Nothrotherium escrivanense ( Reinhardt, 1878 )

Verger, Kévin Le, 2023, Xenarthrans of the collection of Santiago Roth from the Pampean Region of Argentina (Pleistocene), in Zurich, Switzerland, Swiss Journal of Palaeontology (3) 142 (1), pp. 1-39 : 29-32

publication ID	https://doi.org/10.1186/s13358-023-00265-7
persistent identifier	https://treatment.plazi.org/id/96755D53-0738-FFA4-70D5-FE49FB401C5B
treatment provided by	Felipe
scientific name	Nothrotherium escrivanense ( Reinhardt, 1878 )
status

Treatment

Nothrotherium escrivanense ( Reinhardt, 1878)

Referred material: Cranium, seven thoracic vertebrae, caudal vertebrae, ribs, sternum, humerus, radius, ulna, three hand bones: PIMUZ A/ V 477 ( Figs. 5 View Fig , 6 View Fig , 10 View Fig ).

Comment: Nothrotheres are particularly well-known in the northern part of the Pampean Region, especially in the southern part of Santa Fe Province (Vezzosi et al., 2019). Tere are at least four species from the late Pleistocene of the Pampean Region: Nothropus carcaranensis Bordas, 1942 ; Nothropus priscus Burmeister, 1882 ; Nothrotherium torresi Kraglievich, 1926 , and Nothrotherium escrivanense . Only one specimen in the Roth collection at PIMUZ corresponds to a nothrothere according to the work of Schulthess (1920). She attributed the almost complete specimen PIMUZ A/V 477 to the species No. escrivanense . Subsequently, several authors (e.g. Cartelle & Fonseca, 1983; Paula Couto, 1971; Perea, 2007) have proposed that No. escrivanense corresponds to a juvenile of No. maquinense ( Lund, 1839) although Pujos (2001) considered the species to be valid. A revision of the taxonomic diversity of nothrotheres in the Pampean Region should be carried out (Brandoni & Vezzosi, 2019). PIMUZ A/V 477 follows perfectly the diagnosis of the genus proposed by Pujos (2001), with a small size, cylindrical and elongated cranium, distinct area for prominent pterygoid sinuses, globular parietal region higher than the frontal and exhibiting strong posterior inclination, absence of caniniform, anteroposteriorly narrow Mf4, that appear less quadrangular compared to the other teeth based on the tooth alveoli. Te femur also has diagnostic elements, but this bone was not found for PIMUZ A/V 477. Specifically, the diagnosis of No. escrivanense is mainly focused on the upper teeth and several features on the hand and foot ( Pujos, 2001) that are absent in PIMUZ A/V 477 except for the right Mf1. Based on the dental alveoli, the molariforms appear to be weakly mesiodistally compressed and the mesiodistal diameter between the labial and lingual faces of Mf1 to Mf3 shows little difference which supports the validity of the attribution to No. escrivanense ( Pujos, 2001) . Pending a review of the diversity of nothrotheres from the Pampean Region, I propose to retain the attribution proposed by Schulthess (1920). In addition to the completeness of the specimen, PIMUZ A/V 477 is of major interest for the reassessment of the diversity of Pleistocene nothrotheres from Argentina. Te quality of preservation would also allow a future examination of its endocranial structures. Te specimen includes several well-preserved long bones (see above) as partially documented in histological analyses (Houssaye et al., 2016a, b; Straehl et al., 2013).

Diversity and Abundance of Santiago Roth’s Xenarthrans stored in the PIMUZ

Among the 284 specimens in the Roth collection at PIMUZ, 150 belong to Xenarthra (~ 53%) mainly collected in the northern part of the Pampean Region

