Unexpected inhibitory cascade in the molariforms of sloths (Folivora, Xenarthra): a case study in xenarthrans honouring Gerhard Storch’s open-mindedness

The inhibitory cascade (IC) represents a developmental model that explains the evolution of molar relative sizes, originally described in rodents but later validated in several mammalian groups. The IC comprises signalling molecules produced by the first molar buds that inhibit the development of subsequent molars and molecules from surrounding tissues that have opposite effects. Sloths, as xenarthrans, present many peculiarities in their dentition, like tooth and enamel loss, homodonty, and changes in the typically mammalian dental formula. Here, we test the existence of an IC and explore the evolution of the lower dentition in sloths. We studied the variability of molariform proportions in 20 specimens of the Late Pleistocene ground sloth Lestodon armatus. We also analysed molariforms proportions in 53 sloth genera to explore evolutionary trends. Our results show that the lower dentition of most sloths complies with the IC model, despite the difficulties of assessing dental homologies with other mammals. Furthermore, we tested the existence of different patterns among families, obtaining support for models taking mylodontids and orophodontids separately from the rest of sloths. Also, members of Mylodontidae show a unique IC pattern, with a slope considerably higher than 2 and an mf1 ≤ mf2 << mf3 configuration. This pattern could be related to the morphological adaptations to grazing showed by mylodontids during most of their evolutionary history

El legado del megaterio

No es común que un solo animal pueda hacer tantas y tan profundas contribuciones en el campo de las ciencias biológicas. Es aún menos común que esto ocurra cuando el animal es conocido únicamente como fósil. Pero este es precisamente el caso de Megatherium americanum, un mamífero sudamericano extinguido. Esta especie ha jugado un rol sumamente significativo en la historia y el desarrollo de la paleontología de vertebrados y del estudio de la evolución biológica

Balance or imbalance? Paleoecology of the Pleistocene of North and South America

In recent years, the validity of the model proposed by Damuth about the paleoecology of past and present mammalian faunas has been addressed. In previous works such model had been applied to the fauna of Rancho La Brea (North American late Pleistocene), Venta Micena (European early Pleistocene) and to other faunas in South America. In the case of Rancho La Brea, the model had shown that it behaved as expected, i.e., keeping the balance between number of herbivorous species and primary productivity, and between number of carnivore species and secondary productivity. In other words, that the primary productivity was enough to feed the herbivores in the community, and that the secondary productivity (which is the meat available for carnivores to eat) was fully consumed by the carnivores, as in modern, actualistic examples of communities with large mammals. In the South American Lujanian Age (late Pleistocene-early Holocene), an imbalance was proposed, namely that the herbivores did not have enough food to eat according to reconstructions of their environment, and, on the other hand, that the carnivores had too much. In this work twenty six faunas from North America were studied, as well as fifteen from South America. For their study the same model and equations were applied. The results showed that those North American faunas that had number of mammalian species large enough to infer that the community was well represented were balanced, while those with few species or a low number of carnivores were not. In addition, all the Pleistocene South American faunas from diverse origins in the subcontinent were imbalanced. A possible explanation already stated was that in South America there was a great diversity of xenarthrans. In the North American faunas, such diversity was not high, and also not higher than that of any other order of mammals.Sesiones libresFacultad de Ciencias Naturales y Muse

El vuelo de un gigante

Hasta principios de la década de los 70, muchos investigadores entendían que ese era el límite máximo ele tamaño para que un ave fuese capaz de volar. Sin embargo, en 1981 los paleontólogos Kenneth Campbell, del Los Angeles County Museum, Estados Unidos de América, y Eduardo Tonni, del Museo de La Plata, dieron a conocer un ave voladora extinguida cinco veces más grande, a la que bautizaron con el grandilocuente nombre de Argeníavis magnificens. El fósil fue descubierto en Salinas Grandes de Hidalgo, provincia de La Pampa, en sedimentos del Mioceno tardío (con una antigüedad aproximada de seis millones de años).Fundación Museo La Plat

The early release of horses in the current territory of the Republic of Uruguay: archaeology and history

La temprana presencia de caballos en campos de la actual República Oriental del Uruguay abre la posibilidad de que el proceso por el cual las sociedades autóctonas devinieron ecuestres haya ocurrido con escasa participación de la sociedad colonial. En este artículo se presenta un hallazgo realizado en el sitio del arroyo del Vizcaíno y se reflexiona sobre sus alcances.The early presence of horses in the wild in the current territory of the Oriental Republic of Uruguay, opens the possibility that the process by which indigenous societies became equestrian occurred with little involvement of colonial society. In this article we discuss a finding from the arroyo del Vizcaíno site and reflect on its implications

