Monitor lizards are lizards in the genusVaranus, the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species.[1] 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 20 cm (7.9 in) in some species such as Varanus sparnus, to over 3 m (10 ft) in the case of the Komodo dragon, though the extinct megalania (Varanus priscus) may have reached lengths of more than 7 m (23 ft). Most monitor species are terrestrial, but many are also arboreal or semiaquatic. While most monitor lizards are carnivorous, eating smaller reptiles, fish, birds, insects, small mammals, and eggs, a few species also eat fruit and vegetation.[2]
The generic name Varanus is derived from the Arabic word ورلwaral [Standard Arabic] / وررwarar [colloquially] / ورنwaran [colloquially], from a common Semitic root ouran, waran, wararor waral, meaning "lizard beast".[3]
In English, they are known as "monitors" or "monitor lizards". The earlier term "monitory lizard" became rare by about 1920.[4] The name may have been suggested by the occasional habit of varanids to stand on their two hind legs and to appear to "monitor",[3] or perhaps from their supposed habit of "warning people of the approach of venomous animals".[5] But all of these explanations for the name "monitor" postdate Linnaeus giving the scientific name Lacerta monitor to the Nile monitor in 1758, which may have been based on a mistaken idea by Linnaeus that the German word Waran (borrowed from Arabic) was connected to warnen (to warn), leading him to incorrectly Latinize it as monitor ('warner', 'adviser').[6]
InSouth Asia, they are known as hangkokinMeitei, mwpou in Boro, ghorpad घोरपड in Marathi, uḍumbu உடும்பு in Tamil and udumbu ഉടുമ്പ് in Malayalam, bilgohinBhojpuri, gohi (गोहि) in Maithili, in Sinhala as තලගොයා / කබරගොයා (talagoya [land monitor] / kabaragoya [water monitor where kabara means vitiligo]), in Teluguasuḍumu (ఉడుము), in Kannadaasuḍa (ಉಡ), in Punjabi and Magahi as गोह (goh), in Assameseasgui xaap, in Odia as ଗୋଧି (godhi), and in Bengali as গোসাপ (goshaap) or গুইসাপ (guishaap), and गोह (goh) 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.
Most monitor lizards are almost entirely carnivorous,[13] consuming prey as varied as insects, crustaceans, arachnids, myriapods, molluscs, 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 adult Komodo dragons, the largest monitor species.[14] In contrast, three arboreal species from the Philippines, Varanus bitatawa, mabitang, and olivaceus, are primarily fruit eaters.[15][16][17]
Monitor lizards are considered unique among animals in that its members are relatively morphologically conservative, yet show a very large size range.[18] However, finer morphological features such as the shape of the skull and limbs do vary, and are strongly related to the ecology of each species.[19][20]
Monitor lizards maintain large territories and employ active-pursuit hunting techniques that are reminiscent of similar-sized mammals.[21] 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.[22]
Like snakes, monitor lizards have highly forked tongues that act as part of the "smell" sense, where the tips of the tongue carry molecules from the environment to sensory organs in the skull. The forked apparatus allows for these lizards to sense boundaries in the molecules they collect, almost smelling in "stereo".[23]
Monitor lizards have a high aerobic scope[22][24] 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.[25] This allows monitor lizards to create mammalian-equivalent pressure differentials between the pulmonary and systemic circuits,[25] which in turn ensure that oxygenated blood is quickly distributed to the body without also flooding the lungs with high-pressure blood.
