Reptile

Reptile is a member of class Reptilia. It is a group of air-breathing vertebrates that has internal fertilization and epidermal scale covering part of their body. The major group of living reptiles are turtles, Tuatara, Squamata, and a crocodilian. Reptiles is a word derived from Latin, in which reptiles meaning is “one who creeps”. The study of traditional reptile orders is known as herpetology. 

Reptiles Definition

Reptiles are defined as a vertebrate animal of a class that includes snake, lizards, turtles and tortoise. And they are distinguished by having dry scaly skin and typically laying soft-shelled eggs on land. Some of the examples of reptiles are lizards, Turtles, Snakes, Chameleons, Dinosaurs, Crocodiles, Scaled reptiles, Geckos, Skink, Sauria, Diapsid, Plesiosauria and also there are many other examples of reptiles.

Classification of Reptiles 

There are four main types of reptiles discussed below - 

• Turtles 

They have little changes compared to other reptiles from the very first appearance, that is 200 million years ago. They have a protective shell called a carapace. It covers their body and provides camouflage. The turtle shell is composed of two parts: the outer layer is made of scutes and the inner layer is made of bone, so the shell of the turtle is the part of the turtle skeleton. Turtles break their food with the help of sharp beak, as they do not possess teeth. Turtles which live on land are referred to as tortoise and the turtles which live in freshwater are called terrapin. 

• The Squamata 

This type of reptiles mainly consists of lizards and snakes. It is one of the largest order of reptiles also known as scaled reptiles. It is one of the most varied order of reptiles in size ranging from 16 mm (dwarf gecko) to 5.1m (green anaconda) and now a new extinct species called mosasaurs, which reached a length of 14m.  

• The Crocodilian 

In this type of reptile, we mainly discuss crocodiles and alligators. It is mostly large, predatory, and semi-aquatic animals. The body of a crocodilian is large, solidly built, lizard-like reptiles and they have long flattened snouts. They have a laterally compressed tail, and eyes, ears, and nostrils at the top of the head. They can swim well in the water and also they can walk (high walk and the low walk) on the land. 

• The Tuatara 

In this type, we discuss lizard-like species. The name ‘tuatara’  is derived from Maori language and that means peak on the back. It has only one species, that is “Sphenodon punctatus” and it is the only surviving member of its order. It is greenish-brown and grey in colour and its length is 80 cm from head to tail and weighs around 1.3 kg along with the spines on the back.

Characteristics of Reptiles 

Some of the general characteristics of reptiles are given below - 

• All reptiles lay their egg on land, including aquatic ones.

• They reproduce sexually through internal fertilization, in which some of them lay eggs and some of them give birth to the young ones.

• Reptiles have developed impermeable and scaly skin. They moved to the land because their skin cannot be used for respiration in the water. 

• Reptiles mainly depend on the surrounding environment for their body temperature because reptiles are ectotherms. This is an advantage to the reptiles,  as they are not dependent on metabolic energy from food for body heat.

• Reptiles' body temperature varies rather than being stable as they are poikilotherms.

• Sometimes reptiles enter into a state called brumation. It is a long period during cold weather that consists of no eating and a decreased metabolism.

Life Cycle and Life History of Reptiles 

The life histories of reptiles are very diverse and amazingly wide, It often reveals nearly unbelievable reproductive adaptations. Some of the reptiles are the annual species, which hatch, mature, reproduce, and die annually or at most in two years (side-blotched lizards). Other species such as loggerhead sea turtles are a long-living species, which requires almost 25 years to get matured and they have a lifespan of 50 years. There are many unimaginable adaptations made by reptiles. Some of them have mentioned that Some reptiles lay eggs, whereas others are live-bearers. Some of the reptiles lay 1 or 2 eggs, whereas other reptiles lay 100 or more eggs in each nesting event. Some reptiles nest throughout the year, while others may nest once a year or allow two or more years between breeding cycles.

The Circulatory System of Reptiles 

Most of the reptiles have a three-chambered heart, that has two atria and one partially divided ventricle. Despite the fact, the ventricle is partially divided, there will be little mixing of oxygenated and deoxygenated blood in the three-chambered heart. Such type of mixings is controlled by the valves of the heart and the movement of the ventricle walls. The blood flow in the reptiles can be altered to either pump deoxygenated blood to the body or to stop blood flow to the lungs. To pump blood to the lungs, it requires energy, So, by diverting blood flow can save the energy of the reptiles when it is not very active.

All the reptiles do not have a three-chambered heart. For example, Crocodiles have a four-chambered heart like mammals and also like birds. However, the four-chambered heart of these reptiles acts as a three-chambered heart during dives. It is also observed that some of the snakes and lizards have a three-chambered heart which can act as a four-chambered heart during the process of contraction.

The Respiratory System of Reptiles 

All the reptiles breathe through their lungs, as their lung has a much greater surface area for the exchange of gases than the lungs of amphibians. Many reptiles have little sac in their lungs known as alveoli, across which gas is exchanged. Alveoli make their lungs more efficient compared to the amphibians. A different group of reptiles make lung ventilation differently. In squamates, the lungs are ventilated almost exclusively by the muscles of the chest wall. Same muscles are used during movement, so most of them have to hold their breath during running.

Few of the reptiles use their throat muscles for respiration. They gulp the air through the throat muscles and this process is called buccal pumping, this process is also used by amphibians. The animals use a buccal pump system when they take air in through the nose and move their throat up and down. It makes the animal look in the way as it is gulping the air. When lizards fill their mouth with air, they push the air down to the lungs. The nostrils are closed, the glottis is opened, forcing the air into the lungs for gas exchange. The process is reversed in a similar way for deflation.

In reptiles, crocodiles have a muscular diaphragm which is similar to the mammalian diaphragm. The difference in crocodiles is that the muscles of their diaphragm pull part of the pelvis back, which brings the liver down and frees space for the lungs to expand.

The Excretory System of Reptiles 

In reptiles, excretion is performed by two small kidneys. In reptiles like crocodiles, snakes, lizards, and tuatara the main nitrogen-containing waste product is uric acid. Kidneys of reptiles are unable to produce urine like the kidneys of mammals and birds because it is more concentrated compared to their body fluids. This is because reptiles lack the special structure called the loop of Henle, which is present in the nephrons of birds and mammals. In reptiles, the water stored in the bladder is reabsorbed with the help of colon. The excess salt present is excreted by the salt glands present in the nasal passages and tongues for example; marine iguanas excrete excess salt through their nasal glands, and crocodiles excrete its salt through lingual (tongue) salt gland.

General Features of the Reptiles

Some of the general features of reptiles are:

• All the reptiles are vertebrates, which means they all have a backbone.

• All the reptiles do not produce eggs, most of the reptiles lay hard-shelled eggs while the other gives birth to young ones directly.

• All the reptiles have small scales and hard plates that are made from a protein called keratin. Some of the reptiles also have scutes, that is the shells of turtles and armour of crocodiles. It is very similar to the scales. Scutes are the bony structure, which is developed in the deeper level of the skin than scales.

• They are cold-blooded animals known as ectothermic. That means, reptiles cannot control their body temperature; it will depend on the environment for increasing or decreasing the body temperature.

Interesting Fun Facts about Reptiles 

According to the available information about reptiles, some of the interesting fun facts are -

• Reptiles are one the longest-lived species on the planet, for example, Aldabra tortoise can live for over 150 years!

• Reptiles first appeared 350 million years ago in fossil records.

• Reptiles' skin is always cool and dry because they do not have sweat glands, thus they do not produce slime.

• The scales of the snakes are made from the same material, from which our hairs and nails are made, that is keratin.