Reptiles (Reptilia) are the group of vertebrates They breathe air and have internal fertilization, amniotic development, and epidermal scales that cover part or all of their body. The main groups of living reptiles are turtles (order Testudines), tuatara (order Rhynchocephalia [Sphenodontida]), lizards and snakes (order Squamata) and crocodiles (order Crocodylia, or Crocodilia) representing more than 8.700 species. The birds share a common ancestor with crocodiles in the Archosauria subclass and are technically a reptile lineage, but they are treated separately.

Extinct reptiles included an even more diverse group of animals that ranged from marine plesiosaurs, pliosaurs, and ichthyosaurs to the giant plant- and meat-eating dinosaurs of terrestrial environments.

Snakes are part of reptiles

Snakes are part of reptiles

Taxonomically, Reptilia and Synapsida (a group of mammal-like reptiles and their extinct relatives) were sister groups that diverged from a common ancestor during the Central Pennsylvania Era (approximately 312 million to 307 million years ago). For millions of years, the representatives of these two groups were superficially similar. However, lifestyles slowly diverged, and hairy mammals emerged from the synaptic line, possessing endothermic (warm-blooded) physiology and mammary glands to feed their young. All birds and some groups of extinct reptiles, such as selected groups of dinosaurs, also developed endothermic physiology. However, most modern reptiles possess an ectothermic (cold-blooded) physiology. Today only the leatherback turtle (Dermochelys coriacea) has an almost endothermic physiology. Until now no reptile, living or extinct, has developed specialized skin glands to feed its young.


Most reptiles have a continuous outer covering of epidermal scales. Reptile scales contain a unique type of keratin called beta keratin; scales and interscalar skin also contain alpha keratin, which is a trait shared with other vertebrates. Keratin is the main component of reptile scales. The scales can be very small, as in the microscopic tuberculous scales of the dwarf gecko (Sphaerodactylus), or relatively large, as in the body scales of many groups of lizards and snakes. The largest scales are the scales that cover the shell of a turtle or the plates of a crocodile.

The occipital condyle (a protrusion where the skull attaches to the first vertebra) is unique. The cervical vertebrae in reptiles have medioventral keels, and the intercenter of the second cervical vertebra fuses with the axis in adults. Taxa with well-developed members have two or more sacral vertebrae.

The lower jaw of reptiles is made up of several bones but lacks an anterior coronoid bone. In the ear, a single auditory bone, the stapes, transmits sound vibrations from the eardrum to the inner ear.

Chameleons can change color for dangerous situations

Chameleons can change color for dangerous situations

Sexual reproduction is internal, and sperm can be deposited by copulation or by cloacal apposition. Asexual reproduction by parthenogenesis also occurs in some groups. Development can be internal, with embryos retained in the female's oviducts, and the embryos of some species can be attached to the mother through a placenta. However, development in most species is external, with embryos enclosed in shell eggs. In all cases, each embryo is enveloped in an amnion, a fluid-filled membranous sac.

Most reptiles are measured from the snout to the vent (that is, from the tip of the nose to the cloaca). However, measurements of the total length are common for the larger species, and the length of the carapace is used to measure the size of the turtles. The body size of living reptiles varies widely. The dwarf gecko (Sphaerodactylus parthenopion) is the smallest reptile and has a snout-to-vent length of 16-18 mm. In contrast, giant tortoises, such as the leatherback turtle (Dermochelys coriacea), have carapace lengths of almost 2 meters. In terms of overall length, the largest living reptiles are reticulated pythons (Python reticulatus) and saltwater crocodiles (Crocodylus porosus), which can grow to over 7 meters as adults. Some groups of ancient reptiles had members that were the largest animals that ever lived on earth, some sauropod dinosaur fossils measuring 20-30 meters. The largest marine reptiles, the pliosaurs, grew to 15 meters.

The largest modern reptile, the Komodo dragon (Varanus komodoensis) of the East Indies, reaches a total length of 3 meters. In addition, two or three other species of monitors reach 1,8 meters. The water monitor (V. salvator) can grow to a greater total length than the Komodo dragon, but does not exceed its weight. The green iguana (I. iguana), which grows about 2 meters, is close to that size, but no other lizard does.

