Lestodon Research Articles

A window into a late Pleistocene megafauna community: Stable isotopes show niche partitioning among herbivorous taxa at the Arroyo del Vizcaíno site (Uruguay)

The analysis of stable isotopes on fossil mammals has become a widely used tool for understanding the paleoecology and paleodiet of these organisms. In this work, we study the stable isotope composition of collagen (δ13C and δ15N) and bioapatite (δ13C and δ18O) of fossil bones from Arroyo del Vizcaíno, a fossiliferous site in southern Uruguay dated to ∼32 ka cal BP. Fourteen taxa were analyzed: the ground sloths Lestodon armatus, Glossotherium robustum, Mylodon darwinii, Valgipes bucklandi and Nothrotheriops sp.; the glyptodonts Glyptodon reticulatus, Panochthus tuberculatus, and Doedicurus clavicaudatus; the equids Hippidion principale and Equus neogeus; the proboscidean Notiomastodon platensis; the notoungulate Toxodon platensis; the saber-tooth felid Smilodon populator; and an indeterminate cervid. In general, the percentage of nitrogen in collagen and the C:N ratio were within the limits expected for collagen preservation in fossil bone. The δ13C and δ15N results of the herbivores indicated that most taxa consumed high proportions of C3 plants in open, relatively dry environments, but significant variations were observed. Furthermore, relatively high values of δ18O in bone bioapatite, which approximately tracks local drinking water, indicated low precipitation and/or high evaporation. Our results show that the herbivorous taxa present at the site covered a considerable range of the grazer-browser spectrum and support the existence of niche partitioning among closely related taxa. Overall, these kinds of approaches are indispensable to better understand how these communities thrived during the Pleistocene in the region, supporting an outstanding number of giant species, before their extinction at the Pleistocene-Holocene transition.

Histotaphonomy of a Pleistocene megamammal assemblage from Argentine Pampas

This work involves a multy-proxy approach of taphonomic features of the extinct giant ground sloth Lestodon armatus (Xenarthra, Mylodontidae). The study is based on paleohistological, mineralogical, and geochemical analyses from the Late Pleistocene Playa del Barco site (Buenos Aires Province, Argentina). Transverse thin sections of ribs and vertebrae were studied under light microscope, polarizing petrographic microscope, and scanning electron microscope (SEM), combined with chemical analysis using energy dispersive spectroscopy (EDS) and micro-X-ray diffraction (μXRD). The internal crystalline structure and mineral composition remains almost unaltered. The bone microstructure is well preserved in all the samples, although it was affected by different types of microfractures and infillings. Numerous radial microcracks were identified in the secondary osteons of all specimens evidencing wet depositional environment. The mineralogical and geochemical composition of the infillings and encrustations indicates that the enrichment with new elements was due to direct exchange with the sediments in which they were buried. Mineralogical evidence from the infillings allows to identify different diagenetic pathways; most of the skeletal elements were quickly buried in the vadose zone, while others were buried in the phreatic zone, directly or after some time immersed in a continental aquatic context. The fossildiagenetic information obtained from the Lestodon armatus fossils provides novel information to interpret and reconstruct the whole taphonomic history and the environmental and climatic conditions that favored the preservation of the Playa del Barco fossil assemblage during the end of the Last Glacial Maximum.

New postcranial remains of ground sloths (Xenarthra, Folivora, Mylodontidae) from Southern Brazil

Diagnoses of Mylodontidae species are generally based on skull, mandibular, and tooth characteristics, and rarely on postcranial morphology, due to the lack of postcranial material associated with the cranial material. The studies of postcranial anatomy have generally a biomechanical focus and reflect a set of functions of skeletal structures, but their interpretation in phylogenetic analysis is still limited. In Pleistocene deposits of Rio Grande do Sul State, Brazil, an important set of postcranial specimens was collected, belonging to Mylodontidae. They were morphologically and morphometrically analyzed, allowing us to observe some diagnostic characters such as the humeral entepicondylar foramen and crests, shape of the radial shaft, angle of distal articulation of the tibia, as well as the angle of proximal articulation of the astragalus. The material was also compared with specimens from other South American localities. Most of the remains were assigned to Glossotherium robustum and Lestodon armatus. In addition, a new Scelidotheriinae was recorded for Rio Grande do Sul State. The study indicated significant differences in the postcranial morphology, which allowed the recognition of some specific diagnostic characters. Keywords: Mylodontinae, Scelidotheriinae, hindlimb, forelimb, Pleistocene, Rio Grande do Sul.

