Figure 9. Frequency distribution of the number of taxa occurring in the number of collections. This plot shows that most taxa are known from a very small number of collections, usually less than 10. The taxon that occurs most frequently is Squalodon, which is probably over-identified in the fossil record. Most occurrences of Squalodon are identified based on teeth, and Squalodon-like teeth occur in many taxa, not just the genus Squalodon. See Dooley (2005). Whereas many of the taxa that occur in more collections are recent genera (such as Balaenoptera and Delphinapterus), many are not, including the second most frequently occurring taxon, Basilosaurus, which is Eocene in age, which also suggests that this phenomenon is not completely due to the pull of the Recent.