The smallest reptiles are found among salamanders (family Gekkonidae), skinks (family Scincidae) and microteiids (family Gymnopthalmidae); some of these lizards are no larger than 4 cm. Certain blind snakes (family Typhlopidae) are less than 10 cm when fully grown. Several species of turtles weigh less than 450 grams and reach a maximum carapace length of 12.5 cm. The smallest crocodiles are dwarf crocodiles (Osteolaemus tetraspis), which grow to about 2 meters, and dwarf alligators (Paleosuchus), which typically grow to 1,7 meters or less.


The activity of reptiles is highly dependent on the temperature of the surrounding environment. Reptiles are ectothermic, that is, they need an external heat source to raise their body temperature. They are also considered cold-blooded animals, although this label can be misleading, as the blood of many desert reptiles is often relatively warm. The body temperatures of many species approximate the surrounding air or substrate temperature, therefore a reptile can feel cold to the human touch. Many species, particularly lizards, have preferred body temperatures above 28 ° C and only carry out their daily activities when they have raised their body temperature to those levels. These species maintain elevated body temperatures at a relatively constant level when entering and leaving sunlight.

Reptiles are found in most habitats, from the open ocean to the mid-elevation mountainous habitats. The yellow-bellied snake (Pelamis platurus) spends its entire life in marine environments. It feeds and gives birth far from any coast, while other sea snakes live in coastal waters of estuaries and coral reefs. Sea turtles are also predominantly coastal animals, although most species have a pelagic, or open sea, phase, which lasts from the hatching stage to the young juvenile stage.

Many snakes, crocodiles, and some lizards are aquatic and live in freshwater habitats ranging from large rivers and lakes to small mountain streams. On land, turtles, snakes, and lizards are also widely found in forests, grasslands, and even true deserts. In many arid lands, lizards and snakes are the main carnivores of small animals.


The diversity in reptile life is surprisingly wide and often reveals almost unimaginable reproductive adaptations. Some reptiles are annual species that hatch, mature, reproduce, and die within a year or at most two years, as in side spotted lizards (Uta stansburiana). Others, such as the loggerhead turtle (Caretta caretta), are long-lived species that require 25 years or more to mature and have a life expectancy in excess of 50 years. Many other species fall between these extremes. Some reptiles lay eggs, while others are carriers of life. Some species lay 1 or 2 eggs, while others lay 100 or more eggs at each nesting event. Some reptiles nest year-round, while others may nest once a year or allow two or more years to pass between breeding cycles.


The evolution of amniotic development and the shell egg allowed vertebrates to become completely terrestrial. These two evolutionary advances required the prior development of internal fertilization. In other words, the deposition of sperm by the male in the female reproductive tract and the subsequent penetration of the sperm into the egg was necessary before the shelled egg could exist.

In living reptiles, the deposition of male sperm within the female body occurs by cloacal apposition or by the use of an intromiting or copulatory organ. The first method is characteristic of a single group, the tuatara (Sphenodon), which copulates through the close alignment of the male cloaca (i.e., a common chamber and outlet into which the intestinal, urinary and genital tracts open) with that of the female. The male then discharges the semen into the female's cloaca. In all other reptiles, males have a penis, as in turtles (order Testudines) and crocodiles (order Crocodylia) or hemipenes as in lizards and snakes (order Squamata). The penis is a homologue of the mammalian penis, and its presence in reptiles indicates that this organ arose early in the evolution of amniotes and before the origin of reptiles and synapses. In contrast, hemipenes are structurally very different. They are called "hemi" because there are two in each male, although only one is used during a single copulatory event. Either a penis or hemipenis, this organ inserts into the female cloaca.

