Evidence from Precambrian carbonate and siliciclastic sedimentary structures indicates that in marine settings before the Cambrian conditions of seafloor environments were largely controlled by microbes and the mats which they form. During the Ediacaran-Cambrian transition, a vertical component to marine bioturbation evolved, as well as overall increased seafloor bioturbation. The “Cambrian substrate revolution (CSR)” encompasses the evolutionary and ecological effects that occurred due to these substrate changes. The continued evolution of bioturbating organisms caused the development of a significant variety of new microenvironments, which led to the formation of new ecospace and evolutionary opportunities for other benthic organisms. Numerous studies have evaluated the “weird” morphology of early seafloor animals and how they adapted to an increasingly bioturbated substrate. Many early animals adapted to seafloors with strong microbial mat development are stem groups of the phyla we recognize today, and thus have morphological features absent in modern representatives. Fossils of crown groups of modern phyla first began to appear in the Cambrian and subsequently dominated Phanerozoic bioturbated seafloor environments. The CSR is thus a primary component of the evolution of stem and crown groups of the phyla during the Cambrian explosion.

The end-Permian mass extinction resulted in the demise of ∼90% of marine genera. Recent work on the Early Triassic using carbon isotopes, ammonoids, conodonts, and some benthic fauna shows that this supposed recovery period was almost as turbulent as the extinction itself. Carbon isotope records from China, India, and Italy portray a global signal with major perturbations at stage boundaries in the Early Triassic most likely as a result of fluctuating environmental conditions. Comparison of global cycles of extinction and radiation of ammonoids and conodonts to the global carbon signal suggests that the two are related. In order to investigate the ubiquity of the connection between the carbon signal and biological changes, the benthic diversity and ecological structure of the western USA was examined. Instead of the fluctuating patterns that were expected, evidence for gradual increases in both taxonomic and guild diversity was found. The lack of evenness in the recovery suggests ecological stagnation; dominance of a few genera and a few life habits. The prolonged benthic recovery, and trends of pelagic boom and bust, both point to environmental instability in the Early Triassic as the probable cause for the protraction of the biotic crisis.