Three-dimensional reconstructions of the putative metazoan <i>Namapoikia</i> show that it was a microbial construction.

Abstract

Strata from the Ediacaran Period (635 million to 538 million years ago [Ma]) contain several examples of enigmatic, putative shell-building metazoan fossils. These fossils may provide insight into the evolution and environmental impact of biomineralization on Earth, especially if their biological affinities and modern analogs can be identified. Recently, apparent morphological similarities with extant coralline demosponges have been used to assign a poriferan affinity to <i>Namapoikia rietoogensis</i>, a modular encrusting construction that is found growing between (and on) microbial buildups in Namibia. Here, we present three-dimensional reconstructions of <i>Namapoikia</i> that we use to assess the organism's proposed affinity. Our morphological analyses, which comprise quantitative measurements of thickness, spacing, and connectivity, reveal that <i>Namapoikia</i> produced approximately millimeter-thick meandering and branching/merging sheets. We evaluate this reconstructed morphology in the context of poriferan biology and determine that <i>Namapoikia</i> likely is not a sponge-grade organism.