Varanus acanthurus

Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Superclassis: Sarcopterygii
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Infraclassis: Lepidosauromorpha
Superordo: Lepidosauria
Ordo: Squamata
Cladus: Unidentata, Episquamata, Toxicofera
Subordo: Anguimorpha
Infraordo: Paleoanguimorpha

Superfamilia: Varanoidea
Familia: Varanidae
Genus: Varanus
Subgenus: Varanus (Odatria)
Species: Varanus (Odatria) acanthurus
Subspecies: V. (O.) a. acanthurus – V. (O.) a. brachyurus – V. (O.) a. insulanicus
Name

Varanus (Odatria) acanthurus Boulenger, 1885

Type specimen: BMNH 1945.8.30.97

Type location: NW coast of Australia
Vernacular names
Deutsch: Stachelschwanzwaran
English: Ridgetail Monitor, Ridge Tailed Monitor
français: Varanus acanthurus
日本語: トゲオオオトカゲ
polski: Waran kolczastoogonowy
svenska: Taggsvansvaran
References

https://web.archive.org/web/20091026184743/http://www.monitor-lizards.net/species/odatria/acanthurus.html. Accessed on 11 October 2009.
Varanus acanthurus at the New Reptile Database. Accessed on 11 October 2009.

The spiny-tailed monitor[2] (Varanus acanthurus), also known as the Australian spiny-tailed monitor, the ridge-tailed monitor[3] or Ackie's dwarf monitor,[4] is an Australian species of lizard belonging to the genus of monitor lizards (Varanus).

Description

The spiny-tailed monitor, a medium-sized 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.[5] 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.[3] 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.[2]
Distribution and habitat

This arid-adapted[6] lizard is found in northern Western Australia, in the Northern Territory and in the western and north-western parts of Queensland.[6] The spiny-tailed monitor inhabits is associated with arid rocky ranges and outcrops.[2][3] 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.[7]
Subspecies and taxonomy

The spiny-tailed monitor is part of an Indonesian and Australian radiation of dwarf monitor lizards, the subgenus Odatria.[8][9]

Three subspecies of V. acanthurus are recognized:

V. a. acanthurus of northwestern and northern Australia
V. a. brachyurus of western and central Australia, Queensland[10]
V. a. insulanicus of Groote Eylandt and the islands of the Wessel group[2][3]

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.[5][11]

The taxonomic status of the three subspecies is uncertain.[10] 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 (monophyletic) 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.[9] 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.[2]
Two spiny-tailed monitors at the Cincinnati Zoo
Ackies Dwarf Monitor.jpg
Ecology

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.[3] Sheltering underground gives them access to humid microclimates which help keep them hydrated enough to survive the otherwise very arid nature of their habitat.[12] 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.
Diet

They prey mainly on arthropods, such as grasshoppers, beetles, cockroaches, spiders, isopods, caterpillars, cicadas, snails, stick insects, centipedes, crickets, and ticks.[13] Small lizards such as skinks, geckos, or dragon lizards are also eaten, making up about a third of its diet.[14] Approximately 70% of its water requirement comes from food.[6]
Reproduction

There are a number of methods of sexing ackie monitors, although the hemipenal transillumination technique[15] is generally considered to be the easiest and most accurate. Sex can also be guessed using visual markers. 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.[16]

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.[6]
References
Wikimedia Commons has media related to Varanus acanthurus.

Shea, G.; Cogger, H. (2018). "Varanus acanthurus". IUCN Red List of Threatened Species. 2018: e.T83777229A101752285. doi:10.2305/IUCN.UK.2018-1.RLTS.T83777229A101752285.en. Retrieved 19 November 2021.
Wilson S, Swan G. 2010. A complete guide to reptiles of Australia. New Holland Publishers, Sydney, Auckland, London, Cape Town. ISBN 978-1-877069-76-5. P 392.
Cogger H. 2000. Reptiles & Amphibians of Australia. Ralph Curtis Publishing, Sanibel Island, Florida. ISBN 0-88359-048-4. Pp 359-361.
"Cincinnati Zoo & Botanical Garden". Archived from the original on 2012-09-05. Retrieved 2012-08-28.
"Spiny-Tailed Monitor Lizard Care Tips". Reptiles Magazine. 2011-12-01. Retrieved 2020-08-29.
Dryden G. 2004. Varanus acanthurus. In: Varanoid Lizards of the World (Hrsg. Pianka ER, King DR), pp 298-307. Indiana University Press, Bloomington & Indianapolis. ISBN 0-253-34366-6.
Monitor lizards natural history, captive care, breeding. Bernd Eidenmüller, Grant Husband (Rev., enl. and updated ed.). Frankfurt, M. 2007. ISBN 978-3-89973-471-3. OCLC 185009165.
Böhme W. 2003. Checklist of the living monitor lizards of the world (family Varanidae). Zoologische Verhandelingen 341, pp 3–43.
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.
Auliya, Marc; Koch, André (2020). Visual Identification Guide for the Monitor Lizard Species of the World (Genus Varanus). Bundesamt für Naturschutz. doi:10.19217/skr552. ISBN 9783896242907.
Kuhn, Peter; Julander, Justin (1999). "Husbandry and Captive Breeding of the Red Acanthurus Monitor Varanus acanthurus: A Giant Dwarf". Vivarium. 10.
Healey, Mariah. "Ackie Monitor Humidity Requirements". ReptiFiles. Retrieved 2021-02-26.
King, Dennis (2008). "The Diet and Foraging Strategy of Varanus acanthurus" (PDF). Biawak. 2 (1): 11–17.
Losos, Jonathan B.; Greene, Harry W. (1988-12-01). "Ecological and evolutionary implications of diet in monitor lizards". Biological Journal of the Linnean Society. 35 (4): 379–407. doi:10.1111/j.1095-8312.1988.tb00477.x. ISSN 0024-4066.
Brown, Danny (2009). "Hemipenal Transillumination as a Sexing Technique in Varanids" (PDF). Biawak. 3 (1): 26–29.
Healey, Mariah. "How to Sex Ackie Monitors". ReptiFiles. Retrieved 2021-02-26.