Palaeontological data and identifying mass extinctions.

It is often assumed that mass extinctions may be read directly from the fossil record. However, recent work on the Cretaceous-Tertiary (K-T) boundary has shown the difficulty of doing this. For example, it is hard to tell whether the stratigraphic ranges of taxa are complete or not, and what the shape of an extinction really is. Range completeness may be assessed by (1) a statistical approach to the relative completeness of ranges of taxa, and (2) tests based on collecting effort near the ends of ranges. Tests carried out recently suggest that the record is good in parts and getting better. Hence, palaeontologists ought to be able to document the nature of extinction events ever more precisely.