|Rock monitor (Varanus albigularis)|
Monitor lizards are generally large reptiles, although some can be as small as 20 centimetres (7.9 in) in length. They have long necks, powerful tails and claws, and well-developed limbs. Most species are terrestrial, but arboreal and semiaquatic monitors are also known. Almost all monitor lizards are carnivorous, although Varanus bitatawa, Varanus mabitang and Varanus olivaceus are also known to eat fruit. They are oviparous, laying from seven to 37 eggs, which they often cover with soil or protect in a hollow tree stump.
The various species of Varanus cover a vast area, occurring through Africa, the Indian subcontinent from Pakistan, 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. There is also a large concentration of monitor lizards in Tioman Island in the Malaysian state of Pahang.
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 the varanid lizards 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.
Snakes were believed to be more closely related to monitor lizards than any other type of extant reptile, however, it has been more recently proposed that snakes are the 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 the megalania (Varanus priscus unless it falls in its own genus, in which case it is Megalania prisca). This species is an iconic member of the Pleistocene megafauna of Australia.
The generic name Varanus is derived from the Arabic word waral ورل, (alternative word waran). The name comes from a common Semitic root ouran, waran, or waral meaning "lizard". The occasional habit of varanids to stand on their two hind legs and to appear to "monitor" their surroundings has been suggested to have led to this name, as it was Latinized into Varanus. Its common name is derived from the Latin word monere meaning "to warn".
In Malay / Indonesian Language varanids are called biawak. In Tamil and Malayalam, monitor lizards are known as udumbu, ghorpad घोरपड in Marathi, uda in Kannada, in Sinhalese as kabaragoya, in Telugu as Udumu, in Punjabi and Magahi (and other Bihari languages) as goh, in Assamese as "Gui Xaap" and in Bengali as goshaap or guishaap. Due to confusion with the large New World lizards of the family Iguanidae, the lizards became known as "goannas" in Australia. Similarly, in South Africa they are referred to as leguaan, from the Dutch for iguana. The generic name inspired the name of the Japanese movie monster Varan.
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 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, D.C., recognize their keepers and seem to have distinct personalities.
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. Black throated monitors, white throated monitors, water monitors, Nile monitors, mangrove monitors, emerald tree monitors, black tree monitors, acanthurus monitors, quince monitors, crocodile monitors and Komodo dragons have been kept in captivity. Like all reptiles kept as pets, monitors need an appropriately sized enclosure, hiding places, and an appropriate substrate. Some water monitors also need a large water dish in which they can soak their entire bodies. In the wild, monitors will eat anything they can overpower, but crickets, superworms, feeder fish, and the occasional rodent (for calcium) make up most of the smaller captive monitors' diet. Boiled eggs, silkworms and earthworms can also be fed to them. Larger species, such as Nile monitors, Asian water monitors, crocodile monitors, perenties, and Komodo dragons will eventually require larger prey. Paleontologist and biology professor at Temple University, Michael Balsai has observed V. prasinus eating fruit in captivity as has herpetologist and author, Robert G. Sprackland.
All but five species of monitor lizard are classified by CITES (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 in order to avoid utilization 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.
- V. bengalensis, Bengal monitor
- V. dumerilii, Dumeril's monitor
- V. flavescens, yellow monitor
- V. rudicollis, black roughneck monitor
- V. beccarii, black tree monitor
- V. boehmei, golden-spotted tree monitor
- V. bogerti, Bogert's tree monitor
- V. caerulivirens, turquoise monitor
- V. cerambonensis, Ambon monitor
- V. doreanus, blue-tailed monitor
- V. finschi, Finsch's monitor
- V. indicus, mangrove monitor
- V. jobiensis, peach-throat monitor
- V. juxtindicus, Rennell Island monitor
- V. keithhornei, canopy goanna, Nesbit River monitor
