Progenesis (or paedogenesis) can be observed in the axolotl ("Ambystoma mexicanum"). Axolotls reach full sexual maturity while retaining their fins and gills (in other words, still in the juvenile form of their ancestors). They will remain in aquatic environments in this truncated developmental form, rather than moving onto land as other sexually mature salamander species. This is thought to be a form of hypomorphosis (earlier ending of development) that is both hormonally and genetically driven. The entire metamorphosis that would allow the salamander to transition into the adult form is essentially blocked by both of these drivers.