Morphological volatility precedes ecological innovation in early echinoderms.

Abstract

Origins of higher taxonomic groups entail dramatic and nearly simultaneous changes in morphology and ecological function, limiting our ability to disentangle the drivers of evolutionary diversification. Here we phylogenetically compare the anatomy and life habits of Cambrian-Ordovician echinoderms to test which facet better facilitates future success. Rates of morphological evolution are faster and involve more volatile trait changes, allowing morphological disparity to accrue faster and earlier in the Cambrian. However, persistent life-habit evolution throughout the early Palaeozoic, combined with iterative functional convergence within adaptive strategies, results in major expansion of ecospace and functional diversity. The interactions between tempo, divergence and convergence demonstrate not only that anatomical novelty precedes ecological success, but also that ecological innovation is constrained, even during a phylum's origin.