Once the semen is deposited, the sperm must exit the woman's cloaca and enter each oviduct. They go up the oviduct to an opening adjacent to an ovary. The mechanism of how sperm find this pathway remains largely unknown, but for successful fertilization the sperm must be above the oviduct glands that will secrete the egg shell. When ovulation occurs, the eggs are released from the ovary and fall directly into the oviduct, one on each side. In reptiles, copulation can stimulate ovulation, occur simultaneously with ovulation, take place between an hour and a week after ovulation (presumably the most common situation), or occur months before the completion of egg development and ovulation. .

Although spring is the main period of courtship and copulation for most temperate zone reptiles, males commonly complete spermatogenesis (i.e., the production of sperm) in late summer. Occasionally, a male will mate and her sperm will be stored in the female's oviducts until the eggs are ovulated in the spring as in the case of snapping turtles (Chelydra serpentine).

This ability to store sperm appears to be widespread in snakes and turtles, although the phenomenon has not been rigorously tested. One study showed that terrapina diamantina (Malaclemys terrapin) could produce viable eggs four years after copulation, although the percentage of fertile eggs decreased sharply after one year and progressively until the fourth and final year of the experiment.

For copulation to be successful, cooperation between the female and the male is required. In most reptiles, the male courts the female with a series of behaviors to assess her reproductive readiness and receptivity.

Many lizards also have a distinct pattern of blows to the head and push-ups to the front of the body. Combined with water and spray vibrations, male crocodiles also use body movements to woo females and warn other males.

In flying lizards (Draco), males have well-developed and brightly colored throat fans, or dewlaps, that open and close. Throat fans are used to attract females and play an important role in territorial disputes with other males.

Turtles use visual and olfactory displays and tactile cues in courtship. These signals occur in various combinations and depend on the species. For example, in some species of turtles the female appears to be harassed into submission.

Embryonic development and care

Once the eggs are fertilized, development begins and the egg develops into an embryo as it divides into successively smaller cells. The time that elapses between fertilization and egg laying is poorly documented for most reptile species. While copulation and delivery of sperm into a woman's reproductive tract can occur weeks or months before eggs are ovulated, fertilization and egg deposition typically appear to occur within hours or days after ovulation.

Apparently, many egg-laying (or oviparous) reptiles have a mechanism to slow or stop development in the oviduct once the early gastrula stage is reached. However, in most species, development continues as soon as the egg is deposited. During periods of high stress and other relatively unusual conditions (such as in captivity), females have been known to retain shelled eggs in their oviduct for weeks to months. In some situations where there is prolonged retention of the eggs, the eggs have eroded the oviductal wall and have fallen into the body cavity.

Egg laying and nest building vary widely among reptiles. These behaviors range from the "casual" release of the eggs in a relatively suitable site to the preparation of an elaborate nest, and parental care may also occur in some groups.

Most turtles dig an egg chamber exclusively with their hind legs, and attention is paid to the selection of the nesting site, the excavation of the egg chamber, and its closure. Thereafter, the female leaves, and the eggs and young must survive on their own.

Most lizards and snakes also hatch after the eggs have been laid; the egg chamber may be little more than a hole as the lizard or snake crawls through the litter or dirt, or it may be more elaborate. For example, the common or green iguana (I. iguana) digs a deep burrow with a combination of its front and rear limbs; this chamber is often so deep that the female is completely hidden from view. At the end of this burrow, it lays its eggs and fills the entire burrow with loose soil. Often a group of females return to the same nesting site within the same nesting colony year after year.

Some reptiles can give birth to their young live. This mode, called viviparity, is very widespread and has evolved independently dozens of times in the squamous (lizards and snakes). No living crocodile, turtle or tuatara carries life. However, in squamous, the presence of live eggs ranges from the retention of shelled eggs in the oviducts to the development of placentas between the mother and her fetuses.

The evolutionary steps from egg laying to placental development are demonstrated by existing species. For example, the rough green snake (Opheodrys aestivus) retains eggs for variable periods, and can lay eggs containing full-term embryos that hatch within days of deposition.

