Richard Fariña

Sloths represent one of the most successful South American clades that reached North America during the Great American Biotic Interchange (GABI). At least four families are known from the Pleistocene of North America: Mylodontidae, Megalonychidae, Megatheriidae, and Nothrotheriidae. Members of the Nothrotheriidae are known from the Middle Miocene to the Pleistocene/Holocene transition in the Americas, but Nothrotheriops is the only genus in the family recorded in North America. Recently, femora with characteristic nothrothere morphology were recovered from Santa Fe, Argentina, and assigned to Nothrotheriops, thus greatly expanding the geographic distribution of this taxon. In Uruguay, records of Quaternary Nothrotheriidae are scarce, and previous reports are limited to the genus Nothrotherium. In this work, we describe a humerus from Arroyo del Vizcaíno (AdV), a ~30 ka site located in southern Uruguay, and assign it to the nothrotheriid Nothrotheriops sp. We also discuss several specimens from Uruguay originally assigned to Nothrotherium, which upon reexamination can be tentatively reassigned to Nothrotheriops sp. Furthermore, we employ stable isotope analysis to explore the climatic and dietary preferences of this taxon in South America. The new records are consistent with the materials reported from Argentina, thus providing new knowledge of the geographic distribution of the taxon, as well as its climatic and dietary preferences. Stable isotope results showed δ 13 C values consistent with diets based mainly on C 3 plants, similar to those published for N. shastensis in North America.

Abstract Within the subfamily Scelidotheriinae, Valgipes bucklandi represents one of the least known taxa due to its scarce records and material found so far. This Pleistocene ground sloth had been registered only in Brazil, within the Brazilian Intertropical Region (BIR) in the states of Bahia, Minas Gerais, Piaui, Rio Grande do Norte and, more recently, outside the BIR, in Mato Grosso do Sul. A particular feature of this sloth is the proximal and distal fusion of the tibia and fibula in adults. Here, we report a tibia-fibula assigned to V. bucklandi found in Arroyo del Vizcaino (Canelones, Uruguay), a fossiliferous site that harbors a large amount of megamammal remains at an approximate age of 30 ka (29696–32009 cal yr B.P.). We performed stable isotopes analyses and ecological niche models (ENM) to study V. bucklandi distribution and climatic and dietary preferences, as well as to better understand its presence ~2000 km southward of its previous recorded occurrences. δ13C values were consistent with those of the BIR, indicating a similar preference for C3 plants, while the results of δ18O values could be related to colder and more humid environments, clearly different from those obtained from BIR specimens. Furthermore, the ENM results also showed colder and more humid environments for the AdV record, with the occurrence being in the margins of the predicted potential distribution of the taxa. This discovery expands the distribution of this taxa to southern colder climates, indicating a greater climatic tolerance. Moreover, our results support the existence of mixed faunas composed of Southern and Northern taxa coexisting in Southern Uruguay at the onset of the Last Glacial Maximum, and provide evidence of the existence of an open mosaic habitat with patches of mixed vegetation in the region.

With the excuse of writing a critique to Domínguez-Rodrigo et al. (2021, duly replied here: Domínguez-Rodrigo & Baquedano, 2022), Holcomb et al. (this volume) intend to deny the proposal that the Arroyo del Vizcaíno (AdV, Fariña et al. 2014) is a site with evidence of human presence in South America before the LGM. Among the flaws of their critique, it must be mentioned that they decide to utterly ignore a few lines of evidence that sustain the questioned hypothesis (mortality profile of the individuals of the megafauna found there, representation of their anatomical regions, relative proportions of the Voorhies groups, etc.), state misled interpretation of the chronology and stratigraphy, refuse to accept the presence of human-modified lithics and show also non-acceptance of the conclusions of our thorough study of the key evidence, the cut-marks (Fariña et al. 2014, Fariña 2015, Domínguez-Rodrigo et al. 2021), based on a purported ideal of how a site should be researched, which leave aside those that point out at different conclusions from theirs. KEYWORDS: Megafauna; Pre-Clovis; pre-LGM; Pleistocene; South America

