The first animals formed complex ecological communities more than 550 million years ago, laying the evolutionary groundwork for the Cambrian explosion, according to a study by Rebecca Eden, Emily Mitchell and colleagues at the University of Cambridge, UK, published in the open access journal PLOS Biology .
The first animals evolved towards the end of the Ediacaran period, about 580 million years ago. However, the fossil record shows that, after an initial boom, diversity declined in the run-up to the spectacular burst of biodiversity in the so-called Cambrian explosion , almost 40 million years later.
Scientists have suggested that this decline in diversity is evidence of a mass extinction event of the Ediacaran fauna around 550 million years ago - possibly caused by an environmental catastrophe - but previous research has not studied the structure of these ancient ecological communities.
To assess the evidence for a mass extinction in the Ediacaran period, the researchers analyzed the metacommunity structure of three fossil assemblages spanning the last 32 million years of this geological 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 interactions between species.
The analysis revealed an increasingly complex community structure in the latest fossil assemblages, suggesting that species were becoming more specialized and engaging in more interspecies interactions toward the end of the Ediacaran era, a trend often seen during the Ediacaran era. ecological succession.
The results point to competitive exclusion, rather than mass extinction, as the cause of the drop in diversity at the end of the Ediacaran period, the authors say. The analysis indicates that features of ecological and evolutionary dynamics commonly associated with the Cambrian explosion - such as specialization and niche contraction - were established by the first animal communities of the late Ediacaran period.
Mitchell adds that we found that the drivers of that explosion, namely community complexity and niche adaptation, actually began during the Ediacaran period, much earlier than previously thought. The Ediacaran was the fuse that lit the Cambrian explosion .
During the Ediacaran, all the continents were grouped into a single supercontinent called Pannotia, which existed from about 600 million years ago to about 540 million years ago. The fauna of this period consisted of multicellular organisms that had different morphological and physiological characteristics than later organisms. They had not yet developed shells or skeletons and their relationship with organisms after the Cambrian explosion it's hard to interpret.