Successive approximations of diversity curves: Ten more years in the library

Traditional paleontological diversity curves are based on tallies of all ta xa appearing in formally defined time units. These tallies are thought to b e robust to further data collection. Thus, they supposedly do not reflect n uisance factors like variable time unit lengths and sampling intensity bias es. A comparison of a decade-old North American Cenozoic mammal diversity c urve and a newer database shows major differences. At least three major fac tors differentiate the two: use of shorter fixed-length time intervals; res triction of counts to taxa that cross boundaries between intervals; and cor rection for variation in sampling intensity. The difference between genus- and species-level data also was examined, but appears to be minor by compar ison. Because at best only one pattern can be close to the true historical trajectory, the analyses suggest that the new data and protocols together h ave yielded a curve that is converging on an accurate signal.