Monitor lizards are oviparous,[22] laying from seven to 38 eggs,[26] which they often cover with soil or protect in a hollow tree stump. Some species, including the Komodo dragon, are capable of parthenogenesis.[27]
Anatomical and molecular studies indicate that all varanids (and possibly all lizards) are venomous.[28][29] Unlike snakes, monitor lizard venom glands are situated in their lower jaw.[30] The venom of monitor lizards is diverse and complex, as a result of the diverse ecological niches monitor lizards occupy.[31]
For example, many species have anticoagulant venom, disrupting clotting through a combination of fibrinogenolysis and blocking platelet aggregation. Amongst them, arboreal species such as the tree monitors and the banded monitor have by far the strongest fibrinogenolytic venom. As a result, wounds from monitor lizard bites often bleed more than they would if they were simply lacerations. Venom may also cause hypotension.[32]
In some species such as the Komodo dragon and the desert monitor, venom also induces a powerful neurotoxic effect. In the latter species for instance, envenomation causes immediate paralysis in rodents (but not birds) and lesser effects of the same nature in humans.[33]
At least some species of monitors are known to be able to count; studies feeding rock monitors varying numbers of snails showed that they can distinguish numbers up to six.[34][35]Nile monitors have been observed to cooperate when foraging; one animal 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.[34][35]Komodo dragons at the National Zoo in Washington, DC, recognize their keepers and seem to have distinct personalities.[35]Blue and green tree monitors in British zoos have been observed shredding leaves, apparently as a form of play.[36]
Monitor lizards are poached in some South- and Southeast Asian countries, as their organs and fat are used in some traditional medicines, although there is no scientific evidence as to their effectiveness.[37][38]
Monitor lizard meat, particularly the tongue and liver, is eaten in parts of India and Malaysia and is supposed to be an aphrodisiac.[39][40]
In parts of Pakistan and southern India, as well in Northeastern India, particularly Assam, the different parts of monitor lizards are traditionally used for treating rheumatic pain, skin infections and hemorrhoids, and the oil is used as an aphrodisiac lubricant (sande ka tel).[41]
"Large-scale exploitation" of monitor lizards is undertaken for their skins, which are described as being "of considerable utility" in the leather industry.[41]InPapua New Guinea, monitor lizard leather is used for membranes in traditional drums (called kundu), and these lizards are referred to as kundu palai or "drum lizard" in Tok Pisin, the main Papuan trade language. Monitor lizard skins are prized in making the resonant part of serjas (Bodo folk sarangis) and dotaras (native strummed string instruments of Assam, Bengal and other eastern states). The leather is also used in making a Carnatic music percussion instrument called the kanjira.
The meat of monitor lizards is eaten by some tribes in India,[42] Nepal,[43] the Philippines, Australia, South Africa and West Africa as a supplemental meat source.[citation needed] Both meat and eggs are also eaten in Southeast Asian countries such as Vietnam and Thailand as a delicacy.[44]
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 – the Bengal, yellow, desert, and clouded monitors and the Komodo Dragon– are classified under CITES Appendix I, which outlaws international commercial trade in the species.[45]
The yellow monitor is protected in all countries in its range except Bhutan, Nepal, India, Pakistan, and Bangladesh.[46]
InKerala, Andhra Pradesh, Karnataka, Telangana and all other parts of South India, catching or killing of monitor lizards is banned under the Protected Species Act.
Varanus is the only living genus of the family Varanidae. Varanids last shared a common ancestor with their closest living relatives, earless "monitors", during the Late Cretaceous. The oldest known varanids are from the Late Cretaceous of Mongolia. During the Eocene, the varanid Saniwa occurred in North America. The closest known relative of VaranusisArchaeovaranus from the Eocene of China, suggesting that the genus Varanus is of Asian origin. The oldest fossils of Varanus date to the early Miocene.[47]
^Bauer, Aaron M. (1998). Cogger, H.G.; Zweifel, R.G. (eds.). Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 157–159. ISBN0-12-178560-2.
^ abcdRobert George Sprackland (1992). Giant lizards. Neptune, NJ: T.F.H. Publications. p. 61. ISBN0-86622-634-6.
^Horatio Nelson, Matthew Henry Barker, The Life of Nelson Revised and Illustrated. With Original Anecdotes, Notes, Etc. By the Old Sailor, 1836 p. 35
^Heinrich Zimmern (1915). Akkadische Fremdwörter als Beweis für babylonischen Kultureinfluss (Thesis) (in German). Universität Leipzig. p. 52. OCLC697605207.
^Pianka, Eric R.; King, Dennis R; King, Ruth Allen (2004). Varanoid Lizards of the World. Bloomington, Indiana: Indiana University Press.
^Auffenberg, Walter (1981). The Behavioral Ecology of the Komodo Monitor. University Press of Florida.
^Greene, Harry W. (1986). Diet and Arboreality in the Emerald Monitor, Varanus Prasinus, with Comments on the Study of Adaptation. Chicago: Field Museum of Natural History. OCLC14915452. OL7155983M.
