Monitor lizard


Monitor lizards are large lizards in the genus Varanus. They are native to Africa, Asia, and Oceania, but are now found also in the Americas as an invasive species. About 80 species are recognized.
Monitor lizards have long necks, powerful tails and claws, and well-developed limbs. The adult length of extant species ranges from in some species, to over in the case of the Komodo dragon, though the extinct varanid known as Megalania may have been capable of reaching lengths more than. Most monitor species are terrestrial, but arboreal and semiaquatic monitors are also known. While most monitor lizards are carnivorous, eating eggs, smaller reptiles, fish, birds, insects, and small mammals, some also eat fruit and vegetation, depending on where they live.

Distribution

The various species cover a vast area, occurring through Africa, the Indian subcontinent, to China, the Ryukyu Islands in southern Japan, south to Southeast Asia to Thailand, Brunei, Indonesia, the Philippines, New Guinea, Australia, and islands of the Indian Ocean, and the South China Sea. The West Nile monitor is now found in South Florida and in Singapore.

Habits and diet

Most monitor lizards are almost entirely carnivorous, consuming prey as varied as insects, crustaceans, arachnids, myriapods, mollusks, fish, amphibians, reptiles, birds, and mammals. Most species feed on invertebrates as juveniles and shift to feeding on vertebrates as adults. Deer make up about 50% of the diet of adults of the largest species, Varanus komodoensis. In contrast, three arboreal species from the Philippines, Varanus bitatawa, Varanus mabitang, and Varanus olivaceus, are primarily fruit eaters. Although normally solitary, groups as large as 25 individual monitor lizards are common in ecosystems that have limited water resources.

Biology

The genus Varanus is considered unique among animals in that its members are relatively morphologically conservative, yet show a very large size range. Finer morphological features such as the shape of the skull and limbs do vary, though, and are strongly related to the ecology of each species.
Monitor lizards maintain large territories and employ active-pursuit hunting techniques that are reminiscent of similar-sized mammals. The active nature of monitor lizards has led to numerous studies on the metabolic capacities of these lizards. The general consensus is that monitor lizards have the highest standard metabolic rates of all extant reptiles.
Monitor lizards have a high aerobic scope that is afforded, in part, by their heart anatomy. Whereas most reptiles are considered to have three-chambered hearts, the hearts of monitor lizards – as with those of boas and pythons – have a well developed ventricular septum that completely separates the pulmonary and systemic sides of the circulatory system during systole. This allows monitor lizards to create mammalian-equivalent pressure differentials between the pulmonary and systemic circuits, which in turn ensure that oxygenated blood is quickly distributed to the body without also flooding the lungs with high-pressure blood.
Anatomical and molecular studies indicate that all varanids are partially venomous.
Monitor lizards are oviparous, laying from seven to 37 eggs, which they often cover with soil or protect in a hollow tree stump. Some monitor lizards, including the Komodo dragon, are capable of parthenogenesis.

Evolution

The family Varanidae probably originated in Asia at least 65 million years ago, although some estimates are as early as the late Mesozoic. Monitor lizards probably expanded their geographic range into Africa between 49 and 33 million years ago, possibly via Iran, and to Australia and the Indonesian archipelago between 39 and 26 million years ago.
Varanids last shared a common ancestor with their closest living relatives, earless "monitors", during the Late Cretaceous.
During the Late Cretaceous era, monitor lizards or their close relatives are believed to have evolved into amphibious and then fully marine forms, the mosasaurs, some of which reached lengths of or more.
Snakes were believed to be more closely related to monitor lizards than any other type of extant reptile; however, snakes have been more recently proposed to be the sister group of the clade of iguanians and anguimorphs. Like snakes, monitor lizards have forked tongues, which they use to sense odors.
The genus Varanus first emerged in Laurasia. During the late Oligocene to early Miocene, the group had dispersed to Australia, New Guinea, and the Solomon Islands three separate times. By the late Miocene, the genus was also present in Africa, Arabia, Asia, and Eastern Europe.
By the Pleistocene epoch, giant monitor lizards lived in Southeast Asia and Australasia, the best known fossil being the megalania. This species is an iconic member of the Pleistocene megafauna of Australia, thought to have survived until around 50,000 years ago.
Many of the species within the various subgenera also form species complexes with each other:
V. indicus species complex
V. doreanus species complex
V. gouldii species complex
V. bengalensis species complex
V. acanthurus species complex
V. exanthematicus species complex
V. timorensis species complex
V. niloticus species complex
V. salvator species complex
The tree monitors of the V. prasinus species complex were once in the subgenus Euprepriosaurus, but as of 2016, form their own subgenus Hapturosaurus.
V. jobiensis was once considered to be a member of the V. indicus'' species complex, but is now considered to represent its own species complex.

