Overview
The Southern Gastric-brooding Frog (Rheobatrachus silus) is universally regarded in evolutionary biology as one of the most astonishing, miraculous, and tragic amphibians in history. Discovered in 1972 in the mountain streams of Queensland, Australia, this small, aquatic frog possessed a reproductive phenomenon utterly unique among all animals: the female swallowed her fertilized eggs, turned off her stomach acid, and incubated her developing young inside her stomach before giving birth to live froglets through her mouth. Suddenly vanishing into extinction in 1981, it is today the premier global candidate for genetic de-extinction.
Biology and Physical Characteristics
Rheobatrachus silus was a robust, highly aquatic frog featuring smooth, slimy skin, a blunt snout, large upward-facing eyes, and colossal, fully webbed hind feet optimized for swimming against torrential mountain currents. Its coloration was a dull, mottled greyish-brown to slate-olive across the dorsum, with a pale cream-yellow belly and distinctive bright orange or yellow patches in the groin and under the thighs. Its gastrointestinal physiology was a scientific marvel: developing embryos secreted prostaglandin E2, a biological hormone that completely shut down the mother’s gastric hydrochloric acid and digestive enzyme production, converting her stomach into a living, brooding womb without digesting her offspring.
Behavior and Ecology
Completely aquatic, the Southern Gastric-brooding Frog lived submerged among submerged granite boulders and cascading waterfalls, rarely leaving the water. During the six-week brooding period, the mother’s stomach expanded dramatically until her lungs collapsed; she ceased eating entirely and breathed exclusively through her skin. When the 15 to 25 froglets completed metamorphosis, the mother underwent propulsive esophageal contractions, widely opening her mouth as fully formed baby frogs hopped out of her mouth into the mountain stream. Within seven days of birth, her stomach acid reactivated, and she resumed normal hunting.
Conservation and Human Impact
The Southern Gastric-brooding Frog is classified as Extinct on the IUCN Red List. First discovered in 1972, its populations abruptly plummeted and vanished entirely from the wild by 1981, with the last captive individual dying in 1983. Scientists later identified the invasive amphibian chytrid fungus (Batrachochytrium dendrobatidis) as the catastrophic agent of its sudden demise. Because tissue samples were cryopreserved in liquid nitrogen, the ‘Lazarus Project’, led by Australian geneticist Mike Archer, is actively utilizing somatic cell nuclear transfer (cloning) to resurrect the species, successfully growing early-stage embryos in a historic bid for de-extinction.
Interesting Factoid
The Southern Gastric-brooding Frog is the only animal in history that converted its stomach into a womb—the mother swallowed her fertilized eggs, shut off her stomach acid, and weeks later gave birth by literally coughing baby frogs out of her mouth.