The impact of fossil stratigraphic ranges on tip‐calibration, and the accuracy and precision of divergence time estimates

The molecular clock provides the only viable means of establishing realistic evolutionary timescales but it remains unclear how best to calibrate divergence time analyses. Calibrations can be applied to the tips and/or to the nodes of a phylogeny. Tip‐calibration is an attractive approach since it allows fossil species to be included alongside extant relatives in molecular clock analyses. However, most fossil species are known from multiple stratigraphical horizons and it remains unclear how such age ranges should be interpreted to codify tip‐calibrations. We use simulations and empirical data to explore the impact on precision and accuracy of different approaches to informing tip‐calibrations. In particular, we focus on the effect of using tip‐calibrations defined using the oldest vs youngest stratigraphic occurrences, the full stratigraphical range, as well as confidence intervals on these data points. The results of our simulations show that using different calibration approaches lea...