Name

The generic name Varanus is derived from the Arabic word waral/waran ورن/ورل, from a common Semitic root ouran, waran, or waral, meaning "dragon" or "lizard beast".
In English, they are known as "monitors" or "monitor lizards". The earlier term "monitory lizard" became rare by about 1920. The name may have been suggested by the occasional habit of varanids to stand on their two hind legs and to appear to "monitor", or perhaps from their supposed habit of "warning persons of the approach of venomous animals".
In Austronesia, where varanids are common, they are known under a large number of local names. They are usually known as biawak, bayawak, binjawak or minjawak or nyambik, or variations thereof. Other names include hokai, bwo or puo or soa, halo, galuf or kaluf, batua or butaan, alu, hora or ghora, phut and guibang.
In South Asia, they are known as hangkok in Meitei,ghorpad घोरपड in Marathi, udumbu in Tamil and Malayalam, bilgoh in Bhojpuri, gohi in Maithili, in Sinhala as කබරගොයා, in Telugu as udumu, in Punjabi and Magahi as गोह, in Assamese as gui xaap, in Odia as ଗୋଧି, and in Bengali as গোসাপ or গুইসাপ, and गोह in Hindi.
Due to confusion with the large New World lizards of the family Iguanidae, the lizards became known as "goannas" in Australia. Similarly, in South African English, they are referred to as leguaans, or likkewaans, from the Dutch term for the Iguanidae, leguanen.

Intelligence

Some species of varanid lizards can count; studies feeding V. albigularis varying numbers of snails showed that they can distinguish numbers up to six. V. niloticus lizards have been observed to cooperate when foraging; one varanid lures the female crocodile away from her nest, while the other opens the nest to feed on the eggs. The decoy then returns to also feed on the eggs. Komodo dragons, V. komodoensis, at the National Zoo in Washington, DC, recognize their keepers and seem to have distinct personalities. There have also been cases of monitors being trained through encouraging wanted behaviour

Uses

As pets

Monitor lizards have become a staple in the reptile pet trade. The most commonly kept monitors are the savannah monitor and Ackies monitor, due to their relatively small size, low cost, and relatively calm dispositions with regular handling. Among others, black-throated monitors, timor monitors, Asian water monitors, Nile monitors, mangrove monitors, emerald tree monitors, black tree monitors, roughneck monitors, dumeril's monitors, peach-throated monitors, crocodile monitors, and Argus monitors have been kept in captivity.

Medicinal

Monitor lizard meat, particularly the tongue and liver, is eaten in parts of India and Malaysia, and is traditionally considered to also be an aphrodisiac.
In parts of Pakistan and southern India, different parts of monitor lizards are used for a variety of medical purposes. The flesh is eaten for the relief of rheumatic pain, abdominal fat is used as a salve for skin infections, oil and fat are used to treat hemorrhoids or chronic pain, and the oil is used as an aphrodisiac lubricant.
However, consuming raw blood and flesh of monitor lizards has been reported to cause eosinophilic meningoencephalitis, as some monitors are hosts for the parasite Angiostrongylus cantonensis.

Leather

"Large-scale exploitation" of monitor lizards is undertaken for their skins, which are described as being "of considerable utility" in the leather industry. In Papua New Guinea, monitor lizard leather is used for membranes in traditional drums , and these lizards are referred to as kundu palai or "drum lizard" in Tok Pisin, the main Papuan trade language.

Food

The meat of monitor lizards is eaten by some tribes in India, the Philippines, Australia, and West Africa as a supplemental meat source. Both meat and eggs are also eaten in Southeast Asia such as Vietnam and Thailand as a delicacy.
The meat of monitor lizards is used in Nepal for medicinal and food purpose.

Music

The skin of monitor lizards is used in making a carnatic music percussion instrument called a kanjira.

Protected status

According to IUCN Red List of threatened species, most of the monitor lizards species fall in the categories of least concern, but the population is decreasing globally. All but five species of monitor lizards are classified by the Convention on International Trade in Endangered Species of Wild Fauna and Flora under Appendix II, which is loosely defined as species that are not necessarily threatened with extinction, but may become so unless trade in such species is subject to strict regulation to avoid use incompatible with the survival of the species in the wild. The remaining five species – V. bengalensis, V. flavescens, V. griseus, V. komodoensis, and V. nebulosus – are classified under CITES Appendix I, which outlaws international commercial trade in the species.
The yellow monitor, V. flavescens, is protected in all range countries except Bhutan, Nepal, India, Pakistan, and Bangladesh.
In Tamil Nadu and all other parts of South India, catching or killing of monitor lizards is banned under the Protected Species Act.

Classification

'Genus Varanus
Subgenus Empagusia:
Subgenus Euprepiosaurus:
Subgenus Hapturosaurus
Subgenus Odatria:
Subgenus Papusaurus
Subgenus Philippinosaurus:
Subgenus Polydaedalus:
Subgenus Psammosaurus:
Subgenus Solomonsaurus:
Subgenus Soterosaurus:
Subgenus †Varaneades:
Subgenus Varanus: