The type material of Agraulos antiquus Sdzuy, 1961 from the La Herrería Formation, northern Spain, is revised together with additional material and included in the new genus Lunagraulos. The stratigraphical range of Lunagraulos antiquus (Sdzuy, 1961) – occurring below that of the trilobite species of the genera Lunolenus, Metadoxides and Dolerolenus in the type locality of Los Barrios de Luna in the province of León, northern Spain – and the accompanying ichnofossil assemblage demonstrate an Ovetian age (lower part of Cambrian Stage 3, currently being discussed by the International Subcommission on Cambrian Stratigraphy) for this species. Moreover, the trilobite Lunagraulos tamamensis n. gen. n. sp. is found in the Tamames Sandstone near the village of La Rinconada in the province of Salamanca, central Spain. The biostratigraphical position of this new taxon and its accompanying ichnoassemblage is also analysed and assigned to the lowermost Ovetian Stage. The genus Lunagraulos is therefore the oldest agraulid found in the fossil record. The exceptional presence of Lunagraulos in a marine coarse siliciclastic succession – a facies rather typical for the ichnofossils Cruziana and Rusophycus, some of the oldest signs of trilobite activity – suggests that first trilobite representatives may have inhabited high- to middle-energy, marine environments. This hypothesis may also explain both the taxonomic and biostratigraphic heterogeneity of the first trilobite genera appearing across the world, due to preservation problems in this type of facies. Comparison of the Lunagraulos biostratigraphy with other coeval Spanish fossil assemblages allows us to propose its intercontinental correlation with the oldest records of currently known trilobites.
