New records of Neogene Xenarthra (Mammalia) from eastern Puna (Argentina): diversity and biochronology

Abstract

Xenarthra is an endemic South American lineage of mammals, probably the sister clade of the other placental mammals. The oldest records of Xenarthra are from the latest Paleocene, although its current diversity is much lower than that recorded in some intervals of the Cenozoic Era. A new Neogene Xenarthra (Pilosa and Cingulata) assemblage from two localities of the Argentine Eastern Puna (Calahoyo and Casira) is described. The newly recorded taxa—Cingulata, Dasypodidae, Eutatini: Stenotatus sp. indet. and Eutatini indet., Euphractini: Macrochorobates scalabrinii (Moreno and Mercerat, 1891), and Tardigrada, Mylodontinae: cf. Simomylodon sp. indet. and Simomylodon cf. S. uccasamamensis Saint-André et al., 2010—and those already published from Calahoyo—Cingulata: Macrochorobates chapadmalensis (Ameghino, 1908), Eosclerocalyptus sp. indet., and Tardigrada, Megatheriidae: Pyramiodontherium bergi (Moreno and Mercerat, 1891)—suggest a middle–late Miocene age for the fossil-bearing levels. In Calahoyo, the presence of Stenotatus sp. indet., in addition to some rodents currently under study in the lower levels, suggest a closer similarity with the palaeofauna of Cerdas (southern Bolivia), probably involving the last part of the Miocene Climatic Optimum. The Xenarthra recorded in the middle and upper levels of Calahoyo and Casira suggest a late Miocene–Pliocene age. A comparative analysis between Calahoyo and Casira highlights the absence of Cingulata in the latter and a high diversity in the former. This situation probably indicates different paleoenvironmental conditions. Finally, we present the first certain record of the genus Simomylodon Saint-André et al., 2010 in Argentina, which includes the oldest record of dermal ossicles for sloths in South America.

Postcranial anatomy of the extinct terrestrial sloth Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano, and its evolutionary implications

“…In a similar way, several elements of uncertain attribution recovered from the Casira Basin and described by Quiñones et al (2019) can be reassigned to S. uccasamamensis.…”

“…The Neogene Mylodontini species Simomylodon uccasamamensis is an endemic taxon from late Miocene-late Pliocene deposits of the Andean Altiplano (Saint-André et al 2010;Boscaini et al 2019b;Quiñones et al 2019). This species was erected by Saint-André et al (2010), and new abundant remains from the Bolivian Altiplano were subsequently studied by Boscaini et al (2019b, c).…”

“…More precisely, fossil remains come from the latest Miocene/early Pliocene of Choquecota, the early Pliocene of Casira, Inchasi and Pomata-Ayte, and the late Pliocene of Ayo Ayo-Viscachani (for further information on these localities, see Boscaini et al 2019b). Recently, Quiñones et al (2019) reported new remains of S. uccasamamensis from Casira, thereby extending the geographic range of this taxon to the Argentine side of the Casira Basin. Interestingly, the chronological distribution of S. uccasamamensis is bracketed between two major faunal turnover events which took place in the Bolivian highlands, i.e., the Miocene-Pliocene and the Pliocene-Pleistocene transitions (Hoffstetter 1986;Marshall et al 1983;Marshall & Sempéré 1991).…”

The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodón (Última Esperanza, Chile)

“…The earliest records of osteoderms are from the late Miocene–early Pliocene of Argentina and Bolivia (Boscaini et al, 2021; Nasif, Esteban, & Georgieff, 2008; Quiñones et al, 2019; Rovereto, 1914). Towards the end of the Miocene and the beginning of the Pliocene, the diversity of largest predators in South America included caimans such as Purussaurus (e.g., Bona & Barrios, 2015; Bona, Riff, & Gasparini, 2013; Pujos & Salas‐Gismondi, 2020; Salas‐Gismondi et al, 2015; Scheyer et al, 2013), phorusrhacid birds (Degrange, Tambussi, Moreno, Witmer, & Wroe, 2010; Degrange, Tambussi, Taglioretti, Dondas, & Scaglia, 2015), teratorns such as Argentavis (Palmqvist & Vizcaíno, 2003), carnivorous marsupials such as Thylacosmylus and to a lesser extent borhyaenids (Prevosti, Forasiepi, & Zimicz, 2011), and large procyonids such as Cyonasua (Cione, Gasparini, Soibelzon, Soibelzon, & Tonni, 2015; Soibelzon et al, 2020; Tarquini, Vilchez Barral, & Soibelzon, 2016).…”

“…A single osteoderm from the same locality was also referred to Simomylodon cf. S. uccasamamensis (Quiñones et al, 2019). Regarding the North American fossil record, mylodontine osteoderms were recovered from the Pliocene deposits of Mexico (Carranza‐Castañeda, 2006; Montellanos‐Ballesteros & Carranza‐Castañeda, 1986) and USA (Hill, 2006; Robertson, 1976).…”