Difference between revisions of "Monitor lizard" - New World Encyclopedia
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{{Taxobox | {{Taxobox | ||
| name = Monitor lizards | | name = Monitor lizards | ||
| image = Varanus varius1.jpg | | image = Varanus varius1.jpg | ||
| image_width = 240px | | image_width = 240px | ||
| − | | image_caption = An [[Australia]]n [[lace monitor]]<br /> | + | | image_caption = An [[Australia]]n [[lace monitor]]<br />''(Varanus varius)'' on a tree. |
| regnum = [[Animal]]ia | | regnum = [[Animal]]ia | ||
| phylum = [[Chordate|Chordata]] | | phylum = [[Chordate|Chordata]] | ||
| Line 14: | Line 15: | ||
| genus_authority = [[Blasius Merrem|Merrem]], 1820 | | genus_authority = [[Blasius Merrem|Merrem]], 1820 | ||
| subdivision_ranks = [[Species]] | | subdivision_ranks = [[Species]] | ||
| − | | subdivision = | + | | subdivision = |
}} | }} | ||
| − | '''Monitor | + | '''Monitor lizard,''' or '''monitor,''' is the common name for any of the [[Old World]] [[lizard]]s comprising the '''Varanidae''' family, which contains only one extant [[genus]], ''Varanus,'' whose members are characterized by a generally elongate neck, a heavy body, long-forked tongues, and long, non-autonomous tails. While some monitor lizards are small, the genus also contains some very large extant lizards, including the largest living lizard, the [[Komodo dragon]], which reaches three meters in length and 54 kilograms in weight and can even feed on large mammals, like [[deer]], [[pig]]s, and [[buffalo]] (Ast 2003). One [[fossil]] species from about 20,000 years ago reached seven meters in length and 600 kilograms. Monitor lizards today are found in a vast area in the Old World, including [[Africa]], [[Asia]], [[Oceania]], and [[Australia]]. |
| − | The | + | The name, "monitor," is also used for a species in different, but closely related, family, the earless monitor ''(Lanthanotus borneensis)'' in Lanthanotidae, a semi-aquatic, brown lizard from Borneo. This article will be restricted to discussion of the varanids (Varanidae). |
| + | Monitor lizards are important to [[food chain]]s in their various terrestrial and aquatic (including marine) habitats, both as predator and prey. They consume a wide variety of [[invertebrate]]s and [[vertebrate]]s, including [[carrion]] and even [[fruit]] in the case of some varanids. For humans, monitor lizards are important in various cultures for art, folklore, and a source of [[food]], [[leather]], and folk medicine. Thus, as with other [[taxa]], varanids not only advance a function for the individual (survival, reproduction, self-maintenance of the species), but also provide a function for the whole ([[ecosystem]], [[human]]s). | ||
| + | ==Overview and description== | ||
| + | The Varanidae family is part of the infraorder ''Anguimorpha,'' which also includes [[alligator lizard]]s, [[galliwasp]]s, [[legless lizard]]s, [[knobby lizard]]s, and the extinct [[mosasaur]]s, as well as the [[gila monster]] and [[Mexican Beaded Lizard|Mexican bearded lizard]]. | ||
| + | |||
| + | The Varanidae family contains only one extant genus, ''Varanus''. There are extinct varanids that have been placed in other [[genus|genera]], such as ''Telmasaurus'' and ''Megalania'' (although some have reclassifed the latter as part of ''Varanus''). | ||
| + | |||
| + | There are about fifty to sixty modern species of ''Varanus''. | ||
| + | ====Physical description==== | ||
| + | [[Image:KomodoDragonRinca1.jpg|thumb|upright|240px|Komodo dragons]] | ||
| + | Monitor lizards tend to be robust, diurnal lizards, with elongate necks and non-autotomous tails (Ast 2003). They have long, forked tongues, which are used for chemorecption, and their hemipenes are unusually ornate, with paired apical horns (Ast 2003). | ||
| − | + | Unlike lizards in all other families, except Lanthanotidae (''Lanthanotus'' genus), varanids have nine cervical vertebrae, while all other lizards have eight or less (Ast 2002). Notably, some authors consider Lanthanotidae to be a subfamily (Lanthanotinae) of Varanidae (Ast 2003). Monitor lizards differ greatly from other lizards in possessing a relatively high [[metabolism|metabolic rate]] for [[reptile]]s and several sensory adaptations that benefit the hunting of live prey. Recent research indicates that the varanid lizards, including the [[Komodo dragon]], may have very weak [[venom]] (Fry et al. 2006). (''Lanthanotus borneensis'' also is one of the few lizards to possess venom.) | |
