The first animals appear during the late Ediacaran (572 to 541 million years ago); an initial diversity increase was followed reduction in diversity, often interpreted as catastrophic mass extinction. Eden et al. investigated Ediacaran ecosystem structure changes over this time period to assess whether this diversity reduction was likely caused by an external mass extinction, or by internal metacommunity restructuring. They found that the oldest metacommunity was characterized by taxa with wide environmental tolerances, and limited specialization or intertaxa associations. Structuring increased in the second oldest metacommunity, and this pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialization and resulting in competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran. These results reveal that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran. The image shows a group of Ediacaran specimens of Fractofusus and Plumeropriscum from the 'E' surface, Mistaken Point Ecological Reserve, Newfoundland, Canada. Also visible are patches of the volcanic ash that smothered the organisms on the Ediacaran seafloor, preserving all members of the community in their original positions.

Image Credit: Dr Charlotte G Kenchington