What is a Reptile?
A Reptile is a scaly animal that can be characterized by laying their eggs on land.
Reptiles come in a vast amount of shapes and sizes from tiny frogs to huge, primitive looking lizards. There are around 8,000 species of reptile living on the planet today. Reptiles are vertebrates which means they have a back bone. Reptiles have a tough scaly skin which is hard and dry, although some can appear slimy. Scales are made from keratin which is the same substance as human fingernails.
Reptiles are cold blooded creatures (ectothermic) and their body temperature is determined by their surroundings. Some reptiles bask in the sun during the day to increase their body temperature. When they are warm enough, they then actively seek food.
Chameleons and many species of lizards can adjust the colour of their skin to absorb more heat from the sun. Some reptiles can become too hot and therefore adapt to a nocturnal life style whereby they actively seek food during the night. Ectothermic reptiles can survive on one tenth of the amount of food needed by an endothermic (warm blooded) animal of similar size.
The term ‘reptile’ can in fact include birds who were the only survivors of the Cretaceous extinction. They differ from non-avian reptiles as they are warm blooded and their scaly bodies are covered with feathers.
Reptiles live throughout the world but are absent in cold regions and are more common in warm tropical regions. Like amphibians, many reptiles prefer aquatic or semi aquatic habitats, however, some reptiles are more diverse than amphibians and are less dependant on water therefore being able to colonize a wider range of habitats. There are some species of reptile that spend most of their life in water such as Crocodiles and Alligators.
Reptiles lay their eggs on land in a prepared nest, a pile of rotting vegetation or sandy burrow. There is no larval stage during reptile development and no metamorphosis stages as with amphibians. Young reptiles emerge from the eggs fully formed as miniature adults. Reptile eggs are much stronger than amphibian eggs as they have to be able to survive life out of the water. The tough shell prevents the eggs from drying out. Some reptiles, particularly snakes such as the Cobras and Pythons, will protect the eggs and drive away intruders. Crocodilians take more care of their young than most other reptiles who have little interest in their offspring after the eggs have hatched. Crocodilians will aggressively defend their nests and will stay with their young for a few months or a couple of years.
Here are some of the families in the reptile group:
About 300 species of turtle are alive today and some are highly endangered. Turtles have bodies that are covered with a large carapace (cartilaginous shell developed from their ribs).
There are aquatic, semi-aquatic and terrestrial species. The largest turtles are aquatic.
The earliest known turtles date from 215 million years ago, making turtles one of the oldest reptile groups and a more ancient group than lizards and snakes. Turtles breathe air and do not lay eggs underwater, although many species live in or around water.
Iguanas and Relatives
These are lizards that have four functional limbs. They use their tongue to capture and grab food. The two species of lizard within the genus Iguana possess a dewlap, a row of spines running down their back to their tail and a third ‘eye’ on their head. This eye is known as the parietal eye, visible as a pale scale on the top of the head.
Behind their neck are small scales which resemble spikes, known as tuberculate scales. They also have a large round scale on their cheek known as a subtympanic shield. Iguanas have excellent vision and are able to see shapes, shadows, colour and movement at long distances. Iguanas use their eyes to navigate through crowded forests, as well as for finding food. They also use visual signals to communicate with members of the same species.
Snakes and Lizard
These are scaled reptiles of many forms and also known as Squamates. Males usually have paired copulatory organs called ‘hemipenes’. This group also includes:
Scleroglossans – includes Worm Lizards and Geckos.
These are squamates that use their jaws instead of their tongue to catch food. Their tongue is used for smelling. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the braincase.
This is particularly visible in snakes, which are able to open their mouths very wide to accommodate very large prey. They are the most varied in size order of reptiles, ranging from the 16 millimetres for the Jaragua Sphaero to the 8 metres green anaconda.
Autarchoglossans – includes Skinks.
This is the most diverse group of lizards with around 1,200 species. Skinks look roughly like true lizards, but most species have no pronounced neck and have relatively small legs. These squamates have highly developed olfactory capabilities involving the tongue and a sensitive scent organ called the Jacobson’s Organ found in the roof of their mouth.
Skinks are generally carnivorous and mainly eat insects, including crickets, grasshoppers, beetles and caterpillars. They also eat earthworms, snails, slugs, isopods, other lizards and small rodents.
Anguimorph Lizards – includes Knob-scaled Lizards, Alligator Lizards and Glass Lizards.
This is a diverse group of squamates. Many have bony plates (osteoderms) beneath their scales and some species lack legs. These lizards, along with Iguanians and Snakes, comprise the proposed venom clade Toxicofera of all venomous reptiles. It encompasses all venomous reptile species, as well as numerous related non-venomous species.
Monitors and Relatives – includes Bearded Lizards and Monitor Lizards.
This is a group of carnivorous lizards which includes the heaviest living lizard, the Komodo Dragon, with the Crocodile Monitor being the longest in the world. This group of squamates have an excellent sense of smell and well developed teeth, upper jaw and neck. Most are efficient predators that use their long tongues to track prey. Most species are terrestrial, however, arboreal and semi-aquatic monitors are also known.
These squamates have elongated, cylindrical bodies with no limbs. They also lack movable eyelids and have no external ears. Like all squamates, snakes are ectothermic amniote vertebrates covered in overlapping scales. Like lizards, from which they evolved, they have loosely articulated skulls and most can dislocate their lower jaw in order to swallow prey much larger than their own head.
Most species are non-venomous and those that have venom use it primarily to kill and subdue prey rather than for self defence.