ESTIMATING THE DURATION OF THE CAMBRIAN EXPLOSION

The Signor-Lipps effect is most often associated with mass extinctions, but it also affects “mass origination” events. The most important example is the Cambrian explosion, in which representatives of most modern phyla first appear. The general timeline of this pivotal event is well established, but details about the duration and pattern of originations remain unclear. Maloof et al. (2010) found that a dataset of small shelly fossils through the earliest Cambrian showed three pulses of fossil appearances over approximately 16 million years. Here we give a statistically rigorous estimate for the duration of the Cambrian explosion using novel methods that account for Signor-Lipps-type effects. We used a revised dataset of fossil occurrences of 166 genera of small shelly fossils from Mongolia, Siberia, and China, dating from the earliest part of the Cambrian (Nemakit-Daldynian and Tommotian, or Terreneuvian). To estimate the duration of the Cambrian explosion, we construct a confidence interval for the time span between the earliest and latest originations. We used trellis plots to visualize our results and investigate their sensitivity to uncertainty in radiometric dating, stratigraphic correlation, and sedimentation rate.