Helping solve the mystery of world's largest gecko

July 17, 2023

Professor Matthew Heinicke extracted DNA from a femur to clarify origin of the almost 2-foot-long lizard.

The front and underside of a 2-foot long taxidermy gecko

For nearly 200 years, a mysterious giant gecko sat in a French natural history museum’s storage area. No one knew anything about it except that the Natural History Museum of Marseille’s records show it had been there since at least the 1870s and the style of taxidermy pointed closer to the 1830s.

Its size got the attention of researchers who wanted to know more. Larger than any gecko known today, its main body was 380 millimeters or nearly 15 inches — and with the tail, it’s nearly two feet long. Giving a comparison, today’s largest gecko species is in New Caledonia, the archipelago east of Australia. The largest known of those measured about 10 inches, minus the tail.

Helping uncover the mystery is noted herpetologist and CASL Professor Matthew Heinicke. Heinicke said a frequent research collaborator of his, Villanova University Biology Professor Aaron Baur, learned about the gecko from the French museum in the mid-1980s. But DNA analysis wasn’t advanced enough at that time to get conclusive results. About a decade ago, Baur reached out to Heinicke to get involved with this extensive research project.

“For most of the 19th and 20th centuries, the broader scientific community didn't have knowledge of this specimen’s existence until one of my colleagues became aware of it,” said Heinicke, who reached out to the museum with Baur and asked for tissue samples. “We hoped that DNA technology, which they obviously didn’t have at that time, would be able to tell us a lot more about it.”

Known in the scientific community for his reptile DNA analysis work, Heinicke received the specimen’s femur from the museum so that he could extract and analyze its DNA makeup in his UM-Dearborn lab.

Researchers originally thought the gecko was from New Zealand based on similar physical characteristics–like toe pads and color patterns – to the country’s geckos. In addition, it resembled a lizard known in folklore from the Māori, the indigenous Polynesian people of mainland New Zealand. Herpetologists felt so confident in their hypothesis that they scientifically named it Hoplodactylus delcourti. Hoplodactylus refers to geckos originating from New Zealand and Delcourt is the last name of the museum worker who rediscovered it.

So did this giant gecko, which is presumed to be extinct, come from New Zealand? 

To answer this question, Heinicke, his co-researchers from across the nation and his UM-Dearborn undergraduate student research assistants created a dataset that included DNA from 160 species of gecko, essentially creating a family tree. Heinicke then dropped the giant gecko’s DNA sample into the dataset to see where it falls.

They learned the mystery gecko is not from New Zealand. Instead, it’s related to those large — but not as giant — geckos from New Caledonia. The team’s findings were recently published in Scientific Reports and featured in ScienceNews. Heinicke and his colleagues are proposing a change in the lizard’s scientific name. They have dubbed it Gigarcanum, or “giant mystery.”

The importance of this new finding? Heinicke said it helps us understand how different species evolve.

“It’s really nice to live on a planet that has so much variety,” he said. “One of the big questions in the evolution of biology is what are the big factors that promote the evolution of diversity? What causes organisms to change and differentiate from one another? Isolation, when there is a lack of competition, seems to be one of these things. We want to better understand these evolutionary processes because they help explain where biodiversity comes from.”

“Now that we have identified its closest living cousins, we can start to investigate how it adapted to become so large compared to other geckos,” he added.

Also, if there are any more giant geckos out there, researchers and reptile enthusiasts now know where to look.

Article by Sarah Tuxbury and contributor Kristin Palm.