Una Fauna Local Lujanense (Pleistoceno Superior–Holoceno Inferior) del sur de Uruguay: Santa Regina, Departamento de Colonia

A Lujanian Local Fauna (Upper Pleistocene–Lower Holocene) from southern Uruguay: Santa Regina, Colonia Department. On the southwestern coast of Uruguay, in the Colonia and San José departments, sedimentary rocks that correspond to the Neogene and Quaternary are found. Herein we describe the fossiliferous locality of Santa Regina, located on the east coast of the department of Colonia. The stratigraphic profile shows at the base grayish-green sandy rocks belonging to the Camacho Formation (Upper Miocene). Overlying this unit, there is a tough yellowish-greenish siltstone in net contact, in which several pieces of a Notiomastodon platensis specimen were found. Towards the upper part, a thicker greenish-brownish bed is observed, ranging upwards from conglomerates to siltstones. The lower part of this bed includes disarticulated and fragmentary remains of Lestodonarmatus, Glyptodon reticulatus, Pampatheriidae indet., Toxodon cf. T. platensis, Morenelaphus sp., and Lycalopex gymnocercus, and to the top large portions of carapaces of Glyptodon sp. and Panochthus sp. The aforementioned mastofaunistic assemblage corresponds to the Lujanian Mammal Age or regional Stage (Upper Pleistocene-Greenlandian). The lithostratigraphy allows us to refer the two upper levels to the Dolores Formation, a characteristic unit of the Quaternary of southern Uruguay, and not to the Raigón Formation, as indicated in some previous reports for this locality. The presence of Lestodon armatus, Glyptodon reticulatus, Notiomastodon platensis, Lycalopexgymnocercus, and the probable presence of Toxodon platensis, allow us to infer landscapes of open or semi-open areas, with a predominance of grasslands and shrubs during the genesis of the deposits. Keywords: LatePleistocene–Early Holocene, land mammals, stratigraphy, Uruguay.

Sexual dimorphism in the fossil ground sloth Lestodon armatus (Xenarthra, Folivora)

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.

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

Megamammals constituted an important component in the Pleistocene faunal communities of South America. Paleobiological and paleoecological studies involving different megamammal taxa have increased significantly in the last years, but there are still several poorly-known issues of its life history. In this work, we analyze an assemblage composed of 13 individuals of different ontogenetic stages, and possibly different sex, belonging to the giant ground sloth Lestodon armatus (Xenarthra, Folivora), recovered from Playa del Barco site (Pampean Region, Argentina). A dating of 19,849 years Cal BP allows assigning this assemblage to a period of the MIS (Marine Isotope Stage) 2 related to the end of the Last Glacial Maximum. Based on multiple lines of research (e.g. taphonomy, paleopathology, osteohistology, isotopy), we interpret the origin of the assemblage and diverse paleobiological and paleoecological aspects (e.g. social behavior, ontogenetic changes, sexual dimorphism, diseases, resource and habitat use, trophic relationships) of L. armatus. Evidence suggests that the assemblage was formed by a local single event of catastrophic mortality, which affected different members of a social group. This record represents the first accurate evidence of gregariousness for this ground sloth, providing new data on a poorly-known behavior among extinct Folivora.

A Fossil Bone of a Giant Ground Sloth from the Last Millennium of the Pleistocene: New Data from Salto Department, Uruguay

During the Pleistocene-Holocene transition at ~10.0 uncalibrated, or ~11.7 calibrated kya, the Americas were undoubtedly inhabited by humans from north to south ends. The groups living in that time had cultural and adaptive differences in terms of subsistence and technological pursuits. Particularly in the southern cone of South America, archaeological remains witnessed hunter-gatherers living at ~11.0 - 10.0 uncalibrated kya. They mostly used the so-called “fishtail,” or just “Fell” points, a widespread Paleo-American marker. Despite that, they exploited different faunal species, including extant and extinct fauna. At the Salto Department in the northwestern region of Uruguay, on the Itaperibí Grande creek shore, archaeological remains of bones and stones were recovered. One of the most remarkable is a fragmented fossil femur of Lestodon armatus, a mega-mammal giant ground sloth. In its anterior face, this specimen shows diverse kinds of marks. However, no clear association among the findings was documented. Then, in order to check the possible relationship between the bone and the artifacts, the specimen was subjected to radiocarbon dating and it was analyzed in detail from a taphonomic perspective to evaluate the origin of the marks. The radiocarbon assay indicates that the specimen belongs to the last millennium of the Pleistocene. The date is relevant as it is one of the few assays obtained on a sample from that time. The taphonomic study revealed that the marks were not produced by human activity, hence, its primary relationship with the stone artifacts is uncertain. Despite that, these data make an important contribution to the knowledge about the fauna contemporaneously living with the earliest hunter-gatherer that were foraging the regional landscape during one of the colonization events that populated the southern cone of South America.

