Pleistocene Giant Sloths Found in Brazil

New Pleistocene remains of megalonychid ground sloths (Xenarthra: Pilosa) from the intertropical Brazilian region

Authors:

De Iuliisa et al

Abstract:

The Pleistocene fossil sloth Australonyx aquae De Iuliis, Cartelle, and Pujos, 2009 (Mammalia, Xenarthra, Megalonychidae) was described from the intertropical region of Brazil. However, its mandible was not known and only cursory descriptions of the ear ossicles were included. The mandible was subsequently recognized among the remains originally collected from the type locality, and belongs to the holotype individual. As a particularly important skeletal element for specific recognition, it requires description to complement our understanding of this species. The ossicles, usually poorly represented in the fossil record, require further description to allow differentiation from those of other sloths. Comparisons of the mandible and ossicles are conducted with homologous elements of the contemporaneous and sympatric Ahytherium aureum Cartelle, De Iuliis, and Pujos, 2008, the only other megalonychid sloth known from intertropical Brazil, and reinforce the distinction between these two species detailed in their initial descriptions. Comparisons with other sloths (e.g., Acratocnus, Megalonyx, Neocnus) also reveal differences with Au. aquae in such features as form and size of the caniniform tooth, angular process, and mandibular condyle. Differences among the malleus and incus of Au. aquae and several species of other sloth clades reveal clade level distinctions among Megatheriidae, Nothrotheriidae, and Megalonychidae. A well-preserved skull from the Brazilian state of Rondônia is noted as probably belonging to Au. aquae. This skull cannot be assigned formally to this species because it is not deposited in a recognized institution, but it does extend considerably the known range of the species.

Ground Sloths Spread Into North America Multiple Times

The manus of Mylodon darwinii Owen (Tardigrada, Mylodontidae) and its phylogenetic implications

Authors:

Haro et al

Abstract:

The first nearly complete and articulated manus of the ground sloth Mylodon darwinii, from the upper Pleistocene of Argentina, is described. It shares similarities with Mylodonopsis ibseni from Brazil, including a cuneiform with a distinct pisiform facet, an obliquely concave ulnar facet, and a prominent distolateral process, as well as a gracile metacarpal III. It shares a flattened pisiform with Glossotherium robustum. The trapezoid is unique in the obliquely elongate proportions of its dorsal surface. Shapes of the articular facets indicate different functions in digits II and III, with the former having a greater range of motion and the latter greater stability at the joints. Clear arboreal or fossorial adaptations are absent. A phylogenetic analysis recovered M. darwinii as closely related to M. ibseni and agrees with larger phylogenetic analyses of sloths based on craniomandibular evidence. Our data support more than two mylodontine dispersal events to North America.

A Remarkable Neogene Assemblage of Sloths in Colombia

Neogene sloth assemblages (Mammalia, Pilosa) of the Cocinetas Basin (La Guajira, Colombia): implications for the Great American Biotic Interchange

Authors:

Amson et al

Abstract:

We describe sloth assemblages from the Cocinetas Basin (La Guajira peninsula, Colombia), found in the Neogene Castilletes and Ware formations, located in northernmost South America, documenting otherwise poorly known biotas. The tentative referral of a specimen to a small megatherioid sloth, Hyperleptus?, from the early–middle Miocene Castilletes Formation, suggests affinities of this fauna with the distant Santa Cruz Formation and documents a large latitudinal distribution for this taxon. The late Pliocene Ware Formation is much more diverse, with five distinct taxa representing every family of ‘ground sloths’. This diversity is also remarkable at the ecological level, with sloths spanning over two orders of magnitude of body mass and probably having different feeding strategies. Being only a few hundred kilometres away from the Isthmus of Panama, and a few hundred thousand years older than the classically recognized first main pulse of the Great American Biotic interchange (GABI 1), the Ware Formation furthermore documents an important fauna for the understanding of this major event in Neogene palaeobiogeography. The sloths for which unambiguous affinities were recovered are not closely related to the early immigrants found in North America before GABI 1.

