ROTATIONAL GEOMETRIC MORPHOMETRICS SHEDS LIGHT ON 555 MILLION-YEAR-OLD FOSSIL

The Ediacara biota represents the oldest complex, multicellular life in Earth’s history. South Australian fossil localities contain exceptionally preserved fossils from the most morphologically and taxonomically diverse assemblage of this period. Nilpena Station National Heritage Site (South Australia) preserves more than 200 specimens of Eoandromeda octobrachiata, the poorly understood, 1–3 cm diameter, octoradial Ediacaran organism. Due to the inherent rotational symmetry of E. octobrachiata a shape analysis approach had to take into account the lack of correspondence between arms among specimens. This study utilised the novel application of rotational geometric morphometrics on a fossil with the aim to determine the morphology and ecology of E. octobrachiata during life and how they are preserved. A generalised Procrustes analysis (GPA) was conducted to examine the shape variation among preserved specimens. An average shape of all landmarked specimens was used to estimate the shape during life. To determine the shape changes associated with preservation/taphonomy, the asymmetric and symmetric shape components were extracted using a principal components analysis (PCA). Their overall mean shape, and patterns of symmetry and asymmetry were compared with paleoenvironmental conditions and we inferred that they were most likely benthic and highly susceptible to deformation from various environmental and burial conditions.