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Possible links between extreme oxygen perturbations and the Cambrian radiation of animals.

ABSTRACT: The role of oxygen as a driver for early animal evolution is widely debated. During the Cambrian explosion, episodic radiations of major animal phyla occurred coincident with repeated carbon isotope fluctuations. However, the driver of these isotope fluctuations and potential links to environmental oxygenation are unclear. Here, we report high-resolution carbon and sulphur isotope data for marine carbonates from the southeastern Siberian Platform that document the canonical explosive phase of the Cambrian radiation from ~524 to ~514 Myr ago. These analyses demonstrate a strong positive covariation between carbonate ?13C and carbonate-associated sulphate ?34S through five isotope cycles. Biogeochemical modelling suggests that this isotopic coupling reflects periodic oscillations in atmospheric O2 and the extent of shallow ocean oxygenation. Episodic maxima in the biodiversity of animal phyla directly coincided with these extreme oxygen perturbations. Conversely, the subsequent Botoman-Toyonian animal extinction events (~514 to ~512 Myr ago) coincided with decoupled isotope records that suggest a shrinking marine sulphate reservoir and expanded shallow marine anoxia. We suggest that fluctuations in oxygen availability in the shallow marine realm exerted a primary control on the timing and tempo of biodiversity radiations at a crucial phase in the early history of animal life.

SUBMITTER: He T

PROVIDER: S-EPMC6548555 | biostudies-literature | 2019 Jun

REPOSITORIES: biostudies-literature

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Possible links between extreme oxygen perturbations and the Cambrian radiation of animals.

He Tianchen T Zhu Maoyan M Mills Benjamin J W BJW Wynn Peter M PM Zhuravlev Andrey Yu AY Tostevin Rosalie R Pogge von Strandmann Philip A E PAE Yang Aihua A Poulton Simon W SW Shields Graham A GA

Nature geoscience 20190601 6

The role of oxygen as a driver for early animal evolution is widely debated. During the Cambrian explosion, episodic radiations of major animal phyla occurred coincident with repeated carbon isotope fluctuations. However, the driver of these isotope fluctuations and potential links to environmental oxygenation are unclear. Here, we report high-resolution carbon and sulphur isotope data for marine carbonates from the southeastern Siberian Platform that document the canonical explosive phase of th ...[more]

PMID: 31178922

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Project description:BackgroundThe radiation of ecdysozoans (moulting animals) during the Cambrian gave rise to panarthropods and various groups of worms including scalidophorans, which played an important role in the elaboration of early marine ecosystems. Although most scalidophorans were infaunal burrowers travelling through soft sediment at the bottom of the sea, Selkirkia lived inside a tube.ResultsWe explore the palaeobiology of these tubicolous worms, and more generally the origin and evolutionary significance of tube-dwelling in early animals, based on exceptionally preserved fossils from the early Cambrian Chengjiang Lagerstätte (Stage 3, China) including a new species, Selkirkia transita sp. nov. We find that the best phylogenetic model resolves Selkirkia as a stem-group priapulid. Selkirkia secreted a protective cuticular thickening, the tube, inside which it was able to move during at least part of its life. Partly based on measured growth patterns, we construe that this tube was separated from the trunk during a moulting process that has no direct equivalent in other scalidophorans. Although the ontogeny of Selkirkia is currently unknown, we hypothesize that its conical tube might have had the same ecological function and possibly even deep development origin as the lorica, a protective cuticular thickening found in larval priapulids and adult loriciferans. Selkirkia is seen as a semi-sedentary animal capable of very shallow incursions below the water/sediment interface, possibly for feeding or during the tube-secreting phase. Brachiopod epibionts previously reported from the Xiaoshiba Lagerstätte (ca. 514 Ma) also presumably occur in Selkirkia sinica from Chengjiang (ca. 518 Ma).ConclusionsOur critical and model-based approach provides a new phylogenetic framework for Scalidophora, upon which to improve in order to study the evolution of morphological characters in this group. Tube-dwelling is likely to have offered Selkirkia better protection and anchoring to sediment and has developed simultaneously in other Cambrian animals such as hemichordates, annelids or panarthropods. Often lost in modern representatives in favour of active infaunal lifestyles, tube-dwelling can be regarded as an early evolutionary response of various metazoans to increasing environmental and biological pressure in Cambrian marine ecosystems.

Dataset Information

Possible links between extreme oxygen perturbations and the Cambrian radiation of animals.

Publications

Possible links between extreme oxygen perturbations and the Cambrian radiation of animals.

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