Giant Sloth Megatherichnum Trackway From Miocene Neogene Argentina is NOT Bipedal

Late Miocene ground sloth footprints and their palaeoenvironment: Megatherichnum oportoi revisited

Authors:

Melchor et al

Abstract:

Fossil footprints of ground sloths are mostly restricted to the late Miocene to Pleistocene of South America. This study is focused on the oldest known ground sloth trackways, Megatherichnum oportoi Casamiquela, 1974 from the late Miocene Río Negro Formation of northern Patagonia. The section logged at the study site, near Carmen de Patagones (Buenos Aires province), includes the uppermost part of the middle member (marine) and the upper member (aeolian) of the Río Negro Formation. Identified sedimentary facies can be grouped into four facies associations: tidal flat, aeolian dune, dry/damp interdune and wet interdune (shallow lacustrine). M. oportoi trackways are preserved in an upper intertidal mixed flat. Associated trace fossils belong to a wet aeolian system developed close to the sea coast and were mostly preserved in interdune facies. These include Poaceae root and stem traces and Nagtuichnus meuleni (Chlamyphorinae burrow) in dry interdune facies, indeterminate tetrapod footprints in damp interdune facies, Lockeia siliquaria and chevron-like trace fossils (bivalve resting and horizontal locomotion traces) in wet interdune facies (shallow lakes), and Palaeophycus tubularis in aeolian dune facies. The most likely trackmaker of M. oportoi is Pyramiodontherium sp. (Megatheriinae), recorded from the same stratigraphic unit at Chubut province, with a body mass ranging from 2.5 to 3.6 tonnes. M. oportoi is interpreted as a quadrupedal trackway of a late Miocene ground sloth without overlap of the pes on the manus. The previously proposed bipedal interpretation for the trackway requires angles of gait in excess of those permitted for such a large and heavy animal. Pleistocene ground sloth trackways are distinctive because of the much smaller size of the fore footprint. For the latter examples, a quadrupedal locomotion with overlap of the pes on the manus may be applied.

Reconstruction of the Hind Limb of Santacrucian Miocene Neogene Sloths From Patagonia

Muscular Reconstruction and Functional Morphology of the Hind Limb of Santacrucian (Early Miocene) Sloths (Xenarthra, Folivora) of Patagonia

Authors:

Toledo et al

Abstract:

This article presents a morphofunctional analysis of the hind limb of Santacrucian (Early Miocene) sloths from southernmost Patagonia (Argentina). These fossil sloths were mid sized to large animals, ranging from 40 to 120kg, and their postcranial skeleton was markedly different in shape compared to that of extant tree sloths, which vary from 2 to 10kg. The functional anatomy of the hind limb of Santacrucian sloths was compared with that of living xenarthrans (tree sloths, anteaters and armadillos), which involved reconstruction of the hind limb musculature and comparative and qualitative morphofunctional analyses, and hypotheses on the biological role of the hind limb in terms of preferences in substrate, posture and strategies of locomotion were formulated. The hind limb of Santacrucian sloths bears strong resemblances to that of living South American anteaters in stoutness of skeletal elements, form of the characteristics related to muscular and ligamentous attachments, and conservative, pentadactylous strong-clawed pes. The musculature was very well developed, allowing powerful forces, principally in entire limb adduction, crus flexion and extension, pes extension and toe prehension. These functional features, together with those of the forelimb, are congruent with climbing behavior, and support the hypothesis that Santacrucian sloths were good but slow climbing mammals. However, their climbing strategies were limited, owing principally to their comparatively large body size, and they relied to a large extent on their powerful musculature and curved manual and pedal unguals for both moving and standing on the arboreal supports. This article is protected by copyright. All rights reserved.

Lakukullus anatisrostratus: a new Miocene Neogene Nothrotheriid Sloth From Bolivia

Lakukullus anatisrostratus, gen. et sp. nov., a new massive nothrotheriid sloth (Xenarthra, Pilosa) from the middle Miocene of Bolivia

Authors:

Pujos et al

Abstract:

Xenarthra constitute one of the most representative groups of South American endemic mammals. The armored Cingulata is recorded beginning in the Itaboraian SALMA (lower Eocene; Pujos et al., 2012). Its sister group is Pilosa, which includes Tardigrada, the sloths, and Vermilingua, the South American anteaters.

