Paedomorphosis

Paedomorphosis is an evolutionary pattern in which adults retain traits that were juvenile in their ancestors, often because development is slowed or altered.

Heterochrony: Evolutionary change in the timing or rate of development relative to an ancestor. Paedomorphosis is one outcome of evolutionary changes in developmental timing.
Axolotl: A Mexican salamander that commonly reaches reproductive maturity while retaining larval features, including external gills. Its persistent larval form is a celebrated example of paedomorphosis.
Peramorphosis: An evolutionary pattern in which descendants develop beyond the ancestral adult form. It contrasts with paedomorphosis, which retains ancestral juvenile features.
Metamorphic life cycle: A life cycle with distinct immature and adult forms separated by metamorphosis. Paedomorphosis can remove or reduce the transition between aquatic larva and terrestrial adult.
Ontogeny: The course of development of an individual organism from its earliest stage to maturity. Comparing ontogenies reveals which ancestral juvenile traits persist into adulthood.
Axolotl neoteny: The retention of aquatic larval traits by sexually mature axolotls, associated with reduced thyroid-driven metamorphosis. It shows how paedomorphosis can arise when metamorphosis is limited.
Metamorphosis: A developmental transformation in which an animal changes substantially in form after an immature stage. Complete metamorphosis replaces juvenile traits rather than retaining them in the adult.
Polyphenism: The production of distinct phenotypes from the same genotype in response to environmental conditions. Some salamanders express paedomorphic or metamorphic forms depending on environmental conditions.
Sexual maturity: The developmental state at which an organism can reproduce. Its timing relative to body development distinguishes major paedomorphic mechanisms.
Ambystoma tigrinum: A tiger salamander species whose populations may develop either as terrestrial adults or as aquatic, gilled adults. Its contrasting life histories show paedomorphic and metamorphosing forms within one species.

Linked from 9 pages