Varanus salvadorii

The crocodile monitor (Varanus salvadorii), also known as the Papuan monitor or Salvadori's monitor, is a species of monitor lizard endemic to New Guinea. It is the largest monitor lizard in New Guinea and is one of the longest lizards, verified at up to . Its tail is exceptionally long, with some specimens having been claimed to exceed the length of the Komodo dragon, however less massive.

Crocodile monitors are arboreal lizard with a dark green body marked with bands of yellowish spots. It has a characteristic blunt snout and a very long prehensile tail. It lives among the mangrove swamps and coastal rainforests of the southeastern part of New Guinea, feeding opportunistically on everything from birds and small mammals to eggs, other reptiles, amphibians and carrion. Its large, backwards-curving teeth are better adapted than those of most monitors for seizing fast-moving prey. Like all monitors, it has anatomical features that enable it to breathe more easily when running than other lizards, and is sometimes considered one of the most agile monitor species.

Crocodile monitors are threatened by deforestation and poaching, and are protected by CITES. Little is known of its reproduction and development, as it is difficult to breed in captivity. Attempts at captive breeding have been mostly unsuccessful. In New Guinea, the lizard is sometimes hunted and skinned by tribesmen to make drums. It is described as an evil spirit that "climbs trees, walks upright, breathes fire, and kills men", yet the local people maintain that it gives warnings if crocodiles are nearby.

Taxonomy
Varanus salvadorii was first described as Monitor salvadorii by Wilhelm Peters and Giacomo Doria in 1878 based on a female specimen with a snout-to-vent length of , and a  long tail. It was subordinated to the genus Varanus under the name Varanus salvadorii by George Albert Boulenger in 1885.

There are no formally recognized subspecies of V. salvadorii, but the captive reptiles market distinguishes those from Sorong, Jayapura and Merauke based on the color of their snout and the overall brightness of their color pattern.

Etymology 
The generic name, Varanus, is derived from the Arabic waral (), meaning "lizard". The term "monitor" is thought to have come about from confusion between waral and the German , meaning "warning". The term "goanna" came about as a corruption of the name "iguana". The specific name, salvadorii, is derived from a Latinization of Tommaso Salvadori, an Italian ornithologist who worked in New Guinea.

Evolution
The genus Varanus originated in Asia about 40 million years ago (Mya). Around 15 Mya, a tectonic connection between Australia and Southeast Asia allowed the varanids to spread into what is now the Indonesian archipelago.

Based upon DNA sequences of three nuclear and two mitochondrial genes, cladistic analysis identifies the crocodile monitor as a member of a species cluster that includes the lace monitor (V. varius) and the Komodo dragon (V. komodoensis). Morphological considerations suggest that the megalania (V. priscus) was also a member of the group. Monitors apparently colonized Australasia from Asia about 32 Mya; the varius clade then arose about 17 Mya. The Torres Strait separating New Guinea from Australia is less than  long, a distance that could have been covered fairly easily with island hopping.

Distribution
The largest of the seven species of monitors found on the island of New Guinea, crocodile monitors occur in both the state Papua New Guinea and the Indonesian region of West Papua. It inhabits the high and low canopies of the lowland rainforests and coastal mangrove swamps, sometimes venturing out of these areas during floods in the rainy seasons. No detailed field investigation data are available for V. salvadorii, so the full extent of its range is unknown. Its remote and generally inaccessible habitat is an obstacle to detailed study of this monitor in its natural habitat.

Biology and morphology

A characteristic feature of the crocodile monitor is its blunt, bulbous snout, which makes it look different from every other monitor on New Guinea, and suggested the common name "tree crocodile".  The body of the lizard is dark green with rings of yellow spots. The tail is banded yellow and black and is extremely long.

Its teeth are long, straight, and sharp. Its claws are prominent and strongly curved. Males reach a considerably larger size than females in both weight and length, and also tend to have a more robust head.

Like many monitor species, the crocodile monitor has mammal-like aerobic abilities; a positive pressure gular pump in the animal's throat assists lung ventilation.  Unlike most lizards that cannot breathe efficiently while running, because of Carrier's constraint, the gular pump of monitor lizards enables them to overcome the effect of one lung at a time being compressed by their running gait. The evolutionary development of the gular pump is functionally analogous to that of the diaphragm in mammals, which ventilates the lung independently of locomotion. Even amongst monitors, the crocodile monitor is one of the most agile species, quickly running up tree trunks and leaping from branch to branch. Investigation supports the idea that gular breathing is an evolutionary development that masks the effect of Carrier's constraint.

