(Peters & Doria), 1878
|Estimated range of V. salvadorii, indicated by green|
Varanus salvadorii is a monitor lizard found in New Guinea. It is also known by the common names crocodile monitor, Papua(n) monitor, Salvadori's monitor and artellia. The largest monitor lizard in New Guinea, it is believed to be one of the longest lizards in the world, verified at up to 244 cm (8.01 ft), and in rare cases it may rival or exceed the length of the world's largest lizard, the Komodo dragon. It is the sole member of the subgenus Papusaurus. V. salvadorii is an arboreal lizard with a dark green body and yellowish bands, a blunt snout and a very long tail. It lives in mangrove swamps and coastal rainforests in the southeastern part of the island, where it feeds on birds, small mammals, eggs, and carrion in the wild, using teeth 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 can, and V. salvadorii may have greater stamina than most monitors. Little is known of its reproduction and development, as the species is very difficult to breed in captivity.
V. salvadorii is threatened by deforestation and poaching, and is protected by the CITES agreement. The lizard is hunted and skinned alive by tribesmen to make drums, who describe the monitor as an evil spirit that "climbs trees, walks upright, breathes fire, and kills men"; yet the tribesmen maintain that the monitor gives warnings if there are crocodiles nearby.
Taxonomy and etymology
V. salvadorii was first described as Monitor salvadorii by Wilhelm Peters and Giacomo Doria in 1878 from a female specimen with a snout-to-vent length of 48 cm (19 in) long and a tail measuring 114 cm (45 in) in length.
The generic name Varanus is derived from the Arabic waral (ورل), meaning "lizard". The term "monitor" is thought to have come about from confusion between waral and the German warnen, meaning "warning". The term "goanna" came about as a corruption of the name "iguana". The specific name is derived from a Latinization of Tommaso Salvadori, an Italian ornithologist who worked in New Guinea. Later, in 1885, it was renamed Varanus salvadorii by George Albert Boulenger. The Papua monitor is occasionally confused for the Asian water monitor (V. salvator) because of their similar scientific names.
The evolutionary development of V. salvadorii started with the genus Varanus, which originated in Asia about 40 million years ago and migrated to Australia. Around 15 million years ago, a collision between Australia and Southeast Asia allowed the varanids to move into what is now the Indonesian archipelago.
V. salvadorii has been placed cladistically as part of a species cluster with the lace monitor (V. varius) and the Komodo dragon (V. komodoensis). This study was based upon mitochondrial DNA and microcomplement fixation analysis. A theory has been put forth that the species diverged from a common ancestor, as the Torres Strait separating New Guinea from Australia is less than 90 km (56 mi) long, a distance that could have been covered fairly easily with island hopping. However, the similarities between V. salvadorii and V. varius may simply be an example of convergent evolution. Another clade postulated by Eric Pianka places V. salvadorii in a larger "Australian" clade of large monitors, along with other species as the Komodo dragon, the lace monitor, the perentie (V. giganteus), the Argus monitor (V. panoptes), and the sand goanna (V. gouldii).
The largest of the seven species of monitors found on the island of New Guinea, V. salvadorii occurs 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 the main factor in preventing detailed study of this animal in its natural habitat.
Biology and morphology
The most characteristic feature of this monitor is its blunt, bulbous snout, which makes this species look different from every other monitor on New Guinea, and lends to its common name of 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, being more than twice as long as the snout-to-vent length. It has long, straight teeth and prominent, curved claws. There is no external sexual dimorphism.
