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

Parry, Luke A. and Boggiani, Paulo C. and Condon, Daniel J. and Garwood, Russell J. and Leme, Juliana de M. and McIlroy, Duncan and Brasier, Martin D. and Trindade, Ricardo and Campanha, Ginaldo A. C. and Pacheco, Mírian L. A. F. and Diniz, Cleber Q. C. and Liu, Alexander G. (2017) Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil. Nature Ecology & Evolution, 1 (10). pp. 1455-1464. ISSN 2397-334X DOI https://doi.org/10.1038/s41559-017-0301-9

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Official URL: http://doi.org/10.1038/s41559-017-0301-9

Abstract

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.

Item Type: Article
Uncontrolled Keywords: 2017AREP; IA74
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
Journal or Publication Title: Nature Ecology & Evolution
Volume: 1
Page Range: pp. 1455-1464
Identification Number: https://doi.org/10.1038/s41559-017-0301-9
Depositing User: Sarah Humbert
Date Deposited: 21 May 2018 11:09
Last Modified: 21 May 2018 11:09
URI: http://eprints.esc.cam.ac.uk/id/eprint/4280

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