Foregut fermentation is a form of digestion that occurs in the foregut of some animals such as the hamster rat, langur monkey, and the hippopotamus. [1] It has evolved independently in several groups of mammals, and also in the hoatzin, a bird species.
Foregut fermentation is employed by ruminants and pseudoruminants, some rodents and some marsupials. [2] It has also evolved in colobine monkeys and in sloths. [3]