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PALEONTOLOGICAL SOCIETY PAPERS, V. 8, 2002FIGURE 5—Diversity of predatory polychaetes. The dashed line connecting the peaks of maximumdiversity within intervals shows that the diversity revealed by superior preservation in lägerstettenfollows the same general path as the diversity of boundary-crossing genera.fossil record (the records of other taxa to be notedlater also support this idea). The implication is thatpredatory polychaetes became a part of the predatorfauna in the later Ordovician and have maintainedbut not increased their diversity through the restof the Phanerozoic.Gastropods.—Gastropods include manyimportant predators. Several of these taxa makedistinctive drill holes that can be identified in thefossil record. Figure 6a shows the diversity historyof predatory gastropods. From the Ordovician to themid-Cretaceous the diversity of predatorygastropods increased nearly continuously, but verygradually. Since the mid-Cretaceous the diversityof gastropod predators has increased dramatically.This contrasts markedly with the diversity historiesof predator anthozoans and polychaetes.Archaeogastropoda were the dominant Paleozoicprotobranch gastropods and few of them are certainpredators. However, a higher proportion ofMesogastropoda are predators and all theNeogastropoda and most of the readily preservedOpisthobranchia are predators. As shown inFigure 6b, the predatory opisthobranchs increasedin diversity in the Jurassic and again in the Cenozoic;the Mesogastropoda expanded their diversitysomewhat in the Triassic and then more or lessmonotonically from the Early Cretaceous onward;and the Neogastropoda have had an explosivediversification that began in the Late Cretaceous.Taxa containing a higher proportion ofpredators have diversified sequentially, so theproportion of all gastropods that are predators haschanged through time. Figure 7a shows thatpredators were a small part of the total diversity ofPaleozoic gastropods, but increased during theMesozoic to nearly equal the diversity of nonpredatorsin the Late Cretaceous before becomingthe majority of gastropod genera in the Cenozoic.Figure 7b tracks the change in proportion ofgastropod diversity comprised of predators throughthe whole Phanerozoic. Even though the methodused to estimate diversity of predators uses aconstant proportionality for each taxon analyzed(meaning that the proportion of predators within asingle analyzed taxon remains constant and doesnot change over time), the changing mix of the fourdifferent gastropod taxonomic groups used in thisanalysis demonstrates the continuous increase inthe proportion of predatory gastropods from theOrdovician onward. It is interesting to note thatpredatory strategies were added sequentially ingastropods. Drilling, although it had occurred at lowfrequency since the early Paleozoic, first became328