| − | + | Extant monitors range in size form the short-tailed monitors, which reach 20 centimeters in length and 20 grams in weight, to the Komodo dragon at three meters in length and 54 kilograms (119 pounds) (Ast 2003). | |
| + | ====Distribution and habitats==== | ||
| + | These extant species cover a vast area, being found in [[Africa]], the Asian subcontinent from [[India]] and [[Sri Lanka]] to [[China]], down [[Southeast Asia]] to [[Indonesia]], the [[Philippines]], [[New Guinea]], and [[Australia]] and the islands of the [[Indian Ocean]] and [[South China Sea]]. About one half of the species are found in Australia (Ast 2003). | ||
| + | They occupy a wide range of habitats, including terrestrial and aquatic (including marine), including such terrestrial habitats as burrowing, surface, living among rocks, or arboreal (Ast 2003). Those primarily aquatic must still lay their eggs on land as with all reptiles. | ||
| − | Monitor lizards | + | ===Behavior, feeding, and intelligence=== |
| + | [[image:Nile_Monitor.JPG|thumb|240px|right|A [[Nile monitor]]]] | ||
| + | Monitor lizards typically are diurnal and almost all monitor lizards are [[carnivore|carnivorous]]; however, they have diverse feeding behaviors, with not all species fully carnivorous predators. Diets of various species of monitor lizards include fruit, invertebrates, [[mammal]]s, [[bird]]s, [[fish]], and carrion. The Gray's monitor ''(Varanus olivaceus)'' eats [[mollusk]]s, but also eats [[fruit]] and displays foraging type behavior (Ast 2003). The Komodo dragon ''(Varanus komodoensis)'' will eat large mammals, such as [[deer]] and [[buffalo]], utilizing a sit-and-wait or stealthy approach until the prey can be ambushed (Ast 2003). Komodo dragons also eat [[invertebrate]]s, [[bird]]s, and small [[mammal]]s, but their main food source is [[carrion]], which other large monitor lizards are known to eat as well (Mattison 1992). Komodo dragons can locate a dead or dying animal from a range of up to 9.5 kilometers (6 miles) (Darling and Darling-Lyon 1997). Komodo dragons also have been observed knocking down large [[pig]]s and deer with their strong tail (Attenborough 2008). Monitor lizards are also known to capture and eat small [[monkey]]s, fish, [[squirrel]]s, and [[crab]]s. | ||
| − | + | Varanid lizards are considered to be intelligent, with some species showing a capacity to even count (King and Green 1999). Studies at the San Diego Zoo involving feeding of the white-throated monitor ''(Varanus albigularis)'' various numbers of [[snail]]s showed that they can distinguish numbers up to six (King and Green 1999; Pianka 2004). Nile monitors ''(Varanus niloticus)'' have been observed to cooperate when foraging (King and Green 1999). One varanid lures the female [[crocodile]] away from her nest while the other opens the nest to feed on the eggs (King and Green 1999). The decoy then returns to also feed on the eggs (King and Green 1999; Pianka 2004). [[Komodo dragon]]s at the [[Smithsonian National Zoological Park]] in Washington, D.C., recognize their keepers and seem to have distinct personalities (Pianka 2004). | |
| − | + | Monitor lizards produce by sexual reproduction; however, some monitor lizards are apparently capable of [[parthenogenesis]] (Smith 2006). | |
| − | == | + | ==Evolutionary overview== |
| + | Varanids are represented widely in the [[fossil record], with pre-[[Miocene]] fossils found mostly in Asia and North America, and in Europe, Africa, and Australia by the middle Miocene (Ast 2003). A fossil given the genus name ''Telmasaurus'' traces to [[Cretaceous]] deposits of North America and Mongolia. A fossil species, ''Varanus marathonensis,'' may have been in Europe up to the Pliocene. | ||
| + | An extinct giant monitor lizard from [[Quaternary]] deposits in Australia, which died out roughly 20,000 years ago, reached an enormous length of seven meters and a weight of 600 kilograms (Ast 2003). It had two centimeter, curved serrated teeth (Ast 2003). This lizard was originally placed in the varanid genus ''Megalania'' as ''M. prisca,'' although some place it in ''Varanus'' as ''V. priscus''. | ||
| + | The discovery of [[venom]] in monitor lizards, as well as in [[agamid]] lizards, has led to the [[Toxicofera]] hypothesis: That all venomous reptiles share a common venomous ancestor. | ||
| − | + | ==Terminology== | |
| + | The genus name, "Varanus" is derived from the [[Arabic (language)|Arabic]] word ''waral'' ورل, which is translated to English as "monitor." 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 the original Arabic name (Pianka et al. 2004). According to legend, these lizards were supposed to warn people that crocodiles were nearby (Pianka 2004). | ||
