EM - Escola de Minas

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Towards an actualistic view of the Crato Konservat-Lagerstätte paleoenvironment : a new hypothesis as an Early Cretaceous (Aptian) equatorial and semi-arid wetland.
(2021) Ribeiro, Alexandre Cunha; Ribeiro, Guilherme Cunha; Varejão, Filipe Giovanini; Battirola, Leandro Dênis; Pessoa, Edlley Max; Simões, Marcello Guimarães; Warren, Lucas Veríssimo; Riccomini, Claudio; Poyato-Ariza, Francisco José
An alternative hypothesis concerning the paleoecological and paleoenvironmental depositional conditions of the Crato Konservat-Lagerstatte ̈ (CKL), Crato Formation, Aptian, NE Brazil, one of the most extraordinary Gondwana fossil sites, is proposed. Following an actualistic approach, the ecology of extant relatives of the most abundant and diverse fossil groups recorded in the CKL (i.e., vascular plants, arthropods, fishes, and tetrapods) is considered. Data is based on an extensive literature review followed by a re-examination of recently collected fossils. This approach allowed a detailed appraisal of the stratigraphic/ecological distribution of the main fossil groups preserved in the CKL. Plant and animal groups are recorded in three main stratigraphic intervals, named Intervals I–III in ascending order. Most fossils are to be considered autochthonous to parautochthonous and have been preserved in distinct stages of base-level fluctuations within a shallow lacustrine depositional system, subject to periodic flooding in large, depressed areas. Exceptional preservation in such environments was mediated by microbially-induced processes (i.e., microbial mat entombment), mostly in the coastal areas of the alkaline lake. Based on the distinct sedimentary facies and autecological attributes of dominant paleo- bioindicators, a new paleoenvironmental model for the CKL is proposed, encompassing a seasonal, semi-arid, shallow lacustrine wetland. Faunal and floral content were ecologically arranged in long-lasting aquatic zones, surrounded by periodically flooded mesophytic ecotones and outer xeric habitats, as in the modern alkaline lake Chad in Africa. Our data show the relevance of multiproxy analyses (i.e., paleontological, sedi- mentological, geochemical, and stratigraphic) of exceptional fossil sites for assessing paleoenvironmental con- ditions in depositional settings subject to continuous base-level changes, such as those existing in complex, present-day wetland ecosystems. The recognition of key parameters in ancient wetlands is of great importance concerning the formation of non-marine Konservat-Lagerst ̈ atten in the geological record.
Effect of fire on ant assemblages in brazilian cerrado in areas containing vereda wetlands.
(2015) Milanez, Cinthia Borges da Costa; Ribeiro, F. F.; Castro, Paulo de Tarso Amorim; Majer, Jonathan David; Ribeiro, Sérvio Pontes
Cerrado is a biome whose evolution is intimately influenced by constant fire events. Although many species are capable of dealing with this predictable impact, many others may be negatively affected, resulting in community changes after fire. Using ants as bioindicators of changes in biodiversity and environmental conditions, this study evaluated the effects of fire in two Cerrado vegetation types: “cerrado” sensu stricto, a xeric savanna, and wetland “veredas”, a mesic vegetation on floodable soils, where water concentrates and ultimately flows towards rivers. We examined the effects of fire on both habitats in two independent sites, but with special consideration to the wetlands, which are not fully adapted to fire. Ant sampling was conducted twice before and twice after a fire event, using 288 baits and 416 pitfall traps (soil and arboreal), and 16 hand collections along three random replicate transects per area. Ant species richness and abundance were resilient to fire, and exhibited a remarkably consistent seasonal variation at unburned and burned sites. On the other hand, the fire markedly changed the ant species composition. In the wetlands, the fire spread underground due to the high concentration of peat. The impact on ant assemblages was substantial and visually perceptible for some species like Camponotus rufipes, which suffered a considerable reduction in the number of individuals after fire in this habitat. In the cerrado, a similar result was observed for Crematogaster nr. obscurata, which disappeared after fire. The wetland vegetation having little adaptation to fire, plus low resilience in the ant community resulted in a severely changed fauna, both in guild predominance and species composition, and return to an original state is uncertain.

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