The holotype ofX. oviceps is a mostly complete skeleton discovered in anunderwater cave system,[1] whileX. 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 speciesX. 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 holotypeX. oviceps was published[4] In 2021, remains of a form closely related toXibalbaonyx was reported from the Pleistocene of Cueva de Iglesitas nearCaracas, Venezuela.[5]
Xibalbaonyx oviceps was about 2 metres long and weighed about 200 kilograms,[4] with a similar weight suggested forX. exiniferis.[3] The forearms ofX. oviceps are well built and likely had well developed muscles, with the range of mobility of the limbs being high. These are suggested to be adaptations for climbing, as is done by similarly sizedblack bears.[4]
^Stinnesbeck, Sarah R.; Frey, Eberhard; Olguín, Jerónimo Avíles; Stinnesbeck, Wolfgang; Zell, Patrick; Mallison, Heinrich; González González, Arturo; Aceves Núñez, Eugenio; Velázquez Morlet, Adriana; Terrazas Mata, Alejandro; Benavente Sanvicente, Martha; Hering, Fabio; Rojas Sandoval, Carmen (2017). "Xibalbaonyx oviceps, a new megalonychid ground sloth (Folivora, Xenarthra) from the Late Pleistocene of the Yucatán Peninsula, Mexico, and its paleobiogeographic significance".PalZ.91 (2):245–271.Bibcode:2017PalZ...91..245S.doi:10.1007/s12542-017-0349-5.ISSN0031-0220.S2CID134188352.
^Stinnesbeck, Sarah R.; Frey, Eberhard; Stinnesbeck, Wolfgang (2018). "New insights on the paleogeographic distribution of the Late Pleistocene ground sloth genus Xibalbaonyx along the Mesoamerican Corridor".Journal of South American Earth Sciences.85:108–120.Bibcode:2018JSAES..85..108S.doi:10.1016/j.jsames.2018.05.004.ISSN0895-9811.S2CID134541882.
