Limited role of functional differentiation in early diversification of animals.

M.L Knope,J.L Payne,N.A Heim,L.O Frishkoff

doi:10.1038/ncomms7455

Abstract

The origin of most animal phyla and classes during the Cambrian explosion has been hypothesized to represent an ‘early burst’ of evolutionary exploration of functional ecological possibilities. However, the ecological history of marine animals has yet to be fully quantified, preventing an assessment of the early-burst model for functional ecology. Here we use ecological assignments for 18,621 marine animal genera to assess the relative timing of functional differentiation versus taxonomic diversification from the Cambrian to the present day. We find that functional diversity increased more slowly than would be expected given the history of taxonomic diversity. Contrary to previous inferences of rapid ecological differentiation from the early appearances of all well-fossilized phyla and classes, explicit coding of functional characteristics demonstrates that Cambrian genera occupied comparatively few modes of life. Functional diversity increased in the Ordovician and, especially, during the recoveries from the end-Permian and end-Cretaceous mass extinctions. Permanent shifts in the relationship between functional and taxonomic diversity following the era-bounding extinctions indicates a critical role for these biotic crises in coupling taxonomic and functional diversity.

Highlights

The origin of most animal phyla and classes during the Cambrian explosion has been hypothesized to represent an ‘early burst’ of evolutionary exploration of functional ecological possibilities
The structure of the ecology–diversity relationship is clearly distinct in the Cambrian, during the rest of the Palaeozoic, throughout the Mesozoic and again throughout the Cenozoic, with persistent increase across eras in both total number of occupied ecological modes and the trajectories of rarefaction curves describing the functional versus taxonomic diversity relationship (Fig. 2), as previously hypothesized[12,13]
In contrast to the clear differences among eras, there is no systematic relationship between time and the functional versus taxonomic diversity relationship within eras: the post-Cambrian Palaeozoic shows no systematic relationship across geologic periods; Mesozoic rarefaction curves largely separate the Cretaceous from the Triassic, but the Jurassic overlaps both and Cenozoic rarefaction curves display similar ecology–diversity relationships across geologic periods (Supplementary Fig. 2)

Summary

Introduction

The origin of most animal phyla and classes during the Cambrian explosion has been hypothesized to represent an ‘early burst’ of evolutionary exploration of functional ecological possibilities. Work demonstrated that functional diversity increased throughout the Phanerozoic[12,13] and explicit ecological categorization of selected assemblages from modern oceans and the Ediacaran through Ordovician periods (635–444 Myr ago) confirmed that the number of ecological modes of life within marine communities increased at some point during the past 444 million years[14,15,16] These studies lack the taxonomic and temporal coverage to assess quantitatively the timing of taxonomic diversification versus ecological differentiation. This data set covers 63% of genera with stage-resolved stratigraphic ranges[22,23,24] and spans the nine major marine animal phyla in the fossil record: Arthropoda, Brachiopoda, Bryozoa, Chordata, Cnidaria, Echinodermata, Hemichordata, Mollusca and Porifera

Methods

Results

Conclusion