Animal life on Earth is generally accepted to have risen during a period of increasingly well-oxygenated conditions, but direct evidence for that relationship has previously eluded scientists. This gap reflects both the enigmatic nature of the early animal fossil record and the coarse temporal resolution of Precambrian environmental change. Here, we combine paleontological data from the Ediacara Biota, the earliest fossil animals, with geochemical evidence for fluctuating redox conditions. Using morphological and ecological novelties that broadly reflect oxygen demand, we show that the appearance of abundant oxygen-demanding organisms within the Ediacara Biota corresponds with a period of elevated global oxygen concentrations. This correlation suggests that a putative rise in oxygen levels may have provided the necessary environments for the diversification of complex body plans and energetically demanding ecologies. The potential loss of organisms with relatively high oxygen requirements in the latest Ediacaran coupled with an apparent return to low oxygen concentrations further supports the availability of oxygen as a control on early animal evolution. While the advent of animal life was probably the product of a variety of factors, the recognition of a possible connection between changing environmental conditions and the diversification of animal morphologies suggests that the availability of oxygen played a significant role in the evolution of animals on Earth.

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