The yellow-spotted monitor[1][2][3] (Varanus panoptes), also known as the Argus monitor,[4] is a monitor lizard found in northern and western regions of Australia and southern New Guinea.[1][2]
The first description of the species was provided in a revision of the varanids of Western Australia, where the family is represented by diverse taxa in a wide variety of habitats. Early collections and descriptions of the region's species have historically been uncertain, leading the ICZN to issue an opinion that related to this taxon.[5] A third subspecies was published in 1988, based on specimens from southern New Guinea. The describing author discovered that the specimen selected as the type of Varanus gouldii was in fact assignable to this species, recently described by reptile specialist Glenn Storr. By issuing an opinion on the various taxonomic considerations, the voting members conserved the name published with John Edward Gray's description and stabilised the nomenclature of this species name.[6]
Three subspecies are recognised by the Australian Faunal Directory[3] and the Reptile Database:[2]
The epithet panoptes was inspired by a mythological figure with one hundred eyes, the protector of Princess Io named Argus Panoptes.[7] The species may be referred to as the floodplains goanna in the northern regions of Australia.[6]
A ground-dwelling species of Varanus, it somewhat resembles the widespread sand goanna (Varanus gouldii). Large, dark spots appear in rows along its back, becoming especially distinct at the center of the back where they are interspersed with smaller and paler spots. Bands of color occur toward the tip of the tail. The overall coloration is brownish in the nominate subspecies, V. panoptes panoptes, and reddish in V. panoptes rubidus.[7]
The yellow-spotted monitor displays great sexual dimorphism, with the female reaching an average total length of three feet (90 cm), while the male reaches an average of 4–5 feet (120–150 cm).[9] The largest specimens can have a length in 1.6 m (5 ft 3 in) and a mass in 7 kg (15 lb).[10][11] It's the third largest lizard in Australia, after perentie and lace monitor. The larger subspecies is V. panoptes panoptes and the smaller one is V. panoptes horni. It is a reasonably lean monitor and does not put on the bulk that other monitors in Africa and Asia do. Most Varanus panoptes are yellow in color, with a background of brown or dark tan, but their color often varies on an individual basis or on their place of origin.
In Arnhem Land, they lay 6 to 13 eggs between January and February.[8] Due to similar genetic structures, the yellow-spotted monitor is able to naturally hybridise with the Gould's monitor with a stable hybrid zone.
Varanus panoptes is a versatile predator and inhabits a large variety of biomes and habitats. They are primarily terrestrial, meaning they spend a great deal of time on the ground. This species is an avid digger and will dig large burrows or take over an already existing burrow, where they spend a sizable portion of their time. Despite this, they will eagerly forage in trees and in the water. These large lizards are quite fast and will run up to 100 meters away to the nearest tree or burrow when they are chased. Varanus panoptes is riparian in habits and as such, it can usually be found around a permanent source of water. Varanus panoptes will often "tripod" in captivity and in the wild, raising up on their hind legs and supporting themselves with their tail. This unusual behavior is used to spot potential prey or enemies from a distance or when they are threatened. They exhibit this behavior regularly in captivity. This habit provides them a unique characteristic that separates them from most other monitors.
Its prey consists of almost anything that it can overpower. This includes fish, crabs, small birds, rodents, insects and even other monitors. They hunt for prey by keying in on movement, chasing it down and overpowering it. In captivity, this monitor has been observed swinging rodent prey around rapidly by the tail in what appears to be an attempt to stun the animal, before biting at the prey's neck. Varanus panoptes frequently preys on the dwarf monitors that it shares its range with. Spiny-tailed goannas and Kimberley rock monitors are eaten regularly. Varanus panoptes have great senses, with smell being the most acute. Like all monitors, Varanus panoptes has a forked tongue and a vomeronasal organ in the roof of its mouth. It uses this organ in the same manner as snakes and other varanids do and can often be seen flicking their tongues in search of a meal.
Recent studies suggest that the infestation of cane toads, a novel and toxic species, has severely damaged the population structure of Varanus panoptes within the Top End. It is estimated that numbers have dropped by as much as 90% in many areas.[12]
Many individuals of this species are captive bred as a conservation effort against poisoning from the cane toad infestation of the species’ native range and as exotic pets. Varanus panoptes are fed insects, fish and mice. V. panoptes are husky lizards that can be a challenge to physically handle. They do not like to be restrained, and can use their sharp claws in their attempts to squirm free. If left to wander freely on open ground, their ability to suddenly flee makes escape likely.[4] V. panoptes prefer to bask each morning and return to bask as needed to maintain optimal body temperatures at 80 to 90 °F (26.7 to 32.2 °C). Night-time temperatures may drop 20 °F (11.1 °C) or more if the opportunity to warm up the next day exists.
The yellow-spotted monitor (Varanus panoptes), also known as the Argus monitor, is a monitor lizard found in northern and western regions of Australia and southern New Guinea.
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