Reptiles – Characteristics, habitat and anatomy

The Reptilia Class (from the Greek  reptum = crawling), which includes reptiles, is a group of vertebrate animals (which have vertebrae) and ectotherms, that is, they do not have an internal mechanism that regulates their body temperature, so it is very common see alligators, crocodiles and turtles in the sun …

And it is also from the characteristic of ectotherm of reptiles, that the expression “crawling” came up when we mean that we are resting in the sun.

Since the Paleozoic Era, this group has been developing and evolving. Unlike Amphibians, Reptiles do not depend on water for reproduction, they are all amniotics (embryos are surrounded by an amniotic membrane).

Current reptiles are divided into four orders:

Photo: depositphotos

  • Crocodilia: includes groups of crocodiles, gavials, alligators, caimans and alligators;
  • Squamata: also known as “escamados”, they include snakes, amphibians and lizards / iguanas / chameleons / geckos;
  • Testudinea: also known as “turtles”, are sea and freshwater turtles, turtles and turtles;
  • Rhynchocephalia: tuataras from New Zealand (there are only two species that are at risk of extinction).


  • Unlike Amphibians, Reptiles have dry skin (it is not mucous and has few superficial glands), keratinized and usually with scales or shields;
  • They have ossified internal skeleton in all groups, and highly developed musculature in Squamata and Crocodilia;
  • Heart usually with three cavities (two atria and one ventricle), except in the group of Crocodilians, which have four cavities (two atria and two ventricles), but even having four separate cavities and ventricles, the arterial and venous bloods mix.
  • They generally have four limbs (tetrapods), which each have five fingers terminated in claws. However, there are some exceptions: sea turtles, for example, have four limbs, but they are modified for swimming (they do not have fingers and claws), other groups have reduced or absent legs.
  • Breathing is pulmonary (they have lungs with internal folds that make it possible to increase their breathing capacity). Some groups, such as turtles, may spend a few hours holding their breath under water, in this situation bradycardia occurs (a phenomenon in which the animal’s organism works slower, the heart beats at a lower frequency than normal and oxygen dissolved in water is absorbed through the pharynx and cloaca)

Photo: depositphotos


  • Fertilization is internal, usually with the help of copulatory organs, the male introduces the sperm into the female’s body;
  • They are usually oviparous (embryonic development occurs inside the egg, but outside the maternal body). However, some groups of snakes and lizards have ovoviviparity, that is, females produce eggs, embryonic development occurs within these eggs, but the female retains them within her body until development is complete and then expels the fetus;
  • Eggs with horny or limestone shells. Presence of embryonic wraps such as: amnion, chorion, yolk sac and allantois. Like internal fertilization, the characteristics of eggs with shells were important for the establishment of these groups in the terrestrial environment.
  • The sex of some groups, such as turtles, for example, is still determined inside the eggs, depending on the ambient temperature. If the eggs have contact with temperatures <20ºC or> 30ºC, more females will be born; if the temperature varies between 22º-28ºC, more males will be born.

Habitat and Food

Most reptiles have greater activity during the day (when it is hotter) and rest at night (when it is colder), but as with every rule there is an exception, there are some groups that hunt their food at night. Most are carnivorous (they eat from insects to other vertebrates), some species are herbivorous (they eat plants, vegetables) and there are still omnivores (who eat a little of everything!). They have a complete digestive system, which starts in the mouth and ends in the cloaca.

Crocodilians have large, sharp teeth that hold prey and tear its flesh, while Testudines have short, clenched teeth (with the exception of the biting tortoise, which has a jaw modification that allows it to eat animals that have shells like other turtles ). Snakes, on the other hand, have four types of dentition: aglip (without venom, massive teeth), opisthoglyph (venom inoculating tooth – venom, present at the end of the jaw), proteroglyph (pair of non-retractable poison inoculating teeth, found in upper frontal part) and solenoglyph (pair of retractable teeth inoculating poison, found in the upper frontal part).

Snakes have a loreal pit, bifid tongue and Jacobson’s organ, which contribute to the identification of temperature variations and chemical substances, and can then recognize predators or prey. Many people believe that the head of snakes in triangular shape and the presence of pupil of the eye in vertical or elliptical shape (eye in the form of a slit) mean that they are venomous. These are two great myths that deserve to be debunked!

Not all snakes with triangular heads are poisonous, this is very subjective, what exactly would a triangular head be? Compare below the photo of a jararaca (venomous) and a boa constrictor (not constrictive), and draw your own conclusions! In addition, the slit-shaped eyes are related to the Serpents’ nocturnal habit, and not to the type of teeth and / or the presence of poison glands.

by Abdullah Sam
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