Peramorphosis

In developmental biology, peramorphosis is a phylogenetic change in which individuals of a species mature past adulthood and take on hitherto unseen traits. It is the reverse of pedomorphosis.

"hypermorphosis" is a form of peramorphosis which represents a delay in the offset of development.

Peramorphosis in fiction

 * The Pak Protectors in Larry Niven's Known Space universe.