Monitor lizard

Monitor lizards
An Australian lace monitor(Varanus varius) on a tree.
An Australian lace monitor
(Varanus varius) on a tree.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Squamata
Suborder: Scleroglossa
Infraorder: Anguimorpha
Family: Varanidae
Genus: Varanus
Merrem, 1820
Species

See Text

Monitor lizards or biawak are members of the family Varanidae, a group of carnivorous lizards which includes the heaviest living lizard, the Komodo dragon, with the crocodile monitor being the longest in the world. Varanidae is monotypic, containing only the genus Varanus. Their closest living relatives are the anguid and helodermatid lizards.[1]

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.[2] They are oviparous, laying from 7 to 37 eggs, which they often cover with soil or protect in a hollow tree stump[3].

Contents

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.[1] 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.[1]

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.[1]

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.[4]

Etymology

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.[5] According to legend, these lizards were supposed to warn people that crocodiles were nearby.[5]

In Tamil and Malayalam monitor lizards are known as "Udumbu", In Marathi monitor lizards are known as "Ghorpad" while in Australia they are known as goannas. 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 genus iguanidae, the lizards became known as "goannas" in Australia. Similarly, in Southern Africa they are referred to as "leguaan", from the Dutch for iguana.

In Tamil Nadu and all other parts of South India, catching or killing of monitor lizards are banned. This is also one reason why the the Kanjira is not being promoted properly. Like many Hindu traditional arts, Kanjira players are also on the decline.

Intelligence

Varanid lizards are very intelligent, and some species can even count.[6] Careful studies feeding V. albigularis at the San Diego Zoo varying numbers of snails showed that they can distinguish numbers up to six.[6][7][8] V. niloticus have been observed to cooperate when foraging.[9] One varanid lures the female crocodile away from her nest while the other opens the nest to feed on the eggs.[9] The decoy then returns to also feed on the eggs.[9][7] Komodo dragons, V. komodoensis, at the Smithsonian National Zoological Park in Washington, D.C., recognize their keepers and seem to have distinct personalities.[7]

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, and emerald tree monitors 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.

Classification

A Nile monitor
A monitor lizard seen at the Australia Zoo.
White-throated monitor on the Kalahari savannah
Australian lace monitor

Genus Varanus

Emerald tree monitor (also called Green tree monitor) lizard Varanus prasinus
Asian water monitor (Varanus salvator salvator).

References

  1. ↑ 1.0 1.1 1.2 1.3 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: 584–588. doi:10.1038/nature04328. http://www.nature.com/nature/journal/v439/n7076/abs/nature04328.html. 
  2. ↑ 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 9998057760. 
  3. ↑ 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. 
  4. ↑ Smith, Kerri. "Dragon virgin births startle zoo keepers". Nature. Retrieved on 2006-12-20.
  5. ↑ 5.0 5.1 Pianka, E.R.; King, D.R. and King, R.A. 2004. Varanoid Lizards of the World. Indiana University Press.
  6. ↑ 6.0 6.1 King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Varanidae
  8. ↑ The Weekend Australian. July 24-25, 1999, p. 12.
  9. ↑ 9.0 9.1 9.2 King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.

External links

Varanoidea
Kingdom: Animalia · Phylum: Chordata · Class: Reptilia · Order: Squamata
 
Extant species
Helodermatidae
Beaded Lizard · Gila Monster
Varanidae
Spiny-tailed monitor  · Rock monitor  · Black tree monitor  · Bengal monitor  · Short-tailed monitor  · Savannah monitor  · Yellow Monitor  · Perentie  · Sand goanna  · Desert Monitor  · Komodo dragon  · Nile monitor  · Gray's monitor  · Argus monitor  · Emerald tree monitor  · Crocodile monitor  · Water monitor  · Mangrove monitor  · Timor tree monitor  · Lace monitor
Related categories
Monitor lizards · Cretaceous lizards · Helodermas · Mosasaurs