Darroch, Simon AFGutarra Diaz, Susana V.Masaki, HaleOlaru, AndreiGibson, Brandt MDunn, Frances SMitchell, Emily GRacicot, Rachel ABurzynski, GregoryRahman, Imran2023-02-022023-02-0217/02/2023Simon 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, The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life, iScience, Volume 26, Issue 2, 2023, 105989, ISSN 2589-0042, https://doi.org/10.1016/j.isci.2023.105989. (https://www.sciencedirect.com/science/article/pii/S2589004223000664)2589-004210.1016/j.isci.2023.105989http://hdl.handle.net/10141/623040Rangeomorphs 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 dynamicstotesthypothesizedfeedingmodesforthefence-likerangeomorphPectinifrons 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.enopenAccesshttps://creativecommons.org/licenses/by/4.0/Journal ArticleiScience2023-01-28262105989-105989zoologyevolutionary biologypaleobiology