Unexpected inhibitory cascade in the molariforms of sloths (Folivora, Xenarthra): a case study in xenarthrans honouring Gerhard Storch’s open-mindedness

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 homologies with other mammals. Furthermore, we tested the existence of different patterns among families, obtaining support for models taking mylodontids and orophodontids separately from the rest of sloths. Also, members of Mylodontidae show a unique IC pattern, with a slope considerably higher than 2 and an mf1 ≤ mf2 << mf3 configuration. This pattern could be related to the morphological adaptations to grazing showed by mylodontids during most of their evolutionary history.

A new record of Lestodon armatus Gervais 1855 (Xenarthra, Mylodontidae) from the Quaternary of southern Brazil and remarks on its postcranial anatomy

ABSTRACT Mylododontidae (Xenarthra: Folivora) includes ground sloths of medium to large size. Lestodon armatus is a mylodontid that have been found in Pleistocene fossiliferous deposits of South America, with most of its records at the southern portion of the continent. Here, we reported a new specimen assigned to this species recovered from a Quaternary deposit in Caçapava do Sul, southern Brazil. The specimen is composed of cranial fragments, vertebrae, articulated hind limb and pes, as well as other post-cranial elements. We described the post-cranial morphology of this specimen, including some elements not yet described for this species, such as the ossified meniscus, cyamo-fabella, and the fusion of the tibia and fibula. The new record contributes to the knowledge on the anatomy of L. armatus as well as to the study of the diversity of the extinct mammalian fauna from southern Brazil.

Archaeomylodon sampedrinensis, gen. et sp. nov., a new mylodontine from the middle Pleistocene of Pampean Region, Argentina

ABSTRACTThe Mylodontinae from the late Pleistocene (Lujanian Stage/Age) of Argentina, represented by Lestodon armatus, Mylodon darwinii, and Glossotherium robustum, are known from numerous remains, whereas early and middle Pleistocene Mylodontinae are less well characterized owing to insufficient material. In this work, we describe a new genus and species of Mylodontinae from the Ensenadan Stage/Age based on a cranium and comparisons with South and North American Mylodontinae. The new genus is similar to the taxon Mylodon darwinii, but the presence of plesiomorphic characteristics support a more primitive status for this novel sloth. The addition of this new taxon, Archaeomylodon sampedrinensis, gen. et sp. nov., increases the diversity of Mylodontinae during the middle Pleistocene. This new mylodontine in the middle Pleistocene is an important reference point for interpretations of increasing body size in South American Mylodontinae during the Pliocene–Pleistocene. These changes in body size may have been influenced by the arrival of Holarctic immigrants to South America.

Potential Distribution of Fossil Xenarthrans in South America during the Late Pleistocene: co-Occurrence and Provincialism

Species distribution models (SDMs) are helpful for understanding actual and potential biogeographical traits of organisms. These models have recently started to be applied in the study of fossil xenarthrans. SDMs were generated for 15 South American late Pleistocene xenarthrans: eight Cingulata (Glyptodon clavipes, Doedicurus clavicaudatus, Panochthus tuberculatus, Neosclerocalyptus paskoensis, Pampatherium typum, Pampatherium humboldtii, Holmesina paulacoutoi, and Holmesina occidentalis) and seven Folivora (Glossotherium robustum, Lestodon armatus, Mylodon darwinii, Catonyx cuvieri, Catonyx (=Scelidodon) chilensis, Megatherium americanum, and Eremotherium laurillardi). Models were evaluated for three periods: the last interglacial (LIG), the last glacial maximum (LGM), and the Holocene climatic optimum (HCO). Co-occurrence records were studied based on the overlap of the potential distributions and compared with the available biome reconstructions of South America during the LGM to analyze species distribution patterns, ecological requirements, and possible interactions. Our results suggest the existence of provincialization within xenarthran megamammals grouped in at least three bioregions. Northern and southwestern taxa overlap in the Rio de la Plata region where also some endemic taxa are found. We observed overlapping potential distributions but separated and continuous realized distributions between closely related xenarthrans suggesting competitive exclusion. A generalized reduction in potential habitats at the end of the Pleistocene was not obvious as some taxa show stable potential areas during HCO when comparing with LGM. Nonetheless, fragmentation of the most suitable areas due to climate variation and the impact of reduction in available land due to sea level changes cannot be ruled out as involved in the extinction.