Unique among living varanid species, the animal's tail is two-thirds longer than the snout-to-vent length in both juveniles and adults. Herpetologist Robert Sprackland gives the proportion as the tail being 210% of the animal's body length. At hatching, V. salvadorii is about 45 cm (18 in) long, while a sexually mature female may grow to 150 cm (4.9 ft). This is possibly the longest living species of lizards, although it is considerably less massive and heavy than the Komodo dragon. Specimens are known to reach at least 244 cm (8.01 ft) in length. but it may grow longer. A specimen reportedly measuring 323 cm (10.60 ft) was caught in Konedobu by Dr. F. Barker. Several reported specimens have been claimed to exceed 350 cm (11.5 ft), some even to 610 cm (20.0 ft), but most of these were second-hand reports and no museum specimens in this size range are known. Weight in the species has been reported to be up to 90 kg (200 lb), but this is an unverified and possibly dubious report, this species is much more slender even in large specimens than comparable length Komodo dragons. The average size of this species is under 200 cm (6.6 ft) and average body mass is reportedly about 20 kg (44 lb). However 10 adult specimens were found to weigh only 5 to 6.38 kg (11.0 to 14.1 lb) at a length of 1.16 to 2.25 m (3.8 to 7.4 ft) so even the afforementioned weigh is fairly optimistic for this species. The average size of V. salvadorii caught in one study were 99.2 cm (39.1 in) with a weight of 2.02 kg (4.5 lb) but presumably consisted of largely or entirely young specimens.
Varanus salvadorii has mammal-like aerobic abilities; this is accomplished by means of a positive pressure gular pump in the animal’s throat to assist lung ventilation. The majority of lizards cannot run and breathe at the same time due to Carrier's constraint, but monitor lizards are exceptions to this rule. The development of this ventilatory pump is analogous to the evolution of the diaphragm in mammals, which ventilates the lung independently of locomotion; scientists place V. salvadorii as the species with the highest endurance in this regard. This would suggest the lizard is at an evolutionary midpoint, relying on both forms of breathing.
As an arboreal lizard, it can hang onto branches with its rear legs and occasionally use its tail as a prehensile grip. The primary use of the tail, however, is to counterbalance its weight when leaping from one branch to another. The tail may also be used for defense, as captive specimens have attempted to whip their keepers with their tails. This species is occasionally seen in the pet trade, but has earned a reputation of being aggressive and unpredictable. Although they are known to rest and bask in trees, they sleep on the ground or submerged in water.
These monitors will rise up on their hind legs to check their surroundings, a behavior that has also been documented in Gould's monitors (V. gouldii). According to native belief, they will give a warning call if they see crocodiles. In general V. salvadorii avoids human contact, but its 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.
The teeth of V. salvadorii do not resemble those of other monitor species, which are typically blunt, peglike, and face slightly rearward. Their upper teeth are long and fang-like, standing vertical from the jawbone, designed to hook into fast-moving or feathered prey such as birds, bats, and rodents. Their lower teeth are housed in a fleshy sheath. In the wild, V. salvadorii is the top predator in New Guinea, feeding on birds, eggs, small mammals, and carrion. Native have reported it may take down pigs, deer, and hunting dogs, and hauls its prey into the canopy to consume it. Its only competition is the New Guinea singing dog, a type of dingo. 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, V. salvadorii will stalk its prey and anticipate where it will run, meeting it headlong.
Reproduction 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 7.5x3.4 cm (3.0x1.3 in) to 10x4.5 cm (3.9x1.8 in), while weight may vary from 43.3 to 60.8 g (1.53 to 2.14 oz). Most clutches laid in captivity have been infertile, and only four successful breedings have been documented thus far. Hatchlings are about 18 in (45 cm) long and weigh around 56 g (2.0 oz). Like those of many other monitors, the hatchlings of V. salvadorii are more colorful than adults, and feed primarily on insects and small reptiles.
Varanus salvadorii is currently protected under the CITES Appendix II, which requires an exportation permit for international trade. It is not listed on the IUCN Red List or the Endangered Species Act. It faces threats from deforestation and poaching, as it is hunted and skinned alive by native peoples to make drums, who consider the monitor an evil spirit that "climbs trees, walks upright, breathes fire, and kills men". The species is maintained at 17 zoological parks worldwide. The total US captive zoo population totals 52 individuals, with an unknown number in private collections.
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