The Ediacaran period began 635 million years ago and was marked by the development of the first complex multicellular organisms, which evolved into the first animal species about 580 million years ago.
Many bizarre species with no clear ancestry in the fossil record appeared unexpectedly in the Ediacaran oceans, only to disappear without a trace. This period of Earth’s history is marked by intense evolutionary experimentation, when life on Earth first became diverse.
But the Ediacaran ended about 540 million years ago after a sharp decline in biodiversity. The end of the Ediacaran coincides with the beginning of the so-called “Cambrian Explosion” – a dramatic flowering of life that led to the emergence of many recognizable main branches of the tree of life, including the first arthropods (leading to the appearance of insects and spiders) and the first vertebrates.
Initially, the researchers were looking for evidence of a supposed mass extinction 550 million years ago that led to a sudden decline in biodiversity in the dying days of the Ediacaran period.
In search of a metacommunity structure, paleontologists have discovered an increasingly complex community structure in fossils from the later Ediacaran period. The results indicate the specialization of species and interspecific interaction.
Environmental complexity has previously been associated with the Cambrian Explosion. The dynamics observed in the fossils suggest that it was not the mass extinction that led to the decline in diversity towards the end of the Ediacaran period, but “competitive exclusion”.
Competitive exclusion is an evolutionary process in which different species occupying the same ecological niche compete for dominance until a genus emerges that is victorious.
The study shows that specialization and narrowing of niches were first observed not during the Cambrian explosion, but millions of years earlier, in the Ediacaran period.
“We found that the factors behind this explosion, namely community complexity and niche adaptation, actually began in the Ediacaran period, much earlier than previously thought. Ediacaran was the fuse that ignited the Cambrian explosion,” says co-author Emily Mitchell from the University of Cambridge.
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