EM - Escola de Minas

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.

Gonorynchiformes are a small, but morphologically diverse group of teleost fishes with an extensive fossil record. Most extant gonorynchiforms are efficient filter feeders, bearing long gill rakers and other morphological specializations, such as microbranchiospines and an epibranchial organ. The analyses of the gill arch of the Brazilian gonorynchiform fishes Dastilbe crandalli and Tharrias araripis from the Aptian of the Araripe Basin, Northeast Brazil, demonstrate significant morphological variation suggestive of distinct feeding habitats as well as ontogenetic dietary shifts in these closely related gonorynchiforms.

EM - Escola de Minas

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