| − | + | In [[Tamil language|Tamil]] and [[Malayalam language|Malayalam]], monitor lizards are known as "udumbu" and in [[Australia]], they are known as [[goanna]]s. In [[Kannada language|Kannada]], monitor lizards are known as "uda." In [[Sinhalese language|Sinhalese]] the monitor lizard is known as "kabaragoya." | |
| − | |||
==Importance== | ==Importance== | ||
| − | + | In addition to their role in [[food chain]]s, serving as predators and prey (very large monitors, like the adult Komodo dragon, are [[apex predator]]s), monitor lizards also are important to humans. In some cultures, they are represented in art, folklore, and superstitions (Ast 2003). In Africa, Asia, and Australia, monitors are eaten (Ast 2003). Some are commercially important for their skins, which are made into leather, and body parts may be used for folk medicine (Ast 2003). | |
| − | |||
| − | |||
| − | + | Monitors also have become a staple in the [[reptile pet]] trade. The most commonly kept monitors are the savannah monitor, white throated monitor, and Acklin's monitor, due to their relatively small size and ease of domestication. Nile monitors, water monitors, mangrove monitors, and papau monitors have also been kept in captivity. Like all [[reptile]]s that are kept as pets, monitors need hiding places, and an appropriate substrate (bedding). 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 [[cricket]]s, [[superworm]]s, and the occasional [[rodent]] make up most of the captive monitors' diet. Boiled eggs, [[silkworms]], [[earthworm]]s, and [[feeder fish]] can also be fed to monitors. Monitor lizards have been compared to "reptilian [[cat]]s"—independent animals with different personalities. However, due to their predatory nature and large size, some monitors can be dangerous to keep as pets. Adult Nile monitors can reach seven feet in length, and are stronger than an [[alligator]] of equal weight. | |
| − | The [[Bengal | + | |
| + | The [[Bengal monitor]] lizard, also known as the common Indian monitor lizard, is found in Asia and Africa. It is widely said to have been used to scale the fort of Kondana in Pune, India, by [[Tanaji Malusare]], a general in the army of the Maratha ruler [[Shivaji]]. The skin of this lizard has traditionally been utilized in making the [[Kanjira]], a South Indian classical percussion instrument. Now however, it is not in vogue owing to the increased awareness to the dwindling population of the lizard. The lizard evokes mixed responses from the people across the world. It is considered a delicacy in Sri Lanka. It is killed for sport in North Eastern India. It is revered in Maharashtra, India where an entire clan of people use "Ghorpade" as their surname after "Ghorpad," the local name for the Bengal monitor lizard (Bennett 1995). | ||
==Classification== | ==Classification== | ||
| − | [[ | + | [[Image:Monitor lizard australia zoo.jpg|thumb|240px|right|A monitor lizard seen at the [[Australia Zoo]].]] |
| − | [[Image: | + | [[Image:green.tree.monitor.lizard.arp.jpg|thumb|right|240px|[[Emerald tree monitor]] (also called Green tree monitor) lizard ''Varanus prasinus'']] |
| + | [[Image:Asian_water_monitor (Varanus_salvator_salvator).JPG|right|240px|thumb|Asian [[water monitor]] ''(Varanus salvator salvator)''.]] | ||
'''Genus Varanus''' | '''Genus Varanus''' | ||
| − | * [[Spiny-tailed monitor|Spiny-tailed goanna]], '' | + | * [[Spiny-tailed monitor|Spiny-tailed goanna]], ''Varanus acanthurus acanthurus'' |
** Common Ridge-tailed Monitor, ''[[Varanus acanthurus brachyurus]]'' | ** Common Ridge-tailed Monitor, ''[[Varanus acanthurus brachyurus]]'' | ||
** Island Ridge-tailed Monitor, ''[[Varanus acanthurus insulanicus]]'' | ** Island Ridge-tailed Monitor, ''[[Varanus acanthurus insulanicus]]'' | ||
| Line 65: | Line 84: | ||
* Peacock Monitor, ''[[Varanus auffenbergi]]'' | * Peacock Monitor, ''[[Varanus auffenbergi]]'' | ||
* Northern Ridge-tailed Goanna, ''[[Varanus baritji]]'' | * Northern Ridge-tailed Goanna, ''[[Varanus baritji]]'' | ||
| − | * [[Black tree monitor]], '' | + | * [[Black tree monitor]], ''Varanus beccarii'' |
| − | * [[Bengal monitor]], '' | + | * [[Bengal monitor]], ''Varanus bengalensis'' |
* Golden-spotted Tree Monitor, ''[[Varanus boehmei]]'' | * Golden-spotted Tree Monitor, ''[[Varanus boehmei]]'' | ||
* Louisiade Tree Monitor, ''[[Varanus bogerti]]'' | * Louisiade Tree Monitor, ''[[Varanus bogerti]]'' | ||
| − | * [[Short-tailed monitor]], '' | + | * [[Short-tailed monitor]], ''Varanus brevicauda'' |
