Antoinette and Brucie-Baby, believed to be the world's oldest geckos, found on New Zealand's Motunau Island. (Photo Credit: Department of Conservation NZ via CNN Newsource)

(CNN) — At 64 and 60 years old, Antoinette and Brucie-Baby are thin and bony. Their skin hangs looser than it did in their youth, but their eyes still gleam with energy.

But these aren’t just any sexagenarians we’re talking about; these are geckos, believed to be the world’s oldest on record, discovered on a small island in New Zealand.

Marieke Lettink, an expert on reptiles and amphibians, was part of the team that found the pair of Waitaha geckos on Motunau Island, off the coast the country’s South Island. It was an “exciting” moment, she said, adding that it was humbling to realize “that these animals are older than us and still out there doing their thing.”

They were found during a five-yearly survey on the island. “That also means it’s worth going back in five years’ time because we don’t actually know how long they can live for. Every time we go, every trip we’ve done … the oldest gecko we catch is always older than us,” Lettink said.

During each survey, the team sets up a grid of traps on the small island, typically catching a few hundred geckos over a few days. The geckos come out at night – so the team also goes trekking in the dark with flashlights to look for geckos perched on leaves and bushes.

The surveys have been going on since the 1960s, when the late conservationist Tony Whitaker began marking geckos on the island with a practice called toe clipping – which involves clipping a certain number of toes on the geckos, each with a unique pattern. The practice is no longer used by New Zealand’s Department of Conservation.

It was Whitaker’s markings on Antoinette and Brucie-Baby – named after Whitaker and fellow conservationist Bruce Thomas – that helped Lettink identify the lizards.

“It made me think of Tony, who started the work. It was quite a poignant moment,” she said.

Both geckos were fully grown when they were marked – so they could be even older than the 60 and 64 years recorded.

That’s far older than the average lifespan of geckos worldwide, at only about a decade. And this discovery places Waitaha geckos in the top ranks of other long-living lizards – most of which are far larger and better known.

“It’s now actually bypassed all the older lizards, with things like the iguanas and the big Komodo dragons – you know, really big lizards that are quite famous,” Lettink said. “And this is a humble, drab brown gecko that’s not famous at all.”

There are a few reasons it may have lived so long – the main one being that Motunau Island is predator-free, without any of the introduced species that have decimated native animals across mainland New Zealand.

The success of reptile survival in predator-free spaces is one reason conservationists across the country are trying to establish more safe sanctuaries – for instance, building a fenced area to keep predators out and eliminating invasive predators within.

But skewing the ecosystem that way can allow mice populations to thrive. They can prey on geckos, posing another problem, Lettink said – so some groups have set up specific sanctuaries just for lizards and geckos.

There are other factors behind their longevity too – like the cool climate and the island lifestyle, said the Department of Conservation’s Biodiversity Ranger Kaitlyn Leeds, who was on the survey team with Lettink, in a news release.

The team had actually seen Antoinette once before, about a decade ago, and they assumed that would be the last time. “And here, 10 years later, they look no different – they’re still going,” Lettink said.

It makes her hopeful that by the next survey, in five years, they might be able to find a few more of the original geckos tagged in the 1960s. Or better yet – there might be many older geckos out there that just haven’t been found yet. “That would be really exciting,” she said.

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