Isolated teeth referred to the family Haramiyidae are among the earliest known fossil evidence of mammals. First discovered in European Late Triassic deposits a century and a half ago(1), haramiyids have been interpreted as related to multituberculates(2-7), a diverse and widespread lineage that occupied a rodent-like niche from the Late Jurassic to the Early Tertiary. Nonetheless, haramiyid relationships have remained enigmatic(8,9) because the orientation and position of the teeth in the upper or lower jaw could not be determined with certainty; even their mammalian status has been questioned(10). The discovery of haramiyid dentaries, a maxilla and other skeletal remains in the Upper Triassic of East Greenland reveals haramiyids as highly specialized mammals with a novel pattern of puncture-crushing occlusion that differs dramatically from the grinding or shearing mechanisms of other Early Mesozoic mammals.