Lizard is a relatively long-bodied reptile with usually two pairs of legs and a tapering tail. Lizard is not a name of one species but it is a collective term for all species of Lizards. Lizards are reptiles i.e. they require heat to maintain their body temperature and have scaly skin. Having scaly skins give them the term ‘Squamata’ which means scaled reptiles. They are closely related to snakes and it is the presence of feet and external ears that differentiates them from snakes. In fact some lizards don’t have legs and they look almost like snakes. Chameleons, dragons, geckos, gila monster, iguanas, monitors and skinks are all lizards. There are some differences in sizes, colours and some apparent distinguishing features which make them different from a common lizard. Thus ‘Lizard’ is a common term for all these different names. Lizards are the most geographically widespread as compared to other reptiles i.e. snakes, crocodiles, tortoises, turtles and tuataras. This also makes them counted amongst ‘The Largest Group of Reptiles’.

• Facts about Lizards
• Lizard Scientific Classification
• Lizard Species
• Lizard Types
• Physical Features of Lizard
• Lizard Reproduction

Lizard Scientific Classification

Lizard Facts

• Some lizards have only two legs, for example Ajolote Lizard or the Mexican Mole Lizard

• Some lizards don’t have legs and they look like snakes. Such lizards are called Scheltopusik or Glass Lizards

• The basilisk and the collared lizard, found in the American continents, have the ability of running on their hind legs. This action is referred to as bipedal locomotion

• Certain species of the lizard under the genus Draco have the ability to glide from one tree to another. These lizards are commonly known as Flying Lizards or Flying Dragons. These are mostly found in south Asia. These lizards have a membrane that connects their front and rear limbs. This membrane is actually foldable and is supported by elongate ribs. When this membrane is opened during a jump it enables gliding

• Some Horned lizards can squirt blood at a distance of 2-4 feet out of their eyes. They squirt blood as defence mechanism. The blood has very pungent smell and it drives away any predator

• Some species of female lizards like Veiled Chameleons, can store the sperm for later fertilization without the need of a male

• Some lizards like Chuckwallas (Sauromalus) can inflate their bodies as defence mechanism. They live close to rock piles. Whenever there is a danger they move into small crevices and puff up their bodies to make their extrication difficult

• A number of spiny-tailed lizards use their sharp and spiny tale as a defence mechanism. Upon a sign of danger they hide into crevices head-first exposing only its tails which is sharp and spiny. Any predator wouldn’t risk an injury for such a meal

• Some species of lizards i.e. skinks give birth to live young. This true of about one-third of the skink species, many of which live in tropical climates

• Some lizards are herbivorous like iguanas (Iguana, Ctenosaura, and Cyclura) and the spiny-tailed agamid (Uromastyx), eat plants

• Some lizards can live over 30 years, the record, 33 years and 11 months, is held by a Mexican beaded lizard

• Most lizard species hibernate in the summer (estivate) or winter. Those which hibernate in winter are from the temperate regions; they seek warm places beneath the frost line or any suitable warm place. Those found in hot, dry climatic regions escape the heat by crawling into deep holes or fissures in the ground. Here, they can retain their body moisture

• Most lizards can break their tail off and grow another one. The tails breaks at a weak vertebra link and this action is called 'autonomy'. However, the new grown tail is smaller and has no bones

• Lizards smell with their tongue just like snakes

Lizard Species

There are more than 5,600 species lizard species found all over the world, except for the continent of Antarctica where it is too cold for them to survive

Lizard Types

Lacertilia comprises four generally recognized suborders, Iguania, Gekkota, Amphisbaenia and Autarchoglossa

Iguania

Gekkota

Amphisbaenia

Autarchoglossa

Physical Features of Lizard

Cold Blooded and Ectothermic - Lizards being reptiles are cold-blooded and depend on external heat source to regulate their body temperature. To raise their body temperature they bask in the sun or position themselves near any heat source i.e. a bulb, water heater etc. They can also vary their temperature by positioning themselves in such a way as to gain heat through conduction or by seeking shade. The process of regulating internal body temperature by the external absorption of heat is known as Ectothermic.

Highly acute colour vision – Lizards have good colour vision, they can see more colours as compared to other reptiles. Their retinas contain multicoloured oil droplets in their photoreceptors which enables them to perceive more colours as compared to other reptiles and certain other animals. Their colour vision is important to them as they are highly dependent on sight for hunting and communicating.

Visible Ear Openings - Lizards don’t ears like humans or earflaps like mammals. Instead, they have visible ear openings with which they can hear sound. Their eardrums are located just below the surface of their skin and their hearing is better than those of the snakes.

