The replacement of molariform teeth has been documented for the Early Cretaceous gobiconodontid eutriconodontans (Gobiconodon, Repenomamus, and Spinolestes). It was also assumed for the amphidontid eutriconodontan Acinacodus from the Early Cretaceous of Western Siberia, Russia, based on differential wear of lower molars. Here we report on a new specimen of Acinacodus, which preserves a partially mineralised replacing tooth in the first molariform locus. This specimen also shows slit-like pits along the alveolar border lingual to m1-3, which are interpreted as the dental lamina pits (openings for gubernacular canals). The replacement of lower molariforms in Acinacodus occurred in one wave, which affected anterior molariforms (m1-3). The posterior molariforms (m4-5) and premolars (p1-2) possibly were not replaced. The p1, or dp1, was shed early in life and its alveolus was plugged by bone. In contrast to currently adopted view, the replacement of molariform teeth was widely distributed in stem mammals and can be documented for Morganucodon, Megazostrodon, and Dinnetherium. The prolonged functioning of the dental lamina in Morganucodon and tegotheriid docodontans is likely related with a late eruption of the last lower molariform tooth. From the jaw structures associated with the dental lamina in non-mammalian cynodonts (groove and pits), the dental lamina groove is retained at least in some Gobiconodontidae and the dental lamina pits are retained in Amphidontidae.