From Tropical Topics newsletter, No. 78
June 2003, produced by Stella Martin at the Queensland
Environmental Protection Agency. Download the PDF to read the whole
issue. Acknowledgements to Russell Best, Queensland Parks and
Wildlife Service and Tony Griffiths, Key Centre for Tropical
Wildlife, Charles Darwin University.
Family Varanidae | Spotted tree monitor | Gould’s goanna |
 |
|
Gould's goanna: found in most parts of
Australia, its colouring is black with varying amounts of
yellow.
|
What's in a name
Goannas are also known as monitor lizards.
Varanus, their scientific family name, comes from the Arabic word
for monitor, because these lizards had a reputation for warning of
the approach of a crocodile—they were monitoring the
situation. The word ‘goanna’, used only in Australia,
is derived from the Spanish word ‘iguana’, originally
used for large American lizards.
A 5.5 m long Megalania, a goanna with
ancient origins, was present in eastern Australia as recently as
30,000 years ago and would have crossed paths with Aboriginal
settlers.
The largest Australian goanna is the
desert-dwelling perentie which can grow to two and a half metres in
total length but it is dwarfed by the massive Indonesian Komodo
dragon, another goanna which reaches lengths of 3 m and can weigh
250 kg.
|
Goannas tend to be large lizards (although the pygmy goanna of
the central deserts is, at 25 cm total length, the smallest goanna
in the world). They are also among the oldest, early versions
having been around to see the dinosaurs and even the modern
versions dating back 15–20 million years.
Although found elsewhere, Australia has the lion’s share
of goanna species with about 25 of the world’s 30. Thought to
be the most intelligent of lizards, they eat a variety of other
animals, both living and dead, including other reptiles, insects,
baby birds and mammals, including possums. At home on the ground
and in trees, they constantly flick their forked tongues, picking
up scent particles from the air and transferring them to a
structure known as the Jacobson’s organ, on the roof of the
mouth, where they are interpreted.
The spotted tree monitor is found across the northern tropics
almost anywhere there are trees, darker individuals inhabiting
rainforest and lighter ones in drier areas. The varied patterns of
this species tend to match local tree trunk colours but most have
spots of some sort, usually pale with a dark centre. This lizard
hunts on the ground as well as in the trees but if disturbed on the
ground will beat a hasty, and noisy, retreat up the nearest tree,
disappearing into a hollow or keeping on the opposite side to its
pursuer. It feeds on insects, smaller lizards and baby birds and
may drop as much as 4 metres from a tree on to prey.
This goanna is found in most parts of continental Australia,
although it tends to prefer sandy areas and avoids rainforest.
Reaching one and half metres in total length, and weighing several
kilos, Gould’s goanna is black with varying amounts of
yellow. It is at home on the ground, rarely climbing trees, as it
seeks prey of many types — insects, lizards and their eggs
and small mammals — and scavenges for carrion. It digs holes
or uses tree logs or other animals’ burrows as retreats. Eggs
are laid in a deep burrow which is then closed and concealed by the
female.
