In order to gain insight into the function of the extant sloth locomotion and its evolution, we conducted a detailed videoradiographic analysis of two-toed sloth locomotion (Xenarthra: ). Both unrestrained as well as steady-state locomotion was analyzed. Spatio-temporal gait parameters, data on interlimb coordination, and limb kinematics are reported. Two-toed sloths displayed great variability in spatio-temporal gait parameters over the observed range of speeds. They increase speed by decreasing the durations of contact and swing phases, as well as by increasing step length. Gait utilization also varies with no strict gait sequence or interlimb timing evident in slow movements, but a tendency to employ diagonal sequence, diagonal couplet gaits in fast movements. In contrast, limb kinematics were highly conserved with respect to ‘normal’ pronograde locomotion. Limb element and joint angles at touch down and lift off, element and joint excursions, and contribution to body progression of individual elements are similar to those reported for non-cursorial mammals of small to medium size. Hands and feet are specialized to maintain firm connection to supports, and do not contribute to step length or progression. In so doing, the tarsometatarsus lost its role as an individual propulsive element during the evolution of suspensory locomotion. Conservative kinematic behavior of the remaining limb elements does not preclude that muscle recruitment and neuromuscular control for limb pro- and retraction are also conserved. The observed kinematic patterns of two-toed sloths improve our understanding of the convergent evolution of quadrupedal suspensory posture and locomotion in the two extant sloth lineages.
Xenarthra is a monophyletic group, characterized by a particular skeletal architecture, different to other placental mammals. Its current distribution is exclusively Neotropical; however, the fossil record indicates a greater distribution. The aim of this paper is to provide an updated list of the Xenarthra of the lower to middle Pleistocene (Ensenadan Stage) of the Pampean Region (Argentina). The most conspicuous anatomical features that allowed the taxonomic identification of fossil remains, especially those of particular biostratigraphic interest, are also briefly described and figured here. We studied more than 700 fossil remains mostly housed in palaeontological collections of Argentina. The study of these specimens (from the Pampean Region), revealed that during the Pleistocene there were marked variations in the composition and distribution of the faunas in general and particularly in xenarthrans. This situation was closely related to the Great American Biotic Interchange and climatic oscillations occurring in the Pleistocene. Thus, the Ensenadan fossil record of xenarthrans consists on exclusive taxa and numerous cases of first and last records. Finally, we expect that this contribution provide a starting point for future contributions in respect of the Pleistocene fauna, not only from the Pampean Region, but also from the rest of Argentina and South America.
ABSTRACT Although isolated mammalian petrosals often are encountered in the fossil record, few detailed descriptions of these bones exist for extant taxa. As a contribution to that void, isolated petrosals are described in detail for two nine-banded armadillos, Dasypus novemcinctus Linnaeus, 1758, and are placed in the context of the basicranium based on an additional 18 specimens, all from Carnegie Museum of Natural History. Neurovascular structures are reconstructed based on study of serially sectioned fetal specimens from the Anatomisches Instituts in Frankfurt and Heidelberg, Germany. Preliminary comparisons are made with other extinct and extant eutherians that the author has described in recent years. Unexpectedly, quite a few similarities are found between the petrosals of D. novemcinctus and the chiropteran Pteropus livingstonii Gray, 1866, which in light of the divergent phyletic affinities and biologies of these animals are remarkable convergences.
The subfamily Mylodontinae, typified by Mylodon, is known from the Colloncuran (late Miocene of Patagonia, Argentina) to the late Pleistocene of South America and North America. Mylodontinae have been recorded during the Pleistocene of Argentina, including the genera Glossotherium, Paraglossotherium, Lestodon, and Mylodon, with Paraglossotherium and Mylodon not as well known as the other genera. In Argentina there have been traditionally four species of Mylodon, M. darwini, M. zeballozi, M. listai, and M. insigne, although the validity of some has been considered doubtful. A nearly complete skull with an associated mandible of Mylodon darwini from the late Pleistocene of Mesopotamia, Argentina, is described. The specimen represents the first record of the species in the Mesopotamian region. The morphometric analysis indicates that M. darwini had greater individual variability than previously thought. Although based on the results of the morphologic and morphometric analysis, the idea of sexual dimorphism for M. darwini is, for the time being, unwarranted. This new record also supports the idea that Mylodon had great ecological tolerance and was capable of inhabiting climates ranging from cold and arid to warm and humid, and even montane environments.