Thoracic member (pectoral girdle and forelimb) bones of Mylodon darwinii Owen (Xenarthra, Mylodontidae) from the Late Pleistocene of Central Argentina and their phylogenetic implications

A nearly complete skeleton, including most of the thoracic member bones of the sloth Mylodon darwinii, have been found in Upper Pleistocene strata from Anisacate River, Argentina. The thoracic member bones resemble their homologues in Glossotherium robustum, Paramylodon harlani, and Mylodonopsis ibseni in the following traits: (1) the olecranon is mediolaterally compressed; (2) the radius has an acute styloid process; (3) the radial diaphysis medial border is straight for two thirds of its length; (4) the radial shaft medial border forms an angle with the medial border of the styloid process. The radius presents a distinctive, mostly proximally facing articular circumference. The unfused epiphyses and feeble muscle attachment ridges indicate a sub-adult ontogenetic stage. Deviation of the olecranon and weak M. teres major origin and insertion, suggest a low fossorial specialization. The structure of the thoracic limb bones does not support climbing habits, because pronation-related features are reduced and the humeral head is not prominent. The structure of the radius suggests graviportal adaptations: the proximal head is mediolaterally expanded and the diaphysis straight. A phylogenetic analysis adding thoracic member characters recovers M. darwinii as part of a clade that includes Glossotherium robustum and Paramylodon harlani, but excludes Lestodon armatus. This contrasts with the results of previous analyses focusing on the head skeleton, highlighting the relevance of sampling postcranial characters in phylogenetic analyses of mylodontine sloths.

Ungual phalanges analysis in Pleistocene ground sloths (Xenarthra, Folivora)

Ungual phalanges (the most distal bone within a limb) and claws (the overlying corneous sheath) from the third digit of the forefoot of selected Pleistocene ground sloths (Lestodon armatus, Glossotherium robustum, Scelidotherium leptocephalum and Megatherium americanum) are analysed, as well as those of some living xenarthrans for actualistic comparison, aiming at testing hypotheses of substrate usage and locomotor behaviour. The third digits were chosen for this study because of its size and nearly perfect bilateral symmetry, which increases the possibilities of revealing functional differences between taxa. The analyses performed were of inner and external curvature, the strength indicator and the mechanical advantage. The mechanical advantage indicates that the four ground sloths’ species were well adapted for strenuous activities, such as digging, in which force rather than velocity is optimised. Their strength indicator shows expected values for their body size, while in Mylodon darwinii the value obtained was lower than expected. In the two curvature analyses L. armatus, G. robustum and M. americanum fall within the group of armadillos that dig, whereas S. leptocephalum does not, this might be due to a difference in the movements performed while performing an activity such as digging or similar to it.

Co-occurrence of mylodontid sloths and insights on their potential distributions during the late Pleistocene

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 armatus and Mylodon 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 compared to the LIG and HCO. This suggests that there was a drastic reduction in total available areas of preferred habitat at the end of the Pleistocene. The co-occurrence of these sloths at the AdV site suggests the presence of vegetation indicative of mainly open, cold to temperate habitats but with mixed patches typical of humid climates.

