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 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.
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.
Recently, dental microwear analysis has been successfully employed to xenarthran teeth. Here, we present new data on use wear features on 16 molariforms of Orophodon hapaloides and Octodontotherium grande. These taxa count among the earliest sloths and are known from the Deseadan SALMA (late Oligocene). Modern phylogenetic analyses classify Octodontotherium and Orophodon within Mylodontoidea with whom they share lobate cheek teeth with an outer layer of cementum and a thick layer of orthodentine. Similar target areas of 100μm2 were analyzed on the orthodentine surface of each tooth by stereomicroscopic microwear and by SEM microwear. Results were unlike those of extant sloths (stereomicroscopic microwear: Bradypus, Choloepus) and published data from fossil sloths (SEM microwear: Acratocnus, Megalonyx, Megatherium, Thinobadistes); thus, both approaches independently indicate a different feeding ecology for the Oligocene taxa. The unique microwear results suggest that both taxa fed on plant material with low to moderate intrinsic toughness (foliage, twigs) but also proposes intake of tougher food items (e.g., seeds). Frequent gouging of the tooth surfaces can be explained by exogenous influence on microwear, such as possible intake of abrasive grit. We suggest an unspecialized herbivorous diet for Octodontotherium and Orophodon utilizing diverse food resources of their habitat. These interpretations support the reconstruction of (1) Deseadan environments as open habitats with spreading savannas/grasslands and (2) both taxa as wide-muzzled bulk feeders at ground level.
Here, we review population genetic, phylogeographic, and phylogenetic studies on xenarthrans and show how this information fits in current discussions about patterns of diversification within the Neotropics. Specifically, we focus on how the genetic diversity of xenarthrans has been shaped by important historical processes such as Andean uplift, the Great American Biotic Interchange, and fluctuating linkages between the Amazon and Atlantic forests. We also describe latitudinal patterns of differentiation within the Atlantic forest and discuss how these might have been generated. Even with the modest amount of information currently available, our comparative analyses indicate 3 things: the Andes may have promoted events of intraspecific divergence for at least 2 xenarthran species; the biogeographic history of the Neotropical rain forests influenced the divergence of clades in sloths; and inter- and intra-specific genetic patterns reveal a very high diversity in xenarthrans, probably higher than currently recognized from morphological data. Finally, we highlight Xenarthra as an appropriate model for investigating biogeographic patterns in the Neotropics and also point to additional directions to be taken in future studies of this unique mammal group. Revisamos los estudios realizados sobre genética de poblaciones, filogeografía y filogenia de los Xenarthra y mostramos como la información generada se ajusta a la discusión actual acerca de los patrones de diversificación en el Neotrópico. Enfocamos nuestro análisis en la influencia de 4 eventos pasados importantes relacionados con la dinámica del paisaje Neotropical y la diversificación de la fauna, sobre la diversidad genética de los Xenarthra; estos son el levantamiento de los Andes, el gran intercambio de fauna del Pleistoceno, la relación entre el bosque Amazónico y el bosque Atlántico y los patrones latitudinales de diferenciación en el bosque Atlántico. Aunque la información disponible aún es escasa, nuestro análisis comparativo indica que los Andes pudieron haber promovido eventos de diversificación intraespecífica, al menos en 2 especies de Xenarthra; que la historia biogeográfica del bosque húmedo Neotropical tuvo influencia sobre la divergencia de linajes de perezosos; y que los patrones genéticos intra e interespecíficos revelan una gran diversidad en Xenarthra, probablemente mayor que la actualmente reconocida con datos morfológicos. Finalmente, resaltamos a los Xenarthra como un modelo apropiado para investigar patrones biogeográficos en el Neotrópico y sugerimos líneas adicionales a considerarse en futuros estudios sobre este grupo único de mamíferos.
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.