* Pilbara Goanna ''[[Varanus bushi]]'' | * Pilbara Goanna ''[[Varanus bushi]]'' | ||
* Turquois Monitor, ''[[Varanus caerulivirens]]'' | * Turquois Monitor, ''[[Varanus caerulivirens]]'' | ||
| Line 77: | Line 96: | ||
* Dumeril's Monitor, ''[[Varanus dumerilii]]'' | * Dumeril's Monitor, ''[[Varanus dumerilii]]'' | ||
* Desert Pygmy Monitor, ''[[Varanus eremius]]'' | * Desert Pygmy Monitor, ''[[Varanus eremius]]'' | ||
| − | * [[Savannah monitor]], '' | + | * [[Savannah monitor]], ''Varanus exanthematicus'' |
* Finsch's Monitor, ''[[Varanus finschi]]'' | * Finsch's Monitor, ''[[Varanus finschi]]'' | ||
| − | * [[Yellow Monitor|Yellow Mangrove Monitor]], '' | + | * [[Yellow Monitor|Yellow Mangrove Monitor]], ''Varanus flavescens'' |
| − | * [[Perentie]], '' | + | * [[Perentie]], ''Varanus giganteus'' |
* Pygmy Mulga Goanna, ''[[Varanus gilleni]]'' | * Pygmy Mulga Goanna, ''[[Varanus gilleni]]'' | ||
* Kimberley Rock Monitor, ''[[Varanus glauerti]]'' | * Kimberley Rock Monitor, ''[[Varanus glauerti]]'' | ||
* Black-palmed Rock Monitor, ''[[Varanus glebopalma]]'' | * Black-palmed Rock Monitor, ''[[Varanus glebopalma]]'' | ||
| − | * [[Sand goanna]], '' | + | * [[Sand goanna]], ''Varanus gouldii'' |
** Horn's Monitor, ''[[Varanus gouldii horni]]'' | ** Horn's Monitor, ''[[Varanus gouldii horni]]'' | ||
** Yellow-spotted Monitor, ''[[Varanus gouldii rubidus]]'' | ** Yellow-spotted Monitor, ''[[Varanus gouldii rubidus]]'' | ||
| Line 91: | Line 110: | ||
** Eastern Desert Monitor, ''[[Varanus griseus caspius]]'' | ** Eastern Desert Monitor, ''[[Varanus griseus caspius]]'' | ||
** Thar Desert Monitor, ''[[Varanus griseus koniecznyi]]'' | ** Thar Desert Monitor, ''[[Varanus griseus koniecznyi]]'' | ||
| − | * [[Mangrove goanna|Mangrove Monitor]], '' | + | * [[Mangrove goanna|Mangrove Monitor]], ''Varanus indicus'' |
* Peach Throat Monitor, ''[[Varanus jobiensis]]'' | * Peach Throat Monitor, ''[[Varanus jobiensis]]'' | ||
* Hakoi, ''[[Varanus juxtindicus]]'' | * Hakoi, ''[[Varanus juxtindicus]]'' | ||
* Canopy Goanna, ''[[Varanus keithhornei]]'' | * Canopy Goanna, ''[[Varanus keithhornei]]'' | ||
* King's Goanna, ''[[Varanus kingorum]]'' | * King's Goanna, ''[[Varanus kingorum]]'' | ||
| − | * [[Komodo Dragon]], '' | + | * [[Komodo Dragon]], ''Varanus komodoensis'' |
* Kordo Tree Monitor, ''[[Varanus kordensis]]'' | * Kordo Tree Monitor, ''[[Varanus kordensis]]'' | ||
* Panay Monitor, ''[[Varanus mabitang]]'' | * Panay Monitor, ''[[Varanus mabitang]]'' | ||
| Line 104: | Line 123: | ||
* Mitchell's Water Monitor, ''[[Varanus mitchelli]]'' | * Mitchell's Water Monitor, ''[[Varanus mitchelli]]'' | ||
* Clouded Monitor, ''[[Varanus nebulosus]]'' | * Clouded Monitor, ''[[Varanus nebulosus]]'' | ||
| − | * [[Nile monitor]], '' | + | * [[Nile monitor]], ''Varanus niloticus'' |
| − | * [[Gray's monitor]], '' | + | * [[Gray's monitor]], ''Varanus olivaceus'' |
* Ornate Monitor, ''[[Varanus ornatus]]'' | * Ornate Monitor, ''[[Varanus ornatus]]'' | ||
| − | * [[Argus monitor]], '' | + | * [[Argus monitor]], ''Varanus panoptes panoptes'' |
** ''[[Varanus panoptes horni]]'' | ** ''[[Varanus panoptes horni]]'' | ||
** ''[[Varanus panoptes rubidus]]'' | ** ''[[Varanus panoptes rubidus]]'' | ||
* Pilbara Rock Monitor, ''[[Varanus pilbarensis]]'' | * Pilbara Rock Monitor, ''[[Varanus pilbarensis]]'' | ||
* Emerald Tree Monitor, ''[[Varanus prasinus]]'' | * Emerald Tree Monitor, ''[[Varanus prasinus]]'' | ||
| − | |||
* Blunt-spined Goanna, ''[[Varanus primordius]]'' | * Blunt-spined Goanna, ''[[Varanus primordius]]'' | ||
| − | * [[Megalania]], '' | + | * [[Megalania]], ''Varanus prisca'' (extinct) |
* ''[[Varanus rainerguentheri]] | * ''[[Varanus rainerguentheri]] | ||
* Reisinger's Tree Monitor, ''[[Varanus reisingeri]]'' | * Reisinger's Tree Monitor, ''[[Varanus reisingeri]]'' | ||
* Rosenberg's Goanna or Heath Monitor, ''[[Varanus rosenbergi]]'' | * Rosenberg's Goanna or Heath Monitor, ''[[Varanus rosenbergi]]'' | ||
* Black Roughneck Monitor, ''[[Varanus rudicollis]]'' | * Black Roughneck Monitor, ''[[Varanus rudicollis]]'' | ||
| − | * [[Crocodile monitor]], '' | + | * [[Crocodile monitor]], ''Varanus salvadorii'' |
| − | |||
* [[Water Monitor]], ''[[Water monitor|Varanus salvator]]'' | * [[Water Monitor]], ''[[Water monitor|Varanus salvator]]'' | ||
** Asian Water Monitor, ''[[Varanus salvator salvator]]'' | ** Asian Water Monitor, ''[[Varanus salvator salvator]]'' | ||
| Line 131: | Line 148: | ||
** Togian Water Monitor, ''[[Varanus salvator togianus]]'' | ** Togian Water Monitor, ''[[Varanus salvator togianus]]'' | ||
* Spotted Tree Goanna, ''[[Varanus scalaris]]'' | * Spotted Tree Goanna, ''[[Varanus scalaris]]'' | ||