^Zima, Yuliya (December 2019). "On the Toxicity of the Bite of the Caspian Gray Monitor Lizard (Varanus griseus caspius)". Biawak. 13 (2): 115–118 – via ResearchGate.
^ abKing, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN0-86840-456-X, p. 43.
^ abcPianka, E.R.; King, D.R. and King, R.A. (2004). Varanoid Lizards of the World. Indiana University Press.
^Ghimire HR, Phuyal S, Shah KB (2014). "Protected species outside the protected areas: People's attitude, threats and conservation of the Yellow Monitor (Varanus flavescens) in the Far-western Lowlands of Nepal". Journal for Nature Conservation. 22 (6): 497–503. Bibcode:2014JNatC..22..497G. doi:10.1016/j.jnc.2014.08.003.
^ abBöhme, Wolfgang (2019-11-23). "The Kei Islands Monitor Lizard (Squamata: Varanidae: Varanus: Euprepiosaurus) as a Distinct Morphological, Taxonomic, and Conservation Unit". Russian Journal of Herpetology. 26 (5): 272–280. doi:10.30906/1026-2296-2019-26-5-272-280. S2CID213867767.
^ abcdeWeijola, Valter (2019-03-14). "A molecular phylogeny for the Pacific monitor lizards (Varanus subgenus Euprepiosaurus) reveals a recent and rapid radiation with high levels of cryptic diversity". Zoological Journal of the Linnean Society. 186 (4): 1053–1066. doi:10.1093/zoolinnean/zlz002.
^Koch, Andre (2010). "Updated checklist of the living monitor lizards of the world (Squamata: Varanidae)". Bonn Zoological Bulletin. 57: 127–136.
^Koch, Andre (2010-05-06). "Unravelling The Underestimated Diversity Of Philippine Water Monitor Lizards (Squamata: Varanus Salvator Complex), With The Description Of Two New Species And A New Subspecies". Zootaxa. 2446: 1–54. doi:10.11646/zootaxa.2446.1.1.
^Mendyk, Robert (2018). "An Annotated Bibliography of Captive Reproduction in Monitor Lizards (Varanidae: Varanus). Part III. Soterosaurus". Biawak. 12.
^ abcdefghiMolnar, Ralph E. (2004). "The Long and Honorable History of Monitors and their Kin". In Pianka, Eric R.; King, Dennis R.; King, Ruth Allen (eds.). Varanoid Lizards of the World. Indiana University Press. ISBN978-0-253-34366-6.
^Ziegler, Thomas; Schmitz, Andreas; Koch, Andre; Böhme, Wolfgang (2007). "A review of the subgenus EuprepiosaurusofVaranus (Squamata: Varanidae): morphological and molecular phylogeny, distribution and zoogeography, with an identification key for the members of the V. indicus and the V. prasimus species groups". Zootaxa1472: 1-28.
^Eidenmüller, Bernd; Wicker, Rudolf (2005). "Eine weitere neue Waranart aus dem Varanus prasinus-Komplex von den Insel Misol, Indonesian ". Sauria27 (1): 3-8. (Varanus reisingeri, new species). (in German).
^Bucklitsch, Yannick (2016-08-17). "Scale Morphology and Micro-Structure of Monitor Lizards (Squamata: Varanidae: Varanus spp.) and their Allies: Implications for Systematics, Ecology, and Conservation". Zootaxa. 4153 (1): 1–192. doi:10.11646/zootaxa.4153.1.1. PMID27615821.
^Koch, André; Gaulke, Maren; Böhme, Wolfgang (2010). "Unravelling the underestimated diversity of Philippine water monitor Lizards (Squamata: Varanus salvator complex), with description of two new species and a new subspecies". Zootaxa2446: 1-54. (Varanus rasmusseni, new species, p. 28).
Merrem B (1820). Versuchs eines Systems der Amphibien: Tentamen Systematis Amphibiorum. Marburg: J.C. Krieger. xv + 191 pp. + one plate. (Varanus, new genus, p. 58). (in German and Latin).
Data related to Monitor lizard at Wikispecies
Media related to Varanus at Wikimedia Commons
