A Bayesian astrochronology for the Cambrian first occurrence of trilobites in West Gondwana (Morocco)

The first occurrence of trilobites at ca. 520 Ma is an iconic feature of the Cambrian Explosion. Developing a robust evolutionary view on early Cambrian life is generally hindered by large uncertainties in the ages of fossil finds and their global stratigraphic correlation. We developed an astrochronological interpretation for the Tiout section in Morocco that features some of the oldest trilobite fossils. Our novel approach to incorporating individual astronomical cycle durations in an integrated radioisotopic and astrochronological Bayesian age-depth model results in an age estimate of 519.62 Ma (519.70−519.54 Ma 95% highest posterior distribution) for the first occurrence of trilobites in West Gondwana. This level of precise age estimation is exceptional for biological events in deep time and demonstrates the power of our novel approach.