Archaeomalthus synoriacos gen. et sp. nov. from the Upper Permian Babiy Kamen` locality indicates a remarkable evolutionary stability. Herein we report the oldest record of the family Micromalthidae, Archaeomalthus synoriacos gen. et sp. nov., which demonstrates several plesiomorphic character states, but generally retains most of the apomorphies of Micromalthidae. Archaeomalthus suggests that a distinct simplification of the morphology of adults already evolved in the late Paleozoic, suggesting and early reduction of the role of adults in the life cycle of the group. Despite the marked differences between Archaeomalthus and Micromalthus, the former already show a distinct and apparently very stable degree of deviation from the ground plan of Coleoptera s.str. and s.l. The remarkable series of reductional features shared by the Permian fossil and the extant species include a lightly sclerotized body without distinct surface sculpture, a head lacking dorsal protuberances, shortened and apparently thin elytra, exposed membranous areas behind the procoxae and between at least two basal visible abdominal sternites, and the reversal of the invagination of the terminal abdominal segments. It is likely that the reduced role of adults of Micromalthidae was a syndrome of simplified, vestigial adult morphology characters acquired at least 255 million years ago.