( Fig. 2). Tis high abundance of xenarthrans replicates the pattern already highlighted by many researchers in the Pleistocene Pampean faunas compared to other mammals (e.g., Carlini & Scillato-Yané, 1999; Cione et al., 1999; Soibelzon & Tonni, 2009; Soibelzon et al., 2010; Tonni et al., 1999a, b). Te present taxonomic reassessment also revealed a high taxonomic diversity in the Roth collection ( Figs. 2, 12 View Fig ). Among all the xenarthrans studied in the present investigation, 69 specimens belong to the Cingulata (46%), 70 specimens belong to the Folivora (~ 47%), and 11 (7%) correspond to undetermined or lost material. As such, Cingulata and Folivora are both equally abundant in the Roth collection at PIMUZ, with a higher diversity for Cingulata (between 17 and 21 sp.) than for Pilosa (between 10 and 12 sp.) ( Fig. 12 View Fig ). Among the Cingulata , three specimens belong to three extant species of armadillos (~ 4%) ( Gibb et al., 2016). With the inclusion of P. sulcatus , the Roth collection at PIMUZ contains at least three of the four extant armadillos ‘subfamilies’ ( Fig. 12 View Fig ) ( Gibb et al., 2016). Te diversity of small-sized armadillos is low in the Roth collection at PIMUZ compared to that of the extinct large-sized armadillos. Among them, the Eutatini are represented by eight of the smallest specimens (~ 12%) distributed in two species. However, large-sized pampatheres that can reach ~ 200 kg ( McDonald, 2005) are also represented by few (i.e., four) specimens, listed in two species (~ 6%). Tis under-representation of pampatheres in the Pampean Region was already mentioned by previous works (Carlini & Scillato-Yané, 1999; Cione et al., 1999; Soibelzon et al., 2010; Tonni et al., 1999a, b). It is possible that because of their large size and herbivorous diet, the distribution of pampatheres was affected by the exceptional proliferation of giant extinct armadillos, the glyptodonts, the most abundant clades of cingulates in the Pampean Region (e.g., Carlini & Scillato-Yané, 1999; Cione et al., 1999; Tonni et al., 1999a, b; Soibelzon & Tonni, 2009; Soibelzon et al., 2010), with 52 specimens present in the Roth collection at PIMUZ (~ 75%—proportion of glyptodonts among cingulates in the collection). Glyptodonts are represented by at least nine species, with one representative of each of the four ‘subfamilies’ of Pleistocene glyptodonts. Te abundance of each glyptodont ‘subfamilies’ in the collection follows a size gradient. Neosclerocalyptinae, small glyptodonts of about ~ 450 kg (Vizcaíno et al., 2011), are represented by 28 specimens (~ 41%), with at least one representative of each known Pleistocene Neosclerocalyptinae species (Zurita et al., 2011). In the intermediate gigantic sizes, about one to two tons (Fariña et al., 1998), the second most abundant ‘subfamily’ corresponds to the Glyptodontinae, with 16 specimens (~ 23%) indicating the presence of two of the three species of the genus Glyptodon . Except for the species G. jatunkhirkhi , a large part of the diversity of Glyptodontinae from the southern part of South America are represented in the collection (Zurita et al., 2018). Also gigantic in size (Fariña et al., 1998), the third ‘subfamily’, Panochthinae, is particularly scarce in the collection with four specimens (~ 6%), represented by two species of the genus Panochthus . Recently, Brambilla et al. (2020) highlighted a high diversity for this genus in the Pampean Region with six species. With respect to the Panochthinae, the Roth collection at PIMUZ has a relatively low diversity and abundance for this clade, with an over-representation of the species from the Ensenadan. Finally, with the large Doedicurus , up to three tons (Fariña et al., 1998), the Doedicurinae is represented by only two specimens in the collection (~ 3%), including the only doedicurine species known in the Pleistocene (Soibelzon et al., 2010). Te Folivora is less diversified and is represented only by ground sloth specimens through four ‘subfamilies’: Mylodontinae , Scelidotheriinae , Megatheriinae , and Nothrotheriinae . Te Roth collection at PIMUZ is mainly composed of mylodontines and scelidotheriines. Te former is represented by 28 specimens (40%) while the latter is represented by 35 specimens (50%). Tese two ‘subfamilies’ represent giant sloths of gigantic size (Fariña et al., 1998). In contrast, the two ‘subfamilies’ with the most extreme sizes, for the smallest, the nothrotheres with a body mass of more than 171 kg (Dantas, 2022), and for the largest, the megatheres with an extreme bodymass estimated between three and six tons (Fariña et al, 1998), are only marginally present in the Roth collection at PIMUZ, with only one specimen for nothrotheres (~ 1%) and six specimens for megatheres (~ 9%). Tere were likely 44 valid species of xenarthrans in the Pleistocene of the Pampean Region (see Brambilla & Ibarra, 2018a; Carlini & Scillato-Yané, 1999; Cione et al., 1999; Krmpotic et al., 2009; Tonni et al., 1999a, b) ( Fig. 12 View Fig ). With its at least 27 species of xenarthrans, the Roth collection at PIMUZ includes more than half of the known species of xenarthrans from the Pleistocene of the Pampean Region.

