The Adoudou Biota: A new window on the Ediacaran-Cambrian transition from the western Anti-Atlas, Morocco

Abstract

The Ediacaran-Cambrian transition represents one of the most pivotal periods in the history of life, characterized by the decline of the Ediacaran ecosystems and fauna, and the emergence of Phanerozoic-type fauna. Various interpretations have been proposed for this biological event, including the closing of the unique Ediacaran taphonomic window, a sudden extinction event, or an evolutionary “biotic replacement” event. Here, we describe a fossil locality from the western Anti-Atlas of Morocco that preserves metazoan trace fossils and soft-bodied Ediacara biota, mat-related structures (MRS), alongside a paleoenvironmental reconstruction of the siliciclastic deposits of the Tabia Member of the Adoudou Formation. We document various MRS, including mat-related wrinkles and mat destruction features reported from frequently shallow submerged environments and down to permanently sub-wavebase settings. Additionally, we report new trace fossils from this interval, including T. bifurcus, Bergaueria, Helminthopsis, and Archaeonassa preserved on the bedding plane of sandstone beds. Furthermore, we describe new Ediacaran body fossils comprising macroscopic, well-preserved specimens of Aspidella and Nimbia. An integrated study of sedimentary facies and the distribution of associated trace fossils indicates that evolutionary innovations exerted primary control on the distribution of trace fossils in the studied interval, where the stratigraphical distribution of trace fossils strongly aligns with that observed worldwide. The stratigraphic overlap of soft-bodied Ediacara biota and metazoan trace fossils suggests the existence of unique late Ediacaran shallow-water ecosystems housing two distinct multicellular clades.