Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana

Haramiyida was a successful Glade of mammaliaforms, spanning the Late Triassic period to at least the Late Jurassic period, but their fossils are scant outside Eurasia and Cretaceous records are controversial(1-4). Here we report, to our knowledge, the first cranium of a large haramiyidan from the basal Cretaceous of North America. This cranium possesses an amalgam of stem mammaliaform plesiomorphies and crown mammalian apomorphies. Moreover, it shows dental traits that are diagnostic of isolated teeth of supposed multituberculate affinities from the Cretaceous of Morocco, which have been assigned to the enigmatic Hahnodontidae. Exceptional preservation of this specimen also provides insights into the evolution of the ancestral mammalian brain. We demonstrate the haramiyidan affinities of Gondwanan hahnodontid teeth, removing them from multituberculates, and suggest that hahnodontid mammaliaforms had a much wider, possibly Pangaean distribution during the Jurassic-Cretaceous transition.