Inference of facultative mobility in the enigmatic Ediacaran organism Parvancorina

• Published in: Biology letters (2005) Vol. 13; no. 5; p. 20170033
• Main Authors: Darroch, Simon A. F., Rahman, Imran A., Gibson, Brandt, Racicot, Rachel A., Laflamme, Marc
• Format: Journal Article
• Language: English
• Published: England The Royal Society 01.05.2017; The Royal Society Publishing
• Subjects: Appendages; Bilateria; Biological Evolution; Computational Fluid Dynamics; Computer applications; Computer simulation; Drag; Ecosystem; Ediacaran; Evolutionary Biology; Feeding; Feeding behavior; Fluid dynamics; Fossils; Hydrodynamics; Inference; Mobility; Paleobiology; Taxa; Trace fossils; Water flow; Parvancorina; paleobiology; computational fluid dynamics; Ediacaran
• ISSN: 1744-9561; 1744-957X
• DOI: 10.1098/rsbl.2017.0033

Establishing how Ediacaran organisms moved and fed is critical to deciphering their ecological and evolutionary significance, but has long been confounded by their non-analogue body plans. Here, we use computational fluid dynamics to quantitatively analyse water flow around the Ediacaran taxon Parvancorina, thereby testing between competing models for feeding mode and mobility. The results show that flow was not distributed evenly across the organism, but was directed towards localized areas; this allows us to reject osmotrophy, and instead supports either suspension feeding or detritivory. Moreover, the patterns of recirculating flow differ substantially with orientation to the current, suggesting that if Parvancorina was a suspension feeder, it would have been most efficient if it was able to re-orient itself with respect to current direction, and thus ensure flow was directed towards feeding structures. Our simulations also demonstrate that the amount of drag varied with orientation, indicating that Parvancorina would have greatly benefited from adjusting its position to minimize drag. Inference of facultative mobility in Parvancorina suggests that Ediacaran benthic ecosystems might have possessed a higher proportion of mobile taxa than currently appreciated from trace fossil studies. Furthermore, this inference of movement suggests the presence of musculature or appendages that are not preserved in fossils, but which would noneltheless support a bilaterian affinity for Parvancorina.