Recent studies show Xenarthra to be even more isolated systematically from other placental mammals than traditionally thought. The group not only represents 1 of 4 primary placental clades, but proposed links to other fossorial mammal taxa (e.g., Pholidota, Palaeanodonta) have been contradicted. No unambiguous Paleocene fossil xenarthran remains are known, and Eocene remains consist almost exclusively of isolated cingulate osteoderms and isolated postcrania of uncertain systematic provenance. Cingulate skulls are unknown until the late middle Eocene, and the oldest sloth and anteater skulls are early Oligocene and early Miocene age, respectively; there are no nearly complete xenarthran skeletons until the early Miocene. Ecological reconstructions of early xenarthrans based on extant species and the paleobiology of extinct Neogene taxa suggest the group’s progenitors were myrmecophagous with digging and perhaps some climbing adaptations. The earliest cingulates were terrestrial diggers and likely myrmecophagous but soon diverged into numerous omnivorous lineages. Early sloths were herbivores with a preference for forested habitats, exhibiting both digging and climbing adaptations. We attribute the rarity of early xenarthran remains to low population densities associated with myrmecophagy, lack of durable, enamel-covered teeth, and general scarcity of fossil localities from tropical latitudes of South America. The derivation of numerous omnivorous and herbivorous lineages from a myrmecophagous ancestor is a curious and unique feature of xenarthran history and may be due to the peculiar ecology of the native South American mammal fauna. Further progress in understanding early xenarthran evolution may depend on locating new Paleogene fossil sites in northern South America. Los estudios sistemáticos recientes muestran que, a nivel sistemático, los xenartros están aún más aislados de otros mamíferos placentarios de lo que se pensaba tradicionalmente. El grupo no sólo representa una de las cuatro ramas principales de los Placentalia, sino que también se han refutado las hipótesis previas de posibles conexiones con otros taxones de mamíferos fosoriales (por ejemplo Pholidota, Palaenodonta). No se conocen restos fósiles inequívocos de xenartros del Paleoceno y los restos provenientes del Eoceno consisten casi exclusivamente de osteodermos aislados de cingulados y restos postcraneanos aislados de origen sistemático incierto. No se conocen cráneos razonablemente completos de cingulados hasta finales del Eoceno medio; los cráneos más antiguos de perezosos y osos hormigueros provienen del Oligoceno temprano y del Mioceno temprano, respectivamente; y no existen esqueletos completos o casi completos de ninguno de los 3 linajes hasta el Mioceno temprano. Reconstruimos la ecología de los primeros xenartros basándonos en las especies actuales y lo que se sabe de la paleobiología del Mioceno y de los taxones extintos más recientes. Nuestros resultados sugieren que los primeros xenartros eran mirmecófagos y poseían adaptaciones para cavar y tal vez para trepar. Los primeros cingulados eran cavadores terrestres y probablemente mirmecófagos, pero pronto divergieron en numerosos linajes omnívoros. Nuestras reconstrucciones indican que los primeros perezosos eran herbívoros con preferencia de hábitats boscosos, tal vez exhibiendo adaptaciones tanto para cavar como para trepar. Atribuimos la rareza de restos de los primeros xenartros a varios factores: bajas densidades poblacionales asociadas a hábitos mirmecófagos; falta de dientes duraderos y cubiertos de esmalte; y una escasez general de localidades de mamíferos tempranos de las latitudes tropicales de América del Sur. La derivación de numerosos linajes omnívoros y herbívoros de un ancestro mirmecófago es un rasgo curioso y único de la historia de los xenartros y puede deberse a la peculiar ecología de la fauna de mamíferos sudamericanos. Los nuevos avances en la comprensión de la evolución temprana de los xenartros podrían depender de la localización de nuevos sitios fósiles paleógenos en áreas de tierras bajas poco accesibles del norte de América del Sur.
