Analysis of metacommunities suggests succession, not mass extinction, explains decline in Ediacaran diversity


The first animals formed complex ecological communities more than 550 million years ago, paving the way for the evolution of the Cambrian Explosion, according to a study by Rebecca Eden, Emily Mitchell and their colleagues at the University of Cambridge, UK, published May 17 in the open-access journal PLOS Biology.

The first animals evolved towards the end of the Ediacaran period, around 580 million years ago. However, the fossil record shows that after an initial boom, diversity declined in anticipation of the dramatic biodiversity boom in the so-called “Cambrian Explosion” nearly 40 million years later. Scientists have suggested that this decline in diversity is evidence of a mass extinction event around 550 million years ago – likely caused by an environmental catastrophe – but previous research has not investigated the structure of these ancient ecological communities.

To assess the evidence for an Ediacaran mass extinction, the researchers analyzed the metacommunity structure of three fossil assemblages that span the last 32 million years of this geologic period (between 575 and 543 million years ago). ). They used published paleoenvironmental data, such as ocean depth and rock characteristics, to search for metacommunity structure indicative of environmental specialization and species interactions. The analysis revealed increasingly complex community structure in later fossil assemblages, suggesting that species became more specialized and engaged in more interspecies interactions towards the end of the Ediacaran era, a trend often observed during ecological succession.

The results point to competitive exclusion, rather than mass extinction, as the cause of the decline in diversity at the end of the Ediacaran period, according to the authors. The analysis indicates that features of ecological and evolutionary dynamics commonly associated with the Cambrian Explosion – such as niche specialization and contraction – were established by early animal communities in the late Ediacaran.

Mitchell adds, “We found that the factors driving this explosion, namely community complexity and niche adaptation, actually began during the Ediacaran, much earlier than commonly believed. previously thought. The Ediacaran was the fuse that ignited the Cambrian explosion.”

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