title: Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems.
abstract: The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical "pits." These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.
authors.affiliation: School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Imran A
authors.initials: IA
authors.lastname: Rahman
authors.affiliation: Smithsonian Institution, P. O. Box 37012, MRC 121, Washington, DC 20013-7012, USA. ; Department of Earth and Environmental Sciences, Vanderbilt University, 2301 Vanderbilt Place, Nashville, TN 37235-1805, USA.
authors.forename: Simon A F
authors.initials: SA
authors.lastname: Darroch
authors.affiliation: Smithsonian Institution, P. O. Box 37012, MRC 121, Washington, DC 20013-7012, USA. ; The Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, CA 90007, USA.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Racicot
authors.affiliation: Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3359 Mississauga Road, Mississauga, Ontario L5L 1C6, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Laflamme
keywords: Ecology; Ediacara; computational fluid dynamics; ecosystem engineers; suspension feeding