The Zealandia animal sanctuary said the tuatara breached the sanctuary's predator-proof fence and was discovered Sunday by Lorna Borrett, who was walking her dog near the Wellington sanctuary's fence, the Dominion Post reported Tuesday.
Borrett said she had never before seen a tuatara and called her partner, Jacob Rosevear, to help her identify the lizard with an injured tail.
"I only knew of tuatara through the brand of beer, which Jacob drinks," she said.
"It was kind of a cool experience -- there can't be that many people in the world that have come across a tuatara in the wild," she said.
The couple contacted Zealandia rangers and the lizard was taken to the Wellington Zoo's hospital.
"The tail is badly damaged and we will operate on him today so we can assess how bad the damage is. It is likely it will require further amputation," veterinarian Baukje Lenting said.
The sanctuary said the male tuatara would have been unlikely to survive long outside the sanctuary's fence due to the high population of local predators.