Image by AmberBrooke.
Lizards are reptiles belonging to the order Squamata and the suborder Lacertilia. Approximately 3800 species of lizards, ranging from few cms long geckos to 10 feet long Komodo Dragons, exist on the earth. They have worldwide distribution except in the Polar Regions. Reptiles were more widespread, numerous and diverse during the Mesozoic era which is sometimes called the “Age of Reptiles”. The most primitive order of reptiles is Cotylosaurs which were lizard-like, insect eating, heavily limbed reptiles with solid roofed skulls and labyrinthine teeth and are similar to amphibians of the time. There are essentially two waves of evolutionary changes that radiated from the first reptiles. First were mammal-like reptiles or Synapsids and were later replaced by the Diapsids. These two names are given to differentiate a single opening in the skull for the attachment of jaw muscles for the synapsids and two openings for the diapsids. These synapsids dominated the land ecosystem by 280 million years ago (mya) during the Permian and early Triassic period. But by 260 mya they evolved into the Therapsids- carnivorous reptiles. Within 30 mya they had dominated most niches until they became extinct at the end of Permian period at 225 mya and gave way to the diapsids. Earliest of the diapsids is the Petrolacosaurus which was a very lizard-like creature similar to the kind still found today. From this creature came the two most successful reptilian families; the Lepidosaurs and the Archosaurs. The Archosaurs became dinosaurs. At the end of Cretaceous period, 65 mya, a mass extinction caused the archosaurs to disappear from earth. The Lepidosaurs have changed very little in the many million years they have been in the planet and eventually evolved into the present day snakes and lizards. The earliest known fossil remains of a lizard belong to the iguanian species Tikiguania estesi, which dates to the Carnian stage of the Triassic period, about 220 mya. Some slender Australian lizards called skinks have gone from being five-fingered to legless in just 3.6 million years. It is suggested that the skink’s way of life have lead them to lose their limbs because they spend most of their lives swimming through sand and soil during which the limbs cause a major hindrance.
There are ground and tree-dwelling lizards as well as few semi aquatic ones. The gliding form of lizards or flying dragons are found in the forest of South-East Asia. They are usually non- poisonous with the exception of Gila monster and related beaded lizard of North American desert. Lizards are fast- runners, some achieving speed of over 24km/hr. Most lizards eat insects, spiders and scorpions. Iguanas and some others are herbivorous. Monitors and a number of other lizards eat amphibians, reptiles, birds and mammals. The Komodo Dragon catches and eat animals as large as deer. Lizards play an important role in maintaining ecological balance by feeding on insects and being eaten as food source for large animals like birds. They communicate through various body language, gestures and movements to define territory, resolve disputes, entice mates and chase off enemies. Many lizards are protectively coloured which help them to camouflage by blending into its surroundings. To frighten and confuse enemies, some change colour or reveal a bright coloured patch hidden on the underside or between its scales. Many lizards shed off their tails during an encounter with the predator, a phenomenon called caudal autotomy, thus distracting it and increasing the probability to escape. The horned toad squirts blood from its eyes and the frilled lizard spreads the large disk of skin around its neck to ward off enemies.
Lizards have some characteristic physiological traits. Most lizards possess acute colour vision and good auditory power. They carry out chemoreception with the aid of vomeronasal organ, isolated from the nasal cavity. They rapidly flick their tongue in and out during which odour molecules are trapped in the salivary coating of the tongue and from there they are transferred to the vomeronasal organ. Lizards have little physiological control over their internal body temperature. They rely entirely on external heat sources to provide them with adequate energy so that they can execute their natural activities and various metabolic processes. Hence they are labelled “cold- blooded”. Many lizards effectively regulate body temperature by using behavioural adjustments such as basking in the sun when air is cool and seeking shade when air is too warm. Lizards are called as ectotherms since they control the uptake of heat from the environment as a way to control internal body temperature. The suffering of a sick, hurt and chronically distressed lizard is far more prolonged than that experienced by mammals due to the former’s slow metabolic rate. Blood loss and healing of injuries are both relatively slow. Most lizards maintain an optimum temperature ranging between 24°–35°C while performing daily activities. Their entire physiology including immune defense mechanism is temperature dependant and operates optimally at this temperature range. Most species of lizards rely on anaerobic metabolism for short bursts of rapid activity since the levels of oxygen consumption during rest and activity are much less than those of comparably sized homeotherms. The oxygen carrying capacity and oxygen affinity of blood are also less in comparison to mammalian levels as are the activities of aerobic enzymes. Therefore the activities of lizards appear to be limited to either slow movement sustainable by limited aerobic capacities or rapid bursts supported anaerobically. The mode of excretion in lizards is uricotelic, i.e, uric acid is the main nitrogenous waste. Most lizards reproduce sexually while some lizards, such as whiptails, sometimes reproduce asexually- their eggs produce offsprings without being fertilized. Female lizards lay porous, soft-shelled, amniotic eggs but a few give birth to live young. The yellow-bellied three-toed skink found along the warm coastal lowlands of New South Wales lays eggs to reproduce. But individuals of the same species living in the state's higher, colder mountains give birth to live young. The baby lizards that are born in an egg have a special temporary tooth they use to break the shell which allows them to hatch.
Image by wwarby
More than two dozen species of lizards are officially called endangered, and many more are considered vulnerable. Among the endangered species are the Fiji crested iguana, the Coachella Valley fringe-toed lizard, and a legless species of skink.
Brookesia superciliaris - Leaf Chameleon
Chamaeleo calyptratus calyptratus - Veiled Chameleon
Chamaeleo delepis - Flap-knecked Chameleon
Chamaeleo quadricornis - Four-horned Chameleon
Chamaeleo montium - Cameroon Sail-finned Chameleon
Chamaeleo jacksoni xantholophus - Jackson's Chameleon
Furcifer pardalis - Panther Chameleon
For now, why not check our leopard gecko care sheet?
Basiliscus plumifrons - Plumed Basilisk
Sceloporus magister ssp. - Desert swift
Sceloporus malachiticus - Emerald Swift
Leiocephalus carinatus armouri - Northern Curly-tailed Lizard