Rod monochromacy is a rare condition in vertebrates characterized by the absence of cone photoreceptor cells. The resulting phenotype is colourblindness and low acuity vision in dim-light and blindness in bright-light conditions. Early reports of xenarthrans (armadillos, sloths and anteaters) suggest that they are rod monochromats, but this has not been tested with genomic data. We searched the genomes of Dasypus novemcinctus (nine-banded armadillo), Choloepus hoffmanni (Hoffmann's two-toed sloth) and Mylodon darwinii (extinct ground sloth) for retinal photoreceptor genes and examined them for inactivating mutations. We performed PCR and Sanger sequencing on cone phototransduction genes of 10 additional xenarthrans to test for shared inactivating mutations and estimated the timing of inactivation for photoreceptor pseudogenes. We concluded that a stem xenarthran became an long-wavelength sensitive-cone monochromat following a missense mutation at a critical residue in SWS1, and a stem cingulate (armadillos, glyptodonts and pampatheres) and stem pilosan (sloths and anteaters) independently acquired rod monochromacy early in their evolutionary history following the inactivation of LWS and PDE6C, respectively. We hypothesize that rod monochromacy in armadillos and pilosans evolved as an adaptation to a subterranean habitat in the early history of Xenarthra. The presence of rod monochromacy has major implications for understanding xenarthran behavioural ecology and evolution.
In Argentina, Chaetophractus villosus has a wide distribution that overlaps with agricultural areas where soybean is the predominant crop. In such areas the pesticide Roundup Full II (R) (RU) is widely applied. The genotoxic effect of its active ingredient glyphosate (RU is 66.2% glyphosate) on the peripheral blood lymphocytes of C. villosus was tested over a range of concentrations (280, 420, 560, 1120 mu mol/L). Culture medium without glyphosate served as negative control, while medium containing mitomycin C served as positive control. Genetic damage was characterized in terms of the percentage of cells with chromosome aberrations (CA), the mean number of sister chromatid exchanges (SCE) per cell, and the modification of cell proliferation kinetics via the calculation of the replication index. Significant increases (p < 0.0001) were seen in the CA frequency and the mean number of SCEs per cell compared to negative controls at all the RU concentrations tested. Chromatid breaks, the only form of CA observed, under the 560 mu mol/L RU conditions and in presence of mitomycin C were four to five times more common than at lower concentrations, while no viable cells were seen in the 1120 mu mol/L treatment. The mean number of SCEs per cell was significantly higher under the 280 mu mol/L RU conditions than the 420 or 560 mu mol/L RU conditions; cells cultivated in the presence of MMC also showed significantly more SCEs. All the RU concentrations tested (except in the 1120 mu mol/L RU treatment [no viable cells]) induced a significant reduction in the replication index (p < 0.0001). The present results confirm the genotoxic effects of RU on C. villosus lymphocytes in vitro, strongly suggesting that exposure to RU could induce DNA damage in C. villosus wildlife.
The hyoid apparatus reflects aspects of the form and function of feeding in living and extinct organisms and, despite the availability of information about this structure for Xenarthra, it remains little explored from an evolutionary perspective. Here we compare the morphology of the hyoid apparatus in xenarthrans, describing its general morphology and variation in each major clade and score these variations as phylogenetic characters, which were submitted to ancestral states reconstructions. The general hyoid morphology of Xenarthra consists of a v-bone (basihyal fused with the thyrohyals) and three paired bones (stylohyal, epihyal and ceratohyal), which are unfused in the majority of taxa. The clade-specific morphology observed here, allowed us to obtain additional synapomorphies for all major clades of Xenarthra (Cingulata, Pilosa, Folivora and Vermilingua), for Glyptodontididae, and for Nothrotheriidae. The fusion of hyoid elements are convergentelly achieved among the diphyletic extant tree sloths, some extinct ground sloths and glyptodontids. Despite the heavy influence of adaptive evolution related to feeding habits, the morphology of the hyoid apparatus proved to be a valuable source of phylogenetic information.
