THE first ’tetrapod-like’ bones from the Scottish Upper Devonian site of Seat Craig (Seat Craig beds, Upper Frasnian) were figured and discussed in 1991 (ref. 1). Additional specimens have since been discovered that permit a formal description, and the background knowledge of Devonian tetrapod anatomy has greatly improved(2-7). These discoveries emphasize the uniqueness and phylogenetic importance of the Seat Craig material. Elginerpeton pancheni gen. et sp. nov., described here on the basis of cranial remains from Seat Craig, is, together with the fragmentary genus Obruchevichthys from the Upper Frasnian of Latvia and Russia(1,8,9), the oldest known stem tetrapod. Elginerpeton and Obruchevichthys form a clade that is the sister group of all other Tetrapoda. This contrasts with the later Devonian stem tetrapods, which all seem to represent separate plesions. Elginerpeton also has a unique, derived head morphology; it shows that the earliest phase of tetrapod evolution was accompanied by previously unrecognized morphological and phylogenetic diversification.