The trace fossil record of the Nama Group, Namibia: Exploring the terminal Ediacaran roots of the Cambrian explosion

Darroch, Simon A.F.; Cribb, Alison; Buatois, Luís A.; Germs, Gerard J.B.; Kenchington, Charlotte G.; Smith, Emily F.; Mocke, Helke; O’Neil, Gretchen R.; Schiffbauer, James D.; Maloney, Katie; Racicot, Rachel A.; Turk, Katherine A.; Gibson, Brandt M.; Almond, John E.; Koester, Bryce; Boag, Tom H.; Tweedt, Sarah M.; Laflamme, Marc

doi:10.1016/j.earscirev.2020.103435

Cited by 64 publications

(91 citation statements)

References 190 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While Ediacarans kept their less differentiated body designs, tissue-grade organization, and probably osmotic physiology. Consequently, Ediacarans died off at the end of their era for unknown reasons (Darroch 2021). Thereafter metazoans rapidly diversified and generated number of phylum-rank stem or crown lineages with different fates in the first 20 million years of the Cambrian Period.…”

Section: How Did the Cambrian Explosion Happen?mentioning

confidence: 99%

Current understanding on the Cambrian Explosion: questions and answers

Zhang

Shu

2021

PalZ

View full text Add to dashboard Cite

The Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of Linnaean system (classes and above). Some stem groups temporarily succeeded while others were ephemeral and underrepresented by few taxa. The high number of stem groups in the early history of animals is a major reason for morphological gaps across phyla that we see today. Most phylum-level clades achieved their maximal disparity (or morphological breadth) during the time interval close to their first appearance in the fossil record during the early Cambrian, whereas others, principally arthropods and chordates, exhibit a progressive exploration of morphospace in subsequent Phanerozoic. The overall envelope of metazoan morphospace occupation was already broad in the early Cambrian though it did not reach maximal disparity nor has diminished significantly as a consequence of extinction since the Cambrian. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequisites for the Cambrian Explosion. Without the molecular evolution, there could be no Cambrian Explosion. However, the developmental system is alone insufficient to explain Cambrian Explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that make the Cambrian Explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. The Cambrian Explosion is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon.

show abstract

Section: How Did the Cambrian Explosion Happen?mentioning

confidence: 99%

Current understanding on the Cambrian Explosion: questions and answers

Zhang

Shu

2021

PalZ

View full text Add to dashboard Cite

show abstract

“…We test hypotheses surrounding how these dense populations reflect aspects of life history, and/or adaptations to feeding. Given that communities of erniettomorph Ediacara biota thrived immediately prior to the Cambrian boundary (e.g., Elliott et al, 2016;Meyer et al, 2014;Darroch et al, 2018a;Darroch et al, 2021), understanding the structure and function of their communities will shed valuable light on ecological dynamics during the Ediacaran-Cambrian transition (Darroch et al, 2018a).…”

Section: Introductionmentioning

confidence: 99%

The Importance of Size and Location Within Gregarious Populations of Ernietta plateauensis

et al. 2021

Self Cite

View full text Add to dashboard Cite

Ernietta plateauensis is a semi-infaunal macroscopic eukaryote of unknown affinities common in latest Ediacaran (∼548–539 Ma) shallow marine settings in Namibia. The discovery of in-situ assemblages of Ernietta has demonstrated that these organisms lived in aggregated populations, while studies employing computational fluid dynamics (CFD) modeling have supported the hypothesis that these organisms were likely behaving as gregarious suspension feeders, analogous to many extant invertebrate phyla in present-day marine environments. Careful census and measurement of individuals within these in-situ populations offers an opportunity to examine how their size and location within a larger population affect nutrient delivery dynamics. In this study, we build on previous work by simulating fluid flow over aggregations of Ernietta comprising individuals of disparate sizes, and additionally reconstruct a population of Ernietta preserved in-situ from Farm Hansburg, Namibia. We use a combination of stationary and time-dependent CFD to reconstruct nutrient carrying flow paths, and compare the efficiency with which nutrients are partitioned between individuals of different shapes and sizes. Our results demonstrate that smaller Ernietta experience limited recirculation within their cavities compared to larger individuals. Furthermore, in spatially-accurate distributions, reduced recirculation is limited to isolated individuals of any size, while smaller individuals found downstream of larger ones receive enhanced cavity mixing. These reconstructed flow patterns illustrate that the disadvantage associated with small size is apparently mediated by location within the overall aggregation, suggesting a complex interplay of controls on feeding efficiency. This in turn suggests that aggregations of adult Ernietta would likely have performed a ‘nursery’ function, creating localized conditions ideal for the settlement and growth of younger individuals.

show abstract

“…The reduction in taxonomic diversity and community composition complexity has been suggested to correspond to a post-White Sea extinction caused by either an environmental driven catastrophic environmental extinction or biotic replacement driven extinction (12,23,22,24,21,21). Recent work has shown that a biotic replacement driven extinction, whereby mobile metazoans out-competed softbodied Ediacaran organisms through bioturbation and ecosystem engineering, is unlikely due in part to prolonged co-occurrence of trace fossils with soft-bodied biota (5,32). Other currently unknown and/or unpreserved intrinsic causes behind a biotic replacement model cannot not be excluded at the moment.…”

Section: Discussionmentioning

confidence: 99%

Metacommunity analyses show increase in ecological specialisation throughout the Ediacaran

Eden

Manica

Mitchell

2021

Preprint

View full text Add to dashboard Cite

The first animals appear during the late Ediacaran (572 – 541 Ma); an initial diversity increase was followed by a drop, interpreted as catastrophic mass extinction. We investigate the processes underlying these changes using the “Elements of Metacommunity Structure” framework. The oldest metacommunity was characterized by taxa with wide environmental tolerances, and limited specialisation and inter-taxa interactions. Structuring increased in the middle metacommunity, with groups of taxa sharing synchronous responses to environmental gradients, aggregating into distinct communities. This pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialisation and resulting competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran, revealing that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran.

show abstract

The trace fossil record of the Nama Group, Namibia: Exploring the terminal Ediacaran roots of the Cambrian explosion

Cited by 64 publications

References 190 publications

Current understanding on the Cambrian Explosion: questions and answers

Current understanding on the Cambrian Explosion: questions and answers

The Importance of Size and Location Within Gregarious Populations of Ernietta plateauensis

Metacommunity analyses show increase in ecological specialisation throughout the Ediacaran

Contact Info

Product

Resources

About