Completeness of the known graptoloid palaeontological record

Using a high-resolution chronology of graptoloid first and last appearances, we apply mathematical models that allow the simultaneous inference of the probability distribution of species durations and the effective sampling rate relating those durations to the observed stratigraphic ranges. This approach allows the completeness of the documented palaeontological record of graptoloids to be assessed. We estimate that c. 75% of species in the geographical regions that contribute to the stratigraphic data have been sampled and that, of those species known from more than a single stratigraphic horizon, c. 85% of their original durations, on average, are represented by their global composite stratigraphic ranges. As expected in light of their biostratigraphic importance, graptoloids have one of the most completely documented records among groups of fossil organisms. We expect that application of the methods used herein will show comparably complete records for other biostratigraphically relevant groups.