Gigarcanum (Giant Gecko)

The largest gecko in the world…

In the early 1980s, French museum employee Alain Delcourt discovered a forgotten specimen of a single stuffed giant gecko in the basement of the Natural History Museum of Marseille, which had previously been on public display for years. This species was previously unknown to science. The origin of the animal and the date of collection were a mystery, as the specimen had no labeling.

The preservation style of the animal was also unusual – it was gutted, dried, and mounted on a branch, instead of being preserved in alcohol, as is customary for preserved specimens today. Scientists estimated that the gecko entered the museum collection sometime between 1833 and 1869. The giant gecko lacked internal organs and most of its skeleton, except for the skull and limbs.

American herpetologist Aaron M. Bauer of Villanova University in Pennsylvania was a doctoral student when he arrived at the museum in 1983 to study the mysterious giant gecko. Three years later, Bauer and paleontologist Anthony P. Russel published the scientific description of the new species Hoplodactylus delcourti, “the largest known gecko.” The specimen measures 60 centimeters in length, making it 50 percent larger than the largest known gecko in the world, the 40-centimeter-long New Caledonian giant gecko (Rhacodactylus leachianus).

Gigarcanum – Fact sheet

Alternative name	Delcourt’s sticky-toed gecko, Delcourt’s giant gecko, Delcourt’s gecko, (Kawekaweau)
Scientific name	Gigarcanum delcourti, Hoplodactylus delcourti
Original range	New Caledonia (South Pacific)
Date of extinction	unclear, possibly in the middle of the 19th century
Causes of extinction	unclear, perhaps animals introduced to the islands, habitat loss

…but not the Kawekaweau

Due to its morphological characteristics and similarities with some very ancient oral traditions of the Maori regarding a giant lizard, Bauer and Russell assumed that the origin of the giant gecko must be New Zealand. They suspected that H. delcourti was the lost Kawekaweau, a huge forest lizard from Maori legends.

There is only one report of a person claiming to have seen a living Kawekaweau gecko. Records from Major W. G. Mair in 1873 indicate that a Māori chief killed a Kawekaweau in 1870. He discovered it under the bark of a dead Rata tree in the Waimana Valley in Te Urewera on the North Island of New Zealand. Mair reported that the chief described the animal as “two feet long and as thick as a man’s wrist; brown in color, longitudinally striped with dull red.”

So, several reasons suggested that H. delcourti originated from New Zealand: the report of the Maori who had killed such an animal, further Maori traditions about a similarly colored giant lizard named Kawekaweau, as well as morphological characteristics that correspond quite well with the New Zealand brown or gray gecko of the genus Hoplodactylus.

Experts therefore agreed for a long time that H. delcourti was the mysterious giant lizard Kawekaweau from New Zealand – until 2023, when a DNA analysis finally revealed the true origin of the giant gecko.

Kawekaweau became Gigarcanum

Since the 1980s, techniques for retrieving and analyzing ancient DNA have advanced, allowing scientists to extract new information from degraded museum samples, even from extinct species such as the dodo, the thylacine, or the bush moa.

Therefore, American herpetologist Matthew P. Heinicke, Bauer, and colleagues re-examined the mysterious giant gecko by extracting and analyzing aDNA from one of its thigh bones. The result shows that the presumed Kawekaweau giant gecko is not even closely related to existing Hoplodactylus or any other New Zealand gecko. This means that it is almost certain that H. delcourti is not the Kawekaweau from Maori narratives.

Additional sequence data from a broad DNA sample of diplodactylid geckos from the South Pacific island group of New Caledonia revealed that H. delcourti is a member of a clade whose living species are endemic to New Caledonia. The diplodactylid geckos of New Caledonia and those of New Zealand have been separated by about 45 million years of evolution. Based on further phylogenetic investigations, Heinicke and Bauer eventually assigned H. delcourti to a newly established genus: Gigarcanum.

New Zealand or New Caledonia?

Heinicke and Bauer also acknowledge in their study that while their DNA analyses show that Gigarcanum must have had at least one ancestor native to New Caledonia, it cannot be completely ruled out that the discovered giant gecko might have originated from New Zealand after all.

However, for it to have originated from New Zealand, its ancestors would have had to travel to New Zealand. Transoceanic dispersal of diplodactylid geckos is unlikely: Geckos like Gigarcanum either have parchment-like eggs or are viviparous, meaning their survival ability on driftwood in saltwater is limited, making a successful oceanic crossing unlikely. Furthermore, if Gigarcanum were indeed native to New Zealand, it would have had to develop an adaptation to the cooler climate of this region. Whether this adaptability existed, however, is unclear.

