Why do axolotls keep their gills when they grow up?

Axolotls are a famous example of neoteny, the retention of larval features in a sexually mature animal. Unlike many salamanders, they do not normally undergo the hormone-driven metamorphosis that would remove their feathery external gills and shift them fully onto land. In the wild, this is tied to their aquatic life in the Xochimilco system near Mexico City. Scientists have long studied axolotls because their unusual development is linked to regeneration and thyroid hormone signaling. They are one of the best-known amphibians in biology and conservation research.