Mesoceratocanthus Fossils from the Early Cretaceous of China Reinterpreted as the Earliest Passaloids (Coleoptera: Scarabaeoidea)

Abstract

Abstract. 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 (∼125 Ma, Barremian to early Aptian). Resumen. El escarabajo scarabaeoideo Mesoceratocanthus de la Formación Yixian del Cretácico Inferior se asignó originalmente a la tribu existente Ivieolini (Hybosoridae). El nuevo examen del holotipo y de un nuevo espécimen demuestran que Mesoceratocanthus no posee los caracteres diagnósticos de Ivieolini o Hybosoridae. En cambio, debería asignarse al linaje passaloideo (Passalopalpidae + Passalidae) estando estrechamente relacionado con la familia extinta Passalopalpidae. La nueva asignación de Mesoceratocanthus cambia la primera aparición del clado passaloide (∼ 125 Ma, del Barremiano al Aptiano temprano).