Traditional paleontological diversity curves are based on tallies of all taxa appearing in
formally defined time units. These tallies are thought to be robust to further data collection.
Thus, they supposedly do not reflect nuisance factors like variable time unit lengths and
sampling intensity biases. A comparison of a decade-old North American Cenozoic mammal
diversity curve and a newer database shows major differences. At least three major factors
differentiate the two: use of shorter, fixed-length time intervals; restriction of counts to taxa …