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Xibalbaonyx; Temporal range: Late Pleistocene (Rancholabrean) ~0.016–0.010 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Pilosa
Family:	†Megalonychidae
Subfamily:	†Megalonychinae
Genus:	†Xibalbaonyx; Stinnesbeck et al. (2017)
Type species
	†Xibalbaonyx oviceps; Stinnesbeck et al 2017
Other species
	†Xibalbaonyx microcaninus Stinnesbeck et al 2018; †Xibalbaonyx exinferis Stinnesbeck et al 2020;

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.

Discovery and taxonomy

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^[4] In 2021, remains of a form closely related to Xibalbaonyx was reported from the Pleistocene of Cueva de Iglesitas near Caracas, Venezuela.^[5]

Description

Xibalbaonyx oviceps was about 2 metres long and weighed about 200 kilograms,^[4] with a similar weight suggested for X. exiniferis.^[3] The forearms of X. 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 sized black bears.^[4]

References

^ 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. ISSN 0031-0220. S2CID 134188352.
^ 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. ISSN 0895-9811. S2CID 134541882.
^ ^a ^b Stinnesbeck, Sarah R.; Stinnesbeck, Wolfgang; Frey, Eberhard; Avilés Olguín, Jerónimo; González, Arturo González (2020-05-12). "Xibalbaonyx exinferis n. sp. (Megalonychidae), a new Pleistocene ground sloth from the Yucatán Peninsula, Mexico". Historical Biology. 33 (10): 1952–1963. Bibcode:2021HBio...33.1952S. doi:10.1080/08912963.2020.1754817. ISSN 0891-2963. S2CID 219425309.
^ ^a ^b ^c Stinnesbeck, Sarah R.; Frey, Eberhard; Avilés Olguín, Jerónimo; González, Arturo González; Velázquez Morlet, Adriana; Stinnesbeck, Wolfgang (2020-09-21). "Life and death of the ground sloth Xibalbaonyx oviceps from the Yucatán Peninsula, Mexico". Historical Biology. 33 (11): 2610–2626. doi:10.1080/08912963.2020.1819998. ISSN 0891-2963. S2CID 224987707.
^ Rincón, Ascanio D.; Lemoine, Luis A.; McDonald, H. Gregory (2021-10-01). "A new addition to Pleistocene megalonychid sloth diversity in the northern Neotropics". Journal of South American Earth Sciences. 110: 103379. Bibcode:2021JSAES.11003379R. doi:10.1016/j.jsames.2021.103379. ISSN 0895-9811.