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Permian bivalves of the Paraná Basin evolved in a large inland sea, under conditions of extreme isolation and environmental stress. Although known since 1918, its evolutionary history is still obscure due to the incomplete and biased information on faunal composition and stratigraphic distribution of various assemblages. Hence, the description of the Tiaraju assemblage, the only known bivalve occurrence in the Passa Dois Group from the southernmost Brazil, adds new key information on the composition, biocorrelation and age of this unique molluscan fauna. Terraia falconeri, Cowperesia emerita, Holdhausiella elongata, and Terraia altissima were recorded and described. T. falconeri is the commonest species, followed by C. emerita, H. elongata and T. altissima. The faunule is mainly composed by Terrainae, lacking Pinzonellinae. Assemblage is, thus, poorly diversified, both regarding the faunal composition and guild structure (only infaunal, facultatively motile, unattached, suspension feeders present). Cowperesia emerita and T. altissima strongly indicate biocorrelation with assemblages of the Rio do Rasto and Gai-As formations, Brazil and Namibia, providing an age no younger than the mid-Permian (Wordian-Captianian). On the light of this information, the current geological map of the Tiaraju region, São Gabriel, and the local boundary between the Teresina and Rio do Rasto formations requires reevaluation. RESUMO: Bivalves permianos da Bacia do Paraná evoluíram em um imenso mar interior, sob condições de extremo isolamento e estresse ambiental. Embora conhecidos desde 1918, a história evolutiva desses bivalves é ainda obscurecida pelo conhecimento incompleto e enviesado sobre a composição faunística e a distribuição estratigráfica de várias assembleias. Portanto, a descrição da assembleia de Tiaraju, a única conhecida no Grupo Passa Dois do sul do Brasil, contribui com novas informações-chave sobre a composição, biocorrelação e idade dessa fauna de moluscos únicos. Terraia falconeri, Cowperesia emerita, Holdhausiella elongata e Terraia altissima foram registradas e descritas. T. falconeri é a espécie mais comum, seguida por C. emerita, H. elongata e T. altissima. A fauna é maiormente composta por Terrainae, faltando os Pinzonellinae. A assembleia é, desse modo, pobremente diversificada, no que tange à composição faunística e guildas (somente bivalves de infauna, facultativamente móveis, suspensívoros estão presentes). Cowperesia emerita e T. altissima sugerem, fortemente, biocorrelação com assembleias das formações Rio do Rasto e Gai-As, Brasil e Namíbia, indicando idade não mais jovem que o Permiano médio (Wordiano-Capitaniano). À luz dessas informações, o mapa geológico da região de Tiaraju, São Gabriel, e o contato local entre as formações Teresina e Rio do Rasto, requerem, ambos, reavaliação.

Made available in DSpace on 2022-04-28T20:43:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-30 Renewed interest in conulariids has resulted in clarification of problems in the paleobiology of this group. Discoveries of skeletal structures and specimens preserved in situ, coupled with cladistic analyses, have led to a revival of Kiderlen's (1937) hypothesis that conulariids were polypoid scyphozoans or a sister taxon of this class. Until 1979, research on conulariids centered on the description of new species and on the erection of subgroups using phenetic approaches. Few papers addressed the paleobiology and phylogenetic affinities of conulariids, and none employed cladistics. In contrast, the 1980's saw the publication of major papers on the paleoecology of conulariids, and during this decade the hypothesis that conulariids were benthic organisms was corroborated. Also, new ideas concerning the affinities of conulariids, including the proposal that conulariids represent an extinct phylum, were presented. During the 1990's, the problem of conulariid affinities was widely debated, with authors advocating either that conulariids represent a separate phylum or that they were cnidarians. Near the close of that decade, certain advocates of a cnidarian affinity argued that conulariids were most closely related to Cnidaria. Taphonomic evidence indicates that conulariids were benthic animals originally oriented with their aperture opening upward and that they attached to or were embedded in hard and soft substrates. To understand unresolved problems we recommend that (1) conulariid specialists develop a standard morphological nomenclature based on rigorous definitions; and (2) studies on conulariid paleoecology be carried out using a sequence stratigraphy approach. © Asociación Paleontológica Argentina. Depto. Geologia Sedimentar e Ambiental IG USP, Rua do Lago, 562, 05508-900, São Paulo, SP Depto. Zoologia IB UNESP, CP 510, Rubião Júnior, 18618-000, Botucatu, SP Department of Geology Hanover College, Hanover, IN 47243 Depto. de Zoologia Universidade de São Paulo, Rua do Matão, Travessa 14, 321, 05508-900, São Paulo, SP Depto. Zoologia IB UNESP, CP 510, Rubião Júnior, 18618-000, Botucatu, SP

Paleoecology is a discipline that deals with interactions of fossil organisms in their ancient environments. Intrinsically, all paleoecologic interpretations require information on the time resolution of individual samples (hours, days, months, years, centuries). However, one of the major obstacles in dealing with any form of data derived from fossil collections is the effects of time-averaging, which are the result of mixing the remains of organisms that did not lived together. In other words: individual fossils found preserved together in a given geological strata are not necessarily contemporaneous, influencing the paleossinecologic conclusions. Here a seven steps taphonomic/autoecologic protocol is proposed in order to standers some field (e.g., collecting) and laboratory procedures. The protocol emphasizes the need for the recognizance of the time-averaging phenomena in a given paleontologic collection. This is particularly true for the Paleozoic fossil concentration where an absolute age of the bioclasts can not be obtained by radiometric dating. For paleoecologic purposes sampling size must be large and precise enough (bed-to-bed) to generate collections including the full range of taphonomic signatures showed by each individual fossil from the same bedding plane. A sampling strategy of large oriented blocks (0,05 m3) is here proposed, but this collecting methodology seems to be more appropriated applicable for fossil accumulations, such as the internally complex concentrations (e.g., bioclastic sandstones and coquinas) represented by tridimensional bodies that are easily recognized in the geological record.