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Monitor lizards also known as bayawak or goannas, genus Varanus, are members of the family Varanidae. Varanus is a group of carnivorous lizards which includes the heaviest living lizard, the Komodo dragon and the crocodile monitor which is the longest lizard in the world. The closest living relatives are the anguid and helodermatid lizard.

Monitor lizards are generally large reptiles, although some can be as small as 12 centimetres in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semi-aquatic monitors are also known. Almost all monitor lizards are carnivorous, although Varanus prasinus and Varanus olivaceus are also known to eat fruit. They are oviparous, laying from 7 to 37 eggs, which they often cover with soil or protect in a hollow tree stump.

Distribution

The various species of Varanus cover a vast area, occurring through Africa, the neat subcontinent from Indiamarker and Sri Lankamarker to Chinamarker, down Southeast Asia to Indonesiamarker, the Philippinesmarker, New Guineamarker, Australia and islands of the Indian Oceanmarker and South China Seamarker.

Evolutionary overview

Monitor lizards differ greatly from other lizards in several ways, possessing a relatively high metabolic rate for reptiles and several sensory adaptations that benefit the hunting of live prey. Recent research indicates that the varanid lizards, including the Komodo dragon, may have some venom. This discovery of venom in monitor lizards, as well as in agamid lizards, led to the Toxicofera hypothesis: that all venomous lizards and snakes share a common venomous ancestor.

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, which reached lengths of up to 17 m.

It was also believed that snakes are more closely related to monitor lizards than any other type of extant reptile, but it has been proposed that snakes are sister group of the clade of iguanians and anguimorphs.

During the Pleistocene epoch, giant monitor lizards lived in Southeast Asia and Australasia, the best known fossil being Varanus priscus (formerly known as Megalania prisca). This species is an iconic member of the Pleistocene megafauna of Australia.

Some monitor lizards, including the Komodo Dragon, are capable of parthenogenesis.

Etymology

The generic name Varanus is derived from the Arabic word waral ورل, (alternative spelling 'waran'= "lizard"). The name comes from a common semitic root ouran, waran, or waral meaning "lizard". It has been suggested that the occasional habit of varanids to stand on their two hind legs and to appear to "monitor" their surroundings led to this name as it was Latinized into Varanus. Its common name is derived from the Latin word monere meaning "to warn".

In Tamil and Malayalam monitor lizards are known as "Udumbu", in Marathi monitor lizards are known as "Ghorpad" घोरपड. In Kannada monitor lizards are known as "Uda", and in Sinhalese, "Kabaragoya". In Telugu monitor lizards are known as "Udumu". Due to confusion with the large New World lizards of the family iguanidae, the lizards became known as "goannas" in Australia. Similarly, in Southern Africa they are referred to as "leguaan", from the Dutch for iguana.

Intelligence

Varanid lizards are very intelligent, and some species can even count. Careful studies feeding V. albigularis at the San Diego Zoomarker varying numbers of snails showed that they can distinguish numbers up to six. V. niloticus 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.King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43. Komodo dragons, V. komodoensis, at the Smithsonian National Zoological Parkmarker in Washington, D.C., recognize their keepers and seem to have distinct personalities.

In captivity

lizards have become a staple in the reptile pet trade. The most commonly kept monitors are the Savannah monitor and Acklin's monitor, due to their relatively small size, low cost, and relatively calm dispositions. Nile monitors, white throated monitors, water monitors, mangrove monitor, emerald tree monitors, black tree monitors, acanthurus monitors, quince monitors, crocodilemonitors and komodo dragons have also been kept in captivity. Like all reptiles that are kept as pets, monitors need hiding places and an appropriate substrate. Monitors also need a large water dish in which they can soak their entire body. In the wild, monitors will eat anything they can overpower, but crickets, superworms, and the occasional rodent make up most of the captive monitors' diet. Boiled eggs, silkworms, earthworms, and feeder fish can also be fed to them. However, due to their predatory nature and large size some monitors can be dangerous to keep as pets; adult Nile monitors and water monitors, for example can reach seven feet in length.

Protected status

In Tamil Nadumarker and all other parts of South India, catching or killing of monitor lizards is banned.

Classification

White-throated monitor on the Kalahari savannah
Perentie (Varanus giganteus)
Genus Varanus


References

  1. King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.
  2. Pianka, E.R.; King, D.R. and King, R.A. 2004. Varanoid Lizards of the World. Indiana University Press.


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