Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

The evolutionary events during the Ediacaran–Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran–Cambrian siltstones in Brazil, alongside U–Pb radioisotopic dates that constrain the age of the oldest specimens to 555–542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μm in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal–sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

The evolutionary events during the Ediacaran–Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record. We report an assemblage of ichnofossils from Ediacaran–Cambrian siltstones in Brazil, alongside U–Pb radioisotopic dates that constrain the age of the oldest specimens to 555–542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μm in diameter, indicative of small-bodied, meiofaunal tracemakers. Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal–sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran

Re-evaluation of the morphology and systematic affinities of Corumbella werneri Hahn et al., Tamengo Formation (Ediacaran, Neoproterozoic), Corumbá, Brazil

Analysis of specimens of the enigmatic Ediacaran fossil Corumbella werneri Hahn et al., from the Saladeira and Lajinha quarries (near Corumbá, Mato Grosso do Sul, SW Brazil) in the Tamengo Formation - Corumbá Basin, Paraguay Belt - revealed inconsistencies with the original morphological description. Features recorded so far in 50 specimens help elucidate the systematic position of Corumbella werneri within the Cnidaria or the "Vendobionta". Contrarily to the original species description, the present study could not verify such supposedly scyphozoan characters as the bipartite differentiation of the body and the presence of sclerosepta and attachment structures described by Hahn and others. Nevertheless, we have corroborated the oral-aboral organization and tetrarradial symmetry of the initial description. Besides these characteristics, the verification of budding in some specimens strengthens the hypothesis that these organisms were cnidarians, and not vendobionts. Examination of three-dimensionally preserved specimens suggests that the polyps were prismatic rather than cylindrical as described by the original authors and compared to the stephanocyphistoma of coronate scyphozoans. The specimens are segmented with smooth, convex/concave, subrectangular, slightly overlapping plates, which are wider than long and have slightly rounded borders. The arrangement of the plates conferred flexibility to the organisms, as is evident in longer specimens of C. werneri. Thus, on the basis of our present morphological analysis we can safely assign this taxon to the phylum Cnidaria. However, other attributes (e.g., attachment regions and the longitudinal and lateral arrangement of the plates) need to be evaluated in order to define more precisely the systematic position of this important fossil.Sesiones libresFacultad de Ciencias Naturales y Muse

New Cloudina-like morphotype from the Ediacaran Tamengo Formation (Neoproterozoic, Corumbá Group), Southwest Brazil

The late Ediacaran index fossil Cloudina Germs is known for its funnel-in-funnel tubular calcareous shell. The Brazilian species Cloudina lucianoi (Beurlen and Sommer) occurs in limestones of the Tamengo Formation, near the top of the Corumbá Group, in southwestern Brazil. We report a new Cloudina-like morphotype from this formation, based on morphological observations and statistical comparisons of 55 specimens of the new morphotype and 23 of Cloudina from a single rock sample. The new morphotype is more delicate and more completely preserved than shells of C. lucianoi in the same sample. Many of these specimens also bear prominent lateral projections, not previously seen in C. lucianoi, which are interpreted as outward-flaring flanges of distal segments. Statistical analysis of the diameter/ length ratio of the fossils (linear regression and "t" test) revealed significant differences between the two groups, despite the fact that diameters of the new morphotype cluster within the established size limits of C. lucianoi. Hence, the new morphotype may represent a different species and not merely a previously unrecognized ontogenetic stage of C. lucianoi. Statistical analysis further suggests that the shells of C. lucianoi in the sample represent remnants of larger individuals than the new morphotype. Thus, the assemblages in the studied sample bear distinct taphonomic signatures, with the new morphotype representing an in situ biocoenosis, and the C. lucianoi fragments apparently parauthochthonous or allochthonous elements.Sesiones libresFacultad de Ciencias Naturales y Muse

Absorption and Phase Contrast X-Ray Imaging in Paleontology Using Laboratory and Synchrotron Sources

X-ray micro-computed tomography (μCT) is commonly used for imaging of samples in biomedical or materials science research. Owing to the ability to visualize a sample in a nondestructive way, X-ray μCT is perfectly suited to inspect fossilized specimens, which are mostly unique or rare. In certain regions of the world where important sedimentation events occurred in the Precambrian geological time, several fossilized animals are studied to understand questions related to their origin, environment, and life evolution. This article demonstrates the advantages of applying absorption and phase-contrast CT on the enigmatic fossil Corumbella werneri, one of the oldest known animals capable of building hard parts, originally discovered in Corumbá (Brazil). Different tomographic setups were tested to visualize the fossilized inner structures: a commercial laboratory-based μCT device, two synchrotron-based imaging setups using conventional absorption and propagation-based phase contrast, and a commercial X-ray microscope with a lens-coupled detector system, dedicated for radiography and tomography. Based on our results we discuss the strengths and weaknesses of the different imaging setups for paleontological studies

Evidence of artefacts made of giant sloth bones in central Brazil around the last glacial maximum

International audienceThe peopling of the Americas and human interaction with the Pleistocene megafauna in South America remain hotly debated. The Santa Elina rock shelter in Central Brazil shows evidence of successive human settlements from around the last glacial maximum (LGM) to the Early Holocene. Two Pleistocene archaeological layers include rich lithic industry associated with remains of the extinct giant ground sloth Glossotherium phoenesis . The remains include thousands of osteoderms (i.e. dermal bones), three of which were human-modified. In this study, we perform a traceological analysis of these artefacts by optical microscopy, non-destructive scanning electron microscopy, UV/visible photoluminescence and synchrotron-based microtomography. We also describe the spatial association between the giant sloth bone remains and stone tools and provide a Bayesian age model that confirms the timing of this association in two time horizons of the Pleistocene in Santa Elina. The conclusion from our traceological study is that the three giant sloth osteoderms were intentionally modified into artefacts before fossilization of the bones. This provides additional evidence for the contemporaneity of humans and megafauna, and for the human manufacturing of personal artefacts on bone remains of ground sloths, around the LGM in Central Brazil