Amphibians
Gastric-brooding Frog
Rheobatrachus silus · also called southern gastric-brooding frog, platypus frog
The gastric-brooding frog did something no other animal is known to have done: it turned its stomach into a womb. The female swallowed her fertilised eggs, switched off her own digestion, carried the developing young for six weeks, and then coughed up a mouthful of finished froglets. Within about a decade of being discovered, it — and its only close relative — were gone.
Overview
There were two gastric-brooding frogs, both from small, cool, rocky rainforest streams in the ranges of southeast Queensland, Australia. They were highly aquatic, slippery, mottled olive frogs with webbed feet and upturned eyes, spending most of their time in or right beside the water.
A stomach for a womb
After spawning, the female swallowed 20–25 fertilised eggs. A substance released first by the eggs and then by the tadpoles — prostaglandin E2 — shut down her stomach acid, enzymes, and churning, converting the organ into a brood chamber. The young grew there for six to seven weeks on their yolk. The female could not eat the entire time, and her hugely distended stomach so compressed her lungs that she breathed mainly through her skin.
Birth by mouth
When the froglets were ready, the female gaped wide and brought them up — over a day or more, singly or in groups, sometimes with real force. One captive female, startled, expelled all six of her young at once. Afterward her stomach slowly returned to normal.
Discovered, then lost
- Southern species: described 1973, last seen in the wild 1981
- Northern species: found 1984, gone by 1985
Both had tiny ranges and no room for error. The leading cause is the amphibian chytrid fungus, which was sweeping through Australian stream frogs at that exact time, compounded by logging, feral pigs, sedimentation, and drought.
Status
The gastric-brooding frog is Extinct. The Australian “Lazarus Project” has used cloning with frozen 1970s tissue to make early embryos carrying its DNA, but none has developed past a few days, and no living frog has been recreated.
Gastric-brooding Frog: common questions
How did the gastric-brooding frog raise its young in its stomach?
After the male fertilised the eggs, the female swallowed about 20 to 25 of them. Normally this would digest them, but the eggs — and later the tadpoles — released a hormone-like substance, prostaglandin E2, that shut off the secretion of hydrochloric acid and digestive enzymes in her stomach and stopped the muscular churning. Her stomach essentially stopped being a stomach and became a brood chamber. The young developed there for six to seven weeks, nourished entirely by the large yolk in their eggs, while the female could not feed and her lungs were so compressed by her swollen stomach that she breathed largely through her skin.
How did the babies come out?
The female "gave birth" through her mouth. When the froglets were ready, she would gape widely and, over a period that could last more than a day, bring them up — sometimes one at a time, sometimes in small groups — occasionally with enough force to fling them several centimetres clear. Once all the young were out, her stomach gradually returned to normal function and she could eat again. In captivity, a startled female was once seen to expel her entire brood of six at once in a single convulsive "vomit."
Why did the gastric-brooding frog go extinct?
It went from discovery to extinction with shocking speed — the southern species was named in 1973 and gone from the wild by 1981; the northern species was found in 1984 and gone by 1985. The frogs lived in a handful of small, cool, rocky rainforest streams, so they had almost no buffer against anything going wrong. The prime suspect is the amphibian chytrid fungus (Batrachochytrium dendrobatidis), which was spreading through Australian frog populations at exactly that time and hit stream-dwelling species especially hard. Logging, feral pigs, sedimentation, drought, and pesticide drift in the catchments probably contributed.
Could the gastric-brooding frog be brought back?
There is an active attempt. The "Lazarus Project," led by Australian scientists, has taken frozen tissue from gastric-brooding frogs preserved since the 1970s and used cloning techniques — transferring the nuclei into donor eggs of a related living frog — to produce early-stage embryos containing gastric-brooding frog DNA. As of the mid-2020s none of these embryos has developed past a few days, and a living adult has not been recreated. Even if one were, whether a self-sustaining wild population could be re-established in a landscape that still contains chytrid is an open question.