First record of Meizonyx salvadorensis (Mammalia: Xenarthra: Pilosa) from the late Pleistocene of Mexico and its evolutionary implications

The megalonychid sloth Meizonyx salvadorensis was previously known only from the holotype mandible from El Salvador. Here, we describe the first record of M. salvadorensis from the late Pleistocene of Mexico, examine its relationship to other members of the family Megalonychidae and discuss the palaeobiogeographical and palaeoecological implications of this new record. The specimen consists of an associated skull and mandible, and parts of the postcranial skeleton, recovered from the Sistema Huautla cave complex located in the Sierra Mazateca, a part of the Sierra Madre Oriental del Sur, east of Huautla de Jimenez, in the state of Oaxaca, Mexico. Two phylogenetic analyses were carried out utilizing maximum parsimony and Bayesian approaches, and included the new material within the data matrix used for previous studies of members of Megalonychidae. The phylogenetic hypothesis obtained from the Bayesian analysis indicates the closest relationship of Meizonyx salvadorensis is to Xibalbaonyx. The recent discoveries of multiple new members of Megalonychidae in southern Mexico and their proposed relationships to each other and other members of the family resulting from this analysis suggest successive dispersal events complemented by endemic radiation in Central America and southern Mexico, possibly facilitated by the variety of habitats present in the region that allowed for their diversification.