The late Oligocene xenarthran fauna of Quebrada Fiera (Mendoza, Argentina) and its implications for sloth origins and the diversity of Palaeogene cingulates

Abstract

The late Oligocene mammalian fauna of Quebrada Fiera is one of the most diverse of the Deseadan SALMA (South American Land Mammal Age). We describe its endemic xenarthran assemblage, represented by 13 species, consisting of 2 stem sloths and 11 armoured cingulates. The rare folivoran material confirms the presence of Octodontotherium, one of the early known mylodontids, and suggests the existence of a new, small, non-megalonychid megatherioid, Similhapalops nivis. The lumbar vertebrae of Octodontotherium sp. provide the oldest evidence of xenarthry for the order. The presence at the knee joint of an ossified meniscus and cyamo-fabella strongly suggests a plantigrade ancestral condition in Mylodontidae. Armoured xenarthrans are represented by the armadillos Eutatini (Meteutatus sp., M. lagenaformis, and Stenotatus ornatus), an undetermined Euphractinii, the 'horned' peltephilids Peltephilus sp. and P. undulatus, and the palaeopeltid Palaeopeltis inornatus; an undetermined Glyptodontidae, the glyptatelines Glyptatelus cf. tatusinus and Clypeotherium sp., and an undetermined propalaehoplophorine. The xenarthrans represent one-third of the mammals of the Quebrada Fiera fauna, one of the most varied at the end of the Palaeogene in South America. This vertebrate fauna is represented by a mix of endemic taxa and other species of high latitude (Patagonian) origin, but few from low latitude faunas. A detailed study of this mammalian assemblage, complemented by detailed geological and petrographical studies, suggests the existence of strong volcanic activity, and the presence of braided rivers and lagoonal environments in open habitats under a temperate or hot climate, with savannas and/or grasslands and isolated forests during the late Oligocene at the foot of the proto-Andes.

The last horned armadillos: phylogeny and decline of Peltephilidae (Xenarthra, Cingulata)

“…26 Ma; Ameghino 1897; Pujos et al . 2021) should be reassessed, given that they share more character states with older taxa such as the Oligocene Ronwolffia and the Early Miocene Peltecoelus than with later species of Peltephilus and Epipeltephilus (i.e. relatively smooth dorsal osteoderm surface and relatively developed articular surface in mobile osteoderms).…”

“…Most Palaeogene records consist only of isolated osteoderms from the dorsal carapace (Pujos et al . 2021); the oldest cranial and postcranial remains are from the late Oligocene of the Salla locality, Bolivia (Shockey 2017) and correspond to Ronwolffia pacifica Shockey, 2017. The most abundant and complete records come from the Early Miocene (Colhuehuapian and Santacrucian SALMAs) of Patagonian Argentina, including several well‐preserved skulls belonging to the genus Peltephilus Ameghino, 1887 (Ameghino 1894; Scott 1903–1904; Bordas 1936; Vizcaíno et al .…”

Bayesian Total-Evidence Dating Revisits Sloth Phylogeny and Biogeography: A Cautionary Tale on Morphological Clock Analyses

“…The oldest undisputed records of fossil sloths come from the late Oligocene of South America (Deseadan SALMA), with at least 8 identified genera ( Shockey and Anaya 2011 ; Pujos et al 2021 ). Because most of this ancient sloth evidence comes from Patagonia, the southern cone of the continent has been considered the region where sloth evolution took place and from which dispersal to other parts of the continent would have occurred (e.g., Pascual 1984 ; Varela et al 2019 ).…”