Evolutionary escalation in an exceptionally preserved Cambrian biota from the Grand Canyon (Arizona, USA).

Exceptionally preserved fossil assemblages, or Konservat-Lagerstätten, open direct windows on non-biomineralized faunas that chronicle the Cambrian radiation of animal phyla. However, these assemblages do not typically capture the well-oxygenated, resource-rich environments sustaining most metazoan diversity in modern marine systems. We describe exceptionally preserved and articulated carbonaceous mesofossils from the middle Cambrian (~507 to 502 million years) Bright Angel Formation of the Grand Canyon (Arizona, USA). This biota preserves probable algal and cyanobacterial photosynthesizers together with a range of functionally sophisticated metazoan consumers: suspension-feeding crustaceans, substrate-scraping molluscs, and morphologically exotic priapulids with complex filament-bearing teeth, convergent on modern microphagous forms. The Grand Canyon's extensive ichnofossil and sedimentological records show that these phylogenetically and functionally derived taxa occupied highly habitable shallow-marine environments, sustaining higher levels of benthic activity than broadly coeval macrofossil Konservat-Lagerstätten. These data suggest that evolutionary escalation in resource-rich Cambrian shelf settings was an important driver of the assembly of later Phanerozoic ecologies.