Xenarthrans from Sistema Calera Cave, Mexico, and radiocarbon and stable isotope analyses of the cave fauna

Recent investigations at Sistema Calera Cave (21°53’49”N, 98°55’52”W, 103 m a.s.l.), located in the Sierra de El Abra, San Luis Potosí, northeastern Mexico, have established the site as one of exceptional paleontological importance due to its remarkably diverse assemblage of fossilized vertebrate remains. Given the underwater depositional context, which likely contributed to collagen degradation, radiocarbon dating was performed on bioapatite, with results converted to collagen-equivalent values and calibrated to calendar years. Radiocarbon dates place specimens of Bison sp. (8423–8549 cal yr BP), Tremarctos cf. floridanus (12686–12752 cal yr BP), Glyptotherium cylindricum (12986–13166 cal yr BP), Canis dirus (13574–13666 cal yr BP), Mammuthus columbi (13729–13887 cal yr BP), Eremotherium laurillardi (23784–24065 cal yr BP), and Smilodon fatalis (31027–31178 cal yr BP) within the Late Rancholabrean. The range of dates indicates the assemblage represents a time-averaged fauna. The carbon isotopic signature (δ13C) suggests three main types of vegetation animals fed on: low-density forests, an arboreal savanna, and an ecotone between arboreal savanna to open savanna. Of 775 cataloged specimens, 37 are assigned to Xenarthra, including three sloth genera (Eremotherium, Nothrotheriops, and a megalonychid cf. Nohochichak) and one glyptodont (Glyptotherium). The co-occurrence of Nothrotheriops, typically associated with arid environments, with Eremotherium and Glyptotherium, which are linked to tropical and mixed grassland habitats, presents an unusual ecological association. Potential explanations for this uncommon association are discussed.