A statistical reassessment of basal disc circularity in Ediacaran fossils: implications for retrodeformation

Retrodeformation of Ediacaran fossils currently relies on the assumption that basal discs—a morphological feature common to diverse taxa—were originally circular. Despite their widespread application as tectonic strain markers, this foundational premise remains unverified. This study reassesses the reliability of the assumption of initial circularity by analysing a population of 287 basal discs from the E. M. Coombs Surface in Newfoundland, Canada. Using geometric measurements and statistical analyses, three hypotheses regarding the pre-deformation shape of the discs were tested: uniform circularity, uniform ellipticity, and heterogeneous ellipticity. Results support the hypothesis that, prior to deformation, the studied fossil disc population exhibited heterogeneity in ellipticity, ranging from circular to eccentric morphologies. These findings demonstrate that individual basal discs are unreliable tectonic strain markers, highlighting the need for alternative methods. Practical guidelines are proposed to circumvent this issue and improve the robustness of deformation assessments in Ediacaran fossil assemblages.