Palaeognathous birds (Aves, Palaeognathae) are uncontroversially the most basal clade among modern birds (Neornithes), having been defined for more than 100 years on the basis of their palatal morphology. However, because many fossil specimens that have been described to date lack detailed skull material (especially in association with postcrania), aspects of the early evolutionary history of these birds remain unclear, and their relationships on the basis of anatomical characters are as yet unresolved. In this paper we present a new and exceptionally well-preserved specimen of the Lower Eocene fossil palaeognath Lithornis that has a remarkable three-dimensionally preserved and complete skull. New anatomical information provided by this Danish fossil leads us to suggest that a number of cranial characters previously considered diagnostic for ratites may in fact be primitive among palaeognaths. The presence of members of Lithornithidae in the Lower Eocene (earliest Tertiary) is consistent with the hypothesis that basal divergences within Palaeognathae occurred at an earlier geological time, perhaps prior to the Cretaceous–Tertiary (K–T) boundary, as has been proposed based on evidence from much less well-preserved fossil material.