- V. kordensis, Biak tree monitor
- V. macraei, blue-spotted tree monitor
- V. melinus, quince monitor
- V. lirungensis, Lirung monitor
- V. obor, sago monitor
- V. prasinus, emerald tree monitor, emerald monitor
- V. rainerguentheri Rainerguenther's monitor
- V. reisingeri, Reisinger's tree monitor
- V. telenesetes, Rossel Island tree monitor
- V. yuwonoi, tri-colored monitor
- V. zugorum, Zug's monitor
- V. acanthurus, ridge-tailed monitor
- V. a. acanthurus, spiny-tailed monitor
- V. a. brachyurus, common ridge-tailed monitor
- V. a. insulanicus, island ridge-tailed monitor
- V. auffenbergi, peacock monitor
- V. baritji, White's dwarf monitor, black-spotted ridge-tailed monitor, black-spotted spiny-tailed monitor
- V. brevicauda, short-tailed monitor
- V. bushi, Pilbara monitor, Bush's monitor
- V. caudolineatus, stripe-tailed monitor
- V. eremius, desert pygmy monitor
- V. gilleni, pygmy Mulga monitor
- V. glauerti, Kimberley rock monitor
- V. glebopalma, black-palmed rock monitor
- V. kingorum, King's monitor
- V. mitchelli, Mitchell's water monitor
- V. pilbarensis, Pilbara rock monitor
- V. primordius, blunt-spined monitor
- V. scalaris, banded tree monitor
- V. semiremex, rusty monitor
- V. similis, spotted tree monitor
- V. storri, Storr's monitor
- V. timorensis, Timor monitor
- V. tristis, black-headed monitor
- V. t. orientalis, freckled monitor
- V. salvadorii, crocodile monitor
- V. bitatawa, northern Sierra Madre forest monitor lizard, bitatawa
- V. mabitang, Panay monitor
- V. olivaceus, Gray's monitor
- V. albigularis, rock monitor
- V. exanthematicus, savannah monitor
- V. niloticus, Nile monitor
- V. ornatus, ornate monitor
- V. yemenensis, Yemen monitor
- †V. darevskii (extinct)
- V. griseus, desert monitor [endangered]
- V. cumingi, Cuming's water monitor
- V. marmoratus, Phiippine water monitor
- V. nuchalis, large-scaled water monitor
- V. palawanensis Palawan water monitor
- V. rasmusseni Rasmussen's water monitor
- V. salvator, water monitor
- V. togianus, Togian water monitor
- V. giganteus, perentie
- V. gouldii, sand goanna or Gould's goanna
- V. komodoensis, Komodo dragon
- V. mertensi, Mertens' monitor
- V. panoptes
- †V. priscus, megalania (extinct)
- V. rosenbergi, Rosenberg's goanna or heath monitor
- V. spenceri, Spencer's goanna
- V. varius, lace monitor
- Greene, Harry W. (1986). Diet and Arboreality in the Emerald Monitor, Varanus Prasinus, With Comments on the Study of Adaptation. Field Museum of Natural History. ISBN [[Special:BookSources/9998057760|9998057760[[Category:Articles with invalid ISBNs]]]].
- Bauer, Aaron M. (1998). Cogger, H.G. & Zweifel, R.G., ed. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 157–159. ISBN 0-12-178560-2.
- Fry, B.G.; Wroe, S; Teeuwisse, W; van Osch, JP; Moreno, K; Ingle, J; McHenry, C; Ferrara, T; Clausen, P; Scheib, H; Winter, KL; Greisman, L; Roelants, K; van der Weerd, L; Clemente, CJ; Giannakis, E; Hodgson, WC; Luz, S; Martelli, P; Krishnasamy, K; Kochva, E; Kwok, HF; Scanlon, D; Karas, J; Citron, DM; Goldstein, EJC; Mcnaughtan, JE; Norman JA. (June 2009). "A central role for venom in predation by Varanus komodoensis (Komodo dragon) and the extinct giant Varanus (Megalania) priscus.". PNAS 106 (22): 8969–8974. doi:10.1073/pnas.0810883106. PMC 2690028. PMID 19451641.
- Fry, B.G.; Vidal, N; Norman J.A.; Vonk F.J.; Scheib, H.; Ramjan S.F.R; Kuruppu S.; Fung, K.; Hedges, B.; Richardson M.K.; Hodgson, W.C.; Ignjatovic, V.; Summerhays, R.; Kochva, E. (February 2006). "Early evolution of the venom system in lizards and snakes" (PDF). Nature 439 (7076): 584–588. doi:10.1038/nature04328. PMID 16292255.
- Smith, Kerri. "Dragon virgin births startle zoo keepers". Nature. Retrieved 2006-12-20.
- Robert George Sprackland (1992). Giant lizards. Neptune, NJ: T.F.H. Publications. p. 61. ISBN 0-86622-634-6.
- King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.
- Pianka, E.R.; King, D.R. and King, R.A. 2004. Varanoid Lizards of the World. Indiana University Press.
- Balsai, Michael (1997). The General Care and Maintenance of Popular Monitors and Tegus. BowTie. p. 6. ISBN 978-1-882770-39-7.
- "Identification Guides for Wildlife Traded in Southeast Asia". ASEAN-WEN. 2008.
- Varanus keithhornei, The Reptile Database
- Varanus prasinus, The Reptile Database
- Varanus baritji, The Reptile Database
- Varanus spinulosus, The Reptile Database
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