Xibalbaonyx is an extinct genus of megalonychid ground sloth known from the Late Pleistocene of Mexico. Three species are known: X. oviceps and X. exiniferis from the Yucatan peninsula and X. microcaninus from Jalisco. The genus is named after Xibalba, the underworld in Maya mythology.
The holotype of X. oviceps is a mostly complete skeleton discovered in an underwater cave system,[1] while X. microcaninus being known from a complete skull and mandible from the sediments of the former paleolake of lake Jalisco.[2] The overlapping remains of the skull and mandibles have notable differences between them, enough to call them distinct species. A third species X. exiniferis was described in 2020, also from an underwater cave in the Yucatan Peninsula, it is known from a "fragmentary left mandibular ramus, an atlas, and a left humerus".[3] In 2020, a description of the postcranial remains of the holotype X. oviceps was published, suggesting that the taxon had climbing capabilities.[4] In 2021, remains of a form closely related to Xibalbaonyx was reported from the Pleistocene of Cueva de Iglesitas near Caracas, Venezuela.[5]