Pineal Body – Beneath the skin in the skull of a lizard, there is a gland called the ‘Third Eye’ which enables enhanced sight in dark and light.  It is the evolutionary equivalent of the bone-encased, hormone secreting pineal gland in the human brain. The human pineal is denied access to light directly but like the lizard's 'third eye,' it shows enhanced release of its hormone, melatonin, during the night.

Three Chambered Heart – A lizard has 3 chambers - 2 atria and 1 ventricle. A muscular septum partially divides the ventricle. When the ventricle contracts, the opening in the septum closes and the ventricle is momentarily divided into two separate chambers. This prevents mixing of the two bloods. The left half of the ventricle pumps oxygenated blood (received from the left atrium) to the body. The right half pumps deoxygenated blood (received from the right atrium) to the lungs.

Autotomic – Lizards are autotomic i.e. they can shed certain parts of their body voluntarily. In lizards it is the tail which can be shed and re-grown. This is a survival strategy employed by the lizard when it is caught by the tails or when it is under attack. The tails is detached by muscular contraction. When the tails is detached it wriggles and the movement diverts the attention of the attacker, which gives the lizard ample time to flee. The sphincter muscles in the tail stump close off the caudal artery to prevent excessive bleeding. This whole process of shedding the tails is known as Autotomy. The lizard will partially regenerate its tail over a period of weeks. The new tail is composed of cartilage rather than bone and the skin may be distinctly discoloured as compared to the rest of the body.

Scaly Body – All lizards have dry skins and scaly bodies i.e. it is covered in scales. Only clooca, eyes, mouth and nostrils are not covered with scales. Scales come in different shapes, texture and the arrangement of the scales varies among species and by body part. Scales may be smooth and overlapping, form a mosaic of flat plates, or have keels or tubercles. The arrangement varies among species and by body part. The outer parts of the scales are composed of dead horny tissue made up largely of the protein called keratin. The dead layer is shed at intervals and in patches. The dead skin is replaced by proliferating cells in the deep part of the epidermis. Some lizards have scales modified into sharp spines like in horned lizards. Some lizards have scales which are fortified with internal horny plates called Osteoderms like in the Beaded lizards.

Presence of Melanophores – Melanophores are the pigment cells that allow colour change and patterns in lizards. The concentration of pigment granules within these pigment cells determines the type of colour that is produced. The lizards will appear lighter coloured when pigment is concentrated and dark when pigment is dispersed throughout the cells. The presence of Melanophores enables the lizard to change its colour at any given time by a complex interaction of hormones, temperature, and the nervous system. Lizards like chameleons and the anoles are notable species for changing their colour. The colour change can vary from bright green to deep, chocolate brown. Even the patterns such as lines and bars may appear of disappear all together.

Communication through body language – Lizards communicate through body language, they use specific gestures, movements and postures for territory, disputes and attracting mates. Some species of lizard are already colourful while others are able to display their colours only on certain occasions like defending territory or during mating period. Some anole lizards are able to blow a flap which is brightly coloured and is used for display only. It deflates whenever there is a danger. Some lizards bob their head or do push-ups to show dominance, to mate and attract females.

Lizard Reproduction

Male lizards have a skin flap at the base of their tail. The skin flap has two copulatory organs called hemipenes, one on each side of the base of the tail. These are generally short and broad, with pleats or folds, but may also be forked. Either one of the two hemipenes may be used for internal fertilization. Female lizards have sac-like ovaries and large-yolked hard-shelled eggs for the protection of the embryo.

Male lizards will approach the female from the side, with many biting the neck of the female, and try to get their cloaca in a position as close as possible to the female. At this point, the closest hemipenes is erected. The hemipenes of many species of lizard is adorned with thorns or 'hooks' of some kind, securing a hold during mating. At this point, the sperm will travel through the penis, along the hemipenes' channel, to the females cloaca. Fertilization occurs when the sperm enters the oviducts of the female.

Most lizards reproduce by laying eggs and most of the smaller species lay a uniform number of eggs, for example anole lizards. Anoles lay only one egg at a time and large sized Iguanas can lay 50 or more eggs at one time. The clutch size varies with the size, age, and condition of the mother. Most of the lizards bury the eggs in the ground or any other suitable place. Most lizard species do not take care of the eggs or protect them. Lizard eggs are usually leathery-shelled and porous; they can expand by the absorption of moisture as the embryos grow. The incubation period is about 90 to 100 days. Smaller species of lizard reach sexual maturity in the first breeding season after birth but in larger species sexual maturity may take few years.