There are millions of animals in the world and for easy identification, the animals are categorized into groups and given names according to their characteristics and the characteristics that they have in common. This system enables easy identification and classification of animals. Reptiles are a group of animals comprising of all the animals that fall within the Reptilia class. They are found in all the continents of the world apart from Antarctica. There are reptiles that have four legs while others like the snake have no legs; however they are descendants of animals that had four legs.
Scientists believe that reptiles actually came from the amphibians. Amphibians evolved from tetrapods and then reptiles evolved from amphibians, and it is estimated that this process took place around 400 million years ago.
Though they are descended from amphibians, reptiles have no aquatic larval stage and they are mostly oviparous. Reptiles are further categorized in four main groups. These groups are according to characteristics which the reptiles have in common so as to enable easy identification and classification.
There are strange reptiles that almost found in some islands of New Zealand and they are referred to as tuataras. Turtles are also in a group of reptiles and they are characterized by a protective shell that they have. Turtles also have a slow metabolic system.
There is another group called the crocodilians and the last group is referred to as squamates which has snakes and lizards, sharing the ability to open their jaws wide to swallow prey as well as to shed off their skins as they grow.
All reptiles are covered with a scaly skin, which is rough and hard and it offers great protection. It is believed that the fact that reptiles evolved into having scaly skin is what enabled them to move from water and inhabit the land.
Most reptiles today feed on flesh and are therefore carnivorous as opposed to mammals where there is a fairly large number that feed on plants. The only reptiles that live on a strictly herbivorous diet are the iguanas and the turtles. The rest will feed on other animals, their young ones and their eggs.
Unlike mammals that have hearts with four chambers, reptiles in the turtles, snakes and lizards all have three. This is taken to be a sign to show that they evolved from amphibians which have hearts with two chambers only. The only reptiles that have hearts with four chambers like mammals are the crocodilians.
Amphibians laid their eggs in water, however when they evolved into reptiles, they started laying eggs on land as well as incubating their young ones inside the female’s body, making them amniotes. Therefore it is believed that the reptiles that evolved from amphibians were the first amniotes and their ability to lay eggs on land as well as incubate their young ones in the female’s body enabled animals to venture further on land.
Their eggs have a membrane which is for protection and for ease of transportation. The smallest reptile is the tiny gecko which can grow up to a length of just 17 millimeters while the largest reptile is the saltwater crocodile which can grow to a length of up to 6 meters and weigh over 1000 kilograms in weight.
Mammals have big brains that are well developed making them intelligent, however reptiles do not have brains that are as well developed, and therefore they are not so intelligent. Their brain size is just about a tenth of their body size. The crocodilians are the most intelligent amongst the reptiles. Reptiles however are more intelligent compared to the amphibians and fish.
Since reptiles lay eggs, there are reptiles that have their sex determined by the external temperature. This is referred to as temperature-depend sex determination (TDSD). When the embryo is developing, the temperature of the atmosphere around the egg will determine whether the young one will be a female or a male. This especially affects crocodiles and turtles, although there is no advantage that has been seen to arise as a result of this.
All the reptiles will breathe with the use of lungs, however there are some turtles that live in water that have a permeable skin to allow gaseous exchange and there are some reptiles that use the cloaca to breathe as well. Even in such reptiles, the lungs are still involved in breathing.
Defense mechanisms of reptiles
To protect themselves from harm and from predators, animals will use various methods either to ensure that they escape, or to deter predators from attacking them, and reptiles are not any different. They have various methods that they use to protect themselves from harm and from predation.
Some reptiles will use camouflage so as to avoid predation. They have skin that has various colorations and patterns such as gray, brown or green, which allows them to blend in with their environment, making them hard to spot thus they are able to stand still in the sight of danger and go unnoticed.
Apart from camouflage, reptiles also use coloration, having bright colorations that serve as a warning, keeping off other animals and predators simply because the reptile looks dangerous to approach. For example, the Gila monster has a bright coloration that acts to warn off other animals.
Some reptiles which are not venomous will have a bright coloration similar to venomous reptiles and they use mimicry so as to warn of potential attackers by mimicking venomous reptiles such as the how some snakes will mimic the coral snake. The blue-tongued skink will expose its blue tongue when in danger so as to warn the attacker.
Likewise, other reptiles will also use various sounds so as to warn off attackers, such as hissing sounds exhibited by snakes, crocodiles and some lizards while the rattle snake will rattle the tip of its tail so as to warn others.
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Some snakes have different ways of defending themselves, such as elevating their heads and spreading out their necks so as to make themselves look bigger and if this does not work they will use their venom, which they spread using their fangs through bites. Some snakes will play dead when they sense danger.
Crocodiles will open their mouths wide open so as to expose their large and sharp teeth and this is to warn off other animals that if they come any nearer they shall be bitten. They will also pose in such a way such that they look larger and more intimidating.
There are other reptiles that will shed off their tails, which will act to distract the predator while they safely get away. The tail once detached will start to wiggle vigorously and this will attract the attention of the predator, while the reptile safely flees. The tail will regrow after days or weeks. Some of the reptiles that exhibit this form of defense include skinks and geckos as well as some lizards.
Reproduction of Reptiles
Just like all other animals, reptiles have a developed reproductive system with most of the reptiles reproducing through sexual reproduction and a few of them exhibit asexual reproduction. In reptiles, sexual activity occurs using the cloaca which is a single entrance found at the base of the tail and it is the same organ used for eliminating waste material from the body.
Reptiles will lay eggs that have amniotic fluid, and are covered with shells that are leathery in texture. The amniotic fluid works to provide a cushion for the embryo and helps to protect it and the allantois collects waste material produced by the embryo. There is a yolk present which contains nutrients and this is what the embryo uses so as to grow.
Reptiles do not have a larval development stage. There are both cases of viviparity and ovoviviparity that are exhibited by various members of the reptilian class.
Asexual reproduction can be found in squamates in some lizards and in one species of snakes. Some squamates use a method of reproduction, called parthenogenesis, in which the female produces a diploid clone of itself. There are species of the gecko that exhibit this type of asexual reproduction, as well as teiids and some komodo dragons.
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Interaction of reptiles and human beings
Reptiles and human beings interact both on hostile terms as well as due to human beings adoring some of them. There are several reptiles that are venomous or dangerous and therefore human beings will always view them as a threat.
As a result human beings will regularly kill reptiles such as snakes and some lizards so as to protect themselves and prevent the reptiles from harming them. Interestingly enough, some of the reptiles considered dangerous are a source of admiration for human beings and some reptiles have a symbolic role that they play in different cultures.
The cobra, a venomous snake capable of killing an adult human being was worshiped in Egypt as a god. Snakes were also worshiped in Hinduism where they were also considered as gods, where they are taken to be signs of fertility. The interaction between human beings and reptiles seems to be on a love and hate basis.