reptiles and can weigh between 600 and 1,000kgm. Saltwater crocodiles grow to lengths of between 4 and 5.5 meters.