Lizards are distinctive creatures familiar to most Australians. They range in size from the three metre Komodo dragon (Varanus komodoensis) - actually a type of Monitor from Indonesia, down to the tiny Grey's skink (Menetia greyi) of inland Australia which has a body length of about 25 mm. Lizards occupy a broad range of habitats but do not occur in extremely cold environments, such as within the Arctic or Antarctic circle. There are five groups (called families) of lizards in Australia. These include the following:
Monitor lizards (Varanidae) all have long, pointed heads, well developed limbs and long, deeply forked tongues. All species of Monitor lizards lay eggs. They do not occur in Tasmania, but there are about 28 species on Mainland Australia ranging in size from the Perentie with a total length of about 2.2 metres down to the diminutive Short-tailed monitor, which is fully grown at about 20 cm.
Geckos (Gekkonidae) are generally small, nocturnal egg-laying lizards with large eyes which are cleaned with the tongue. Many gecko species are vocal, producing chirping sounds which are often heard at night in tropical Australia. There are no native geckos occurring in Tasmania. The name of this group comes from the sound produced by a species from South-east Asia. Many geckos have sticky pads under their toes which allows these lizards to run on apparently smooth surfaces, such as glass.
Jewelled gecko on dry grass
Flap-footed lizards (Pygopodidae) are only found in the Australian region. They lack forelimbs and their hind limbs are reduced to a small flap on either side of the cloaca. Like geckos, many Flap-footed lizards make chirping noises when handled. They can be distinguished from snakes by the presence of ears, a fleshy, notched (rather than deeply forked) tongue and a tail which is usually as long as the head and body. Legless lizards are not found in Tasmania.
Common scaly-foot in dead leaves
Skinks (Scincidae) are the most successful family of lizards in the world. The group is well represented in Tasmania with
17 described Scincidae species, of which seven are endemic (restricted to Tasmania). Tasmanian skinks are diurnal lizards, ranging in size from the
Delicate skink through to the
Blotched Blue-tongue. Skinks generally have glossy scales, each containing a small bone or osteoderm, and enlarged head shields. Most species occurring in Tasmania give birth to live young.
Tasmanian tree skink
Dragons (Agamidae) are poorly represented in Tasmania with only one species, the
Mountain dragon, occurring here. Other more famous members of the dragon family living in Australia include the Frilled Lizard of northern Australia and the Thorny Devil of the sandy deserts. Dragons tend to have long hind limbs, small, coarse scales and large heads. All dragons lay eggs and they are most numerous in the warmer parts of Australia.
Mountain dragon on rock
The Tasmanian reptile fauna may not be particularly
diverse but it is certainly fascinating nonetheless. Tasmania's
relatively cool climate and high mountain ranges provide challenges for
reptiles. Reptiles need to raise their body temperature by basking or by
absorbing warmth from rocks which have been heated by the sun. Most
species only become active when the air temperature is well above 15
degrees Celcius. Consequently, some species of lizard enter a torpor
over winter and most have developed strategies and adaptations to thrive
in Tasmania's cooler environment.Tail dropping:
Many people have witnessed a lizard dropping its tail. Geckos, skinks, legless lizards and some dragons have the ability to lose their tail quickly if it is grasped by a predator, then grow a new tail. Dropping a tail is not something a lizard does casually. A tail is a useful part of a lizard, storing body fat, providing balance and increasing the surface area of the lizard relative to its body mass, which is doubtlessly important in temperature regulation.
In many species the tail is used in social signalling (although this has not been studied in Tasmania) so a tailless lizard is at a disadvantage, physically and socially. Nonetheless, although a skink that loses its tail might starve later, a skink that has been grabbed by the tail can be pretty sure it will die much sooner if it doesn't leave in a hurry. The tail breaks at a fracture plane in one of the bones, and immediately small muscle rings constrict the blood vessels around the break so the lizard doesn't bleed to death. At the same time muscles in the severed part of the tail begin to twitch rapidly. This usually has the effect of making the predator hold onto the tail more tightly, becoming distracted while the lizard makes good its escape.
The tail will slowly grow back, but a change in colour pattern on the tail will identify the tail as regrown. Regenerated portions of tails do not have bones in them. The tail is supported by a rod of cartilage instead. Sometimes a lizards tail will not break off completely, and a new tail will grow from the break, giving the lizard a forked tail. This can cause difficulties for the lizard because it will not be able to slough effectively.