Spiny-tailed monitor (Ackies Dwarf Monitor)

Naming

The spiny-tailed monitor is part of an exclusively Australian radiation of small monitor lizards, the subgenus ''Odatria''.

In the past, three subspecies of ''V. acanthurus'' were recognised: The continental subspecies ''V. a. acanthurus'' and ''V. a. brachyurus'', and ''V. insulanicus'', that only inhabits Groote Eylandt and the islands of the Wessel group. In 2006, the results of a study on the mtDNA of Australian monitors were published, according to which the two continental subspecies do not form natural , taxonomic entities. ''V. a. insulanicus'' was proven to be monophyletic, but it is more closely related to ''V. baritji'' than to other ''V. acanthurus''. Therefore ''V. a. insulanicus'' might represent a distinct species. Wilson and Swan still accept ''V. a. insulanicus'' as a valid subspecies of ''V. acanthurus'', which is easily distinguished from other spiny-tailed monitors by its dark colouration and more-banded pattern.

Distribution

This arid-adapted lizard is found in northern Western Australia, in the Northern Territory and in the eastern and northeastern parts of Queensland. The spiny-tailed monitor inhabits arid areas, and is associated with rocky ranges and outcrops.

Habitat

This arid-adapted lizard is found in northern Western Australia, in the Northern Territory and in the eastern and northeastern parts of Queensland. The spiny-tailed monitor inhabits arid areas, and is associated with rocky ranges and outcrops.Spiny-tailed monitors are diurnal, solitary ground-dwellers. This species is most often found in its shelter, mainly under rock slabs, boulders or in rock crevices. Only rarely do they hide in spinifex. As the spiny-tailed monitor has a lower level of activity compared to other monitor lizards, as well as a lower metabolic rate, it is often found in its hideout at day, and most likely it is a sit-and-wait-predator. They prey mainly on insects, especially orthopterans, beetles and cockroaches, and on small lizards such as skinks, geckoes or small dragon lizards. Less often, this species feeds on other insects, spiders, snails or young marsupials. Approximately 70% of its water requirement comes from food.

Reproduction

In captivity, a clutch consists of up to 18 eggs. The young hatch after 3–5 months of incubation, and measure 15 cm. The knowledge on reproduction in the wild is sparse. Males most likely mature at 12 cm snout-vent length, females mature at 10–14 cm snout-vent length. Ovulation occurs in August and November. The eggs are deposited in self-dug tunnels.