New mammal material from the Campano-Maastrichtian locality of Laño, Spanish Basque Country documents two new zhelestid eutherian species referred to the genus Lainodon. This material enlightens the upper molar pattern of the European zhelestids and confirms their originality and homogeneity. The European zhelestids are included in the new subfamily Lainodontinae, which is distinct and characterized by a mosaic of primitive and specialized features. The Lainodontinae clade adds to other endemic vertebrate taxa (among multituberculates, flightless birds, dinosaurs, and turtles) that typify the Late Cretaceous fauna of the European Archipelago. The material from Laño provides further evidence of a modest but significant lainodontine radiation known by five or six species belonging to two or three genera (Lainodon, Labes, ? Valentinella), which is currently restricted to western Europe, i.e. to the Ibero-Armorican Island. The plesiomorph features of the Lainodontinae (lower molar trigonid poorly compressed, upper molar without lingual cingulum) recall the earliest known zhelestids, and suggest an Asian origin from a Sheikhdzheilia-like stem lineage at the beginning of the Late Cretaceous. This dispersal event from Asia probably involved other vertebrate taxa, such as the multituberculate stem group of the kogaionid mammals and the hadrosaurid dinosaurs. The zhelestid subfamily Lainodontinae represents the most diverse and dominant taxon in the western European Late Cretaceous mammal fauna, which is eutherian-dominated, by contrast to the eastern European Late Cretaceous mammal fauna which is dominated by an original and at that time exclusive radiation of kogaionid multituberculates.

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