Australian water dragonPosted on September 30, 2019 - Last modified: September 30, 2019
australian water dragon (Physignathus lesueurii) is Australia's largest dragon lizard and can be found living along Sydney's most prosperous canals.
Table of Contents
- 1 Species
- 2 Features
- 3 Habitat
- 4 Food
- 5 Predators
- 6 Reproduction
- 7 State of conservation
- 8 Relationship with humans
- 9 Popular culture
- 10 List of other interesting animals
The genus Physignathus was described by George Cuvier (1769-1832) in 1829 based on the specimen of the genus; he Green Water Dragon, Physignathus cocincinus from Southeast Asia.
The name Physignathus translates to "swollen cheek" and refers to the bulging appearance of the throat and lower jaw. Physignathus comprises two recognized species: Physignathus lesueurii y physignathus concincinus. The specific name lesueurii honors the French naturalist Charles-Alexandre Lesueur (1778-1846) who collected this species on the Baudin expedition of 1800.
There are two recognized subspecies of the water dragon: the eastern water dragon (Physignathus lesueurii lesueurii) And the gippsland water dragon (Physignathus lesueurii howittii).
A recent taxonomic review concluded that the Australian species of Physignathus shows enough different characteristics to classify it into its own genus, since Physignathus was first assigned to P. cocincinus, a new genre to be created for Australian water dragons. In 2012 the species was officially renamed Itellagama lesueurii.
The Australian Water Dragon can be identified by a distinctively deep angular head and a nuchal ridge of spiny scales that attach to the vertebral ridge extending the length of its body to the tail. Enlarged spiny scales are also present on the lateral surface, unevenly distributed among the regular keel scales, as in most of the lizards. The dewlap is large and the ear is exposed and the same size as the eye. The dorsal crest and tail are laterally compressed and the limbs are strong and robust, with especially long toes on the hind legs. The tail is able to regenerate when it is lost, in addition, regenerated tails can also grow back when they are cut.
The coloration differs between the subspecies; The eastern water dragon, Itellagama lesueurii lesueurii, is gray to greyish in color above with black stripe patterns along the dorsal ridge as well as on the underside of the tail. There is also a horizontal dark streak from the eye back over the eardrum and down the neck. The limbs are mostly black with gray spots and stripes and the tail is patterned with gray and black stripes. The ventral surface is yellowish brown, with the chest and upper part of the belly bright red in mature males.
The Gippsland water dragon, Itellagama lesueurii howittii, is identical in morphology except for slightly smaller spiny scales, but differs in coloration and pattern. Dorsally the body is olive green to brown with transverse black stripes. The dark stripe from eye to ear is absent. Mature males have dark blue-green breast and yellow and blue streaks around the neck and throat.
The Australian water dragon is usually active in the Sydney region from September to June, remaining inactive during the colder months. To survive the cold winter temperatures, water dragons will enter established burrows or scrape their own burrows and logs on or near river banks and collect dirt in the opening to seal themselves. Once buried, they will slow down their metabolism and enter a state of brumation (Hibernation for reptiles, also called dormancy) until spring comes.
Water dragons are usually active in the Sydney region from September to June, becoming inactive during the colder months. To survive the cold winter temperatures, water dragons will enter established burrows or scrape their own burrows and logs on or near river banks and collect dirt in the opening to seal themselves. Once buried, they will slow down their metabolism and enter a state of brumation until spring comes.
The Water Dragon is more heard than seen when submerging in water when disturbed. It can stay submerged for about an hour. This species has a much lower preferred body temperature than other great dragons and can stay in water or in the shade on hot days. They are often seen on cloudy days or in the morning basking in the sun with available heat.
Water dragons have quite contrasting activity patterns that depend on the season and the average daily temperature within their range. During spring and summer, water dragons of all ages and sizes can be seen in the various riparian environments that they inhabit (sunbathing on riverbanks and rocks, lounging in trees, swimming, as well as looking for food on earth).
They can be difficult to observe at times, and even those accustomed to human attention will quickly escape if you pass them too close, either falling from ledges and rock branches into the water or running bipedally into the water or a thick cover. Young water dragon hatchlings prefer to be on the ground and appear to be more cautious than larger adults.
The offspring of I. l. lesueurii remain completely immobile when discovered in a section of grass yards from the water, relying heavily on their dull gray camouflage to blend in with grass and fallen leaves.
