Vitamin C
Most species of animals synthesise their own vitamin C. It is therefore not a vitamin for them. It is made by a series of enzyme-driven steps which convert glucose to ascorbic acid. This is done either in the kidneys (reptiles and some birds), or the liver (mammals and perching birds). The loss of an enzyme which is essential for ascorbic acid synthesis has occurred quite frequently in evolution. It has happened in most fish, many birds; some bats, guinea pigs and most but not all primates, including humans. The mutations have not been lethal because ascorbic acid is so common in various food sources, especially fruit.