Dasypodidae and Chlamyphoridae (Xenarthra, Cingulata) armadillos from the Río Bermejo Formation (Late Pleistocene), Formosa Province, Argentina

Abstract

Late Pleistocene vertebrate fossils have been recorded at multiple localities in Formosa Province, specifically between the localities of General Mansilla and El Colorado. The fossiliferous levels belong to the Río Bermejo Formation, represented by swamp-like deposits associated with oxbow lakes from an ancient river channel. Absolute dating (14C) of this formation at the Villa Escolar area indicates a Late Pleistocene to earliest Holocene (ca. 10–20 ka BP) age. The faunal assemblage of this unit stands out for its high diversity of mammals, which includes representatives of Notoungulata, Litopterna, Proboscidea, Artiodactyla, Carnivora, and Xenarthra. Within Xenarthra, Cingulata is particularly well represented including remains of glyptodonts, pampatheres, and armadillos. Since there are no studies focusing on armadillos, and previous contributions only reached a genus level, this study aims to refine our knowledge about their taxonomy and diversity. The analyzed materials include several isolated and articulated osteoderms of the carapace of Dasypodidae and Chlamyphoridae, which are housed at the collection of the Museo Provincial de Ciencias Naturales de Villa Escolar (Formosa, Argentina). The taxa identified are restricted to Propraopus sulcatus (Dasypodidae, Dasypodinae) and Chaetophractus villosus (Chlamyphoridae, Euphractinae). The specimens PVE-F72 (one fixed and one mobile osteoderm), PVE-F101 (one fixed and one mobile osteoderm), PVE-F105 (three fixed and four mobile osteoderms), PVE-F108 (two semimobile osteoderms), PVE-F122 (six articulated fixed osteoderms and four broken mobile osteoderms), and PVE-F157 (articulated fragments of the caudal armor) are assigned to P. sulcatus for having both fixed and mobile osteoderms exhibiting a typical Dasypodinae ornamentation pattern, dorsal foramina restricted to the anterior half of the osteoderm, and a much larger size than Dasypus spp. The specimen PVE-F54 (articulated fragments of the caudal armor and dorsal carapace and several associated fixed and mobile osteoderms) is assigned to C. villosus for having an ornamentation pattern of fixed osteoderms including an additional peripheral figure placed anteriorly to the central figure, a character only present in this species. This fossil diversity is much lower than expected, since the living association of armadillos in Formosa Province, which includes a total of seven genera recorded, is one of the largest in South America. In this context, it is hypothesized that there is a taphonomic or sample bias in the fossil diversity recorded so far from the Río Bermejo Formation that is probably not reflecting the real diversity of the formation, which is expected to be higher.