The earliest widely accepted presence of humans in America dates to approximately 17.5 cal kyr BP, at the end of the Last Glacial Maximum (LGM). Among other evidence, this presence is attested by stone tools and associated cut-marks and other bone surface modifications (BSM), interpreted as the result of the consumption of animals by humans. Claims of an older human presence in the continent have been made based on the proposed anthropogenic modification of faunal remains; however, these have been controversial due to the highly subjective nature of the interpretations. Here, we employ advanced deep learning algorithms to objectively increase the accuracy of BSM identification on bones. With several models that exhibit BSM classification accuracies greater than 94%, we use ensemble learning techniques to robustly classify a selected sample of BSM from the approximately 30 kyr BP site of Arroyo del Vizcaíno, Uruguay. Our results confidently show the presence of cut-marks imparted by ...

La temprana presencia de caballos en campos de la actual República Oriental del Uruguay abre la posibilidad de que el proceso por el cual las sociedades autóctonas devinieron ecuestres haya ocurrido con escasa participación de la sociedad colonial. En este artículo se presenta un hallazgo realizado en el sitio del arroyo del Vizcaíno y se reflexiona sobre sus alcances.The early presence of horses in the wild in the current territory of the Oriental Republic of Uruguay, opens the possibility that the process by which indigenous societies became equestrian occurred with little involvement of colonial society. In this article we discuss a finding from the arroyo del Vizcaíno site and reflect on its implications

<strong>Left_inner_ear_Doedicurus.stl</strong>: digital model of the inner ear of <em>Doedicurus </em>in stl format. <strong>Left_inner_ear_Glyptodon.stl</strong>: digital model of the inner ear of <em>Glyptodon </em>in stl format. <strong>Left_inner_ear_Holmesina.stl</strong>: digital model of the inner ear of <em>Holmesina</em> in stl format. <strong>Left_inner_ear_Panochthus.stl</strong>: digital model of the inner ear of <em>Panochthus </em>in stl format. <strong>Left_inner_ear_Pseudoplohophorus.stl</strong>: digital model of the inner ear of <em>Pseudoplohophorus </em>in stl format. <strong>Matrix.nex:</strong> Matrix used to perform the phylogenetic analysis of xenarthrans based on inner ear characters. <strong>PC1, PC2, PC3 loadings plot.pdf:</strong> Figures showing the loadings of the morphometric variables in each of the first three principal components. <strong>Principal Components Analysis.xlsx:</strong> Spreadsheet with the results of the Principal Components Analysis: PC summary, PC scores, and PC loadings. T<strong>able S1. Deviation from orthogonality.pdf:</strong> Deviation from orthogonality (log<sub>10</sub>90var), and agility categories from Spoor et al. (2007). <strong>Tree-PGLS.tre:</strong> Tree based on the most recent phylogenetic hypotheses using molecular and morphological data and time-scaled a posteriori, to perform the PGLS analysis with the morphological data of the inner ear.

Sloths, like other xenarthrans, are an extremely interesting group of mammals that, after a long history of evolution and diversification in South America, became established on islands in the Caribbean and later reached North America during the Great American Biotic Interchange. In all three regions they were part of the impressive Pleistocene megafauna. Most taxa became extinct and only two small, distantly related tree-dwelling genera survived. Here we incorporate several recently described genera of sloths into an assembled morphological data supermatrix and apply Bayesian inference, using phylogenetic and morphological clock methods, to 64 sloth genera. Thus, we investigate the evolution of the group in terms of the timing of divergence of different lineages and their diversity, morphological disparity and biogeographical history. The phylogeny obtained supports the existence of the commonly recognized clades for the group. Our results provide divergence time estimates for the major clades within Folivora that could not be dated with molecular methods. Lineage diversity shows an early increase, reaching a peak in the Early Miocene followed by a major drop at the end of the Santacrucian (Early Miocene). A second peak in the Late Miocene was also followed by a major drop at the end of the Huayquerian (Late Miocene). Both events show differential impact at the family level. After that, a slight Plio-Pleistocene decline was observed before the marked drop with the extinction at the end of the Pleistocene. Phenotypic evolutionary rates were high during the early history of the clade, mainly associated with Mylodontidae, but rapidly decreased to lower values around 25 Ma, whereas Megalonychidae have lower values at the beginning followed by a steady increase, peaking during the Late Miocene and the Pliocene. Morphological disparity showed a similar trend, with an early increase, followed by a slowly increasing phase through the Late Oligocene and Early Miocene, and ending with another increase beginning at the middle of the Miocene. Biogeographic analysis showed southern South America as the most probable area of origin of the clade and the main region in which the early diversification events took place. Both Megatheriinae and Nothrotheriinae basal nodes were strongly correlated with Andean uplift events, whereas the early history of Mylodontidae is closely associated with southern South America and also shows an early occupation of the northern regions. Within Megalonychidae, our results show Choloepus as a descendant of an island dispersing ancestor and a probable re-ingression to South America by a clade that originated in Central or North America

