A deep root for the Cambrian explosion: Implications of new bio- and chemostratigraphy from the Siberian Platform

Abstract

Much uncertainty remains as to the temporal relationship between the Ediacaran and Cambrian biotas, yet this is critical to our understanding of the rise of metazoans. Here we present new high resolution carbon isotope chemostratigraphy and biostratigraphy for a terminal Ediacaran to Cambrian succession on the eastern Siberian Platform, Russia, which shows the presence of a succession of diverse fossil assemblages before the start of the basal Cambrian negative carbon isotope excursion (BACE). Softbodied Ediacaran biota (Beltanelliformis) occur before the start of the late Ediacaran positive carbon isotope plateau (EPIP), a mixed Ediacaran and Cambrian skeletal biota (Cloudina, Anabarities, Cambrotubulus) appear within the EPIP, and diverse Cambrian-type small shelly fossils including Protohertzina and other protocondonts, halkieriids, chancelloriids, hyoliths, hyolithelminthes and the burrowing trace fossil (Diplocraterion) appear at the beginning of the BACE. These integrated data show that taxa attributed to so-called Ediacaran and earliest Cambrian skeletal biotas in fact overlap without notable biotic turnover, and thus refute the presence of a large isotope excursion coincident with mass extinction of all Ediacaran biota. We propose a new biozone, the Cloudina-Namacalathus-Sinotubulites Assemblage Zone, to precede the known small shelly fossil (SSF) zones. These observations raise doubts as to whether there is any true separation between the Ediacaran and Cambrian skeletal biotas, and suggest that there is a deep root for the Cambrian Explosion of metazoans. Response to Reviewers:Many thanks for support from three reviewers that our work will be an excellent contribution to GEOLOGY, and their helpful comments and corrections on our manuscript. We considered the comments carefully and made necessary revisions and Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporationcorrections in text and figures. Major changes and responses to reviewers' comments are listed here, you will find more detail responses to reviews as attached file.

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“…Because halkieriid-like sclerites occur so early in the Cambrian period 70,71 , their affinity has profound implications for the timing of early trochozoan evolution. Removing halkieriids from Mollusca would shift the origin of this phylum significantly later: notwithstanding hyoliths (now interpreted as brachiozoans, i.e.…”

New high‐resolution age data from the Ediacaran–Cambrian boundary indicate rapid, ecologically driven onset of the Cambrian explosion

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Updated stratigraphic framework and biota of the Ediacaran and Terreneuvian in the Alcudia-Toledo Mountains of the Central Iberian Zone, Spain

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