| − | * [[Mangrove pygmy goanna]], '' | + | * [[Mangrove pygmy goanna]], ''Varanus semiremex'' |
* Spencer's Goanna, ''[[Varanus spenceri]]'' | * Spencer's Goanna, ''[[Varanus spenceri]]'' | ||
* St. Isabel Mangrove Monitor, ''[[Varanus spinulosus]]'' | * St. Isabel Mangrove Monitor, ''[[Varanus spinulosus]]'' | ||
| Line 147: | Line 164: | ||
==References== | ==References== | ||
| − | + | * Ast, J.C. 2003. [http://animaldiversity.ummz.umich.edu/site/accounts/information/Varanidae.html Varanidae.] ''Animal Diversity Web''. Retrieved June 5, 2008. | |
| − | + | * Attenborough, D. 2008. ''Life in Cold Blood''. Princeton, NJ: Princeton University Press. ISBN 0691137188. | |
| − | * Ast, J. C. 2003. [http://animaldiversity.ummz.umich.edu/site/accounts/information/Varanidae.html Varanidae] ''Animal Diversity Web''. Retrieved June 5, 2008. | + | * Bennett, D. 1995. ''A Little Book of Monitor Lizards: A Guide to the Monitor Lizards of the World and Their Care in Captivity''. Aberdeen: Viper Press. ISBN 095266321X. |
| − | + | * Darling, K., and T. Darling-Lyon. 1997. ''Komodo Dragon''. New York: Lothrop, Lee & Shepard Books. ISBN 0688137776. | |
| − | * Integrated Taxonomic Information System (ITIS). 2006a. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174114 Varanidae] ''ITIS Taxonomic Serial No.: 174114''. Retrieved June 5, 2008. | + | * Fry, B. G., N. Vidal, J. A. Norman, F. J. Vonk, H. Scheib, S. F. R. Ramjan, S. Kuruppu, K. Fung, B. Hedges, M. K. Richardson, W. C. Hodgson, V. Ignjatovic, R. Summerhays, and E. Kochva. 2006. [http://www.nature.com/nature/journal/v439/n7076/edsumm/e060202-11.html Early evolution of the venom system in lizards and snakes.] ''Nature'' 439: 584-588. Retrieved June 5, 2008. |
| − | + | * King, D., and B . Green. 1999. ''Goannas: The Biology of Varanid Lizards''. University of New South Wales Press. ISBN 086840456X. | |
| − | * Integrated Taxonomic Information System (ITIS). 2006b. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174115 ''Varanus'' Merrem, 1820] ''ITIS Taxonomic Serial No.: 174115''. Retrieved June 5, 2008. | + | * Integrated Taxonomic Information System (ITIS). 2006a. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174114 Varanidae.] ''ITIS Taxonomic Serial No.: 174114''. Retrieved June 5, 2008. |
| − | + | * Integrated Taxonomic Information System (ITIS). 2006b. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=174115 ''Varanus'' Merrem, 1820.] ''ITIS Taxonomic Serial No.: 174115''. Retrieved June 5, 2008. | |
| − | + | * Mattison, C. 1992. ''Lizards of the World''. New York: Facts on File. ISBN 0816057168. | |
| − | * | + | * Pianka, E. R. 2004. Varanidae. Pages 359-368 in B. Grzimek, S. F. Craig, D. A. Thoney, N. Schlager, and M. Hutchins. ''Grzimek's Animal Life Encyclopedia,'' 2nd edition. Detroit, MI: Thomson/Gale. ISBN 0787657786. |
| − | *[http://www. | + | * Pianka, E. R., D. King, and R. Allen King. 2004. ''Varanoid Lizards of the World''. Bloomington: Indiana University Press. ISBN 0253343666. |
| + | * Smith, K. 2006. [http://www.nature.com/news/2006/061218/full/061218-7.html Dragon virgin births startle zoo keepers. Non-sexual reproduction could lower the fitness of captive animals.] ''Nature News'' December 20, 2006. Retrieved June 5, 2008. | ||
| Line 164: | Line 182: | ||
[[Category:Reptiles]] | [[Category:Reptiles]] | ||
| − | {{credit|Monitor_lizard|217185477}} | + | {{credit|Monitor_lizard|217185477|Komodo_dragon|215181433}} |
Latest revision as of 13:35, 6 June 2008
| Monitor lizards | ||||||||||||||||
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 An Australian lace monitor
(Varanus varius) on a tree. | ||||||||||||||||
| Scientific classification | ||||||||||||||||
|
Monitor lizard, or monitor, is the common name for any of the Old World lizards comprising the Varanidae family, which contains only one extant genus, Varanus, whose members are characterized by a generally elongate neck, a heavy body, long-forked tongues, and long, non-autonomous tails. While some monitor lizards are small, the genus also contains some very large extant lizards, including the largest living lizard, the Komodo dragon, which reaches three meters in length and 54 kilograms in weight and can even feed on large mammals, like deer, pigs, and buffalo (Ast 2003). One fossil species from about 20,000 years ago reached seven meters in length and 600 kilograms. Monitor lizards today are found in a vast area in the Old World, including Africa, Asia, Oceania, and Australia.