We report a phylogeographic study of populations in Argentina. Control Region (CR) sequences (484 bp) were obtained for 76 from 20 locations across the species whole distribution range. Seventeen new haplotypes were identified. The highest genetic variation and the earliest fossils were found in the Pampean Region, thus appearing as the most probable area of origin of the species. A general pattern of Contiguous Range Expansion (CRE) was revealed by Nested Clade Analysis (NCA) supported by mismatch analysis and Fu’s test. The Pampean Region would have been the pre-expansion area, while Patagonia would have been the main dispersal route of contiguous expansion, possibly after the Pleistocenic glaciations.
Abstract Cyclobulura superinae n. sp. collected from Zaedyus pichiy and Chaetophractus vellerosus is herein described as the second species in Cyclobulura Quentin, 1977, and the first subulurid in armadillos. The species is unique in the spur-like structures present at the tip of both spicules, yet they conform to the description of Cyclobulura in the structure of the buccal parts. Specimens of the new species show longer chordal lobes and more conspicuous radial lobes and are smaller than specimens of C. lainsoni. In addition, males of C. superinae exhibit a spur-like process in the distal end of the spicules and a shorter tail (170 vs. 300 µm) with no spine. Finally, the eggs of C. superinae are smaller (60–89 × 45–71 vs. 95–100 × 80–85). To our knowledge, the new species is the first subulurid nematode found in an armadillo.
The Glyptodontidae (Mammalia, Xenarthra) are one of the most common paleofaunistic elements in the South American megafauna. In this context, of the six genera most frequently recorded in the South American Pleistocene ( , , , , and ), at least four ( , , and ) present structures in their caudal armor that could have had defensive/offensive functions, in addition to a solid dorsal carapace and cephalic shield. In this article, we provide the first record and description of a series of highly modified osteoderms, located at the anterolateral region and over the cephalic notch of the dorsal carapace. These “spine”-like osteoderms were found in two of the largest Pleistocene glyptodonts: (early-middle Pleistocene) and, (late Pleistocene-early Holocene). We propose that they are structures for protection of the neck and abdomen, the most vulnerable body regions of these large armored animals, since they are not covered by the cephalic shield, carapace or caudal armor. Noteworthy, structures like those described herein are not known in glyptodonts recorded before the Great American Biotic Interchange (GABI), so it could be a reaction to the arrival of and (Carnivora, Mammalia) the largest terrestrial carnivores that ever lived in South America. Les Glyptodontidae (Mammalia, Xenarthra) sont l’un des éléments paléofaunistiques les plus communs de la mégafaune en Amérique du Sud. Dans ce contexte, des six genres le plus souvent enregistrés dans le Pléistocène ( , , , , et ), au moins quatre ( , , et ) présentent dans leur armure caudale des structures qui auraient pu avoir des fonctions défensives/offensives, en plus d’une carapace dorsale solide et un bouclier céphalique. Dans cet article, nous proposons le premier enregistrement et la description d’une série d’ostéodermes très modifiés, situés dans la région antérolatérale et au-dessus de l’encoche céphalique de la carapace dorsale. Ces structures se rencontrent chez deux espèces du genre , l’une des plus grandes formes de Glyptodontidae du Pléistocène, (Pléistocène inférieur et moyen), et (Pléistocène supérieur - Holocène inférieur). D’un point de vue morphologique, ces ostéodermes montrent une forme caractéristique en « épine ». Les ostéodermes décrits ici sont interprétés comme des structures de protection et de défense du cou et du ventre, régions les plus vulnérables de ces grands animaux à armure, car elles ne sont pas recouvertes par le bouclier céphalique, la carapace ou l’armure caudale. Enfin, il est intéressant de noter que ces types de structure ne sont pas enregistrés dans la paléofaune de Glyptodontidae qui vivaient avant le (GABI), un processus migratoire qui marque l’arrivée de certains des plus grands prédateurs (Carnivora), ayant jamais vécu en Amérique du Sud (par exemple , ).
New ground sloths (Mammalia, Xenarthra, Mylodontidae) from the Neogene of the Bolivian Altiplano. Two new Mylodontinae (Xenarthra, Tardigrada, Mylodontoidea) from the Bolivian Altiplano are described. One of them, Pleurolestodon dalenzae n. sp., was discovered a few meters below a volcanic tuff, Toba 76, that may be used as a reference stratigraphic level and is dated at 5.4 Ma; it could be Huayquerian (late Miocene) or at the Huayquerian-Montehermosan boundary in age. The other taxon, Simomylodon uccasamamensis n. gen., n. sp., was recovered from many localities of a horizon bounded below by Toba 76 and above by another volcanic level, the 2.8 Ma Ayo Ayo tuff; its age is Montehermosan-Chapadmalalan (early and middle Pliocene). Analysis of these taxa indicates that they are Mylodontidae more closely related to Glossotherium, Glossotheridium, Kiyumylodon and Paramylodon than to Lestodon or Thinobadistes.