EDIACARAN TEST TUBES: EARTH'S EARLIEST EXPERIMENTS IN MULTICELLULARITY RECORDED IN THE MORPHOLOGY AND ECOLOGY OF THREE TUBULAR TAXA FROM THE EDIACARA MEMBER, SOUTH AUSTRALIA

The Ediacara biota represent the oldest complex, community forming organisms on Earth (~579–541 Ma), exhibiting successive increases in complexity and diversity that can be divided into three evolutionary assemblages: the Avalon, the White Sea, and the Nama. The White Sea Assemblage marks an initial increase in complexity, wherein the first mobile, bilaterian-grade organisms are identified. The most abundant morphotype of the White Sea Assemblage, however, are not the charismatic bilateriomorphs, but the hollow, elongate, and simple morphotype: tubular organisms. Upon their appearance in the fossil record, tubes are highly abundant and diverse. Importantly, these tubular taxa persist as a part of the Nama Assemblage and into the Early Cambrian, whereas characteristic Ediacaran bilateriomorphs (e.g. Dickinsonia, Spriggina) disappear from the fossil record. For these reasons, tubular organisms of the Ediacara Biota hold broad evolutionary significance. However, the nature of this importance remains unconstrained as the relationship between members of the tubular morphotype, and whether their success describes a phylogenetic lineage or convergent evolution, is unclear.

To broach this complex issue, and to define the origin of successful tubular taxa, a comparative analysis of the tubular organisms, Funisia dorothea, Plexus ricei, and Somatohelix sinuous, from the Nilpena Station National Heritage Site in the Flinders Ranges of South Australia is conducted. These taxa are the most abundant tubular organisms preserved at Nilpena, and hold a central commonality in that they possess taphonomic complexity as a result of their elongate and hollow body plans. Otherwise, these taxa differ in morphology in that Funisia and Plexus exhibit modularity, whereas Somatohelix does not. Additionally, the taxa differ in their abundance: Funisia is found primarily as densely packed populations covering entire bedding planes and rarely as individuals, Plexus is found rarely in densely packed populations (dominating three beds at Nilpena) and is more frequently found as individuals, and Somatohelix occurs only in low density populations of distinct individuals. The implications of this multifaceted variability is that these taxa played distinct yet significant roles within their ecosystems.