The Neoproterozoic, 1000–541 million years (Myr) ago, saw the transition from a largely bacterial world to the emergence of multicellular grazers, suspension feeders and predators. This article explores the hypothesis that the first appearance of large, multicellular heterotrophs was fueled by an elevated supply of nutrients and carbon from the bottom of the food chain to higher trophic levels. A refined record of molecular fossils of algal sterols reveals that the transition from dominantly bacterial to eukaryotic primary production in open marine habitat occurred between 659 and 645 Myr ago, in the hot interlude between two Snowball Earth glaciations. This bacterial–eukaryotic transition reveals three characteristics: it was rapid on geological timescales, it followed an extreme environmental catastrophe and it was permanent — hallmarks of an ecological hysteresis that shifted Earth's oceans between two self-stabilizing steady states. More than 50 million years of Snowball glaciations and their hot aftermath may have purged old-world bacterial phytoplankton, providing empty but nutrient-rich ecospace for recolonization by larger algae and transforming the base of the food web. Elevated average and maximum particle sizes at the base of the food chain may have provided more efficient energy and nutrient transfer to higher trophic levels, fueling an arms race toward larger grazers, predators and prey, and the development of increasingly complex feeding and defense strategies.
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Cover Image
Cover Image
Gently inclined strata of the upper Bylot Supergroup in Edwin Inlet, Baffin Island (Canada). Bangiomorpha pubescens, a fossil red alga and the oldest taxonomically resolved eukaryote, occurs in the Bylot Supergroup and equivalent rocks in northeastern Canada. Recent radiometric dating has tightly constrained the first appearance of this fossil to ca. 1045 million years ago. Image kindly provided by Galen Halverson (McGill University), who with his co-authors in this issue, reviews the methods by which the Proterozoic time scale is dated and provide an up-to-date compilation of age constraints on key fossil first and last appearances, geological events, and horizons during the Tonian and Cryogenian periods. Their article also develops a new age model for a ca. 819–740 Ma composite section in Svalbard. For details, see pages 137–147.
The transition from a cyanobacterial to algal world and the emergence of animals
Timothy W. Lyons, Mary L. Droser, Kimberly V. Lau, Susannah M. Porter, Jochen J. Brocks; The transition from a cyanobacterial to algal world and the emergence of animals. Emerg Top Life Sci 28 September 2018; 2 (2): 181–190. doi: https://doi.org/10.1042/ETLS20180039
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