The phylogenetic positions of the 4 clades, Euarchontoglires, Laurasiatheria, Afrotheria, and Xenarthra, have been major issues in the recent discussion of basal relationships among placental mammals. However, despite considerable efforts these relationships, crucial to the understanding of eutherian evolution and biogeography, have remained essentially unresolved. Euarchontoglires and Laurasiatheria are generally joined into a common clade (Boreoeutheria), whereas the position of Afrotheria and Xenarthra relative to Boreoeutheria has been equivocal in spite of the use of comprehensive amounts of nuclear encoded sequences or the application of genome-level characters such as retroposons. The probable reason for this uncertainty is that the divergences took place long time ago and within a narrow temporal window, leaving only short common branches. With the aim of further examining basal eutherian relationships, we have collected conserved protein-coding sequences from 11 placental mammals, a marsupial and a bird, whose nuclear genomes have been largely sequenced. The length of the alignment of homologous sequences representing each individual species is 2,168,859 nt. This number of sites, representing 2840 protein-coding genes, exceeds by a considerable margin that of any previous study. The phylogenetic analysis joined Xenarthra and Afrotheria on a common branch, Atlantogenata. This topology was found to fit the data significantly better than the alternative trees.
Associated osteoderms of unique aspect have been found in Ensenadan age deposits near San Pedro, in the Pampean Region of Argentina. Their general shape closely resembles that of mylodontid sloths. They are unique in presenting a homogeneous octahedral shape, contrasting with the heterogeneous shape of other ground sloth osteoderms. The lack of expanded spaces within the bone is shared with some other mylodontid sloths. Histologically, the bone is well vascularized, full of fiber bundles (including Sharpey's fibers), and very similar to the condition in . The lack of individualized fibers near and perpendicular to the external surface suggests a relatively deeper position in the dermis than in the Pleistocene ‘ ’ . The taxon to which these novel osteoderms belonged is uncertain, but the possible carriers are discussed.
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.
Armadillos comprise a particular group of armoured animals whose functional morphology of locomotion remains unclear. For the first time, the kinematic patterns of Dasypus novemcinctus are analysed. Eight specimens of nine‐banded armadillos were studied at a research institute in São Paulo State, Brazil. The individuals were induced to cross a horizontal corridor and each gait performed during the time each of them was kept inside this structure was recorded to a detailed analysis posteriorly performed in a computer program. Four parameters regarding speed range were considered: stride frequency (Hz) (1/stride period), stride length (m), speed (ms −1 ) and duty factor (%). A total of 89 strides have been analysed among symmetrical (60.6%) and asymmetrical gaits (39.4%), and six footfall patterns were here reported as follows: lateral sequences (symmetrical), transverse gallop, canter, bound, half‐bound and crutch walk (asymmetrical). This kind of analysis implements our knowledge on the locomotory aspects of these animals, hence contributing to the improvement of our knowledge on this still poorly known group.
Arthritic lesions have been frequently diagnosed in the fossil record, with spondyloarthropathy (a type of erosive and panmammalian arthritis) being one of the most common types described to date for mammals, though not restricted to this group. Here, we identify spondyloarthropathy in fossil bones from the late Pleistocene in Brazil assignable to a large glyptodont individual. Bone erosions in the peripheral joints (viz., the ulna, radius, left femur and tibiae-fibulae) associated with osteosclerosis allow the diagnosis of spondyloarthropathy. The presence of osteophytes in seven bones of the forelimbs (viz., the ulna and radius) and hind limbs (viz., the tibiae-fibulae, left femur and patellae) and a subchondral cyst in one element (viz., the left femur) indicate secondary osteoarthritis. A calcified deposition on the articular surface of the left patella indicates the presence of calcium pyrophosphate deposition disease, which, like the observed osteoarthritic alterations, likely represents a complication of spondyloarthropathy. This is the first report of spondyloarthropathy for xenarthrans.