Mesoceratocanthus fossils from the early cretaceous of china reinterpreted as the earliest passaloids (coleoptera: scarabaeoidea)

The scarabaeoid beetle Mesoceratocanthus from the Early Cretaceous Yixian Formation was originally placed in the extant tribe Ivieolini (Hybosoridae). Our re-examination of the holotype and a new specimen demonstrates that Mesoceratocanthus does not possess the diagnostic characters of Ivieolini or Hybosoridae. Instead, it should be assigned to the passaloid lineage (Passalopalpidae + Passalidae) and appears closely related to the extinct family Passalopalpidae. The revised placement of Mesoceratocanthus further extends the earliest occurrence of the passaloid clade (similar to 125 Ma, Barremian to early Aptian).