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Minerals are the fundamental record of abiotic processes over time, while biominerals are one of the most common records of life due to their easy preservation and abundance. However, distinguishing between biominerals and abiotic minerals is challenging due to the superimposition and repetition of geologic processes and the interference of ubiquitous and diverse life on Earth's surface and crust. Mineral dubiofossils, being potential outcomes of both abiotic and biotic environments, emerge as valuable entities that can contribute significantly to the understanding of this issue, facilitating the testing and refinement of biogenicity criteria. The aim of this contribution is to decipher the origin and history of branched mineralized structures that were previously considered mineral dubiofossils from the Pennsylvanian of the Paraná Basin, Brazil. While this material has different forms and refers to biological aspects, it is challenging to associate it with any known fossil group due to the overlapping geological processes occurring in a transitional deposit of Rio do Sul Formation (Itararé Group of the Paraná Basin), particularly in close proximity to a sill from the Serra Geral Group (Lower Cretaceous), which has undergone thermal effects. Given the absence of attributes essential for supporting the initial hypotheses proposing the material as a potential set of sponge spicules or a result of contact metamorphism in Pennsylvanian turbidites, the objects are now investigated as mineral dubiofossils. To address this challenge, we have developed a descriptive protocol for dubiofossils, building upon prior research in the field. This protocol evaluates the following aspects: (1) morphology, texture, and structure; (2) relationship with the matrix; (3) composition; and (4) context. This is done by assessing indigeneity and syngenicity and comparing the specimens with abiotic and biotic products. Applying this protocol to our samples revealed a wide range of morphologies with internal organization, predominantly composed of calcite with impurities such as iron, magnesium, aluminum, and oxygen. The inferred indigeneity suggests the presence of these minerals concurrently with or prior to the intrusion of the sill. Extensive comparisons were made between the studied samples and a broad spectrum of abiotic minerals, as well as controlled, induced, and influenced biominerals from similar contexts. These comparative analyses encompassed sponge spicules; sea urchin and algae skeletons; minerals induced or influenced by fungi, bacteria, and microbial mats; and inorganic pre- and synsedimentary–eodiagenetic minerals like evaporites, springs, and other precipitates, and mesodiagenetic–metamorphic crystals. Despite this comprehensive analysis, no hypothesis emerged as significantly more likely than others. The comparative analysis did allow us to exclude the possibility of the samples being controlled biominerals due to their patternless diversity of morphologies, as well as purely thermometamorphic in origin due to their branched elongated forms. The occurrence of these structures suggests a complex history: a syn-depositional or eodiagenetic origin of some carbonate or sulfate (gypsum, ikaite, dolomite, calcite, aragonite, siderite), potentially associated with the presence of microbial mats, which may have served as templates for mineralization and mediated mineral growth. Mesodiagenesis could have further modified the occurrence through processes such as mineral stabilization, agglutination, aging, and growth. However, the primary agent responsible for the formation of the dubiofossil was the Cretaceous intrusion, which dissolved and replaced the initial minerals, resulting in the precipitation of calcite. Throughout these steps, a combination of physical–chemical and biological reactions, influenced by intrinsic matrix characteristics, organic matter content, and distance from the intrusive body, may have contributed to the heightened morphological complexity observed, thus corroborating the origin of the material becomes even more challenging. Consequently, both the hypotheses pertaining to the formation of biotic and abiotic sulfates and carbonates remain plausible explanations, hence sustaining the classification of the material as a dubiofossil. This material illustrates how dubiofossils can be a result of a complex history and overlapping geological processes. It also highlights the difficulty in differentiating biominerals from abiotic minerals due to the scarcity of biogenicity arguments.