Description of the stylohyal bone of a giant sloth (Lestodon armatus)

The hyoid apparatus in fossil Xenarthrans is rarely preserved. Its largest bone, the stylohyal, is the most frequently found as an isolated element. It is known for some species of Pleistocene ground sloths (Megalonyx jeffersonii, Megatherium americanum, Paramylodon harlani, Nothrotheriops shastensis, Glossotherium robustum and Scelidotherium leptocephalum) but not for the largest mylodontid Lestodon armatus. Here we describe a right stylohyal found in the late Pleistocene megafaunal bonebed of the Arroyo del Vizcaino site, Uruguay, as two perfectly matched pieces that were within a few centimeters of each other. A small notch, possibly a conchoidal flaked perimortem fracture, is observed in the lateral face. The specimen, whose general form is a sinusoid cylinder with the proximal end expanded and compressed, must have belonged to a juvenile individual, since it lacks both the distal and proximal surfaces that articulate with the skull and the epihyal, respectively. Instead, both ends show an irregular surface as those seen in the contact with the growth cartilage. Additionally, its maximum length is 105 mm, larger than the equivalent part of the stylohyal of adult Glossotherium. At the expanded proximal end that articulates with the skull the large fossa found in Glossotherium and Scelidotherium cannot be observed, which could be due to a taxonomic difference, to the stage of growth or both of them. The bone shows marks, several interpreted as caused by trampling and at least one with features as those left by human tools. P. Sebastian Tambusso. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay pasebita@gmail.com H. Gregory McDonald. Museum Management Program, National Park Service, 1201 Oakridge Drive, Fort Collins, Colorado 80521 USA greg_mcdonald@nps.gov Richard A. Farina. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay dogor@netgate.com.uy

Megafauna from the Late Pleistocene-Holocene deposits of the Upper Ribeira karst area, southeast Brazil

The carbonate caves of the Upper Ribeira Valley, southeastern São Paulo State, Brazil, preserve an abundant fossil record of Pleistocene-Holocene South American megafauna. Nevertheless, in comparison with other localities of the country, its paleontological knowledge still can be considered sparse and in need of further research. This work presents an update taxonomic survey of the megafauna material collected since the beginning of the explorations in the area. Based on this, it discusses paleobiogeographic and paleoecological questions. The fossil megafauna of the Upper Ribeira karst region include: Eremotherium laurillardi, Nothrotherium maquinense, Lestodon armatus, Catonyx cuvieri, ‘Ocnopus gracilis’, Ahytherium aff. a ureum, Glyptodon clavipes, G. reticulatus, Hoplophorus cf., Toxodon spp., Stegomastodon waringi, Equidae ( Hippidion cf.), Tapirus terrestris, Panthera onca and Smilodon populator. Only P. onca and T. terrestris still remain in the region. Despite the occurrence of some typical taxa of the pampean paleobiogeographical province, the fossil assemblage recorded shows greater affinity to the mega-mammal community of the intertropical region. The ecology of species found suggests the previous occurrence of fairly different environmental settings than the existing one in the area. There were more temperate climates – both dry and wet – until the current mesophytic forest was finally established. The studied material does not show any kind of chrono-correlation, given the type of genesis of the cave accumulations. These fossils depict different faunistic moments related to climate changes during the Quaternary. To better understand the information provided by these deposits, efforts on dating and detailed taphonomic investigations should be conducted. The studies of the Quaternary fauna in the state of São Paulo fill an important gap in the intricate biogeographical history of the South American megafauna.

Fósseis de Scelidotheriinae Ameghino, 1904 (Xenarthra, Pilosa) em depósitos pleistocênicos do Rio Grande do Sul, Brasil

O registro fossil da familia Mylodontidae no sul do Brasil tem se mostrado abundante e inclui formas de tres generos da subfamilia Mylodontinae, Mylodon, Glossotherium e Lestodon e o Scelidotheriinae Catonyx. Neste trabalho, sao apresentados novos registros da subfamilia Scelidotheriinae, coletados em depositos fossiliferos da regiao costeira do Rio Grande do Sul. Os especimes consistem em um fragmento de dentario direito e outros quatro dentes isolados. E apresentada tambem uma descricao detalhada do unico registro de Catonyx para o Rio Grande do Sul, que consiste de um dentario direito quase completo. A ausencia de outros elementos associados e mais completos dificulta uma completa identificacao taxonomica do material. Os especimes, contudo, apresentam caracteres que possibilitam identifica-los ao genero Catonyx. Aqui, sao tentativamente classificados como C. cuvieri, com base na premissa de que este e o unico scelidoterineo valido ate o momento para o sul do Brasil. Palavras-chave: Xenarthra, Pilosa, Scelidotheriinae, Catonyx sp., Pleistoceno, Brasil.

Body mass estimation in xenarthra: A predictive equation suitable for all quadrupedal terrestrial placentals?

