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.
Northwestern Argentina contains one of the most complete continental late Neogene (ca. 9–2.58 Ma) fossiliferous sequences in South America, especially in the current territories of the Catamarca, Tucumán and Jujuy provinces. More precisely in Jujuy Province several localities bearing mainly fossil mammals have been reported at the Quebrada de Humahuaca in the Uquía, Maimará and Tilcara formations, in which the clade Xenarthra (Mammalia) is well-represented. In this scenario, the fossiliferous potential of other localities of Jujuy Province are less known, especially in those areas located at the northwest end of Argentina, bordering Bolivia in the Northern Puna. A new late Neogene fossiliferous locality near Calahoyo (3639 m.a.s.l), Jujuy Province, is here reported. The materials, belonging to Xenarthra, were exhumed from the base of the Tafna Formation which was deposited in a sedimentary basin by alluvial and/or fluvial currents, undergoing transitions of various lacustrine episodes. The taxa include the Tardigrada (Megatheriidae) and the Cingulata sp. (Glyptodontidae) and (Dasypodidae). From a biostratigraphic viewpoint, this assemblage suggests a Late Miocene-Pliocene age for the base of the Tafna Formation, and partially contradicts the supposed Plio-Pleistocene age of this unit. Finally, the new specimens here described indicate that Xenarthra were taxonomically and ecologically diverse during the late Neogene in the northwest end of Argentina, since they are represented by at least three main lineages (sloths, glyptodontids and armadillos).
Glyptodonts were giant (some of them up to ~2400 kg), heavily armoured relatives of living armadillos, which became extinct during the Late Pleistocene/early Holocene alongside much of the South American megafauna. Although glyptodonts were an important component of Cenozoic South American faunas, their early evolution and phylogenetic affinities within the order Cingulata (armoured New World placental mammals) remain controversial. In this study, we used hybridization enrichment and high‐throughput sequencing to obtain a partial mitochondrial genome from Doedicurus sp., the largest (1.5 m tall, and 4 m long) and one of the last surviving glyptodonts. Our molecular phylogenetic analyses revealed that glyptodonts fall within the diversity of living armadillos. Reanalysis of morphological data using a molecular ‘backbone constraint’ revealed several morphological characters that supported a close relationship between glyptodonts and the tiny extant fairy armadillos (Chlamyphorinae). This is surprising as these taxa are among the most derived cingulates: glyptodonts were generally large‐bodied and heavily armoured, while the fairy armadillos are tiny (~9–17 cm) and adapted for burrowing. Calibration of our phylogeny with the first appearance of glyptodonts in the Eocene resulted in a more precise timeline for xenarthran evolution. The osteological novelties of glyptodonts and their specialization for grazing appear to have evolved rapidly during the Late Eocene to Early Miocene, coincident with global temperature decreases and a shift from wet closed forest towards drier open woodland and grassland across much of South America. This environmental change may have driven the evolution of glyptodonts, culminating in the bizarre giant forms of the Pleistocene.
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...
A set of lesions are re-described and new pathological findings in foot bones of Panochthus sp. (Xenarthra, Cingulata) are presented. The material reexamined in fact presents enthesiophytes instead of osteoartrithis, as previously interpreted. Furthermore, Calcium Pyrophosphate Deposition Disease (CPPD) was observed, a lesion absent in previous report. CPPD also was found in another set of foot bones and it was associated with a congenital fusion of two sesamoids. The material studied were collected in two natural tank deposits, one in Paraiba (material reexamined) and other in Rio Grande do Norte (new pathological findings) State.
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.
To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.