Taphonomy at the Turn: Early Cambrian Cloudinomorphs from Estonia’s Blue Clays

Fossils from the early Cambrian (Terreneuvian Series) blue clays of Estonia challenge long-held assumptions about the evolutionary transition across the Ediacaran–Cambrian boundary (~539 Ma). Among them are cloudinomorphs from the Lontova Formation—tube-building organisms that have long been thought to have vanished at the end of the Ediacaran Period. These recent discoveries, along with similar examples from China, indicate that cloudinomorphs possibly persisted into the early Cambrian, suggesting a much more complicated ecological transition between the Ediacaran and Cambrian than previously recognized. To refine our understanding of this pivotal transition period, we have examined the structure, preservation, and ecology of these blue clay cloudinomorph fossils.

Using advanced imaging techniques, including high-resolution X-ray tomographic microscopy (µCT) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), we have identified three distinct preservation modes for these fossils and discovered previously undetected fibrous structures that vary in density throughout the samples. EDS analyses indicate fossil-associated mineral phases, including gypsum, barite, and halite, offering new insights into the burial environment and taphonomic history of these fossils.

By integrating µCT imaging, SEM analysis, and traditional light microscopy, our study aims to resolve long-standing taxonomic uncertainties and reconstruct the ecological landscape of the Baltic Basin at this critical evolutionary juncture. These findings provide fresh perspectives on the survival of cloudinomorphs through the Ediacaran–Cambrian transition and contribute to broader models of ecological resilience during one of Earth’s most dramatic evolutionary episodes.