Erwin, Douglas H.

Disentangling the factors underlying the appearance of macroscopic, often skeletonized, bilaterians during the Ediacaran-Cambrian diversification of animals requires carefully parsing the contributions of ecological opportunity, environmental potential and developmental capacity. The early evolution of animals involved the introduction of genomic, developmental, morphologic and behavioural novelties, identified as the individuation of new characters, which led to the construction of new ecological networks (innovation). Here I employ a recently introduced conceptual framework for novelty and individuation that distinguishes between potentiation, novelty, innovation and adaptive adjustments to the Ediacaran-Cambrian Radiation, and focus on the roles of potentiation and novelty in the expansion of developmental capacity. Comparative developmental studies combined with molecular clock estimates and data from the fossil record suggest that developmental capacity, the potential to generate a range of morphologies, may expand rapidly through developmental novelties without leading directly to morphological novelties, or to innovation. The expected patterns from this framework are markedly different from those in adaptive radiation scenarios.