Reptilia are the class of animals which is regarded as the first animal class that adopted life on the globe. The ancestors of the reptilia were amphibians and from there reptiles evolved millions of years ago. It’s vital to understand the life cycle of the reptilia to comprehend adequate knowledge. Reptiles are cold-blooded animals belonging to the phylum Chordata of Animal kingdom.

Definition of Reptiles and Reptilia

Reptiles are described as vertebrate animals of a category that contains snakes, crocodiles, lizards, turtles, and tortoises. Reptilia are the class of available reptile animals on Earth. As of now, scientists have identified 8000 species of the reptilia class.

Figure 1: Evolution from Fish to Reptiles

Classification of Reptiles

Different species of reptiles that come under the reptilia class have some common classifications. They include −


The first appearance of the turtles was around 200 million years ago. Turtles have a carapace which is a protective cell which covers and protects the body. It is useful as their body gets covered and they get camouflaged. The composition of the turtle shells has two parts. Scutes form the outer layer and the inner layer is constructed with bones. The shell of the turtle is another part of its skeleton.

Turtles break their food with the help of sharp beak, as they do not have teeth. Turtles that live on land are referred to as tortoises and the turtles which live in freshwater are called terrapin.


A type of reptile which is often recognised as a large, predatory, and semi-aquatic animal. The body seems to be large, lizard-like, and solidly built. They often have a compressed tail and eyes. It can swim in water as well as walk on land.

Figure 2: Reptiles

Characteristics of Reptiles

Generally, there are different characteristics of reptiles which are mentioned in the following points −

  • The animals of the reptilia classes lay eggs on the land, even the aquatic animals.

  • The system of reproduction happens among the reptiles with the internal fertilisation that make them lay eggs and give birth to new ones.

  • Reptiles have a scaly skin, often they move to land from the water as their skin is not useful to process respiration in water.

  • The animals of the reptilia classes depend on the surrounding environment.

  • Reptiles are poikilotherms implying they can regulate the temperature of their body depending on the temperature.

  • During the cold weather, reptiles can stay without eating which decreases metabolism.

Life Cycle and History of Reptiles

The life history of the animals of the reptilia class is wide and diverse. Some reptiles are recognised as the annual species, that hatch, grow, produce, and die yearly or the maximum life cycle is about two years. Other species such as loggerhead sea turtles are long-living species, which mandate almost 25 years to get evolved and they have a lifespan of 50 years.

Figure 3: Life cycle of a Turtle

There are many incredible adaptations made by animals of the reptilia group. Some reptiles lay eggs after fertilisation, whereas in different cases some reptiles are live-bearers. Some animals of the reptilia class can lay one or two eggs; however, there are other species of reptiles that can lay around a hundred or more eggs in the nesting events.

Different Systems in the Reptile's Body

The followings are the different stems of reptile classes' bodies −

Circulatory System

Most reptiles have a three-chambered heart that has one separated ventricle and two atria. Moreover, the ventricle is also divided partially. It functions to mix the blood that consists of both oxygenated and deoxygenated. Heart valves can make the mixing of blood and control the continuous process of blood circulation in the body. In the reptile body, the process of blood flow is diverted often which can save their energies. It often leads to usefulness as reptiles produce less energy as they move less.

Respirator System

Reptiles can breathe through their lungs as lungs can exchange gases. Many reptiles have little sacs in their lungs which help to exchange gases. The process of lung ventilation is constructed differently in different reptiles. Commonly, the nostrils are closed and the glottis is opened which forces air exchange via the lungs.


Some reptiles can nest for the entire year, while others are capable of nesting only once a year or allowing two or more years between breeding cycles. Additionally, reptiles are characterised by the aspects such as dry scaly skin and naturally laying soft-shelled eggs on land. Reptiles are available in land as well as in the water also.


Q1. What is ectothermic in reptilia?

Ans. The animals of the reptilia groups are known as cold-blooded which is referred to as the ectothermic. It seems that reptiles cannot control their body temperature on their own and they are relying on the environment to decrease or increase the temperature in the body.

Q2. What is the life cycle of reptiles?

Ans. The animals of the reptilia group have diversified life histories. The life span is depending on the actual species. It is considered some of them can live up to 2 years whereas some reptiles live as long as 150 years like the Aldabra tortoise.

Q3. How many chambers do the heart of reptilia possess?

Ans. The heart of reptilia has 3 chambers in usual which define one ventricle and two atria. However, there are some distinctions like; the heart of crocodiles has 4 chambers.

Updated on: 24-Apr-2023


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