Data from: The stratigraphy of mass extinction

Patterns of last occurrences of fossil species are often used to infer the
tempo and timing of mass extinction, even though last occurrences
generally precede the time of extinction. Numerical simulations with
constant extinction demonstrate that last occurrences are not randomly
distributed, but tend to cluster at subaerial unconformities, surfaces of
forced regression, flooding surfaces and intervals of stratigraphical
condensation, all of which occur in predictable stratigraphical positions.
This clustering arises not only from hiatuses and non-deposition, but also
from changes in water depth. Simulations with intervals of elevated
extinction cause such clusters of last occurrences to be enhanced within
and below the interval of extinction, suggesting that the timing and
magnitude of extinctions in these instances could be misinterpreted. With
the possible exception of the end-Cretaceous, mass extinctions in the
fossil record are characterized by clusters of last occurrences at these
sequence stratigraphical horizons. Although these clusters of last
occurrences may represent brief pulses of elevated extinction, they are
equally likely to form by stratigraphical processes during a protracted
period (more than several hundred thousand years) of elevated extinction
rate. Geochemical proxies of extinction causes are also affected
similarly, suggesting that many local expressions of mass extinction
should be re-evaluated for the timing of extinction and its relation to
environmental change. We propose three tests for distinguishing pulses of
extinction from clusters of last occurrences produced by stratigraphical
processes.