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Open access, freely available online Synopses of Research Articles Space Matters: Estimating Species Diversity in the Fossil Record DOI: 10.1371/journal.pbio.0030286 To get a sense of the challenges in with fossil datasets, called the Miocene measuring biodiversity, consider this: Mammal Mapping Project (MIOMAP). estimates for the number of living species MIOMAP includes all western North on earth range from 3.5 million to over American mammals from 5–30 million 30 million. Only 1.9 million species have years ago—3,100 localities and 14,000 been classifi ed and described. (Of these, occurrences of species in all. 15,589 currently face extinction.) Now The authors fi rst tested the fossil data imagine trying to calculate patterns of for species–area effects with species from biodiversity through the paleontological a time period with robust geographic record. One tool ecologists rely on to data (the Early Barstovian, about identify patterns of biological diversity is 14.8–15.9 million years ago). They plotted DOI: 10.1371/journal.pbio.0030286.g001 a long-established rule of thumb called species richness against geographic area, the species–area effect: the tendency for using what’s known as nested sets of A new, comprehensive database compiles species number, or richness, to increase in fauna (species that occur in a smaller area mammalian fossils including this upper jaw a regular way with area. represent a subset of species in a larger of the Sthenicitis campestris, a weasel from Paleontologists typically have been area) by starting wi