She's around 80 years old. He's 100. Breathless scientists watched as the world's most endangered turtles successfully mated.
But the attempt to breed the species' last known female with the last known male in China has failed because the eggs didn't hatch, disappointed conservationists said Saturday.
The elderly pair can try again next year, part of a delicate attempt to keep the species alive.
Just four known Yangtze giant soft-shell turtles are left, and three are male.
The only female was found in a Chinese zoo just last year after a long and desperate search. She was quickly protected with a surveillance camera, a guard and bulletproof glass, and given the nickname "China Girl."
A successful batch of baby turtles would be a welcome environmental win for China. The country's efforts to save its pandas are famous, but scientists have said about 40 percent of China's mammal species are endangered. Pollution and hunting almost erased the Yangtze turtles.
Conservationists were thrilled this spring when the female and male finally were introduced, nudged each other curiously and slowly got down to business. Artificial insemination was deemed too risky.
Within weeks, dozens of eggs were found in the sandy nesting area at the Suzhou Zoo, about an hour's drive west of Shanghai. Conservationists predicted possible hatchlings by early August. But this week, they said the effort had failed.
"Unfortunately, none of the eggs successfully hatched this time," Stephen C. Sautner, a communications official with the Wildlife Conservation Society, said in an e-mail Saturday.
While more than half of the eggs seemed fertile, the embryos died early, a statement released Wednesday by the U.S.-based Turtle Survival Alliance said.
The statement did not indicate whether the female turtle's age was a factor and instead blamed years of a low-calcium diet.
"A number of the eggs had very thin or cracked eggshells, suggesting that the diet of the animals prior to breeding was not optimal," the statement said.
Besides the pair that mated, the only other known Yangtze turtles are two males in Vietnam.
For years, the female turtle's keepers at the Changsha Zoo hadn't even known what kind of turtle she was or that she was one of the last of her kind.
The zoo responded last year to an urgent appeal sent to all of China's zoos, saying it had a female that looked like the turtle in the photo sent with the appeal.
A team of experts from the U.S. and China then prepared her for the potentially stressful move to the Suzhou Zoo, about 600 miles away.
"I hate to call this a desperation move, but it really was," Rick Hudson, co-chair of the turtle alliance, said at the time.
Now, settled together in Suzhou, the two turtles are preparing for another attempt next year with a high-calcium diet of whole fish, whole crayfish and chicken necks, meant to result in eggs with stronger shells.
During a visit to the zoo Saturday, the turtles were nowhere to be seen. Their watery home was split by a metal gate to keep the male and female separate until the next breeding season. The male can be too aggressive otherwise, workers explained.
"We've worked very hard on this," said Liu Jinde, the director of the organization that manages the zoo. "Wait until next year. We ought to succeed. The turtles are very healthy."
He said one reason breeding failed this year was the hurry to get the turtles mating soon after the female joined the male at the zoo this spring.
There is, after all, not much time left. Though it isn't clear how long Yangtze turtles can live, the female's fertility is the key.
Conservationists had been relieved when the newly discovered female at 80 years or more was still producing eggs.
Now the turtles' supporters must wait until spring, when the female should be ready for the next attempt.
The turtle alliance is optimistic. Despite their advanced ages, the two turtles "should be in top form" next year, its statement said.