(CNN) -- At well over 100 years old and showing no interest in sex for over four decades, Henry is on his way to becoming a dad.

Henry, the oldest tuatara to mate at Southland Museum, enjoys a cold shower in his home in New Zealand.

Henry is a tuatara, a rare lizard-like creature that descended from dinosaurs. The tuatara has been endangered since the 1890s, and it's only found on a handful of New Zealand's offshore islands.

At about 110 years old, Henry is the oldest tuatara ever to mate at Southland Museum on the country's South Island.

"I had given up on old Henry," said curator Lindsay Hazley.

He kept Henry in "solitary confinement" because the animal not only showed no interest in females but attacked them when they were looking to mate.

The beginning of Henry's libido rebound came in 2002, when veterinarians realized that a lump in the animal's nether regions was a cancerous tumor. They removed it and, over the next few years, his attitude began to change.

"I say that he had a personality transplant at the same time," Hazley said Thursday. "If I had a tumor underneath my [genitals], when girls were passing by, I'd be a very grumpy boy too."

In March, Henry mated with Mildred, whose age is estimated between 70 and 80. Last month, she laid 12 fertile eggs, 11 of which remain healthy.

Healthy hatchlings would be a boost for the tuatara, who are the only living descendants of the order Sphenodontian, which flourished 200 million years ago.

They max out at about 32 inches from head to tail -- much smaller than their ancestors -- but the spiny ridges along their back suggest their prehistoric parentage.

The word "tuatara" is derived from a Maori word meaning "spiny back." In Maori legend, they are messengers of Whiro, the god of death and disaster, and they were featured on one side of a New Zealand five-cent coin that was phased out in 2006.

Hazley estimated that as many as 40,000 tuataras live on one of New Zealand's tiny, outlying islands, with much smaller populations on several others.

There are 51 at Southland Museum, where Hazley, who has cared for tuataras for the past 35 years, has been breeding them. He said he hopes Henry and Mildred's hatchlings will be the latest success. Watch curator take care of the reproducing dinosaur kin »

"I'm excited, but I don't want to get too excited because Mother Nature's always got the power to ground you," he said. "I really don't like counting the chickens before they hatch, but each day that goes by, I'm becoming more confident they're going to be fine."

As for Henry, his best years as a ladies' man may be ahead of him. At 110 years old, he's just hitting middle age for a species that can live well past 200.

"I think he'll be at these girls long after I'm gone," Hazley said.

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