The spiny-tailed monitor (''Varanus acanthurus''), also known as the Australian spiny-tailed monitor, the ridge-tailed monitor the Ackie's dwarf monitor, and

colloquially Colloquialism (), also called colloquial language, everyday language or general parlance, is the linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employed in conversa ...

simply ackie monitor, is an

Australian Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal A ...

species of

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia altho ...

belonging to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

monitor lizard Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are rec ...

s (''Varanus'').

Description

The spiny-tailed monitor, a somewhat small monitor lizard, can attain a total length of up to 70 cm (27 in), although there are unconfirmed reports of wild individuals growing up to 34 inches. The tail is about 1.3-2.3 times as long as the head and body combined. The upper side is a rich, dark brown and painted with bright-yellowish to cream spots, which often enclose a few dark scales. Its tail is round in section and features very spinose scales. There are 70-115 scales around the middle of the body. The spiny-tailed monitor is distinguished from the similar-looking species '' V. baritji'' and '' V. primordius'' by the presence of pale longitudinal stripes on the neck.

Distribution and habitat

This

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...

-adapted lizard is found in northern

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...

, in the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...

and in the western and north-western parts of

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , establishe ...

. The spiny-tailed monitor inhabits is associated with arid rocky ranges and outcrops. ''V. a. acanthurus'' is native to northern Australia, from Broome on the west coast, through the Kimberley and the Top End, to the Gulf of Carpentaria. ''V. a. brachyurus'' can be found in the center, western, and eastern parts of the ackie's total range, as far west as Carnarvon and as far east as Mt. Isa. ''V. a. insulanicus range is limited to Groote Eylandt and the Wessel Islands.

Subspecies and taxonomy

The spiny-tailed monitor is part of an Indonesian and Australian

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

of dwarf monitor lizards, the subgenus '' Odatria''. Three

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...

of ''V. acanthurus'' are recognized: * ''V. a. acanthurus'' of northwestern and

northern Australia The unofficial geographic term Northern Australia includes those parts of Queensland and Western Australia north of latitude 26° and all of the Northern Territory. Those local government areas of Western Australia and Queensland that lie p ...

* ''V. a. brachyurus'' of

western Western may refer to: Places *Western, Nebraska, a village in the US *Western, New York, a town in the US *Western Creek, Tasmania, a locality in Australia *Western Junction, Tasmania, a locality in Australia *Western world, countries that id ...

and

central Australia Central Australia, also sometimes referred to as the Red Centre, is an inexactly defined region associated with the geographic centre of Australia. In its narrowest sense it describes a region that is limited to the town of Alice Springs and ...

* ''V. a. insulanicus'' of

Groote Eylandt Groote Eylandt ( Anindilyakwa: ''Ayangkidarrba'' meaning "island" ) is the largest island in the Gulf of Carpentaria and the fourth largest island in Australia. It was named by the explorer Abel Tasman in 1644 and is Dutch for "Large Island" i ...

and the islands of the Wessel group '' Varanus primordius'' was at one point considered a subspecies (''V. a. primordius''), but has since been elevated to full species status. In the pet trade, two "variants" of spiny-tailed monitors are commonly available. The "red ackie" monitor is likely the subspecies ''V. a. acanthurus'', while the "yellow ackie" is likely ''V. a. brachyurus''. The red ackie is generally larger and less commonly available than the yellow ackie. The taxonomic status of the three subspecies is uncertain. In 2006, the results of a study on the

mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DNA ...

of Australian monitors were published, according to which the two continental subspecies do not form natural (

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

) taxonomic entities. ''V. a. insulanicus'' was found 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 (2010) 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. Varanus acanthurus25

Ecology

Spiny-tailed monitors are diurnal, typically solitary ground-dwellers. This species is most often found in its shelter, mainly under rock slabs, wedged among boulders or in rock crevices, and in underground burrows. Only rarely do they hide in spinifex. Sheltering underground gives them access to humid microclimates which helps keep them hydrated enough to survive the otherwise arid nature of their habitat. Their diet is consistent with the diet of intensive foragers, implying that they likely spend quite a bit of their time hunting.

Diet

They prey mainly on arthropods, such as grasshoppers, beetles, cockroaches, spiders, isopods, caterpillars, cicadas, snails, stick insects, centipedes, crickets, and ticks. Small lizards such as

skinks Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Sk ...

geckos Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos ar ...

, dragon lizards, or possibly smaller

s are also eaten, making up about a third of its diet, as well as

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in ...

joeys. Approximately 70% of its water requirement comes from food. In captivity, they are sometimes fed cat and dog food as well as processed canned food. This isn't recommended as this type of food doesn't contain the correct nutrients for this species. A varied diet rich with different vertebrate and invertebrate prey (such as Dubia roaches, crickets, mealworms, eggs, shrimp, and, on a monthly basis, rodents) is important to the health of captive spiny-tailed monitors, as they naturally have a wide range of prey in the wild.

Reproduction

There are a number of methods of sexing ackie monitors, although the hemipenal transillumination technique is generally considered to be the easiest and most accurate. Sex can also be guessed using visual markers, but it is typically not nearly as accurate. Male ackie monitors are generally larger, have blockier heads, and have grippy scales on the underside of their tail. Females are generally smaller with narrower, pointier heads, and smooth scales under their tail. In captivity, a clutch consists of up to 18 eggs. The young hatch after three to five months of incubation, and measure 15 cm (6 in). The knowledge on reproduction in the wild is sparse. Males most likely mature at 30 cm (12 in) snout-vent length, females mature at 25–36 cm (10–14 in) snout-vent length. Ovulation occurs in August and November. The eggs are deposited in self-dug tunnels. In the wild, females have been shown to share massive burrows, nesting communally.Doody, J. & Clulow, Simon & McHenry, Colin & Brown, Michael & Vas, Gary & Canning, Gordon. (2017). Varanus acanthurus (Spiny-tailed Monitor Lizard). Communal nesting and commensalism. Herpetological Review. 48. 203.

References

Böhme W. 2003. ''Checklist of the living monitor lizards of the world (family Varanidae)''. Zoologische Verhandelingen 341, pp 3–43. Cogger H. 2000. ''Reptiles & Amphibians of Australia''. Ralph Curtis Publishing, Sanibel Island, Florida. . Pp 359-361. Dryden G. 2004. ''Varanus acanthurus''. In: ''Varanoid Lizards of the World'' (Hrsg. Pianka ER, King DR), pp 298-307. Indiana University Press, Bloomington & Indianapolis. . Fitch AJ, Goodman AE, Donnellan SC. 2006. ''A molecular phylogeny of the Australian monitor lizards (Squamata:Varanidae) inferred from mitochondrial DNA sequences''. Australian Journal of Zoology 54, p 253-269. Wilson S, Swan G. 2010. ''A complete guide to reptiles of Australia''. New Holland Publishers, Sydney, Auckland, London, Cape Town. . P 392. {{Taxonbar, from=Q1757161 Varanus Reptiles of Western Australia Reptiles described in 1885 Monitor lizards of Australia Taxa named by George Albert Boulenger