The early release of horses in the current territory of the Republic of Uruguay: archaeology and history

La temprana presencia de caballos en campos de la actual República Oriental del Uruguay abre la posibilidad de que el proceso por el cual las sociedades autóctonas devinieron ecuestres haya ocurrido con escasa participación de la sociedad colonial. En este artículo se presenta un hallazgo realizado en el sitio del arroyo del Vizcaíno y se reflexiona sobre sus alcances.The early presence of horses in the wild in the current territory of the Oriental Republic of Uruguay, opens the possibility that the process by which indigenous societies became equestrian occurred with little involvement of colonial society. In this article we discuss a finding from the arroyo del Vizcaíno site and reflect on its implications

Harnessing Natural Resources with Shared Sovereignty for Power Generation in the Parana River Basin: Systematization of Lessons Learned

The objetive is systematize the lessons learned in the international negotiations carried out during the stages of preparation, construction and operation of binational entities.CONACYT - Consejo Nacional de Ciencias y TecnologíaPROCIENCI

Late Miocene mammalian burrows in the Camacho Formation of Uruguay reveal a complex community of ecosystem engineers

We report fossil mammal burrows from backshore beach facies in the Camacho Formation of southern Uruguay, of Late Miocene (Huayquerian SALMA) age. The presence of desiccation cracks and rhizoliths indicate the occurrence of relatively extended periods of subaerial exposure and the incipient development of vegetation. The analysis of the burrows' spatial extent, size, and structure reveals the existence of exceptionally well-preserved and intercrossing tunnel systems. We show the existence of different size classes of burrows, which indicate that at least four different taxa were responsible for their construction. Considering the inferred body masses of the trace makers obtained from allometric relationships and the body masses of taxa recovered for the Camacho Formation, the burrows may have been produced by a combination of the following mammals: one of several rodents, notoungulates, cingulates, folivorans, and a carnivoran. The fossil association represents an exceptional case of a community of ecosystem engineers in the Late Miocene of southeastern South America.ANII: POS_NAC_2014_1_10237

Ulnar dimensions and fossoriality in armadillos

Ulnar dimensions were measured in 14 species of armadillos (Xenarthra: Dasypodidae). An index of fossorial ability (IFA) was constructed, relating the length of the olecranon process to the remaining length of the ulna. For comparative purposes, the same measurements were taken in 14 other species of mostly South American mammals belonging to 3 orders and 11 families. The fossorial habits of these mammals were classified into 3 categories: (1) species mostly cursorial and non-digging; (2) species that often dig, but to which digging plays no essential part in their alimentary strategy and are not burrowers; and (3) species that are burrowers. IFA means of the studied mammal orders were compared using one-way analysis of variance on log-transformed data. Bivariate size allometry between ulnar dimensions and body mass was assessed by fitting (least squares and geometric mean) linear regressions of log-transformed data. It is concluded that the IFA discriminates among the species according to their fossorial habits within orders, but it is not equally useful in distinguishing fossorial species between orders. In armadillos, the relationships between ulnar dimensions and body mass are isometrical. Finally, the IFA is independent of body size.Facultad de Ciencias Naturales y Muse

Collagen sequence analysis of the extinct giant ground sloths <i>Lestodon</i> and <i>Megatherium</i>

For over 200 years, fossils of bizarre extinct creatures have been described from the Americas that have ranged from giant ground sloths to the 'native' South American ungulates, groups of mammals that evolved in relative isolation on South America. Ground sloths belong to the South American xenarthrans, a group with modern although morphologically and ecologically very different representatives (anteaters, armadillos and sloths), which has been proposed to be one of the four main eutherian clades. Recently, proteomics analyses of bone collagen have recently been used to yield a molecular phylogeny for a range of mammals including the unusual 'Malagasy aardvark' shown to be most closely related to the afrotherian tenrecs, and the south American ungulates supporting their morphological association with condylarths. However, proteomics results generate partial sequence information that could impact upon the phylogenetic placement that has not been appropriately tested. For comparison, this paper examines the phylogenetic potential of proteomicsbased sequencing through the analysis of collagen extracted from two extinct giant ground sloths, Lestodon and Megatherium. The ground sloths were placed as sister taxa to extant sloths, but with a closer relationship between Lestodon and the extant sloths than the basal Megatherium. These results highlight that proteomics methods could yield plausible phylogenies that share similarities with other methods, but have the potential to be more useful in fossils beyond the limits of ancient DNA survival.Facultad de Ciencias Naturales y Muse