Trevor H. Worthy, a paleozoologist from New Zealand, was not particularly surprised by Heinicke and Bauer’s DNA analysis, as he had previously suggested that the giant gecko could originate from New Caledonia. He bases this on the absence of the giant gecko in New Zealand’s extensive fossil record, as such a large animal would likely have been found. However, other extinct geckos related to the largest extant New Zealand species, Duvaucel’s gecko (H. duvaucelii), have been documented. Worthy overlooks the fact that we also have no (sub)fossil remains of Gigarcanum from New Caledonia.

The Conservation Status of New Zealand Reptiles (2021) suggests that previous reports of large geckos in New Zealand are likely attributable to Duvaucel’s gecko, which reaches a total length of 30 centimeters. However, Duvaucel’s gecko does not match the descriptions of the Kawekaweau given by the Maori in terms of size and coloration, as Gigarcanum does. There are currently no other living or extinct reptile species in New Zealand that correspond to the Kawekaweau.

Conversely, there are no known reports from New Caledonia concerning a gecko larger than the New Caledonian gecko. On the other hand, New Caledonia is part of France, and the only specimen of the giant gecko was found in a French museum.

Overall, many indications suggest that Gigarcanum originates from the New Caledonian island group; Heinicke and Bauer also support this. The genetic analyses as well as the absence of subfossil remains in New Zealand support this assumption. The unlikely possibility of transoceanic dispersal and the potential adaptation to the cooler climate cast doubt on a New Zealand origin.

Why did Gigarcanum go extinct?

The International Union for Conservation of Nature (IUCN) estimates that the giant gecko Gigarcanum became extinct around the mid-19th century when the only known specimen was collected. The exact reasons for the extinction of this species are unknown, but possible causes can be inferred from the history of New Caledonia’s colonization and the resulting environmental changes.

The New Caledonian island group is a biodiversity hotspot, with its flora and fauna exhibiting a particularly high degree of endemism. Many animal and plant species exist only there and nowhere else in the world. The pristine habitat of New Caledonia, covering nearly 5,000 square kilometers out of a total area of more than 18,500 square kilometers, once included evergreen forests that once covered 23 percent of New Caledonia but now exist only on an area of about 45 square kilometers.

The global initiative Critical Ecosystem Partnership Fund (CEPF) states that since European colonization in the 18th century, New Caledonia has experienced significant environmental problems that have led to the decline or extinction of some species. Besides hunting, nickel mining, which has led to extensive deforestation and habitat destruction, and introduced invasive species are the main threats.

Especially the deliberate or accidental introduction of foreign species for food or recreational purposes has had devastating effects on the island group. Nearly 800 alien plant species, more than 400 alien invertebrates, and about 35 alien vertebrate species have established themselves on the islands, displacing much of the original flora and fauna. Most of the problems are associated with black rats (Rattus rattus), the Javan deer (Rusa timorensis), and the electric ant (Wasmannia auropunctata). In addition, pigs and cats are widespread throughout the main island at all altitudes. Originally, the only endemic mammals in New Caledonia were bats (Chiroptera).

The causes of the extinction of the giant gecko Gigarcanum likely lie in the destruction of its habitat due to deforestation and the threat posed by invasive mammal species such as cats, rats, and pigs, which prey on the gecko’s eggs or young. If the giant gecko was indeed native to New Zealand, the causes of extinction would essentially be the same.

Gigarcanum: Arboreal and nocturnal

Belonging to the family of diplodactylid geckos, Gigarcanum likely climbed trees – indicated by the pads and long claws on its toes. Heinicke mentioned in this context that the species had probably reached the maximum size at which a gecko could still cling to vertical surfaces with its characteristic sticky grip.

Based on comparisons with its living relatives, the Gigarcanum giant gecko was likely a nocturnal predator large enough to prey on birds, lizards, including other geckos. However, its main diet probably consisted of invertebrates (such as insects, spiders, or centipedes), and it may have consumed fruits seasonally. Whether Gigarcanum was an egg-laying or viviparous gecko is uncertain.

Could the giant gecko Gigarcanum still exist?

When European explorers reached New Caledonia in the late 18th century, Gigarcanum must have already been extinct or extremely rare, as there are no reports of such a gigantic gecko from there. In their scientific description in 1986, Bauer and Russel considered the possibility of a small relict population surviving, but they assumed it would be on the North Island of New Zealand. They also acknowledged that if the species survived, it would have been in small numbers for over a century.

Subsequent authors were more inclined to believe that Gigarcanum was extinct. Since both New Caledonia and New Zealand are well-explored herpetologically, Heinicke and Bauer stated in their 2023 study that it is highly unlikely that the giant gecko Gigarcanum has survived to the present day.

However, new gecko species continue to be discovered on the islands of New Caledonia, so it is not entirely implausible that Gigarcanum still exists. As a nocturnal animal that may also inhabit beneath tree bark, the giant gecko could still be living undiscovered in the more remote forests of New Caledonia…