The procedure that created the bantengs has given animal conservationists hope that cross-species breeding can help reverse the daily disappearance of 100 living species and add genetic diversity to dwindling animal populations.
If they survive, the two bantengs will be transferred to the San Diego Wild Animal Park and encouraged to breed with the captive population there.
The technology is still fraught with problems and a long way from paying significant dividends. The cloned bantengs, for instance, won't begin breeding until they reach maturity in about six years.
Nonetheless, animal conservationists are excited about the two unnamed bantengs.
"The fact that it can happen at all just astounds me," said Oliver Ryder, a geneticist at the San Diego Zoo's Center for Reproduction of Endangered Species.
As CBS News Correspondent Sandra Hughes reports, while the news of the births is astonishing, it also worries some conservationists.
"If you don't deal with protecting habitat and dealing with the root causes of endangerment, it doesn't matter how many animals you're able to produce in a lab and try to sort of fling back into the wild, they're going to face the same fate as their wild counterparts," says Karen Baragona of the World Wildlife Fund.
The scientists at Advanced Cell Technology in Massachusetts, where both the banteng and gaur were cloned, agree to some extent.
"However, it doesn't make much sense to preserve habitat if you don't have the animals to preserve," says Robert Lanza.
In 1977, the zoo began preserving cells and genetic material from hundred of animals in a program it dubbed the Frozen Zoo. Tissue samples from each animal are stored in small plastic vials, which are submerged and frozen in liquid nitrogen at minus-196 degrees Centigrade.
"At the time we did not know how this resource might be used, but we knew it was important to save as much information about endangered species as we could," Ryder said.
Now, that foresight is beginning to pay off with the banteng, a white-stockinged animal hunted for its slender, curved horns. Fewer than 8,000 bantengs exist in the wild, mostly on the island of Java.
Ryder and his colleagues sent frozen skin cells from a long-dead banteng to researchers at the cloning company Advanced Cell Technology. Scientists there fused the banteng skin cells with 30 cow eggs that had their genetic material removed.
Another biotechnology company, Trans Ova Genetics, of Hull, Iowa, then implanted the cloned eggs into cows in Sioux City, Iowa, and 16 pregnancies resulted.
Of the 16 pregnancies, only two came to term last week and one of the bantengs is 80 pounds, about twice as heavy as expected. The researchers are concerned about the fatter banteng's prognosis: It's not nearly as active as his brother, born with normal birth weight.
This is not the first cross-species cloning experiment that resulted in a birth. Two years ago, a cow gave birth to an endangered cloned wild ox named Noah. But Noah died two days later of dysentery.
All of which underscores the many problems with cloning technology.
Animal rights activists criticize cloning's low success rate as cruel. Even same-species cloning has a high failure rate, and surviving animals are often less healthy than naturally born animals.
Dolly the sheep, the first cloned mammal, was put to death in February after premature aging and disease marred her short existence. The decision to end Dolly's life at age 6 about half the life expectancy of her breed was made because she had a progressive lung disease.
Others fear scientists will embrace cloning technology at the expense of tried-and-true conservation practices like habitat preservation and conservation.
But Ryder and others who embrace the technology say they would be remiss to ignore cloning, which can augment, rather than replace, existing methods.
Despite conservation efforts, habitats around the world are still disappearing quickly.
"Look at Iraq," said Betsy Dresser, director of the Audubon Institute Center for Research of Endangered Species in New Orleans. "Nobody mentions it, but I'm sure wildlife is disappearing there."
Dresser's projects include working to impregnate domestic felines with cloned endangered wild cats.
"Cloning could be a powerful tool," Dresser said. So far, though, she hasn't succeeded in bringing such a cat to term.
Researchers in China, meanwhile, are working with rabbits as surrogates for cloned pandas, which are about the size of a stick of butter when they're born.
There's even talk about bringing extinct animals like the woolly mammoth back to life, a premise Ryder dismisses as unrealistic.
Genetic material from the woolly mammoth and other extinct animals has never been properly stored in high-tech freezers like those at the San Diego Zoo, so their DNA has long since disappeared from the planet.
"There needs to be an expanded effort to bank more cells from endangered animals," Ryder said.