The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life

Simon A F Darroch; Susana Gutarra; Hale Masaki; Andrei Olaru; Brandt M Gibson; Frances S Dunn; Emily G Mitchell; Rachel A Racicot; Gregory Burzynski; Imran A Rahman

doi:10.1016/j.isci.2023.105989

The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life

iScience. 2023 Jan 16;26(2):105989. doi: 10.1016/j.isci.2023.105989. eCollection 2023 Feb 17.

Authors

Simon A F Darroch^{1

2

3}, Susana Gutarra⁴, Hale Masaki¹, Andrei Olaru¹, Brandt M Gibson^{1

5}, Frances S Dunn⁶, Emily G Mitchell⁷, Rachel A Racicot^{1

2

3}, Gregory Burzynski⁸, Imran A Rahman^{4

6}

Affiliations

¹ Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA.
² Evolutionary Studies Institute, Vanderbilt University, Nashville, TN 37235, USA.
³ Senckenberg Research Institute and Natural History Museum Frankfurt, 60325 Frankfurt, Germany.
⁴ The Natural History Museum, London SW7 5BD, UK.
⁵ Department of Chemistry and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada.
⁶ Oxford University Museum of Natural History, University of Oxford, Oxford OX1 3PW, UK.
⁷ Department of Zoology, Museum of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
⁸ Department of Biology, Fairfield University, Fairfield, CT 06824, USA.

Abstract

Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P. abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P. abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals.

Keywords: Evolutionary biology; Paleobiology; Zoology.