Recolonisation strategies of early animals in the Avalon (Ediacaran 574 - 560 Ma)

Abstract

The first geographically widespread metazoans are found in the Avalon assemblage (Ediacaran; 574 - 560 Ma). These early animals were regularly disturbed by sedimentation events such as ash flows and turbidites, leading to an apparent "resetting" of communities. However, it is not clear how biological legacies - remains or survivors of disturbance events - influenced community ecology in the Avalon. Here, we use spatial point process analysis on 19 Avalon palaeocommunities to test whether two forms of biological legacy (fragmentary remains of Fractofusus and surviving frondomorphs) impacted the recolonisation dynamics of Avalon palaeocommunities. We found that densities of Fractofusus were increased around the Fractofusus fragments, suggesting that they helped to recolonise the post-disturbance substrate, potentially contributing to the Fractofusus dominance found in 8 of the 19 palaeocommunities. However, we found no such effects for survivor fronds. Our results suggest that the evolution of height was for long-distance dispersal rather than local recolonisation. In modern deep-sea environments, there is a trade-off between local and long-distance dispersal, and our work demonstrates that this differentiation of reproductive strategies had already developed in the early animals of the Avalon.