The name, "monitor," is also used for a species in different, but closely related, family, the earless monitor (Lanthanotus borneensis) in Lanthanotidae, a semi-aquatic, brown lizard from Borneo. This article will be restricted to discussion of the varanids (Varanidae).
Monitor lizards are important to food chains in their various terrestrial and aquatic (including marine) habitats, both as predator and prey. They consume a wide variety of invertebrates and vertebrates, including carrion and even fruit in the case of some varanids. For humans, monitor lizards are important in various cultures for art, folklore, and a source of food, leather, and folk medicine. Thus, as with other taxa, varanids not only advance a function for the individual (survival, reproduction, self-maintenance of the species), but also provide a function for the whole (ecosystem, humans).
Overview and description
The Varanidae family is part of the infraorder Anguimorpha, which also includes alligator lizards, galliwasps, legless lizards, knobby lizards, and the extinct mosasaurs, as well as the gila monster and Mexican bearded lizard.
The Varanidae family contains only one extant genus, Varanus. There are extinct varanids that have been placed in other genera, such as Telmasaurus and Megalania (although some have reclassifed the latter as part of Varanus).
There are about fifty to sixty modern species of Varanus.
Physical description
Monitor lizards tend to be robust, diurnal lizards, with elongate necks and non-autotomous tails (Ast 2003). They have long, forked tongues, which are used for chemorecption, and their hemipenes are unusually ornate, with paired apical horns (Ast 2003).
Unlike lizards in all other families, except Lanthanotidae (Lanthanotus genus), varanids have nine cervical vertebrae, while all other lizards have eight or less (Ast 2002). Notably, some authors consider Lanthanotidae to be a subfamily (Lanthanotinae) of Varanidae (Ast 2003). Monitor lizards differ greatly from other lizards in 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 very weak venom (Fry et al. 2006). (Lanthanotus borneensis also is one of the few lizards to possess venom.)
Extant monitors range in size form the short-tailed monitors, which reach 20 centimeters in length and 20 grams in weight, to the Komodo dragon at three meters in length and 54 kilograms (119 pounds) (Ast 2003).
Distribution and habitats
These extant species cover a vast area, being found in Africa, the Asian subcontinent from India and Sri Lanka to China, down Southeast Asia to Indonesia, the Philippines, New Guinea, and Australia and the islands of the Indian Ocean and South China Sea. About one half of the species are found in Australia (Ast 2003).
They occupy a wide range of habitats, including terrestrial and aquatic (including marine), including such terrestrial habitats as burrowing, surface, living among rocks, or arboreal (Ast 2003). Those primarily aquatic must still lay their eggs on land as with all reptiles.
Behavior, feeding, and intelligence
Monitor lizards typically are diurnal and almost all monitor lizards are carnivorous; however, they have diverse feeding behaviors, with not all species fully carnivorous predators. Diets of various species of monitor lizards include fruit, invertebrates, mammals, birds, fish, and carrion. The Gray's monitor (Varanus olivaceus) eats mollusks, but also eats fruit and displays foraging type behavior (Ast 2003). The Komodo dragon (Varanus komodoensis) will eat large mammals, such as deer and buffalo, utilizing a sit-and-wait or stealthy approach until the prey can be ambushed (Ast 2003). Komodo dragons also eat invertebrates, birds, and small mammals, but their main food source is carrion, which other large monitor lizards are known to eat as well (Mattison 1992). Komodo dragons can locate a dead or dying animal from a range of up to 9.5 kilometers (6 miles) (Darling and Darling-Lyon 1997). Komodo dragons also have been observed knocking down large pigs and deer with their strong tail (Attenborough 2008). Monitor lizards are also known to capture and eat small monkeys, fish, squirrels, and crabs.
Varanid lizards are considered to be intelligent, with some species showing a capacity to even count (King and Green 1999). Studies at the San Diego Zoo involving feeding of the white-throated monitor (Varanus albigularis) various numbers of snails showed that they can distinguish numbers up to six (King and Green 1999; Pianka 2004). Nile monitors (Varanus niloticus) have been observed to cooperate when foraging (King and Green 1999). One varanid lures the female crocodile away from her nest while the other opens the nest to feed on the eggs (King and Green 1999). The decoy then returns to also feed on the eggs (King and Green 1999; Pianka 2004). Komodo dragons at the Smithsonian National Zoological Park in Washington, D.C., recognize their keepers and seem to have distinct personalities (Pianka 2004).