In other taxa the eggs are not peeled, but remain in the oviducts throughout development. The yolk nourishes each embryo, although there is a gas exchange through the amniotic membranes and oviducal walls. Placental development ranges from simple wall contact and gas exchange between the mother and a developing embryo to complete interdigitation of maternal and fetal tissue for nutrition and gas exchange as in snakes (Thamnophis). There are several types of placenta that have evolved into the squamous ones that use various components of the amniotic membranes.

Egg clutches and hatchlings vary widely in reptiles and are species dependent. Among layers, a clutch can range from a single egg to more than 100. Among live reptiles, a litter can range from 1 to about 50 newborns. The body size of adults is only one of the aspects associated with the number of children; genetic makeup and nutrition are also important factors.

The smallest of living reptiles typically have the fewest young, often laying only one or two eggs or producing only one or two hatchlings. Many salamanders and some snakes have genetically fixed clutch sizes of two eggs, and each ovary typically produces one egg during a given reproductive cycle.

In contrast, turtles and crocodiles produce some of the largest clutches among living reptiles; sea ​​turtles often produce more than 100 eggs at a time, while larger crocodiles produce an average of 40-50 eggs per clutch. Some of the larger snakes also produce clutches or litters of 40-50 eggs or embryos, but most scaly, even large-bodied species, produce fewer than 20 eggs or embryos during each reproductive cycle.

Reptiles are oviparous animals

Reptiles are oviparous animals

Nutrition clearly affects the number of young produced, and undernourished females lay fewer eggs or give birth to fewer young. A female lizard suffering a year of drought or facing loss of her tail may reabsorb maturing egg follicles in the ovary or give up egg development entirely during that year.

The frequency of reproduction also depends on the availability of power. The female wood rattlesnake (Crotalus horridus) usually reproduces every three years because the female eats little during the summer of her pregnancy. You need the following summer to rebuild your fat (energy) stores for the following year's pregnancy and egg development.

The duration of egg incubation and pregnancy depends on the temperature. Because reptiles are ectothermic, live female embryos and oviparous female eggs deposited on the ground or elsewhere are subject to fluctuating temperatures.

In general, cold temperatures slow development and warm temperatures accelerate development, but extreme heat and cold are lethal to developing embryos. On average, temperate zone reptiles have incubations or pregnancies of 8 to 12 weeks. Tropical species tend to have similar incubation periods; however, the incubations of some species can last almost a year or more as in the Fiji iguana (Brachylophus fasciatus).

In addition to hereditary or genetic factors, the sex of many reptile species can be manipulated by the environment in which embryonic development takes place. Environment-dependent sex determination (ESD) is the collective term for all factors (such as temperature, humidity, and others) that affect the ratio of males to females produced in a given clutch of eggs. or a litter of newborns. Temperature-dependent sex determination (TSD), discovered in the early 1970s, is the most researched of these factors.

The sex of the offspring in TSD species is influenced by temperature during a critical incubation period, rather than by hereditary factors. In most turtles, the females are produced at high temperatures and the males at low temperatures. In a narrow range of intermediate temperatures, roughly equal numbers of males and females are produced. The opposite occurs in many crocodiles, with females resulting from colder temperatures. Some squamosals also have TSD, but the sex of most species appears to be determined primarily by genetics.

In reptiles that lay eggs, hatching must break the eggshell. For this purpose, turtles, crocodiles and tuataras carry a pointed horny caruncle on their snouts. The hatchling uses the caruncle to open the amniotic membranes and then the eggshell. The squamosal have an egg tooth, a special premaxillary tooth that extends forward and out of the mouth, to cut through the membranes and shell.

Generally, the hatchling rests briefly once out of the shell. If the nest is buried underground or other material, a hatch must dig upward to emerge on the surface. Sometimes this occurs in concert with other hatchlings in the nest; coordinated behavior is necessary for sea turtles and other species whose eggs are deeply buried. In some species of turtles, such as the North American painted turtle (Chrysemys picta), the hatchlings leave the eggshell, but remain in the nest during the winter and emerge in the spring. Each painted turtle can tolerate short periods of extreme cold that freeze much of the water on its body.

Living reptiles give birth in the same way as mammals. If the amniotic membranes do not rupture during delivery, the newborn must struggle to free itself from the encapsulated membranes.

