Gigarcanum

Extinct species of lizard

Gigarcanum delcourti, formerly Hoplodactylus delcourti, is an extinct species of gecko in the family Diplodactylidae. It is the largest known of all geckos, with a snout to vent length (SVL) of and an overall length (including tail) of at least It is only known from a single taxidermied specimen collected in the 19th century that was rediscovered unlabelled in a museum in France. The origin of the specimen was undocumented. DNA evidence from the specimen suggests that it originates from New Caledonia.

According to the report of Major W. G. Mair in 1873, in 1870, a Māori chief said that he had killed a kawekaweau he found under the bark of a dead rata tree in the Waimana Valley in Te Urewera on the North Island of New Zealand. This is the only documented report of anyone ever seeing a kawekaweau alive. Mair reported the chiefs description of the animal as being "two feet long and as thick as a man’s wrist; colour brown, striped longitudinally with dull red". A single stuffed specimen was "discovered" in the basement of the Natural History Museum of Marseille in 1986; the origins and date of collection of the specimen remain a mystery, as it was unlabelled when it was found. Trevor Worthy suggested in 2016 that the specimen originated on an island of New Caledonia rather than New Zealand, due to a lack of fossil evidence for the lizard in New Zealand caves despite abundant remains of all other known species of New Zealand gecko. This was confirmed by the successful sequencing of the specimen's mitochondrial DNA in 2023, which found that it was nested within the New Caledonian species of Diplodactylidae rather than the New Zealand species, and distinctive enough to warrant placement in the new genus Gigarcanum. According to the authors, the genus name Gigarcanum derives from "a combination of two words: the Latin adjective gigas, meaning giant and taken from the Ancient Greek Γίγᾱς, and the Latin noun arcanum, meaning secret or mystery. The combination refers to the size of the type species and the unknown provenance of the only known specimen".

Gigarcanum delcourti is 50% longer and was likely several times heavier than the largest living gecko, the also New Caledonian Rhacodactylus leachianus, with a snout to vent length (SVL) of and an overall length (including tail) of at least The body is robust, and the tail is tapering, cylindrical and weakly annulated. The skull is large, and makes up about 20% of the SVL. The digits bear claws, and are weakly moderately webbed. The digit pads are rectangular and broad. The body colour is yellowish brown, with dark reddish brown stripes running along the length of the upper body.

Based on comparison with its living relatives, it was probably a nocturnal arboreal animal that climbed trees. It probably had a diet mainly of arthropods, but possibly also seasonally consumed fruit. It likely had a clutch size of two, as all other known New Caledonian geckos do, though whether it was oviparous or viviparous is uncertain.

Gigarcanum delcourti was likely extinct or extremely rare by the time of the colonisation of New Caledonia in the mid 19th century, due to the absence of any other records of the species.