Reptiles: Different Types, Definitions, Photos and More

Lizards, dinosaurs, crocodiles, turtles, and snakes—all belong to the ancient, stout class of animals known as reptiles. This is a diverse group with more than 10,000 different species that feature prominently in the fossil record. Once the dominant terrestrial vertebrates on Earth, reptiles still occupy nearly every ecosystem beyond the extreme north and south.

8 reptile traits – list

Most importantly, reptiles are an evolutionary classification. Each species in this category has a common ancestor dating back more than 300 million years. But it also has a set of common characteristics. At a basic level, all reptiles have four legs, or are descended from four-legged creatures (including snakes, which apparently still carry some genes for making legs). They are also vertebrates, with a backbone that houses the spinal cord. Additionally, most reptiles have the following characteristics:

• Rough Scale – The skin of reptiles is covered with rough scale cuticles, bony plates, or a combination of both. These scales are made of keratin, the same substance found in nails, hair and claws. The skin is actually much thinner than you might think because it lacks the same layer of dermis as mammals. But waterproof skin does allow reptiles to survive and thrive in dry ecosystems.
• Regular Shedding – Reptiles shed their skin continuously throughout their lives. Shedding tends to be most common during puberty because the skin doesn't actually grow in proportion to the body. Once the reptile becomes an adult, the frequency of shedding decreases. At this point, it's mostly about keeping your body healthy.
• Cold-blooded animals – Reptiles have an inherently low metabolic rate, which helps conserve energy, but also means they lack any internal means of keeping their body temperature constant. Without fur or feathers to insulate, reptiles cannot keep warm in frigid temperatures. Without sweat glands, they also cannot stay cool in the heat. To compensate, they rely on sunlight or shade to alter their internal temperature as needed. Leatherback turtles are the only reptiles with elements of a warm-blooded physiology.
• Spawning eggs – With the exception of some snakes and lizards, which lay live young, all reptiles are oviparous and lay their eggs in nests. The soil temperature at this time determines whether the pups are born male or female. Asexual reproduction is very rare, but known to occur in some lizards and snakes.
• Highly developed lungs – All reptiles rely on lungs to breathe air. Even species with permeable skin and other adaptations cannot breathe fully without using their lungs.
• Short digestive tracts – With a few exceptions, reptiles are carnivores with relatively short digestive tracts. Because of their slower metabolism, they can digest food slowly and eat smaller meals. In the most extreme cases, crocodiles, pythons and other reptiles can survive for months on a single meal. Herbivorous reptiles do exist, but they face a problem: Because they don't have any complex dental system, they have to swallow rocks and pebbles to grind up plant matter in their digestive system, like some birds do.
• Chemosensory – Many but not all reptiles have chemosensory organs on the top of the nose or mouth to identify prey. This ability supplements and even replaces the sense of smell. Snakes in particular can sense chemicals in the air by quickly sticking out their tongues. This has the effect of moving odor particles from the tongue to the roof of the mouth.
• Skull Morphology – Several features of the skull distinguish reptiles from other kinds of animals. For example, they have only one bone (the skull connects to the first vertebrate), one auditory bone (the stapes) that transmits vibrations from the eardrum to the inner ear, and a very strong jaw. An interesting aspect of reptilian morphology is that some of these jaws actually correspond to the two ear bones of mammals. It is believed that at some point in the evolution of early mammals, these jaws moved to the back of the head and eventually formed the malleus and incus in mammalian ears to aid in hearing higher frequency sounds.

Exceptions to oviparous reproduction

As mentioned earlier, reptiles primarily reproduce by laying eggs, or laying eggs, but there are some notable exceptions. About 20 percent of lizards and snakes, including pythons, do lay live young instead of eggs. These viviparous reptiles have a non-mammalian placenta or some other means by which nutrients are transferred from mother to offspring and vice versa. The main advantage of viviparity is that it protects the eggs from predators in a hostile environment. But there is a tradeoff with this method of delivery, as it places a burden on the mother.

Only three reptile species, including Australia's yellow-bellied three-toed skink, actually combine egg and live birth methods (a rarity that suggests evolution may have worked against this intermediate stage). The skink's offspring begin life in eggs, like any other reptile. But as the embryo develops, the egg begins to thin until it is born with only a small membrane remaining. The main problem with this method is that there is not enough calcium in the thin eggshells to nourish the offspring. Mothers seem to compensate for this by secreting calcium from the uterus so that it can be taken up by the developing embryo. Evidence suggests that skinks may choose to lay eggs weeks earlier if the danger to offspring seems less. In harsher climates, mothers will keep their offspring inside for longer to protect them.

