The baby tuatara was discovered by staff during routine maintenance work at the Karori Wildlife Sanctuary in the capital, Wellington, its conservation manager, Raewyn Empson, said.

"We are all absolutely thrilled with this discovery," Ms Empson said. "It means we have successfully re-established a breeding population back on the mainland, which is a massive breakthrough for New Zealand conservation."

Tuatara are the last lizard-like descendants of a reptile species that walked the Earth with the dinosaurs 225 million years ago, zoologists say.

There are estimated to be about 50,000 of them living in the wild on 32 small islands cleared of predators, but this is the first time a hatchling has been seen on the mainland in about 200 years.

Tuatara were nearly extinct on the country's three main islands by the late 1700s due to the introduction of predators such as rats.

Ms Empson said the hatchling was thought to be about one month old and likely came from an egg laid about 16 months ago. Two nests of eggs were unearthed in the sanctuary last year and tuatara had been expected to hatch at about this time.

"He is unlikely to be the only baby to have hatched this season, but seeing him was an incredible fluke," she said.

The youngster faces a tough journey to maturity despite being in the 250-hectare sanctuary and protected by a predator-proof fence.

It would have to run from the cannibalistic adult tuatara, and would make a tasty snack for the morepork [native owl], kingfisher and weka [endemic flightless rail], Ms Empson said.

Lindsay Hazley, the tuatara curator at the Southland Museum and Art Gallery in the South Island, said they had been extinct on the mainland for a long time. "You can breed tuatara by eliminating risk, but to have results like this among many natural predators [like native birds] is a positive sign," he said.

Associated Press