Sloths appear during the Eocene–Oligocene transition (Tinguirirican SALMA) in Chile, represented by Pseudoglyptodon (McKenna et al., 2006). The late Oligocene Deseadan SALMA saw the emergence of Mylodontidae (e.g., Octodontotherium and Orophodon) and Megalonychidae (e.g., Deseadognathus) in Patagonia and the Bolivian altiplano (Pujos et al., 2007). Megatherioidea appear later during the middle Miocene, Megatheriidae in the Santacrucian SALMA (i.e., Megathericulus; Pujos et al., 2013), and Nothrotheriidae in the Huayquerian SALMA (i.e., Mionothropus; De Iuliis et al., 2011). According to De Iuliis et al. (2011), Nothrotheriidae is supported by 13 unequivocal synapomorphies and includes at least five genera: Mionothropus, Pronothrotherium, Thalassocnus, Nothrotherium, and Nothrotheriops. Several possible nothrotheriids, generally represented by poor material, have been described from Colombia (Huilabradys), Argentina (e.g., Nothropus, Chasicobradys, Amphibradys, and Xyophorus), and Bolivia (Xyophorus and Hiskatherium). Those from Argentina are poorly diagnosed, cannot certainly be differentiated morphologically from other taxa such as Hapalops, and are likely invalid. Nothropus priscus is exclusive to the Pleistocene of Argentina and is not present in the Amazon (see De Iuliis et al., 2011, for further details). By its central geographical position in South America, the present territory of Bolivia (Fig. 1) has played an important role in the evolution and diversity of mammals during the Paleogene and Neogene periods (Croft, 2007), although few nothrotheriids have been recorded from this country. St.-Andr e (1996) assigned a dentary and an astragalus to Xyophorus villarroeli from the Huayquerian SALMA of Achiri; previously this genus was known from the Santacrucian (Ameghino, 1887, 1891, 1894) and Chasicoan of Argentina with X. bondesioi (Scillato-Yan e, 1979). A partial skull and mandible of X. villarroeli is also recorded from the Laventan SALMA of Quebrada Honda (D Hapalops angustipalatus Frailey, 1988; Fig. 3 A–D; see Scillato-Yan e and Carlini, 1999, for further details), which also yielded the dentary of the peculiar Megatherioidea Hiskatherium saintandrei, recently described by Pujos et al. (2011). Croft et al. (2009) noted the presence of Xyophorus cf. bondesioi in the Friasian SALMA of Cerdas.

The Laventan SALMA Quebrada Honda vertebrate locality was identified by Hoffstetter (1977). Croft (2007) presented the most recent list of the vertebrate fauna, which includes the marsupials Didelphimorphia, Paucituberculata, and Sparassodonta, native ungulates Litopterna, Notoungulata, and Astrapotheria, five rodent clades (Dasyproctidae, Eocardiidae, Octodontidae, Echimyidae, and Chinchillidae), and xenarthrans, represented by dasypodids, glyptodontids, and sloths. Three sloths have previously been reported from Quebrada Honda: the nothrotheriid Xyophorus villarroeli, the megatherioid Hiskatherium saintandrei, and a mylodontid indet. (Takai et al., 1984). Here we describe the fourth sloth, a massive Nothrotheriidae.

Megistonyx oreobios: Pleistocene Mountain Dwelling Giant Sloth Found?

A new genus of megalonychid sloth (Mammalia, Xenarthra) from the late Pleistocene (Lujanian) of Sierra de Perija, Zulia State, Venezuela

Authors:

1. H. Gregory McDonald (a)
2. Ascanio D. RincÓN (b)
3. Timothy J. Gaudin (c)

Affiliations:

a. Park Museum Management Program , National Park Service , 1201 Oakridge Drive, Fort Collins , Colorado , 80525 , U.S.A.

b. Instituto Venezolano de Investigaciones Científicas (IVIC) , Laboratorio de Biología de Paleontología–Centro de Ecología , Km 11 de la Carretera Panamericana, Edo. Miranda. Aptdo. 21.827, Cod., 1020-A , Caracas , Venezuela

c. Department of Biological and Environmental Sciences , University of Tennessee at Chattanooga, 615 McCallie Avenue , Chattanooga , Tennessee , 37403-2598 , U.S.A.

Abstract:

A skull and a partial skeleton of a large late Pleistocene megalonychid sloth recovered from a cave on Cerro Pintado, Sierra de Perijá Mountain Range, a branch of the northern Andes, in Zulia State, Venezuela, is described as a new genus and species, Megistonyx oreobios. A cladistic analysis of the new taxon based on cranial characters indicates that it is closely related to Ahytherium, another late Pleistocene megalonychid from South America known from cranial remains, and suggests that there may have been at least two distinct clades within the family since the late Miocene. Megistonyx oreobios is one of a number of extinct sloth taxa found at high elevations in South America and suggests that many extinct sloth taxa were not as thermally sensitive as their modern relatives and were capable of living under colder climatic conditions.