A new genus and species of lydekkerinid amphibian, Eolydekkerina magna, is described from the lower part of the Lystrosaurus Assemblage Zone of South Africa. Most distinctions between Eolydekkerina and Lydekkerina (other than those related to width of interorbital area and structure of choana and squamosal occipital flange) are linked to late growth stages and particularly preorbital elongation of the skull in the former genus. The developmental trends in Lydekkerina and the Lydekkerinidae in general are analysed by comparison with the cranial pattern of juvenile rhinesuchids. The evidence suggests that the Lydekkerinidae evolved from more fully developed capitosauroid (rhinesuchid-like) ancestors by gradual truncation of ontogeny in parallel with the acquisition of many advanced features, unknown in the Permian capitosauroids. The composition of the Lydekkerinidae is reviewed, and it is suggested that the family includes six to seven valid genera known from Antarctica, Greenland, India, Russia, South Africa and Tasmania. The smaller, and obviously most paedomorphic forms come from the reptile-dominated assemblages in which Lystrosaurus is abundant, whereas the larger ones belong to amphibian-dominated assemblages.