Changes In Feeding Strategies across the Ediacaran/Cambrian Boundary: Who's New and Who's Missing?

The startling contrast in biodiversity and paleoecology across the Ediacaran–Cambrian boundary has received significant attention as being one of the greatest faunal changes in Earth's history. The Ediacaran period (635-543 Ma) showcases life's first attempt at large size and complex morphology with the dominance of the Ediacara biota, a group of entirely soft-bodied organisms that may have included the oldest animals, precursors to all animal life, and/or failed attempts at complex life that went extinct at the Ediacaran-Cambrian boundary.

Ecological interactions have been proposed as a possible feedback mechanism responsible for the faunal transition across the Ediacaran-Cambrian boundary. In order to test the role of ecological interactions during the transition, we quantitatively evaluated the morphological and ecological evolution across the boundary. A comprehensive analysis of Ediacaran-Cambrian paleoecology and morphospace, using functional morphology and morphometric techniques, was used to infer and compare the feeding strategies of Ediacaran vs. Cambrian benthic epifaunal organisms. A data matrix of important morphological characters was tabulated from published type material. Characters focused on overall shapes, symmetry, appendages, and feeding structures.

In addition, to test whether there was any significant change across the Ediacaran–Cambrian boundary in surface-to-volume ratio of dominant macroorganismal body plans, the surface area/volume ratios of Ediacaran fronds and Cambrian sponge/archaeocyathan/cnidarian forms were quantified. The combination of morphometric and functional morphology data allowed for the evaluation of how the evolution of feeding strategies was tied to patterns of morphological evolution across the Ediacaran–Cambrian boundary. It is proposed that the distinct changes in tiering morphology observed across the Ediacaran–Cambrian boundary reflect a transition from the Ediacara biota dominated by organisms with nutrient-absorption feeding strategies to the Cambrian biota dominated by active filter-feeders.