Growth and longevity

Reptiles, especially turtles, are characterized by their extreme longevity. Many tortoises have long lives, but few species have individuals that live more than a century. Longevity records are derived from captive animals that led protected and satisfied lives. Many species of North American tortoises require 12 to 18 years to reach sexual maturity. Once they reach adulthood, mortality rates decrease substantially, with many individuals reaching and exceeding 30 years as in the case of the Blanding's tortoise (Emydoidea blandingii) and the eastern boxwood tortoise (Terrapene carolina). Generally, the larger the animal, the longer its life expectancy, which is why crocodiles, large snakes (such as boas and pythons), and large lizards often live more than 20 years.

Although growth patterns are poorly documented for most reptiles, most species probably follow a determined, or asymptotic, growth pattern as they mature. Most reptiles are characterized by a period of rapid youthful growth that slows down as they reach adulthood. Growth ceases a few years after maturity.

Some large-bodied species probably have what is known as attenuated or indeterminate growth. Typically, rapid growth occurs in juveniles and slows down as the individual approaches maturity and shifts its energy resources toward reproduction. During most adult years, growth is extremely slow or non-existent. However, when food resources are high, active growth can occur. Therefore, the size of an individual of a species characterized by stunted growth is limited only by its food supply.


Evasion is the most common form of defense in the animal kingdom, as it also occurs in reptiles. Recognizing danger for the first time, most snakes and lizards crawl or scamper through undergrowth; turtles and crocodiles plunge into the water and sink without being seen. Still, if danger arises so suddenly and so close that it can be dangerous, other behaviors are adopted.

Body and posture

The change in body shape is relatively common in snakes. It usually involves the extension of the neck, as in cobras (family Elapidae), or the entire body, as in the harmless hog-nosed snakes (Heterodon) and DeKay's snake (Storeria dekayi) of the United States. Some snakes inflate the front parts of their bodies; inflation is one of the defensive behaviors of the great South American snake Pseustes poecilonotus and the African boomslang (Dispholidus typus).

Snakes can also assume threatening postures as they change their body shape. A cobra raises the front of its body and spreads its hood when threatened. The typical defensive posture of vipers is the body curled up and the neck held in an S curve, the head ready to strike.

Some lizards squash their bodies, inflate their throats, and turn towards the enemy. The Australian Bearded Lizard (Pogona barbata) spreads its throat down and out. The Australian lizard (Chlamydosaurus kingii) suddenly raises a wide membrane, or frill, that extends backward from the throat. Many lizards and snakes open their mouths when threatened but do not strike. A common African lizard, the black-necked agama (Acanthocercus atricollis), faces an enemy with its head held high and its mouth open to show the bright orange interior.


The display of bright colors is often defensive. This behavior occurs in some red or yellow-bellied snakes that turn or curl their tails, exposing the brightly colored underside.

This behavior is known in harmless snakes, such as the American ring-necked snake (Diadophis), as well as in poisonous snakes, such as the southern coral snake (Micrurus frontalis), with a red, orange or yellow back. Although not fully understood yet, these colors must have some meaning to predators. Many other red, orange, or yellow animals are unpleasant to predators or possess defenses capable of killing or injuring them. Therefore, these colors are believed to serve as a coloration warning to potential predators.

Camouflage involving both shape and color is common in reptiles. For example, many tree snakes and lizards are green in color; Some of the green-colored snakes, such as the South American (Oxybelis) and South Asian (Ahaetulla) creeper snakes, are very thin and resemble plants common in the habitat. Likewise, lizards from semi-arid and rocky habitats are frequently pale and have spotty patterns that resemble pebbles and gravel, as in the leopard lizard (Crotaphytus wislizeni) of the southwestern United States.

Imitation of dangerous species by harmless species is a passive defense; however, its validity as a real defense mechanism is sometimes questioned. However, evidence of mimicry appears between different groups of snakes. For example, venomous American coral snakes (Micrurus) have various red, yellow, white, and black ring patterns. These patterns often correspond to non-venomous or mildly venomous snake species found in the same area.