Monitor lizards produce by sexual reproduction; however, some monitor lizards are apparently capable of parthenogenesis (Smith 2006).
Evolutionary overview
Varanids are represented widely in the [[fossil record], with pre-Miocene fossils found mostly in Asia and North America, and in Europe, Africa, and Australia by the middle Miocene (Ast 2003). A fossil given the genus name Telmasaurus traces to Cretaceous deposits of North America and Mongolia. A fossil species, Varanus marathonensis, may have been in Europe up to the Pliocene.
An extinct giant monitor lizard from Quaternary deposits in Australia, which died out roughly 20,000 years ago, reached an enormous length of seven meters and a weight of 600 kilograms (Ast 2003). It had two centimeter, curved serrated teeth (Ast 2003). This lizard was originally placed in the varanid genus Megalania as M. prisca, although some place it in Varanus as V. priscus.
The discovery of venom in monitor lizards, as well as in agamid lizards, has led to the Toxicofera hypothesis: That all venomous reptiles share a common venomous ancestor.
Terminology
The genus name, "Varanus" is derived from the Arabic word waral ورل, which is translated to English as "monitor." 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 the original Arabic name (Pianka et al. 2004). According to legend, these lizards were supposed to warn people that crocodiles were nearby (Pianka 2004).
In Tamil and Malayalam, monitor lizards are known as "udumbu" and in Australia, they are known as goannas. In Kannada, monitor lizards are known as "uda." In Sinhalese the monitor lizard is known as "kabaragoya."
Importance
In addition to their role in food chains, serving as predators and prey (very large monitors, like the adult Komodo dragon, are apex predators), monitor lizards also are important to humans. In some cultures, they are represented in art, folklore, and superstitions (Ast 2003). In Africa, Asia, and Australia, monitors are eaten (Ast 2003). Some are commercially important for their skins, which are made into leather, and body parts may be used for folk medicine (Ast 2003).
Monitors also have become a staple in the reptile pet trade. The most commonly kept monitors are the savannah monitor, white throated monitor, and Acklin's monitor, due to their relatively small size and ease of domestication. Nile monitors, water monitors, mangrove monitors, and papau monitors have also been kept in captivity. Like all reptiles that are kept as pets, monitors need hiding places, and an appropriate substrate (bedding). 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 monitors. Monitor lizards have been compared to "reptilian cats"—independent animals with different personalities. However, due to their predatory nature and large size, some monitors can be dangerous to keep as pets. Adult Nile monitors can reach seven feet in length, and are stronger than an alligator of equal weight.
The Bengal monitor lizard, also known as the common Indian monitor lizard, is found in Asia and Africa. It is widely said to have been used to scale the fort of Kondana in Pune, India, by Tanaji Malusare, a general in the army of the Maratha ruler Shivaji. The skin of this lizard has traditionally been utilized in making the Kanjira, a South Indian classical percussion instrument. Now however, it is not in vogue owing to the increased awareness to the dwindling population of the lizard. The lizard evokes mixed responses from the people across the world. It is considered a delicacy in Sri Lanka. It is killed for sport in North Eastern India. It is revered in Maharashtra, India where an entire clan of people use "Ghorpade" as their surname after "Ghorpad," the local name for the Bengal monitor lizard (Bennett 1995).
Classification
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Genus Varanus
- Spiny-tailed goanna, Varanus acanthurus acanthurus
- Common Ridge-tailed Monitor, Varanus acanthurus brachyurus
- Island Ridge-tailed Monitor, Varanus acanthurus insulanicus
- Rock Monitor, Varanus albigularis
- White-throated Monitor, Varanus albigularis albigularis
- Angola White-throated Monitor, Varanus albigularis angolensis
- Black-throated Monitor, Varanus albigularis ionidesi
- Peacock Monitor, Varanus auffenbergi
- Northern Ridge-tailed Goanna, Varanus baritji
- Black tree monitor, Varanus beccarii
- Bengal monitor, Varanus bengalensis
- Golden-spotted Tree Monitor, Varanus boehmei
- Louisiade Tree Monitor, Varanus bogerti
- Short-tailed monitor, Varanus brevicauda
- Pilbara Goanna Varanus bushi
- Turquois Monitor, Varanus caerulivirens
- Stripe-tailed Goanna, Varanus caudolineatus
- Ceram Mangrove Monitor, Varanus cerambonensis
