Xibalbaonyx Exinferisn. Sp. (Megalonychidae), A New Pleistocene Ground Sloth From The Yucatan Peninsula, Mexico

Recent palaeontological research in submerged caves of the north-eastern Yucatan Peninsula (YP) in Mexico has resulted in the identification of a diverse megafaunal assemblage in the area, among them Late Pleistocene ground sloths assigned to the family Megalonychidae (Xenarthra). Here we report on a new species of Megalonychidae,Xibalbaonyx exinferisn. sp., from a new fossil locality named cenote Tortugas, located west of Puerto Morelos in the federal state of Quintana Roo. The taxon is based on a fragmentary left mandibular ramus, an atlas, and a left humerus. The new taxon is diagnosed by the presence of two mental foramina on the short symphyseal spout, a caniniform being the smallest mandibular tooth, and the anterolaterally directed aperture of the mandibular foramen on the lateral surface of the mandible.Xibalbaonyx exinferisis the third endemic megalonychid documented for the north-eastern Yucatan Peninsula and thus provides increasing evidence for an ecological isolation of the area from the rest of Mexico during the Pleistocene.