ABSTRACT Mylodontidae (Mammalia, Xenarthra) is a family of ground sloths widely distributed in the South American fossil record, with members also present in Central and North America. Within the Mylodontidae, Lestodon armatus is the largest species, with an estimated body mass of more than three tonnes. This work focuses on the enlarged lower caniniforms of L. armatus as possibly exaggerated sexually dimorphic structures. Lower caniniforms from the late Pleistocene of Argentina, Uruguay, and Bolivia were studied using specimens from seven palaeontological collections. The possible sexual dimorphism in the caniniforms and its implications regarding the existence of sexual selection was assessed through morphometric analyses. The results support the existence of sexual dimorphism in L. armatus. Sexual dimorphism in an exaggerated structure in a large mammal suggests the existence of sexual selection, via competition between males or female mate choice, resulting in the evolution of the dimorphic structure. In L. armatus, the enlarged caniniforms would correspond to males and could have functioned as armaments in intraspecific fights or ornaments for sexual display. Based on observations in extant mammals, a polygynous mating system is proposed as highly probable in L. armatus, although the existence or composition of social groups cannot be certainly determined.

The inhibitory cascade (IC) represents a developmental model that explains the evolution of molar relative sizes, originally described in rodents but later validated in several mammalian groups. The IC comprises signalling molecules produced by the first molar buds that inhibit the development of subsequent molars and molecules from surrounding tissues that have opposite effects. Sloths, as xenarthrans, present many peculiarities in their dentition, like tooth and enamel loss, homodonty, and changes in the typically mammalian dental formula. Here, we test the existence of an IC and explore the evolution of the lower dentition in sloths. We studied the variability of molariform proportions in 20 specimens of the Late Pleistocene ground sloth Lestodon armatus. We also analysed molariforms proportions in 53 sloth genera to explore evolutionary trends. Our results show that the lower dentition of most sloths complies with the IC model, despite the difficulties of assessing dental homolo...

... Karen Perelmuter, Pablo Peraza, Marcelo Lanzilotta, Patricia Polero and Andres Rey helped in collecting the data. 6. References Astrand, PO and Rodahl, K. (1980) Fisiología del trabajo físico. Ed. Panamericana, Buenos Aires. Barfield, WR, Kirkendall, DT and Yu B. (2002). ...

Sloths, like other xenarthrans, are an extremely interesting group of mammals that, after a long history of evolution and diversification in South America, became established on islands in the Caribbean and later reached North America during the Great American Biotic Interchange. In all three regions, they were part of the impressive Pleistocene megafauna. Most taxa became extinct and only two small, distantly related tree-dwelling genera survived. Here we incorporate several recently described genera of sloths into an assembled morphological data supermatrix and apply Bayesian inference, using phylogenetic and morphological clock methods, to 64 sloth genera. Thus, we investigate the evolution of the group in terms of the timing of divergence of different lineages and their diversity, morphological disparity and biogeographical history. The phylogeny obtained supports the existence of the commonly recognized clades for the group. Our results provide divergence time estimates for the...