Contribution to the reconstruction of the Pampean Region paleoenvironment

Te Pleistocene is a period marked by a large temperature amplitude associated with a greater frequency of glacial and interglacial periods (e.g., Prado et al., 2021; Sanz-Pérez et al., 2022; Soibelzon, 2019). Tis epoch was therefore subject to drastic changes oscillating rapidly between cold and warm periods. Climatic variations affected the environments, triggering abiotic and biotic events of ample magnitude while causing a multitude of retroactive phenomena (see Prado et al., 2021). Some regions were more prone to suffer these drastic climatic variations. Bordered by the subtropical forest at the north and the Patagonian arid environment at the south, the Pampean Region was one of these regions. Terefore, the Pampean Region is cyclically transformed by the southward extent of wet environments in interglacial periods and the northward extent of arid environments in glacial periods ( Quattrocchio et al., 2008; Tonni, 2017). Te environment of the Pampean Region during the Pleistocene was therefore continuously transformed and impacted by changes in the flora sometimes towards grassy steppes in cold periods, and tree savannas or forests in warm periods ( Quattrocchio et al., 2008; Tonni, 2017). Tese floral changes likely affected strong faunal changes especially for herbivores. Despite a few species with omnivorous diets, such as euphractines (Carlini et al., 2016; Superina & Abba, 2014), or occasional meat consumption in some sloths, such as Darwin’s ground sloth (Tejada et al., 2021), xenarthrans were predominantly herbivorous (e.g., Bargo & Vizcaíno, 2008; Gaudin & Croft, 2015; Toledo et al., 2015; Vizcaíno & Loughry, 2008). Te high herbivore dominance of xenarthrans from this period thus makes them good indicators of paleoenvironmental change as already highlighted by many studies (e.g., Soibelzon & Tonni, 2009; Soibelzon, 2019; Tonni et al., 1999a, 1999b). Tis observation is supported by isotopic analyses of the teeth of several herbivores, demonstrating a modification of the herbivorous diet associated with environmental changes induced by climate change (e.g., De Melo França et al., 2015—see below). According to some authors, some xenarthran species were associated with arid environments such as Neosclerocalyptus paskoensis and Scelidotherium bravardi ( Miño-Boilini & Quiñones, 2020; Zurita et al., 2011) while other species to closer environments such as Pampatherium humboldtii (Varela et al., 2018) and Catonyx cuvieri ( Miño-Boilini & Quiñones, 2020) based on their cranial and/or dental anatomy. Following these paleobiological interpretations, the Roth collection at PIMUZ contains a mix of these specialized species likely due to the high concentration of localities found in the northern Pampean Region ( Fig. 2). Differences in the diet of the species have been suggested for some taxa, using isotope analysis (De Melo França et al., 2015). For example, Glyptodon from latitude 37°S had an exclusively C 3 grasses consumption while a Glyptodon from latitude 32°S had a mixed consumption of C 4 plants and C 3 grasses, demonstrating the higher aridity of the southern Pampean Region compared to the north, during the Late Pleistocene (De Melo França et al., 2015).

During the Ensenadan, Roth collection at PIMUZ shows the presence of Chaetophractus vellerosus , Eutatus pascuali , a great abundance of Glyptodon munizi , Neosclerocalyptus pseudornatus , Neosclerocalyptus ornatus , a representative of Lestodon , Glossotherium robustum , Mylodon darwinii , Scelidotherium bravardi , Catonyx tarijensis , and Megatherium americanum ( Fig. 2). During this time span, two mayor glaciations’ events have been reported, the Great Patagonian Glaciation and the Matuyama/Brunhes Glaciation, that may suggest that the animals were inhabitants of mostly arid/open environments. At the end of the Ensenadan and during the Bonaerian, Roth collection at PIMUZ seems to indicate a greater diversity with the appearance in the Pampean Region of a representative of Tolypeutes , Pampatherium humboldtii , Pampatherium typum , Doedicurus clavicaudatus , Neosclerocalyptus gouldi , Panochthus intermedius , Panochthus tuberculatus , Lestodon armatus , Archaeomylodon sampedrinensis , Scelidotherium leptocephalum , and Nothrotherium escrivanense , although the collection shows a disappearance from the Pampean Region of Chaetophractus vellerosus , Neosclerocalyptus pseudornatus , and Neosclerocalyptus ornatus ( Fig. 2). Tis period is associated with a global warming marked by two peaks of warming highlighted by Marine Isotope Stages, suggesting that the Ensenadan fauna mixed with fauna that inhabited more humid/closed environments. Finally, during the Lujanian, Roth’s collection at PIMUZ exhibits a disappearance of much of the Bonaerian fauna and the presence of Propraopus sulcatus , Zaedyus pichiy , Eutatus seguini , Pampatherium humboldtii , Glyptodon reticulatus , Neosclerocalyptus paskoensis , a representative of Panochthus , Glossotherium robustum , Mylodon darwinii , Scelidotherium leptocephalum , Catonyx tarijensis , and Catonyx cuvieri ( Fig. 2). Te Lujanian is marked by a major cooling notably well marked by the Last Glaciation Maximum and corresponds to the return of an arid/open environment, but with a different faunal assemblage than the Ensenadan, suggesting a faunal replacement following the warming during the Bonaerian ( Fig. 2). Trough the various climatic and environmental changes occurring during the Pleistocene, the Roth collection at PIMUZ shows changes in faunal assemblages but the collection does not indicate a major loss of diversity. Te Roth collection at PIMUZ shows several phases of extinction and appearance of several xenarthran species, evidence that xenarthran species have undergone drastic turnovers in the Pleistocene of the Pampean Region.

Due to the limitation of the relative dating of the specimens and the partial nature of the associated data, especially because this collection was sold to different buyers, I cannot propose a further interpretation of the relationship between the xenarthrans of the Santiago Roth collection of the PIMUZ and paleoenvironmental variation. However, the major faunal trends detected among Pleistocene subdivisions are in agreement with most previous studies (Carlini & Scillato-Yané, 1999; Cione et al., 1999; Soibelzon & Tonni, 2009; Soibelzon et al., 2010; Tonni et al., 1999a, b). A few exceptions are represented in the collection by the presence of Megatherium and Doedicurus from the Ensenadan/Bonaerian. However, these same taxa are those for which paleontologists call for further revisions of their diversity, a next step for our understanding of the evolution of Pleistocene mammalian faunas from the Pampean Region.