Bizarrely, many species of animals, such as the carp and platypus, lost their stomachs in the evolutionary past, and new research suggests they may never evolve the organs back.
The stomach is the part of the gut where the main part of digestion takes place. Glands in this organ secrete enzymes known as pepsins, which break down proteins, and strong acids that soften food and help the enzymes work. The glands first appeared about 450 million years ago, and they represent an evolutionary innovation found exclusively in jawed creatures with backbones.
Read the full, original story here: Why the Platypus Will Never Have a Stomach