Metazoan diversification characterized by elevated rates of evolution during the middle Ediacaran to earliest Cambrian

Abstract

To test causal hypotheses for the emergence of animal body plans, we analyze rates of molecular and phenotypic evolution across Opisthokonta, focusing on divergences within the Tonian-Ordovician interval. Both molecular and phenotypic rates increase through the Ediacaran, peaking in an Ediacaran and earliest Cambrian interval before declining thereafter. Partitioning phenotypic characters into categories relating to development, feeding, fossilization potential, locomotion, and nervous systems reveals distinct temporal patterns, with developmental traits contributing disproportionately to elevated rates in the metazoan stem lineage. Rate patterns show a temporal lag between the ecological changes integral to hypotheses of developmental evolution and the Cambrian agronomic, substrate, and information revolutions and earlier peaks in the evolution of the associated phenotypic characters. These patterns are largely independent of the timescale used. Overall, our results indicate that the primary phase of elevated evolutionary novelty occurred during the Ediacaran and culminated in the late Ediacaran-earliest Cambrian, providing the foundation for later ecological and taxonomic innovation.