In this study, we focused on the exceptionally large mammals inhabiting the Americas during the Quaternary period and the paramount role of body size in species ecology. We evaluated two main features of Pleistocene food webs: the relationship between body size and (i) trophic position and (ii) vulnerability to predation. Despite the large range of species sizes, we found a hump-shaped relationship between trophic position and body size. We also found a negative trend in species vulnerability similar to that observed in modern faunas. The largest species lived near the boundary of energetic constraints, such that any shift in resource availability could drive these species to extinction. Our results reinforce several features of megafauna ecology: (i) the negative relationship between trophic position and body size implies that large-sized species were particularly vulnerable to changes in energetic support; (ii) living close to energetic imbalance could favour the incorporation of ...

Species distribution models (SDMs) for the last interglacial (LIG), the global last glacial maximum (LGM) and the Holocene climatic optimum (HCO) were generated for three extinct South American Pleistocene mylodontid giant sloths,Glossotherium robustum,Lestodon armatusandMylodon darwinii. They are recorded co-occurring in some localities including Arroyo del Vizcaíno site (AdV) in Uruguay. Co-occurrence records were studied based on the overlap of their generated areas of potential distributions, and compared with the available biome reconstructions of South America during the LGM to analyze their distribution patterns, ecological requirements and possible interactions between them. Our results suggest that these sloths could have co-existed mainly in the Chaco-Paraná Basin and the plains in the Río de la Plata area. Areas of high suitability were observed for submerged parts of the continental shelf that were exposed during the LGM showing an overall increase in potential habitat c...

For over 200 years, fossils of bizarre extinct creatures have been described from the Americas that have ranged from giant ground sloths to the 'native' South American ungulates, groups of mammals that evolved in relative isolation on South America. Ground sloths belong to the South American xenarthrans, a group with modern although morphologically and ecologically very different representatives (anteaters, armadillos and sloths), which has been proposed to be one of the four main eutherian clades. Recently, proteomics analyses of bone collagen have recently been used to yield a molecular phylogeny for a range of mammals including the unusual…

Con una masa corporal y una envergadura alar estimadas en 80 kilogramos y 7 metros (Fig. 1), respectivamente, Argentavis magnificens debe haber sido la mayor ave voladora que haya surcado los cielos (Vizcaino, S.F. & Farina, R.A. 1999. Lethaia, 32:271). Conocida a partir de diversos vestigios fosiles recuperados en tres localidades del Mioceno superior de Argentina, con una antiguedad aproximada de seis millones de anos, esta gran ave extinta estaba emparentada con los teratornitidos, grupo bien conocido por los esqueletos completos conservados en las trampas de asfalto de Rancho La Brea, en California. La anatomia de estas aves es muy similar a la del condor, por lo que cabe suponer que las plumas del ala tendrian un metro de longitud. Con tales magnitudes resulta ciertamente dificil concebir que pudiesen despegar simplemente por el hecho de batir las alas, ya que de entrada deberian alcanzar al menos los tres metros de altura, a fin de poder realizar una batida completa; ademas, sus miembros posteriores no parecen haber estado bien configurados para efectuar una carrera que les permitiese alcanzar la velocidad suficiente para el despegue. No obstante, las condiciones climaticas reinantes en la region pampeana por aquel entonces pudieron ser bastante propicias para subsanar este problema, ya que la cordillera no era tan alta como en la actualidad, por lo que no desviaria la trayectoria de los vientos provenientes del Pacifico; de esta manera, el ave quizas podria despegar gracias al mero despliegue de las alas, corriendo lentamente contra el viento o dejandose caer desde altos penascos, como suelen hacerlo los condores.

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics,...

Discovered in 1997 during a severe drought, the Arroyo del Vizcaíno site is a richly fossiliferous Pleistocene locality usually covered by waters in a stream near the town of Sauce, Uruguay. Some of the bones show marks with features consistent with those made by human tools. Radiocarbon dates yielded an unexpectedly old age, ca. 30,000 years before present, which makes it the oldest date for a site with human evidence in the Americas. Apart from its scientific importance, several activities are in progress or planned to share this knowledge of the site with the general public. These plans include the creation of a museum where the recovered material will be kept and exhibited, which will also serve as a place for research and cultural events. Additionally, a project is being developed to involve the local high school students (and, through them, also their families) to expand community awareness of the value of the discovery, both in terms of its contribution to scientific knowledg...