Lifespans of the first animals

Lifespans fundamentally impact life history traits. These traits influence the tempo of biological cycles such as nutrient cycling and macroevolutionary patterns over geological time. Yet, the lifespans of the first animals, found during the Ediacaran Period ( 580 – 539 Ma) are not well constrained, limiting our understanding of ecological and evolutionary change of early animals. In this study we use the metabolic theory of ecology to estimate the maximum lifespans and evolutionary rates of ten key Ediacaran taxa, constraining maximum lifespan variation for different environmental temperatures and modularity. We find a large range of different maximum lifespans for Ediacaran taxa (0.53 -30.2 years), with longer lifespans in colder environments and for modular organisms (up to 40.2 years). Evolutionary rates were most impacted by environmental temperature, with the fastest evolutionary rates found in small, warm-water taxa have. Ediacaran organisms predate macro-predation and so do not suffer this key downside of small body size. Therefore, these small, warm-water taxa keep the advantages of these higher evolutionary rates, without the predatory downside. The release from predation coupled to these fast evolutionary rates could help to explain the large morphological and taxonomic diversity found in the shallow-water Ediacaran assemblages, in contrast to the colder, deep-water assemblages