In this file photo, a tiny froglet can be seen in the mouth of its mother, the southern gastric-brooding frog Rheobatrachus silus. (Related: "Resurrecting the Extinct Frog with a Stomach for a Womb.")
In this novel form of parental care, the female swallowed her fertilized eggs. Her stomach then stopped producing acid, becoming a makeshift womb. Later, she regurgitated fully formed froglets. (Watch a video of a frog father spitting out his young.)
Two species of gastric-brooding frogs made their homes in creeks in a relatively small area of tropical forest in Queensland, Australia: R. silus and the northern gastric-brooding frog, R.vitellinus.
The species were discovered in 1973 and 1984, respectively, but by the mid-1980s they had both disappeared, possibly due to habitat degradation, pollution, and disease, including chytrid fungus.
A few specimens of gastric-brooding frogs are preserved in Australian museums, leading scientists to ponder whether the animals could be reborn. (Related pictures: "Extinct Species That Could Be Brought Back.")
Now, scientists with the Lazarus Project have started to revive R. silus using cloning technology—the first attempt to revive any vanished species and a play to "get over this idea that extinction is forever," project leader Mike Archer told National Geographic.
Archer was speaking at Friday's TEDx Conference on DeExtinction at National Geographic headquarters in Washington, D.C.
As part of the project, Archer and colleagues have implanted a "dead" cell nucleus from a frozen gastric-brooding frog into a fresh egg from a distantly related frog species, the great barred frog.
During five years of experiments, the team has been able to get some of the eggs to spontaneously divide and grow into early embryos. (Related: "How to Resurrect Lost Species.")
Although none of the embryos survived more than a few days, genetic tests confirmed that the dividing cells contain genetic material from the extinct frog, according to the team.
Archer, of the University of New South Wales in Sydney, isn't sure why they can't get past the embryo stage, but he suspects it may have to do with how the scientists are handling the eggs-a process that his team is working on right now.
"We're all very optimistic that we're going to get this frog hopping glad to be back in the world."
—Brian Howard and Christine Dell'Amore