In the wild, water dragons can be found in large numbers in areas of suitable habitat. These groups are usually made up of several females, youngsters of different ages, and a dominant male who will defend as much of the territory as possible from other males. Water dragons communicate through a variety of dominant and submissive signals, including headshots, salutes, and licking substrates. The real meaning of some of these gestures has not yet been fully understood.
The habitats available for this species differ greatly in their distribution, from the rainforest in the north to the alpine streams in the south. Flowing water with extensive tree cover and sunbathing sites appears to be the key to this species' habitat preference. Water dragons will be found in built-up urban areas provided the above conditions are met and the water quality is good.
Australian water dragons are found in eastern Australia as well as southern New Guinea. The eastern subspecies, Itellagama lesueurii lesueurii, is found along the eastern coast of Australia, from Cooktown in the north to the southern coast of New South Wales (roughly in the Kangaroo Valley), where it is replaced by the Gippsland subspecies Itellagama lesueurii howittii, which is distributed in the extreme south and in the Gippsland region of eastern Victoria. There is also at least one anthropologically introduced wild population found in the Mount Lofty range near Adelaide in South Australia.
Water dragons are completely insectivorous in their early stages, in youth, however as they grow they become more omnivorous and plant matter gradually makes up almost half of the diet.
In nature, water dragons have been observed to feed on insects such as ants and that they feed between the branches of the trees in search of arboreal invertebrates such as cicadas. They can also consume mollusks and crustaceans such as yabbies (a species of Australian lobster), and some of these reptiles have been reported in search of algae and crabs in the intertidal zones of the Sydney region.
Baby water dragons have also been observed feeding on mosquitoes and leaping into the air to catch them. The types of vegetation that are consumed include figs, the fruits of the evergreen tree lilly pilly and other fruits and flowers. Water dragons are believed to feed underwater, however this is based on an observation of water dragons returning to the surface and moving their jaws.
Small Water Dragons have been observed being captured by the Brown Tree Snakes, Boiga irregularis, which hunt them in the branches of the trees while they sleep. Other species of snakes known to prey on the baby water dragons are Acanthophis antarcticus, Austrelaps proud y Pseudechis porphyriacus.
Hatchlings and young dragons are also known to be cannibalized by adult water dragons in some wild populations.
Breeding timing is determined by the onset of warmer weather in spring, which occurs earlier in populations living in North Queensland and later in populations living in Gippsland. In the Sydney region, the breeding season begins in September, when courtship and mating begin, and ends in January, when the last clutches of eggs are laid.
Males are believed to be sexually mature with a snout about 210mm long and a mass of 400g. In nature this occurs at approximately 5 years of age; however, in captivity this can occur as early as 2 years. A single captive female was recorded reproducing from 4 years of age to 27 years of age. It is not clear how long the males can remain reproducing.
Males of similar size will fight each other when they face off. A male will first try to dissuade his opponent through intimidation, for example by walking with his mouth open, and will try to appear as big as possible. If this does not deter the opponent, a ritual combat will ensue. Male combat involves both animals placed side by side on the ground, so that each animal has its head next to the hip area of its opponent. Both animals surround each other while biting with short bites on the hip and neck parts. They can then stop before taking action and repeat this pattern several more times. Before the end of the battle, both opponents will have biting and scratching wounds on their hips and necks. Fights between wild males have been observed lasting ten minutes.
Females can reproduce twice a season in captivity; however, this has not been reported in tagging and recapture studies of wild populations.
Females begin digging test holes in sandy soil from one week to three days before laying. The egg-laying size of the water dragon ranges from 6 to 18. The average mass of individual eggs ranges from 4,0 to 5,1 g.
State of conservation
Protected in all states and territories where they naturally inhabit: Queensland, New South Wales, Australian Capital Territory and Victoria. It is listed as Vulnerable (VU).
This species is protected in Australia. Wild specimens cannot be collected from the wild and a permit is required in most states and territories to keep this species in captivity.
Relationship with humans
Large adult water dragons will appear confident and friendly, however they should not be approached as they have very sharp claws and can take a serious bite.
Fossils belonging to the genus Physignathus and resembling existing water dragons have been discovered in Miocene deposits in Riversleigh, Queensland, indicating that this genus has existed in Australia for at least 20 million years.