The gastric-brooding frog was a small species of frog that lived in Australia until it went extinct in the 1980's. This was a unique frog with an incredibly unusual method of caring for its young. Normal frogs lay their eggs in water, where they hatch into tadpoles that eventually metamorphose into little froggies. Fish, turtles, birds, and many other animals consider frog eggs and tadpoles to be quite tasty, so most never make it to the terrestrial stage. The gastric-brooding for, however, has solved this problem by swallowing its eggs and letting them hatch, swim, and metamorphose inside its stomach.
When the little tadpoles have become frogs, the parent urps them up and sends them off to live their lives.
Can you imagine swallowing your baby and barfing up a teenager years later?