Within the Late Neogene Glyptodontidae of the Pampean region of Argentina, Urotherium antiquum was described on the basis of some associated osteoderms of the dorsal carapace, which in addition include a partial skull and left hemimandible. The diagnostic characters are located on the exposed surface of the osteoderms of the dorsal carapace which somewhat resembles those of the Pleistocene genus Neuryurus. Although the relationship of U. antiquum to the remaining Glyptodontidae has never been clarified, some cladistic analyses suggest a close phylogenetic affinity with the clade composed of Plohophorus + (Glyptodon + Doedicurus). A careful comparison of U. antiquum to well-characterized taxa with similar stratigraphic and geographic provenance reveals that no significant skull differences are observed from Plohophorus figuratus Ameghino. It seems likely that the alleged ornamentation pattern that characterizes this species was produced by a taphonomic alteration of the exposed surface of the osteoderms, a process broadly distributed in glyptodonts having a rosette ornamentation pattern. Finally, some characters present in the osteoderms of the type specimen of U. antiquum suggest that it may be a juvenile specimen. In summary, U. antiquum should be considered a junior synonym of P. figuratus.(C) 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Glyptodon Owen is one of the most frequently recorded glyptodonts in the Pleistocene of South America, especially between 20°S and 38°S. A high specific diversity has traditionally been proposed for the genus, including some species of assumed biostratigraphic importance (e.g., G. perforatus and G. clavipes). However, most of these species are poorly characterized, and the morphological variability in the different regions of the dorsal carapace has not been considered. Recent reviews have indicated that its diversity was lower than previously supposed, particularly in the late Pleistocene. In this scenario, this contribution aims to (1) review the late Pleistocene Glyptodon species from southern South America and (2) discuss the primary aspects of the geographic and chronological distribution of the species that are deemed as valid. Morphological and morphometric analyses indicate that the diversity in the late Pleistocene of southern South America is reduced to a single well-characterized species, G. reticulatus Owen. This species is recorded in MIS 3 and MIS 2 and is distributed in the Pampean, Mesopotamian, and north-central regions of Argentina, southern Bolivia, and Uruguay (∼20°S-38°S). In summary, the diversity of Glyptodontinae in the Pleistocene of southern South America was limited to two well-characterized species: G. munizi in the early-middle Pleistocene and G. reticulatus in the late Pleistocene-early Holocene.
The presence of osteoderms in the skin of some extinct sloths and in cingulates (armadillos, pampatheres, and glyptodonts) has often been considered a pleisomorphic character of the Xenarthra. While osteoderms are known from the earliest cingulates, they are absent in most sloths including the two extant taxa and only appear late in their fossil record. Osteoderms are currently only reported from five genera of mylodonts and two megatheres, out of the over 100 currently recognized genera of sloths. Consequently, rather than a plesiomorphic character of the Xenarthra, which has been secondarily lost in sloths, it is more likely that osteoderms in sloths are the result of parallel evolution to the cingulates that independently evolved in one, possibly two different sloth clades.
The main function of the hyoid apparatus in mammals is to control the entry and exit of air in the body, provide support to the tongue, hold it in position and give it movement. In some species, it also participates in the modulation of sounds produced by vocal cords. Its preservation as fossil is exceptional and very little known. It allows proposing hypotheses about how the mentioned functions would be carried out. The finding and study of two new specimens assigned to the glyptodontid Pano- chthus sp., from Lujanian sediments (Late Pleistocene) of the Pampean Region, permitted: 1) to study the anatomy and propose a new organization of the hyoid apparatus in glyptodontids, 2) to describe in detail its elements (even the thyroid cartilage), 3) to compare it with materials already published of Glyptodon cf. G. clavipes, and 4) to analyze and compare the muscles' actions. In adult mammals, this apparatus is formed generally by ten bony elements, (1) stylohyals (paired), (2) epihyals (paired), (3) ceratohyals (paired), (4) thyrohyals (paired) and (5) basihyal (unpaired); and 2 paired cartilaginous elements, (a) tympanohyals and (b) chondrohyals. In glyptodonts, the elements (1), (2), (3) form the sigmohyals (paired), and (4) and (5) the V-bone (unpaired). The bony elements of Panochthus sp. are more gracile and long than those of Glyptodon cf.G. clavipes, and in the former, the musculature is more developed. The study of the new specimens suggests that Panochthus sp. could have more freedom of tongue movement than Glyptodon cf. G. clavipes, which possibly implied a different use of food resources.