Large igneous provinces (LIPs) are major magmatic events that have a significant impact on the global environment and the biosphere, for example as triggers of mass extinctions. LIPs provide an excellent sedimentological and geochemical record of short but intense periods of geological activity in the past, but their contribution towards understanding ancient life is much more restricted due to the destructive nature of their igneous origin. Here, we provide the first paleontological evidence for organic walled microfossils extracted from wet peperites from the Early Cretaceous Paraná-Etendeka intertrappean deposits of the Paraná basin in Brazil. Wet peperites are a volcaniclastic rock formed by the interaction of lava and subaqueous sediments.The Paraná-Etendeka was formed during the Valanginian (ca. 132 Ma) as a continental flood basalt in present day South America and Namibia, and released enormous amounts of carbon dioxide, sulfur dioxide, methane and hydrogen fluoride into the atmosphere. The organic walled microfossils recovered from the Paraná-Etendeka peperites include pollen grains, spores, acritarchs, and other remains of unidentifiable organic matter. In addition to the peperites, organic walled microfossils were also found in heterolithic sandstones and interpillow sandstones. Our findings represent the first insight into the biodiversity of the Paraná Basin during the Early Cretaceous during a period of intense magmatism, and the microfossil assemblages corroborate a regional paleoclimatic transition from arid to more humid conditions that were likely induced by the volcanic activity. We corroborate the potential of wet peperite rocks as a valuable source of paleobiological data and emphasize the importance of sampling volcaniclastic units that have been traditionally considered with lower fossiliferous potential due to their igneous origin.

Modern poriferans are classified into four classes—Calcarea, Demospongiae, Hexactinellida and Homoscleromorpha—the recognition of which in fossil specimens almost exclusively relies on spicule morphology and arrangement. Early fossil representatives of the phylum Porifera are morphologically diverse, and many of them problematically display characteristics that are incompatible with the classification scheme developed for modern taxa. Critically, hexactine spicules—a diagnostic feature of hexactinellids among modern taxa—are found in various Cambrian and Ordovician taxa that cannot be accommodated within the hexactinellid body plan. Here we describe a new poriferan from the Drumian Marjum Formation of Utah, Polygoniella turrelli gen. et sp. nov., which exhibits a unique combination of complex anatomical features for a Cambrian form, including a syconoid-like organization, a thick body wall, and a multi-layered hexactin-based skeleton. The hexactinellid-like body wall architecture of this new species supports a Cambrian origin of the hexactinellid body plan and provides valuable insights into character evolution in early glass sponges.

The evolutionary onset of animal biomineralization in the late Ediacaran ( ca 555–538 Ma) is marked by the global appearance of enigmatic tubular fossils with unresolved phylogenetic relationships. Among these, Corumbella werneri from the Tamengo Formation (Corumbá Group, Brazil) has been variously interpreted as affiliated with cnidarians or bilaterians. Using synchrotron imaging and machine learning, we analysed new specimens of C. werneri to reconstruct their original skeletal organization. Our findings reveal that Corumbella’ s tubes were originally conico-cylindrical. Large individuals of Corumbella , including less compacted specimens, and compression experiments with modern annelid tubes all indicate that previous reconstructions of a quadrate outline and midline features were misled by taphonomic artefacts. We also show that the wall of Corumbella is composed of a single layer of ring-shaped elements. Unlike the fourfold symmetry of scyphozoans or the complex cataphract-like structures of Cambrian bilaterians (e.g. halkieriids, tommotiids and wiwaxiids), Corumbella displays structural similarities with other late Ediacaran corumbellomorphs, such as Costatubus . These taxa exhibit a distinctive barrel-on-barrel tube construction, with modular elements stacked on each other rather than nested. Our findings redefine Corumbella ’s morphology and phylogenetic affinities, contributing to a broader understanding of early biomineralizing metazoans and their ecological roles in the Ediacaran biosphere.

A geologically rapid Neoproterozoic oxygenation event is commonly linked to the appearance of marine animal groups in the fossil record. However, there is still debate about what evidence from the sedimentary geochemical record—if any—provides strong support for a persistent shift in surface oxygen immediately preceding the rise of animals. We present statistical learning analyses of a large dataset of geochemical data and associated geological context from the Neoproterozoic and Palaeozoic sedimentary record and then use Earth system modelling to link trends in redox-sensitive trace metal and organic carbon concentrations to the oxygenation of Earth’s oceans and atmosphere. We do not find evidence for the wholesale oxygenation of Earth’s oceans in the late Neoproterozoic era. We do, however, reconstruct a moderate long-term increase in atmospheric oxygen and marine productivity. These changes to the Earth system would have increased dissolved oxygen and food supply in shallow-water habitats during the broad interval of geologic time in which the major animal groups first radiated. This approach provides some of the most direct evidence for potential physiological drivers of the Cambrian radiation, while highlighting the importance of later Palaeozoic oxygenation in the evolution of the modern Earth system. Oxygen in shallow shelf waters rose linearly with atmospheric oxygen in the Neoproterozoic era, potentially driving the first radiation of marine animals, but widespread ocean oxygenation came later, according to reconstructions of oxygen levels and marine productivity.