The Magnorder Xenarthra includes strange extinct groups, like glyptodonts, similar to large armadillos, and ground sloths, terrestrial relatives of the extant tree sloths. They have created considerable paleobiological interest in the last decades; however, the ecology of most of these species is still controversial or unknown. The body mass estimation of extinct species has great importance for paleobiological reconstructions. The commonest way to estimate body mass from fossils is through linear regression. However, if the studied species does not have similar extant relatives, the allometric pattern described by the regression could differ from those shown by the extinct group. That is the case for glyptodonts and ground sloths. Thus, stepwise multiple regression were developed including extant xenarthrans (their taxonomic relatives) and ungulates (their size and ecological relatives). Cases were weighted to maximize the taxonomic evenness. Twenty-eight equations were obtained. The distribution of the percent of prediction error (%PE) was analyzed between taxonomic groups (Perissodactyla, Artiodactyla, and Xenarthra) and size groups (0-20 kg, 20-300 kg, and more than 300 kg). To assess the predictive power of the functions, equations were applied to species not included in the regression development [test set cross validation, (TSCV)]. Only five equations had a homogeneous %PE between the aforementioned groups. These were applied to five extinct species. A mean body mass of 80 kg was estimated for Propalaehoplophorus australis (Cingulata: Glyptodontidae), 594 kg for Scelidotherium leptocephalum (Phyllophaga: Mylodontidae), and 3,550.7 kg for Lestodon armatus (Phyllophaga: Mylodontidae). The high scatter of the body mass estimations obtained for Catonyx tarijensis (Phyllophaga: Mylodontidae) and Thalassocnus natans (Phyllophaga: Megatheriidae), probably due to different specializations, prevented us from predicting its body mass. Surprisingly, although obtained from ungulates and xenarthrans, these five selected equations were also able to predict the body mass of species from groups as different as rodents, carnivores, hyracoideans, or tubulidentates. This result suggests the presence of a complex common allometric pattern for all quadrupedal placentals.

New Mylodontoidea (Xenarthra, Phyllophaga) from the Middle Miocene‐Pliocene of Venezuela

Synopsis Two new genera of Mylodontoidea, Mirandabradys and Bolivartherium, and five new species, M. socorrensis (Socorro Formation, Middle Miocene), M. urumaquensis and B. urumaquensis (Urumaco Formation, Upper Miocene), M. zabasi and B. codorensis (Codore Formation, Pliocene) are described. There is a high diversity of tardigrades from Middle Miocene to Pleistocene sites of Northern Venezuela. Almost all the recorded species are large and close to the size of the late Pleistocene Glossotherium robustum or Lestodon armatus. This implies that either the ‘faunas’ were composed only of large‐sized tardigrades, or that the smaller taxa are missing because of taphonomic bias and that the faunal diversity was actually higher than currently indicated.

Muzzle of South American Pleistocene ground sloths (Xenarthra, Tardigrada)

Sloths are among the most characteristic elements of the Cainozoic of South America and are represented, during the Pleistocene, by approximately nine genera of gigantic ground sloths (Megatheriidae and Mylodontidae). A few contributions have described their masticatory apparatus, but almost no attention has been paid to the reconstruction of the muzzle, an important feature to consider in relation to food intake, and particularly relevant in sloths because of the edentulous nature of the muzzle and its varied morphology. The relationship between dietary habits and shape and width of the muzzle is well documented in living herbivores and has been considered an important feature for the inference of alimentary styles in fossils, providing an interesting methodological tool that deserves to be considered for xenarthrans. The goal of this study was to examine models of food intake by reconstructing the appearance and shape of the muzzle in five species of Pleistocene ground sloths (Megatherium americanum, Glossotherium robustum, Lestodon armatus, Mylodon darwini, and Scelidotherium leptocephalum) using reconstructions of the nasal cartilages and facial muscles involved in food intake. The preservation of the nasal septum, and the scars for muscular attachment in the rostral part of the skulls, allow making a conservative reconstruction of muzzle anatomy in fossil sloths. Wide-muzzled ground sloths (Glossotherium and Lestodon) had a square, nonprehensile upper lip and were mostly bulk-feeders. The lips, coupled with the tongue, were used to pull out grass and herbaceous plants. Narrow-muzzled sloths (Mylodon, Scelidotherium, and Megatherium) had a cone-shaped and prehensile lip and were mixed or selective feeders. The prehensile lip was used to select particular plants or plant parts.