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 the are the anguid and helodermatid lizards.
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 Asian subcontinent from India and Sri Lanka to China, down Southeast Asia to Indonesia, the Philippines, New Guinea, Australia and islands of the Indian Ocean and South China Sea.
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 weak 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 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 that view has been modified recently to make snakes a 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 are apparently 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 Zoo 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. Komodo dragons, V. komodoensis, at the Smithsonian National Zoological Park in Washington, D.C., recognize their keepers and seem to have distinct personalities.
In captivity:
Monitor 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 monitors, emerald tree monitors, 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 Nadu and all other parts of South India, catching or killing of monitor lizards is banned.
Classification:
Genus Varanus
*V. acanthurus
....*V. a. acanthurus, Spiny-tailed Monitor or Spiny-tailed Goanna
....*V. a. brachyurus, Common Ridge-tailed Monitor
....*V. a. insulanicus, Island Ridge-tailed Monitor
*aranus albigularis, Rock Monitor
....*V. a. albigularis, White-throated Monitor
....*V. a. angolensis, Angola White-throated Monitor
....*V. a. ionidesi, Black-throated Monitor
*V. auffengbergi, Peacock Monitor
*V. baritji, Northern Ridge-tailed Goanna
*V. beccarii, Black Tree Monitor
*V. bengalensis
....*V. b. bengalensis, Bengal Monitor
....*V. b. nebulosus, Clouded Monitor
*V. boehmei, Golden-spotted Tree Monitor
*V. bogerti, Louisiade Tree Monitor
*V. brevicauda, Short-tailed Monitor
*V. bushi, Pilbara Goanna
*V. caerulivirens, Turqois Monitor
*V. caudolineatus, Stripe-tailed Goanna
*V. cerambonensis, Ceram Mangrove Monitor
*V. cumingi, Cuming's Water Monitor
*V. doreanus, Blue-tailed Monitor
*V. dumerilii, Dumeril's Monitor
*V. ermius, Desert Pygmy Monitor
*V. exanthematicus, Savannah Monitor
*V. finschi, Finsch's Monitor
*V. flavescens, Yellow Monitor
*V. giganteus, Perentie
*V. gilleni, Pygmy Mulga Goanna
*V. glauerti, Kimberley Rock Monitor
*V. glebopalma, Black-palmed Rock Monitor
*V. gouldii, Sand Goanna
....*V. g. horni, Horn's Monitor
....*V. g. rubidus, Yellow-spotted Monitor
*V. griseus, Desert Monitor
....*V. g. griseus, Western Desert Monitor
....*V. g. caspius, Eastern Desert Monitor
....*V. g. koniecznyi, Thar Desert Monitor
*V. indicus, Mangrove Monitor
*V. jobiensis, Peach Throat Monitor
*V. juxtindicus, Hakoi Monitor
*V. keithhornei, Canopy Goanna
*V. kingorum, King's Goanna
*V. komodoensis, Komodo Dragon
*V. kordensis, Kordo Tree Monitor
*V. lirungensis, Lirung Monitor
*V. mabitang, Panay Monitor
*V. macraei, Blue-spotted Tree Monitor
*V. marmoratus, Marbled Water Monitor
*V. melinus, Quince Monitor
*V. mertensi, Merten's Water Monitor
*V. mitchelli, Mitchell's Water Monitor
*V. niloticus, Nile Monitor
*V. nuchalis, Spiny-necked Water Monitor
*V. olivaceus, Gray's Monitor
*V. ornatus, Ornate Monitor
*V. panoptes
....*V. p. panoptes, Argus Monitor
....*V. p. horni, Horn's Monitor
....*V. p. rubidus
*V. pilbarensis, Pilbara Rock Monitor
*V. prasinus, Emerald Tree Monitor
*V. primordius, Blunt-spined Goanna
*V. priscus, Megalania
*V. rainerguentheri
*V. reisingeri, Reisinger's Tree Monitor
*V. rosenbergi, Rosenberg's Goanna or Heath Monitor
*V. rudicollis, Black Roughneck Monitor
*V. salvadorii, Crocodile Monitor
*V. salvator, Water Monitor
....*V. s. salvator, Asian Water Monitor
....*V. s. andamanensis, Andaman Islands Water Monitor
....*V. s. bivittatus, Two-striped Water Monitor
....*V. s. komaini, Black Water Monitor
....*V. s. macromaculatus, Southeast Asian Water Monitor
*V. scalaris, Spotted Tree Goanna
*V. semiremex, Mangrove Pygmy Goanna
*V. spenceri, Spencer's Goanna
*V. spinulosus, St. Isabel Mangrove Monitor
*V. storri, Storr's Goanna
....*V. s. storri, Eastern Storr's Goanna
....*V. s. ocreatus, Western Storr's Monitor
*V. telenesetes, Rossel Island Tree Monitor
*V. timorensis, Timor Tree Monitor
*V. togianus, Togian Water Monitor
*V. tristis, Black-headed Monitor
....*V. t. orientalis, Freckled Monitor
*V. varius, Lace Monitor
*V. yemenensis, Yemen Monitor
*V. yuwonoi, Tri-colored Monitor
*V. zugorum, Zug's Monitor
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