Bite and hit

If a threatening posture fails to scare off an enemy, many reptiles can become more aggressive. Some snakes (such as DeKay's snake (S. dekayi) strike, but with their mouths closed. Others, such as plover-nosed snakes (Heterodon) strike with their mouths open but do not bite, but snakes of many species strike and bite viciously Among the non-venomous snakes of North America, few bite as fast as the water snakes of the genus Nerodia, yet they are not poisonous.

Most dangerously poisonous snakes - snakes, pit vipers, and cobras - bite in self-defense. Vipers and pit vipers generally strike from a horizontal spiral stance. From this position, the head can be fired rapidly forward, stabbing the enemy, and thrown back in preparation for the next blow. From the typical elevated posture, a cobra sweeps its head forward and down to bite. To strike again, raise your head and neck once more; These aggressive and defensive movements of cobras are slower than those of pit vipers.

Many lizards, regardless of their family and size, also bite in defense. For example, the tokay gecko (Gekko gecko) of Southeast Asia bites if it is sufficiently threatened. Although small lizards have a bite that is effective only against smaller predators, a large monitor lizard (Varanus) can inflict a painful wound with its large teeth and strong jaws. Some turtles, particularly the soft-shelled turtles of the Trionychidae family and the snapping turtles of the Chelydridae family, bite frequently and vigorously.


Spitting venom by some cobras is a purely defensive act directed against large animals. Instead of a straight channel ending in a long opening near the tip of each tusk as in most cobras, the specialized tusk of the spitting cobra has a channel that turns sharply forward to a small round opening in the surface. frontal. At the moment of ejection, the mouth opens slightly, and a fine stream of venom is forced out of the fangs by the contraction of the muscle that envelops the venom gland. A spitting cobra generally raises its head and front of its body in the characteristic cobra defensive posture before spitting, but the venom can be expelled from any position. The effect on the skin is negligible; the eyes, however, can be severely damaged and blindness can occur unless the poison is quickly washed away.

Eating habits

With few exceptions, modern reptiles feed on some form of animal life (such as insects, mollusks, birds, frogs, mammals, fish, and even other reptiles). Tortoises are vegetarians, eating leaves, grass, and even cacti in some cases. Green iguanas are also herbivores. The marine iguana (Amblyrhynchus cristatus) from the Galapagos Islands dives into the sea in search of algae.

Most carnivorous reptiles have unspecialized diets and eat a variety of animals. In general, the smaller the reptile, the smaller its prey. Only the largest living snakes, the reticulated python (Python reticulatus), the Indian python (P. molurus), and the green anaconda (Eunectes murinus) are capable of eating large mammals such as small pigs and deer. Among crocodiles, the largest species, the Nile crocodile (Crocodylus niloticus), the saltwater crocodile (C. porosus), and the Orinoco crocodile (C. intermedius) are known to attack and eat humans. Presumably, large carnivorous dinosaurs such as Allosaurus and Tyrannosaurus-Rex devoured even larger prey. These predators were almost certainly capable of killing the largest of their herbivorous contemporaries.

List of reptiles

The alligator spends most of its life in water.


alligator, brown alligator o common alligator (Caiman crocodilus) is a semi-aquatic reptile. The American is the reptile largest in North America and has been a successful predator for 200 million years.


chameleon (Chamaeleonidae), is a reptile which is part of the iguana suborder. These colorful lizards are known as one of the few animals that can change the color of their skin. However, it is a misconception for the chameleon to change color to suit its surroundings.

A crocodile cooling off.


Asian water dragon

asian water dragon (Physignathus cocincinus) is a reptile bright green found in Thailand, Vietnam, Cambodia, Laos, Burma, and southern China.

Australian water dragon

australian water dragon (Physignathus lesueurii) is Australia's largest dragon lizard and can be found living along Sydney's most prosperous canals.

Komodo dragon

Komodo dragon (Varanus komodoensis) is the largest living lizard in the world. They are identified by their massive size, flat heads, arched legs, and long, thick tails.