Cloning is also fairly rare, although more common than live spawning. About 50 species of lizards and one species of snake participate in this breeding method. Evidence suggests that these reptiles may have adopted a sexless lifestyle out of necessity — because they were genetically isolated from the rest of the group. The problem with asexual reproduction is the lack of genetic variability: offspring inherit the same disease susceptibility as their parents. But asexual reptiles seem to maintain genetic variation by starting the reproductive process with twice the normal number of chromosomes.

Four orders of reptiles

Modern reptiles are generally divided into four distinct orders, each with its own unique characteristics and morphology.

Testudines – As the only order classified within the subclass Anapsida, Testudines consist of all known species of turtles. Its main distinguishing feature is a hard cartilaginous shell extending from the ribs, which acts as a protective shield. Terms such as turtle, tortoise, and terrapin are based on local dialects and do not represent any specific taxonomic or biological differences.

Squamates – the youngest reptiles also happen to be the most common. It consists of most reptiles, including all known lizards, snakes, geckos and skinks. Many of the world's smallest reptiles are classified as scaly. Venom is a common feature of at least some species in this order as a means of defense against prey. Because venom evolved from different pre-existing proteins found throughout the body, the form and function of venom is very diverse.

Crocodiles —an ancient order that includes all modern alligators, crocodiles, caimans, and gharials—are among the largest carnivorous carnivores on Earth. With flat snouts, tough skin, long tails and rows of large teeth, crocodiles spend most of their lives in or near water. This order is the closest living relative to birds. That's because the ancestors of crocodiles were closely related to dinosaurs.

Rhynchocephalia – This order dates back to the Triassic period about 200 to 250 million years ago. Once incredibly diverse, it has been reduced to just one living genus, the New Zealand lizard-like lizard, which includes just two species. Despite their lizard-like appearance (they are a sister group of scaly animals), this order actually shares some basic morphological traits with crocodiles and dinosaurs.

Evolutionary History of Reptiles

About 400 million years ago, when four-legged vertebrates emerged on land, semi-aquatic amphibians evolved most. This semi-aquatic lifestyle is reflected in its morphology and behaviour. But several advances in lungs, bone structure and egg composition allowed the earliest reptiles to leave the water and thrive in otherwise unexplored ecological niches around the world.

Some 310 to 320 million years ago, the first clear signs of reptiles appeared in the fossil record. At that time, most of their territory was covered in swamps. Characterized by the lack of a hole in the back of the skull, anaporas were among the first reptiles to evolve. Diapsids have two holes near the back of their skulls, including modern reptiles, and indeed nearly all reptiles from the past 250 million years. Currently only the tortoise is classified in the anaporid group (and even then, it can't really be considered a "true" anapora, since the solid posterior skull probably evolved later).

Over millions of years, reptiles have continued to undergo many evolutions and changes. Archosaurs, including dinosaurs, crocodiles, and birds, first appeared in the fossil record during the Late Triassic period, about 200 million years ago. They flourished and became especially prominent during the Jurassic period. Primitive turtles first emerged around the same time and have remained the same size ever since. Squamates likely evolved during the Middle Jurassic, about 16 to 170 million years ago, but true snakes did not evolve until about 100 million years ago.

Part of this evolution was due to huge, sudden changes in ecosystems, including a mass extinction event 250 million years ago that killed roughly 90% of all species on Earth, and of course, asteroid impacts and volcanic activity that killed all non-avian dinosaurs Extinct about 65 million years ago. Since then, reptiles have evolved to be smaller and to share ecosystems with birds and mammals (which actually split off from early reptiles about 300 million years ago).

types of reptiles

list of reptiles

Reptiles: Different Types, Definitions, Photos and More FAQs (Frequently Asked Questions)

What are reptiles?

Reptiles are a group of cold-blooded animals characterized by rough skin and egg laying. It's just one of three vertebrates, along with mammals and birds, that have an amniotic membrane, or internal sac, at the embryonic stage of development.

What are the characteristics of reptiles?

The reptile's skin is covered with rough scales, or bony plates, which shed periodically. These cold-blooded organisms are unable to maintain a constant body temperature and are completely dependent on the external environment to heat up or cool down.

What are the types of reptiles?

The three main orders of reptiles are turtles, lizards and snakes, crocodiles and all their varieties. A fourth order, the Rhynchocephalia, consists of only two extant species but many extinct ones.

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