Pedomorphosis

In developmental biology, pedomorphosis (also spelled paedomorphosis) or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Peramorphosis is change in the reverse direction. Pedomorphosis was first proposed by Walter Garstang in 1922. The underlying mechanisms for this include heterochrony.

There are several kinds of pedomorphism which may appear independently or in combination:
 * Neoteny, in which somatic (or physical) development is slowed, resulting in a sexually mature juvenile or larval form.
 * Progenesis, in which development is halted before full maturity.
 * Postdisplacement, in which the start of development is delayed.

Fauna
Natural paedomorphosis occurs in many species of amphibians, especially ambystomatid and protean salamanders. In amphibians it can be obligate or facultative. Some salamanders retain their gills during adulthood, unlike most other amphibians. It is assumed that at some point in the past, they too would lose their gills, but some genetic change caused them to be retained, at a point where it was evolutionarily advantageous or neutral. A specific example of an amphibian species which exhibits paedomorphism is the Northwestern Salamander population at Crater Lake, Oregon, USA. Paedomorphosis also occurs in termites and several species of cockroach.