Biomineralized and organic metazoan tubular skeletons are by far the most common in the fossil record. However, several groups of organisms are also able to agglutinate particles to construct more rigid structures. Here we present a novel type of agglutinated tube from the austral and endemic palaeobiota of the Malvinokaffric realm (Devonian, Brazil). This fossil is characterized by an agglutinated tube made of silt-sized particles forming an unusual flanged morphology that is not known from the fossil record. Besides being able to select specific particles, these organisms probably lived partially buried and were detritus/suspension feeders. Comparisons across different modern groups show that these fossils are strongly similar to tubes made by polychaetes, specifically from the family Maldanidae. If this interpretation is correct, then an early divergence of the Sedentaria clade may have occurred before the Devonian.

Biomineralized and organic metazoan tubular skeletons are by far the most common in the fossil record. However, several groups of organisms are also able to agglutinate particles to construct more rigid structures. Here we present a novel type of agglutinated tube from the austral and endemic palaeobiota of the Malvinokaffric realm (Devonian, Brazil). This fossil is characterized by an agglutinated tube made of silt-sized particles forming an unusual flanged morphology that is not known from the fossil record. Besides being able to select specific particles, these organisms probably lived partially buried and were detritus/suspension feeders. Comparisons across different modern groups show that these fossils are strongly similar to tubes made by polychaetes, specifically from the family Maldanidae. If this interpretation is correct, then an early divergence of the Sedentaria clade may have occurred before the Devonian.

Microfossils have been found in most of the Mesozoic basins of Brazil, allowing the establishment of important biozones. Despite being recognized for more than half century in the Barremian from the Recôncavo Basin, the taxonomy of the benthic foraminifera remained unsolved likewise its paleoenviromental implications. In this study, we have applied 2D and 3D imaging techniques to resolve this issue and have identified two agglutinated foraminiferal genera (Glomospirella and Paratrochamminoides) and a new species Paratrochamminoides kaminskii sp. nov. Moreover, based on the taxonomy, few paleoenvironmental insights on the foraminifera-bearing strata are discussed. The occurrence of the typically shallow marine species Glomospirella arctica in the studied section, does not allow the proposition of a marine ingression, since it is not supported by a marine/ transitional association of microfossils. On the other hand, the hypothesis of transport of foraminifera by birds (avian zoocoria) is plausible, although there are no further elements to corroborate it.

The evolutionary onset of animal biomineralization in the late Ediacaran (ca 555-538 Ma) is marked by the global appearance of enigmatic tubular fossils with unresolved phylogenetic relationships. Among these, Corumbella werneri from the Tamengo Formation (Corumba Group, Brazil) has been variously interpreted as affiliated with cnidarians or bilaterians. Using synchrotron imaging and machine learning, we analysed new specimens of C. werneri to reconstruct their original skeletal organization. Our findings reveal that Corumbella's tubes were originally conico-cylindrical. Large individuals of Corumbella, including less compacted specimens, and compression experiments with modern annelid tubes all indicate that previous reconstructions of a quadrate outline and midline features were misled by taphonomic artefacts. We also show that the wall of Corumbella is composed of a single layer of ring-shaped elements. Unlike the fourfold symmetry of scyphozoans or the complex cataphract-like structures of Cambrian bilaterians (e.g. halkieriids, tommotiids and wiwaxiids), Corumbella displays structural similarities with other late Ediacaran corumbellomorphs, such as Costatubus. These taxa exhibit a distinctive barrel-onbarrel tube construction, with modular elements stacked on each other rather than nested. Our findings redefine Corumbella's morphology and phylogenetic affinities, contributing to a broader understanding of early biomineralizing metazoans and their ecological roles in the Ediacaran biosphere.

The vertebrate fossil record of the Guabirotuba Formation, Curitiba Basin (Cenozoic), South Brazil, was restricted to a crocodyliform tooth and indeterminate bone fragments. New specimens collected in an outcrop located in Curitiba city, in the State of Paraná, are herein described and represent the first record of Pleurodira (Testudines) to this basin. The presence of aquatic Testudines associated to Crocodyliformes corroborates the lacustrine and fluvial paleoenvironment for the Guabirotuba Formation deposition and indicates a more humid climate than previously proposed.