In the mid-Neoproterozoic, a narrow and unchanged shelf habitat offered icehouse-dictated (blue for cold temperatures in air and water) modest diel benthic fluctuations (left panels). Towards the end-Neoproterozoic, warmer climate (pink for warm temperatures in air and water) increased amplified diel redox fluctuations and physiological stress while the unchanged habitat and low productivity maintained harsh ecological conditions (middle panels). In the early Palaeozoic, global flooding of shallow shelf area with the severe diel benthic redox periodicity expands dramatically, thus lifting the biological stress by surplus of metabolic energy in the short term (right panels). The combination of stress-induced needs for oxygen-sensing and increased metabolic energy led to new needs, adaptations and radiation of animals with adequate oxygen sensing mechanism, e.g. sponges (without HIF-α) and Bilateria (with HIF-α).
