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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.

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Fig. 1: Locality map and stratigraphic column of the Ediacaran–Early Cambrian Corumbá Group: composite section compiled from logs in the Corumbá–Ladário region, Mato Grosso do Sul State, Brazil.
Fig. 2: Hand specimens and scanning electron microscopy photomicrographs of M. minima and D. lyelli traces from the Guaicurus Formation, Laginha Mine, Mato Grosso do Sul State, Brazil.
Fig. 3: Photographs and CT volume renders of M. minima burrows from the Ediacaran Tamengo Formation, Ladário, Mato Grosso do Sul State, Brazil.
Fig. 4: CT slices and 3D reconstructions of a burrow assemblage in specimen OUMNH ÁU.3 from the Early Cambrian/latest Ediacaran Guaicurus Formation.
Fig. 5: Specimen OUMNH ÁU.4/p1 from the Guaicurus Formation from which burrow measurement data were obtained.
Fig. 6: Plot showing the temporal distribution of body and trace fossils from key Ediacaran and earliest Cambrian stratigraphic sections that are radio-isotopically constrained to a useful level of precision.


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We acknowledge the support and guidance of our co-author M. Brasier in the early stages of this work, and particularly his invitation for L.A.P. to undertake fieldwork in Brazil in 2012. Field costs for L.A.P. were supported by an undergraduate travel grant from St. Anne’s College, University of Oxford. Fieldwork costs for M.D.B. were supported by CNPq-Conselho Nacional Desenvolvimento Científico e Tecnológico- Brazil (Proc. 451245/2012-1). This project was supported by an NERC Isotope Geoscience Facilities Steering Committee grant (project IP-1560-0515). J.M.L., P.C.B., R.T., G.A.C.C., C.Q.C.D. and M.L.A.F.P. were supported by grant numbers 2009/02312-4, 2010/02677-0, 2013/17835-8 and 2016-06114-6, São Paulo Research Foundation (FAPESP), Brazil. A.G.L. and L.A.P. are supported by the Natural Environment Research Council (grant numbers NE/L011409/2 and NE/L501554/1, respectively). R.J.G. is a Scientific Associate at the Natural History Museum, London, and a member of the Interdisciplinary Centre for Ancient Life (UMRI). D.M. recognizes the support of an NSERC discovery grant. We are grateful to L. A. dos Santos Reis (Votorantim Cimentos) for facilitating access to the Laginha Mine. We thank L. Tarhan and S. Darroch for constructive reviews.

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L.A.P. found and initially identified the Multina specimens in the Guaicurus Formation. P.C.B., A.G.L., C.Q.C.D. and J.M.L. found the Multina specimens in Tamengo Formation. All authors collaborated to develop this research project. A.G.L. and D.J.C. secured funding for geochronological dating. L.A.P., D.J.C. and R.J.G. conducted the analyses. P.C.B., R.T., J.M.L., C.Q.C.D., M.L.A.F.P. and G.A.C.C. measured the stratigraphic section and collected samples for dating. L.A.P., D.M., D.J.C. and A.G.L. developed the manuscript, and all the authors were involved in data interpretation and the final redrafting of the manuscript.

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Parry, L.A., Boggiani, P.C., Condon, D.J. et al. Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil. Nat Ecol Evol 1, 1455–1464 (2017).

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