Size
Crocodile monitors are unique among extant varanid species in that the animal's tail is much longer than the snout-to-vent length in both juveniles and adults. The tail generally is 2–2.7 times the snout-to-vent length.

Crocodile monitors upon hatching measure about  long and they reach maturity when about . Reports of the maximal length vary greatly and are the subject of much dispute. It possibly attains the greatest length among extant species of lizards, although it is considerably less massive than the Komodo dragon. Crocodile monitors have been confirmed to reach up to  in length (record by a specimen at Museum Koenig). Some have been claimed to be much larger, including an individual from Konedobu that reportedly was  long, one from Kikori that reportedly was  and an individual from Port Moresby that reportedly was  long, but these sizes are unverified.

Claims of crocodile monitors attaining large weights also are unverified; the species is much more slender than Komodo dragons of comparable length. The typical reported length of this species is less than  with a matching body mass of about , but such a weight is questionable for healthy (i.e., not obese) individuals of this slender, arboreal species. Ten specimens were found to weigh only  at a length of , and a review of healthy adults in captivity found that a typical weight was up to . The average size of crocodile monitors caught in one study was  with a weight of , but these must have been young specimens.

Behavior

The crocodile monitor is a highly arboreal lizard. It can hang onto branches with its rear legs, and occasionally use its tail as a prehensile grip. The primary function of the tail, however, is as a counterbalance when leaping from branch to branch. As in some other Varanus species, the tail also may be used for defense, as captive specimens may attempt to lash keepers with their tails. This species occasionally is seen in the pet trade, but has a reputation for aggression and unpredictability. Although they are known to rest and bask in trees, they sleep on the ground or submerged in water.

These monitors rise up on their hind legs to check their surroundings, behaviour that also has been documented in Gould's monitors (V. gouldii). They are known to exhibit a warning posture, in which they carry their tails rolled up behind them. According to native belief, they give a warning call if they see crocodiles. In general crocodile monitors avoid human contact, but their bite is capable of causing infection, like the Komodo dragon's. One fatality was reported from a bite in 1983 when a Papuan woman was bitten and later died from an infection.

Diet
The teeth of crocodile monitors do not resemble those of other monitor species, which typically are blunt, peglike, and face slightly rearward. Their upper teeth are long, fang-like, set vertically in the jawbone, adapted to hooking into fast-moving prey such as birds, bats, and rodents. Their lower teeth are housed in a fleshy sheath. In the wild, crocodile monitors are the top predator in New Guinea, feeding on birds (such as Cacatua sp.), eggs, small mammals (such as rats and bandicoots), frogs, reptiles, and carrion. Natives have reported that it can take down pigs, deer, and hunting dogs, and hauls its prey into the canopy to consume it. Captive specimens have been known to eat fish, frogs, rodents, chickens, and dog food.

This species has been observed hunting prey in a unique fashion for monitor lizards.  Rather than following its prey to ambush it from behind, the crocodile monitor may stalk its prey and anticipate where it will run, meeting it headlong.

Reproduction
Reproduction of crocodile monitors has only been observed in captivity, so nothing is known about its reproduction in the wild. The egg clutches, comprising four to 12 eggs, are deposited around October to January, with the eggs showing a remarkable difference in dimensions, a phenomenon for which no explanation is known. Dimensions may vary from , while weight may vary from . Most clutches laid in captivity have been infertile, and only four successful breedings have been documented thus far. Hatchlings are about  long and weigh around . Like those of many other monitors, hatchling crocodile monitors are more colourful than adults, and feed primarily on insects and small reptiles.

Conservation
Varanus salvadorii is currently protected under the CITES Appendix II, which requires an exportation permit for international trade. It is not listed as a threatened species on the IUCN Red List or on the Endangered Species Act. It faces threats from deforestation and poaching, as it is hunted and skinned by native peoples, who consider the monitor an evil spirit that "climbs trees, walks upright, breathes fire, and kills men", to make drums .  In 2008,  52 individuals were maintained at 17 zoological parks in the United States, with an unknown number in private collections.

References

 Honoluluzoo.org

Varanus
Monitor lizards of New Guinea
Reptiles of Western New Guinea
Reptiles of Papua New Guinea
Endemic fauna of New Guinea
Reptiles described in 1878
Taxa named by Wilhelm Peters
Taxa named by Giacomo Doria
Apex predators