Reptiles are vertebrates (with a backbone) that have four limbs or, as in the case of snakes, are descended from four-limbed ancestors. Most reptiles lay eggs, although some give birth to live young.
Modern reptiles, which number around 8 700 species, are cold-blooded animals, which inhabit every continent except Antarctica.
Four sub-groups represent various reptiles: Testudines (turtles, terrapins and tortoises – over 300 species), Sphenodontia (2 tuatara species), Squamata (9 150 species of lizards, snakes and worm lizards and Crocodilia (23 species of crocodiles, gavials, caimans and alligators).
Reptiles have external scales made of keratin which vary in size from the tiny ones found on small geckos to those found on large lizards and snakes. The big scales that cover the shell of a turtle or the plates of a crocodile are known as scutes.
Reptiles range greatly in size from a tiny gecko of just 17mm in length to saltwater crocodiles of 6 metres which weigh around 1 000kg.
Reptiles are believed to have evolved from reptile-like amphibians that became increasingly adapted to life on dry land. Proof lies in fossil evidence of many extinct groups such as the dinosaurs.
The name of this highly venomous snake suggests that it is black in colour, when it's actually grey. So why not grey mamba then? Well it's name comes from the colour of the inside of the snake's mouth. When it is frightened it opens its mouth to reveal a dark inner lining. The snake also spreads a small narrow hood in an effort to make itself appear larger than it actually is. Heeding this warning is good advice as the next step could be a bite.
The puffadder is one of South Africa's most common yet dangerous snakes. This is because it is an ambush predator which relies on its superb camouflage in order to trap its prey. As such, it does not always move away when a human approaches and will readily bite if stepped on. As a result most bites are found on the lower legs of victims. Puffadders have long, hinged fangs and cytotoxic venom.
The rinkhals is an amazing cobra-type snake that is not considered a true cobra, even though it does spread its hood like a cobra and also sprays venom. True cobras are egg-laying, while the rinkhals gives birth to live young. True spitting cobras are able to spray venom up to about three metres by constricting their venom glands and forcing venom through adapted fangs. Rinkhals can spray about a metre, which makes them far less effective than true spitting cobras.
(Thelotornis capensis capensis)
The vine snake, also known as the twig snake or bird snake, is unique for a number of reasons. It is one of Southern Africa's most venomous snakes, since there is no known anti-venom. However, its bite is treatable, and there have only been a few bites recorded over the last 40 years, and not one recorded death. A vine snake's vision is aided by a keyhole-shaped pupil, which gives it the ability to spot animals that are standing still.
One of only two species of venomous lizard found in the world, the gila monster is endemic to the deserts of the southern United States and Mexico. Gila monsters have venom glands, but do not inject their venom like snakes do. Instead they grasp their prey in extremely powerful jaws and bite down hard, tearing the flesh with their razor-sharp fangs and causing wounds into which their venom flows. Gila monsters bite so hard that they cannot be disengaged without the use of pliers. They have enough venom to cause the death of three to four adult humans. Gila monsters generally eat small animals and eggs.