2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 338-1
Presentation Time: 1:30 PM


DARROCH, Simon A.F., Earth and Environmental Sciences, Vanderbilt, 5726 Stevenson Center, 7th floor, Nashville, TN 37240; Earth and Environmental Sciences, Vanderbilt University, PMB 351805 2301 Vanderbilt Place, Nashville, TN 37235-1805, RAHMAN, Imran A., School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, United Kingdom, WAGNER, Peter J., Dept. of Paleobiology, Smithsonian Institution, National Museum of Natural History, Washington, DC 20560, RACICOT, Rachel, The Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, CA 90007 and LAFLAMME, Marc, Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, ON L5L 1C6, Canada, simon.darroch@gmail.com

Ediacaran ecosystems are thought to have been relatively ‘simple’ compared to those of the Paleozoic, comprising few interspecific biotic interactions and few unique modes of nutrient acquisition. Establishing the feeding modes of Ediacaran organisms is thus critical to determining the complexity of Ediacaran ecosystems; however, inferring feeding strategies has long proven problematic because many Ediacarans are characterized by body plans that lack clear modern analogues. Here, we use computational fluid dynamics (CFD) to rigorously analyze the hydrodynamic behavior of the iconic Ediacaran organism Tribrachidium heraldicum, thereby testing between hypothesized feeding modes. We show that the external morphology of Tribrachidium passively directs water flow towards the apex of the organism, and generates low-velocity eddies above apical ‘pits’. These patterns of current flow support the interpretation of Tribrachidium as a passive suspension feeder, and thus provide evidence for suspension feeding ~10 million years before the Cambrian. We further test the hypothesis that Ediacaran communities were surprisingly complex by analyzing Ediacaran through early Cambrian benthic communities using rank abundance distributions (RADs), which reflect community complexity (i.e., the number and division of available resources, and the diversity of ecological guilds). We find that the proportion of ‘complex’ vs. ‘simple’ community RADs remains largely equivalent through the Ediacaran and Cambrian, with the exception of the latest Ediacaran (Nama assemblage), consistent with an end-Ediacaran extinction ('biotic replacement') scenario. Our combined results demonstrate that the Ediacara biota formed ecosystems in the latest Precambrian with equivalent complexity to those that characterized the Cambrian, and suggests hidden ecological diversity among Ediacaran problematica.