- Blue-tailed Monitor, Varanus doreanus
- Dumeril's Monitor, Varanus dumerilii
- Desert Pygmy Monitor, Varanus eremius
- Savannah monitor, Varanus exanthematicus
- Finsch's Monitor, Varanus finschi
- Yellow Mangrove Monitor, Varanus flavescens
- Perentie, Varanus giganteus
- Pygmy Mulga Goanna, Varanus gilleni
- Kimberley Rock Monitor, Varanus glauerti
- Black-palmed Rock Monitor, Varanus glebopalma
- Sand goanna, Varanus gouldii
- Horn's Monitor, Varanus gouldii horni
- Yellow-spotted Monitor, Varanus gouldii rubidus
- Desert Monitor, Varanus griseus
- Western Desert Monitor, Varanus griseus griseus
- Eastern Desert Monitor, Varanus griseus caspius
- Thar Desert Monitor, Varanus griseus koniecznyi
- Mangrove Monitor, Varanus indicus
- Peach Throat Monitor, Varanus jobiensis
- Hakoi, Varanus juxtindicus
- Canopy Goanna, Varanus keithhornei
- King's Goanna, Varanus kingorum
- Komodo Dragon, Varanus komodoensis
- Kordo Tree Monitor, Varanus kordensis
- Panay Monitor, Varanus mabitang
- Blue-spotted Tree Monitor, Varanus macraei
- Quince Monitor, Varanus melinus
- Mertens' Water Monitor, Varanus mertensi
- Mitchell's Water Monitor, Varanus mitchelli
- Clouded Monitor, Varanus nebulosus
- Nile monitor, Varanus niloticus
- Gray's monitor, Varanus olivaceus
- Ornate Monitor, Varanus ornatus
- Argus monitor, Varanus panoptes panoptes
- Varanus panoptes horni
- Varanus panoptes rubidus
- Pilbara Rock Monitor, Varanus pilbarensis
- Emerald Tree Monitor, Varanus prasinus
- Blunt-spined Goanna, Varanus primordius
- Megalania, Varanus prisca (extinct)
- Varanus rainerguentheri
- Reisinger's Tree Monitor, Varanus reisingeri
- Rosenberg's Goanna or Heath Monitor, Varanus rosenbergi
- Black Roughneck Monitor, Varanus rudicollis
- Crocodile monitor, Varanus salvadorii
- Water Monitor, Varanus salvator
- Asian Water Monitor, Varanus salvator salvator
- Andaman Islands Water Monitor, Varanus salvator andamanensis
- Two-striped Water Monitor, Varanus salvator bivittatus
- Cuming's Water Monitor, Varanus salvator cumingi
- Black Water Monitor, Varanus salvator komaini
- Marbled Water Monitor, Varanus salvator marmoratus
- Negros Water Monitor, Varanus salvator nuchalis
- Togian Water Monitor, Varanus salvator togianus
- Spotted Tree Goanna, Varanus scalaris
- Mangrove pygmy goanna, Varanus semiremex
- Spencer's Goanna, Varanus spenceri
- St. Isabel Mangrove Monitor, Varanus spinulosus
- Storr's Goanna, Varanus storri
- Eastern Storr's Goanna, Varanus storri storri
- Western Storr's Monitor, Varanus storri ocreatus
- Rossel Island Tree Monitor, Varanus telenesetes
- Timor Tree Monitor, Varanus timorensis
- Black-headed Monitor, Varanus tristis
- Freckled Monitor, Varanus tristis orientalis
- Lace Monitor, Varanus varius
- Yemen Monitor, Varanus yemenensis
- Tri-colored Monitor, Varanus yuwonoi
- Varanus zugorum
ReferencesISBN links support NWE through referral fees
- Ast, J.C. 2003. Varanidae. Animal Diversity Web. Retrieved June 5, 2008.
- Attenborough, D. 2008. Life in Cold Blood. Princeton, NJ: Princeton University Press. ISBN 0691137188.
- Bennett, D. 1995. A Little Book of Monitor Lizards: A Guide to the Monitor Lizards of the World and Their Care in Captivity. Aberdeen: Viper Press. ISBN 095266321X.
- Darling, K., and T. Darling-Lyon. 1997. Komodo Dragon. New York: Lothrop, Lee & Shepard Books. ISBN 0688137776.
- Fry, B. G., N. Vidal, J. A. Norman, F. J. Vonk, H. Scheib, S. F. R. Ramjan, S. Kuruppu, K. Fung, B. Hedges, M. K. Richardson, W. C. Hodgson, V. Ignjatovic, R. Summerhays, and E. Kochva. 2006. Early evolution of the venom system in lizards and snakes. Nature 439: 584-588. Retrieved June 5, 2008.
- King, D., and B . Green. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 086840456X.
- Integrated Taxonomic Information System (ITIS). 2006a. Varanidae. ITIS Taxonomic Serial No.: 174114. Retrieved June 5, 2008.
- Integrated Taxonomic Information System (ITIS). 2006b. Varanus Merrem, 1820. ITIS Taxonomic Serial No.: 174115. Retrieved June 5, 2008.
- Mattison, C. 1992. Lizards of the World. New York: Facts on File. ISBN 0816057168.
- Pianka, E. R. 2004. Varanidae. Pages 359-368 in B. Grzimek, S. F. Craig, D. A. Thoney, N. Schlager, and M. Hutchins. Grzimek's Animal Life Encyclopedia, 2nd edition. Detroit, MI: Thomson/Gale. ISBN 0787657786.
- Pianka, E. R., D. King, and R. Allen King. 2004. Varanoid Lizards of the World. Bloomington: Indiana University Press. ISBN 0253343666.
- Smith, K. 2006. Dragon virgin births startle zoo keepers. Non-sexual reproduction could lower the fitness of captive animals. Nature News December 20, 2006. Retrieved June 5, 2008.
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