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The Nama Group (Kalahari Craton) is an archetypal stratigraphic record of the Ediacaran–Cambrian transition. The upper Schwarzrand Subgroup preserves key biostratigraphic markers of this interval, including erniettomorphs, cloudinomorphs, and trace fossils, yet has a complex stratigraphic architecture due to deposition in a foreland basin. Here, we describe the stratigraphy of the upper Schwarzrand Subgroup of the Nama Basin, and collate sedimentologic, geochronologic, carbon isotope chemostratigraphic, and biostratigraphic data. We argue that strata previously identified as the Nomtsas Formation in the Witputs Subbasin are lithostratigraphically and tectonostratigraphically distinct from those in the type area (Farm Nomtsas) in the Zaris Subbasin. Therefore, we introduce the Swartkloofberg Formation as a new name for the terminal Schwarzrand Subgroup in the Witputs Subbasin. While carbonates of the underlying Urusis Formation were deposited within shallow marine environments, the Swartkloofberg Formation records a transition to dominantly siliciclastic deposition, mostly below fair-weather wave base, and with extensive evidence of slope instability. High-relief stromatolite reefs formed diachronously at different localities within both the Urusis and Swartkloofberg formations due to laterally variable accommodation space within the foreland basin. Strata of the Swartkloofberg Formation are interpreted as flysch deposits within an underfilled basin. We propose that the distinct deltaic peritidal and shoreface strata that—in some localities—were previously assigned to the upper Nomtsas Formation, are placed within the unconformably overlying molasse deposits of the Fish River Subgroup. These strata contain the stratigraphically lowest identified occurrences ofTreptichnus pedumwithin the Nama Group, and thus the base of the Cambrian Period. This stratigraphic revision solves several longstanding issues with regional correlation and revises the position of the Ediacaran–Cambrian boundary in the Witputs Subbasin. Accordingly, the Swartkloofberg Formation in the Witputs Subbasin (538.5–<537.6 Ma) is Ediacaran in age, as defined by biostratigraphy, supporting recent interpretations that the base of the Cambrian Period may be younger than 537.6 Ma. With increasingly refined age-stratigraphic models for the Nama Group, the upper Schwarzrand Subgroup provides a high-resolution record of the evolution of increasingly complex benthic invertebrate behaviors in the terminal Ediacaran lead-up to the classical Cambrian radiation of biomineralized invertebrate phyla. 

Abstract Ecosystem engineers are organisms that modify their physical habitats in a way that alters resource availability and the structure of the communities they live in. The evolution of ecosystem engineers over the course of Earth history has thus been suggested to have been a driver of macroevolutionary and macroecological changes that are observed in the fossil record. However, the rise to dominance of ecosystem engineers has not been thoroughly reconstructed. Here, we investigate the history of bioturbation and reef‐building (two of the most important marine ecosystem engineering behaviours today) over the Phanerozoic. Using fossil occurrences from the Paleobiology Database, we reconstruct how common communities influenced by ecosystem engineers were in the oceans, how dominant ecosystem engineers were within their own communities, and the taxonomic and ecological composition of bioturbators and reef‐builders. We find that bioturbation has become an increasingly common ecosystem engineering behaviour over the Phanerozoic, while reef‐building ecosystem engineers have not become more dominant since their Devonian apex. We also identify unique bioturbation and reef‐building regimes that are characterized by different ecosystem engineering taxonomic groups, ecological modes, and dominance, suggesting that the nature of ecosystem engineering has at times rapidly shifted over the course of the Phanerozoic. These reconstructions will serve as important data for understanding how ecosystem engineers have driven changes in biodiversity and ecosystem structure over the course of Earth history. 

Himatiichnus manganoigen. et isp. nov., a new trace fossil from the late Ediacaran Huns Member of the Urusis Formation, southern Namibia, comprises intertwining tubes exhibiting dual lineation patterns and reminiscent of both modern and early Cambrian examples of priapulid worm burrows. These similarities support the interpretation of a total-group scalidophoran tracemaker forH. mangano, thus providing direct evidence for the first appearance date of Scalidophora in the late Ediacaranca539 Ma. This new material is thus indicative of the presence of total-group scalidophorans below the Cambrian boundary and supports inference of a lengthy Precambrian fuse for the Cambrian explosion.