The number of species identified in the fossil record within any given geological time period must partly be explained by both the total number of fossil specimens sampled from that interval and the geographic spread of those samples. The influence of numerical sampling intensity has been well studied, but the effects of geographic variance in sampling are comparatively unknown. To investigate this question, we repeatedly resample a dataset of modern global marine organisms (from the Ocean Biodiversity Information System) using spatial sampling parameters determined by the real geographic spread of fossil organisms as found in the Paleobiology Database. Our findings show that a significant proportion of the variance in fossil diversity through time can be attributed only to changes in the numbers and locations of fossils sampled. This is consistent with the claim that the spatial structure of the fossil record and how it is sampled largely determine the diversity history drawn from it and with the ossibilit that lobal diversit has been relativel constant over time

Variation in observed global generic richness over the Phanerozoic must be partly explained by changes in the numbers of fossils and their geographic spread over time. The influence of sampling intensity (i.e., the number of samples) has been well addressed, but the extent to which the geographic distribution of samples might influence recovered biodiversity is comparatively unknown. To investigate this question, we create models of genus richness through time by resampling the same occurrence dataset of modern global biodiversity using spatially explicit sampling intensities defined by the paleo-coordinates of fossil occurrences from successive time intervals. Our steady-state null model explains about half of observed change in uncorrected fossil diversity and a quarter of variation in sampling-standardized diversity estimates. The inclusion in linear models of two additional explanatory variables associated with the spatial array of fossil data (absolute latitudinal range of occurrences, percentage of occurrences from shallow environments) and a Cenozoic step increases the accuracy of steady-state models, accounting for 67% of variation in sampling-standardized estimates and more than one-third of the variation in first differences. Our results make clear that the spatial distribution of samples is at least as important as numerical sampling intensity in determining the trajectory of recovered fossil biodiversity through time and caution against the overinterpretation of both the variation and the trend that emerge from analyses of global Phanerozoic diversity.