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.
The specimen described herein and assigned to 'Xyophorus' sp. (Mammalia, Xenarthra, Tardigrada) was collected in the locality Cerro Zeballos, northwestern Chubut Province, Argentina. The fossiliferous sediments bearing the specimen are correlated with Collón Curá Formation. The specimen has the features described for other members of 'Xyophorus' (e.g. shape and size of the molariforms, relationship between diastema length, m1 and m2 length) and has a Diastema Length/Tooth Row Length index (DL/TRL index) of ca. 14, between that of 'X.' villarroeli (12.07) from the Mauri Formation, Bolivia (ca. 10.3 Ma) and that of 'X.' bondesioi (16.45) from Arroyo Chasicó Formation, Argentina (ca. 10-8.7 Ma). The relationship between DL/TRL index and age of the bearing sediments, would suggest a Tortonian age (late Miocene) for the deposits of Collón Curá Formation at Cerro Zeballos, which results in a 'younger age' compared to the middle Miocene age traditionally accepted for the Collón Curá Formation bearing the Colloncuran fauna sensu stricto. Although no absolute ages for Cerro Zeballos are available yet, the geographic proximity of Cerro Zeballos to Cushamen River (with levels dated at ca. 11.2 Ma) supports the tentative Tortonian age indicated by the presence of 'Xyophorus' sp.
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.
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.
Xenarthrans comprised an ecologically significant and diverse group of small to gigantic sized terrestrial insectivorous, omnivorous and herbivorous mammals during the Cenozoic in South America and during the Pleistocene in North America. Their peculiar tooth morphology has proven to be challenging for palaeodietary analyses of this group. Here we introduce a new approach to this problem by utilising the recently developed mesowear angle analysis for xenarthran palaeodietary analyses. The method is based on recording the relief of worn teeth as angles measured from the occlusal surfaces. We compare our results with other lines of evidence of extant and fossil xenarthran diets, based on direct observation, orthodentine microwear analyses and analyses of fossilised faecal material. Our results support previous findings and hypotheses on fossil xenarthran diets, but also provide new information on the diversity of dietary preferences in the diverse assemblages of large Pleistocene xenarthrans such as ground sloths and glyptodonts.
The Mylodontidae Scelidotheriinae (Mammalia, Xenarthra, Tardigrada) are a diversified clade of South American fossil ground sloths, with a wide geographic distribution, especially in high and middle latitudes. According to the last revision, the Quaternary diversity includes the genera Scelidotherium, Catonyx, and Valgipes. The clade Scelidotheriinae is well represented in the Pleistocene of the Tarija-Padcaya basin, and the first mention of these ground sloths correspond to the middle of the XIX Century. Since then, several species (i.e., Scelidotherium tarijensis, Scelidodon tarijensis, Scelidotherium capellini) have been reported as inhabiting the Tarija-Padcaya basin during the Pleistocene. Despite the abundance of fossil records of Scelidotheriinae in this area, no modern taxonomic revisions are available. In consequence, in this contribution a revision of the remains assigned to Scelidotheriinae from the Tarija-Padcaya basin is accomplished, and some biostratigraphic and geographic implications are discussed. Our results show that one single species (Catonyx tarijensis) can be recognized in the studied area, whereas a supposed smaller one (Scelidotherium patrium) actually corresponds to juvenile specimens of C. tarijensis.
ABSTRACT Increased field collecting over the last few years, combined with the examination of historical collections in Uruguay, has resulted in the discovery of a great number of specimens of the Scelidotheriinae, indicating that this subfamily is better represented in Uruguay's Pleistocene fauna than previously thought. Because much of this new material is diagnostic, in this work we provide a fuller description of some specimens (a skull with associated mandible and the manus, another almost-complete skull, and two partial dentaries) from the late Pleistocene of Uruguay for which only preliminary descriptions have been previously made, with tentatively assignments to Catonyx. A discriminant analysis was performed using 48 adult specimens including Scelidotherium, Catonyx, and Proscelidodon and supports the contention that Catonyx is a valid genus and the inclusion of these new specimens within this genus. This analysis also allows us to identify those cranial characters that better differentiate the ge...
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.
An upper fourth molariform of a Scelidotheriine ground sloth is reported from Carneiro Cave, which is located in the karstic region of Serra da Mesa (Goiás). In this limestone cave the tooth was found at the base of a depositional sequence, associated with a 2 m thick debris flows deposit, which is covered by the lowest carbonate crust – dated at approximately 200,000 yr BP. Detailed morphological description, stable isotope data and stratigraphic context are provided. This represents the first megafauna record for this region of Central Brazil, where this record is found in direct association with a diverse microvertebrate fauna.